Chem Volume 3

CHEMISTRY IN ACTION

1

Chapter 8: Organic Chemistry EPISODE 31: HYDROCARBONS

OVERVIEW

Organic chemistry is study of the compounds of carbon. Carbon compounds comprise more than 90% of all known compounds. The simplest of these organic compounds are those that contain only two elements, carbon and hydrogen. These are the hydrocarbons. This lesson deals with the properties, reactions, and uses, as well as the system of naming of the different classes of hydrocarbons.

OBJECTIVES

At the end of this lesson, the student should be able to: 1. explain why carbon can form a large number and variety of compounds; 2. define or describe a hydrocarbon; 3. classify hydrocarbons based on their structures; 4. give the systematic names of alkanes, alkenes, and alkynes according to

IUPAC standards; 5. draw structural formulas of hydrocarbons; 6. differentiate saturated from unsaturated hydrocarbons; 7. discuss the solubility of hydrocarbons

in water and in non-polar solvents; 8. write equations for the combustion of hydrocarbons; and 9. identify some carcinogenic hydrocarbons.

INTEGRATION WITH OTHER LEARNING AREAS

This lesson makes use of a number of basic concepts discussed in earlier episodes: covalent bonding and the Octet Rule, geometry of molecules, polarity of molecules, solubility, reactions, and writing formulas, among others. This lesson is the first of several episodes that deal with organic compounds. The system of nomenclature used in the other compounds of carbon is based on the guide presented in this lesson.

SCIENCE PROCESSES

Observing Classifying

Interpreting Applying concepts

CHEMISTRY IN ACTION

2

VALUES

Interpreting Applying concepts Appreciation for nature

Acknowledging the importance of our natural resources Care for the environment Critical mindedness

LIFE SKILLS

Making accurate observation Formulating inferences and conclusions

Applying to new instances knowledge previously learned

IMPORTANT CONCEPTS

1. Hydrocarbons are organic compounds that are composed only of carbon and hydrogen.

2. Hydrocarbons are non-polar substances since the carbon-carbon bonds and the carbon-hydrogen bonds are essentially non-polar.

3. Alkanes are saturated hydrocarbons – all carbon-carbon bonds being single

bonds.

4. Alkenes and alkynes are unsaturated hydrocarbons since they contain carbon-carbon double bonds and carbon-carbon triple bonds, respectively.

5. Hydrocarbons undergo combustion with carbon dioxide and water as products. 6. Isomers are compounds of the same molecular formula and composition but

differ in properties because they differ in structures.

BACKGROUND INFORMATION/EPISODE CONTENT

Carbon and Its Compounds. Why are there so many compounds of carbon? This is mainly because carbon atoms, unlike those of any other element, are able to form strong bonds with one another and to a great extent, a property called catenation. Thus, carbon atoms bond with other carbon atoms into chains and rings, form branches and crosslinks, and use their other valence electrons to form bonds with other elements like hydrogen, oxygen, nitrogen, the halogens, phosphorous and sulfur, to name a few. Organic compounds come in a wide variety of sizes and complexities that a system of classification has been used to study them and systems of nomenclature were developed to name them.

CHEMISTRY IN ACTION

3

CC

H

H

H

H

C

H

H

H

H

CC

H

H

H

H

C

H

H

C

H

H

H

H

Despite the huge number of known carbon compounds, we find some simple underlying features of these compounds: a. They are molecular rather than ionic in nature. b. Carbon is a strict follower of the octet rule and forms a total of four covalent bonds which can be all single or a combination of single and multiple bonds. c. Carbon can form bonds with other carbon atoms or with atoms of other nonmetallic elements. Hydrocarbons. Hydrocarbons are organic compounds that are made up solely of carbon and hydrogen. This big class of compounds is further classified into several subgroups as shown in the following diagram.

Organic compounds Hydrocarbons Derivatives of hydrocarbons Aliphatic hydrocarbons Aromatic hydrocarbons Alkanes Alkenes Alkynes Cyclic hydrocarbons Alkanes. Alkanes are open-chain aliphatic hydrocarbons with the general formula CnH2n+2, where n is the number of carbon atoms in the molecule. All the bonds present in alkanes are single bonds and are thus referred to as saturated hydrocarbons. Examples of alkanes are propane and butane whose structural formulas are given below. propane, C3H8 butane, C4H10 Alkanes can also be branched. An example of a branched alkane is 2-methyl propane.

CHEMISTRY IN ACTION

4

CC

H

H

H

C

C

H

H

H

H

H HH

CC

H

H

H

H

C

H

H

C

H

H

H

H

2-methyl propane, C4H10 Notice that butane and 2-methyl propane have the same molecular formula, C4H10. They are called structural isomers. Structural isomers are compounds with the same molecular formula but differ in the way the atoms are arranged and connected to one another. This difference in structural formulas makes them different compounds with different physical and chemical properties. Writing Structural Formulas. The structural formula of organic compounds can be written in the expanded or dash form, condensed form or line structure. The expanded form clearly shows the difference in the arrangement of atoms in structural isomers, but sometimes the condensed or line structures can suffice. In the condensed formula, the carbon-carbon bond may be represented by a line or completely omitted. On the other hand, each line of the line structure represents a carbon-carbon bond and the carbon-hydrogen bonds no longer shown. Shown below are the expanded, condensed, and line structures of butane. CH3–CH2–CH2–CH3 or

CH3CH2CH2CH3 Expanded Condensed Line formula formula formula

There are only two kinds of bonds in alkanes and in all hydrocarbons: the carbon-carbon bonds and the carbon-hydrogen bonds both of which are essentially non-polar. Hydrocarbons are therefore non-polar compounds. Alkanes are most soluble in non-polar solvents and are immiscible in water. Hence, vegetable oil, a hydrocarbon, is completely miscible in benzene, another hydrocarbon and a non-polar solvent, but will not mix and will form two layers with water.

Being non-polar, the only intermolecular forces of attraction that exist between and among hydrocarbon molecules are London dispersion forces. Hence, the low molecular weight alkanes, particularly those containing up to four carbon atoms, are gaseous at room temperature. Gasoline is composed mainly of five to twelve carbon atoms and is a liquid at room conditions. Waxes and paraffins are high molecular weight alkanes made up of sixteen to twenty carbon atoms and are solids at room temperature.

Many fuels that we use are hydrocarbons. Methane is often referred to as fuel gas, propane is the main component of cooking gas or LPG, and butane is the

CHEMISTRY IN ACTION

5

fuel in cigarette lighters! Gasoline, a mixture of hydrocarbons, is used as fuel in motor engines and we burn candle wax to provide light during brown-outs. The combustion reaction of alkanes is a reaction with oxygen gas and produces carbon dioxide and water in addition to energy in the form of heat and light. The equation given for the combustion of propane, C3H8, is given below.

C3H8 (g) + 5 O2 (g) ® 3 CO2 (g) + 4 H2O (g)

Naming Hydrocarbons. The number of known organic compounds is so large that remembering their names becomes very difficult. To address this problem, the International Union of Pure and Applied Chemistry, IUPAC, developed a systematic way of naming organic compounds. The systematic name of a hydrocarbon has three parts: (1) the stem, which is the main part and refers to the parent carbon chain or backbone, (2) a suffix to indicate the type of hydrocarbon the compound belongs to, and (3) a prefix to refer to the groups attached to the parent backbone. The following steps would help you name the alkanes: 1. From the structural formula, determine the longest carbon chain. This will be the

parent backbone. Use the root word corresponding to the number of carbon atoms in the chain as the stem of the name. The root words for up to a chain of 10 carbon atoms are given in the table below:

Number of

carbon atoms Root word Number of carbon atoms Root word

1 meth- 6 hex- 2 eth- 7 hept- 3 prop- 8 oct- 4 but- 9 non- 5 pent- 10 dec-

2. Add the suffix to the stem. For alkanes, the suffix is –ane. Thus, the one-carbon

alkane is methane, two- carbon is ethane, and the three-carbon compound is propane.

3. Some alkanes have side chains or branches. To locate the position of the side

chain(s), number the carbon atoms in the backbone such that the first side chain is given the lowest position number. The side chains are indicated by the prefix which is composed of the root word corresponding to the chain of carbon atoms with the ending –yl. The name of the side group(s) is accompanied by a number to show which carbon atom it is attached to in the parent backbone.

4. The complete name of the alkane is written as a single word with hyphens to

separate the numbers from prefixes and commas between numbers.

CHEMISTRY IN ACTION

6

12

34

56

78

Let us name some examples following the steps listed above.

Example A:

Step 1. The longest chain is made up of six (6) carbon atoms. Step 2. The name of the parent backbone is hexane. Step 3. There is a side group attached to the 2nd carbon (not the 5th!) and it is

a one-carbon group. The side group is a methyl group. Remember again that when locating side groups, number the carbon atoms in the backbone such that the carbon atom carrying the first side group has the lowest possible number.

1 23

45

6

and NOT 1

23

456

Step 4. The name of the alkane is 2-methylhexane.

Example B:

Step 1. The parent backbone is a chain made up of eight (8) carbon atoms. If you counted only seven (7), count again.

Step 2. The parent backbone is octane. Step 3. There are two (2) methyl side groups: the first is on the 3rd carbon

and the second is on the 5th carbon of the backbone. Step 4. The name of the alkane is 3,5-dimethyloctane. Alkenes and Alkynes. Alkenes are hydrocarbons with at least one carbon-carbon double bond, -C=C- , and alkynes are those with at least one carbon-carbon triple bond, -C≡C- . The general formula for alkenes is CnH2n and that for alkynes is CnH2n-2. Alkenes and alkynes are referred to as unsaturated which means that multiple bonds between carbon atoms are present. Naming alkenes and alkynes follow rules that are very similar to those for alkanes. We first identify the longest continuous chain as the parent chain, but this chain should contain the double bond for alkenes and the triple bond for alkynes. The stem used for the parent chain is the same as in alkanes, but the suffix -ene is used for alkenes and –yne for alkynes. The numbering of the carbon atoms starts at the end nearest the double or triple bond.

CHEMISTRY IN ACTION

7

1

23

45

67

1

23456

Let us name alkenes and alkynes. Examples are given below. Example A:

Step 1. The longest chain is made up of seven (7) carbon atoms. This chain is a heptene.

Step 2. The double bond is at carbon 2. Step 3. There is a 3-carbon or propyl substituent attached to carbon 3. Step 4. The name of this alkene is 3-propyl-2-heptene. Example B: Step 1. The stem is a six-carbon chain, a hexyne. Step 2. The triple bond is at carbon 2. Step 3. There is an ethyl substituent at carbon 4, and a methyl substituent at

carbon 5. Substituents are named alphabetically. Step 4. The name of the alkyne is 4-ethyl-5-methyl-2-hexyne. The simplest alkene is ethene or more familiarly, ethylene, CH2=CH2. Ethylene occurs naturally in plants and plays an important role in fruit ripening. It is also used as an industrial raw material in the production of plastics. The simplest alkyne is ethyne, H-C≡C-H. Ethyne is more familiarly known as acetylene, the gas used as fuel in acetylene torches. Saturated vs Unsaturated Hydrocarbons. The presence of at least one multiple bond between carbon atoms makes a hydrocarbon unsaturated. Unsaturation may be detected using simple laboratory tests based on reactions of the carbon-carbon multiple bonds in alkenes and alkynes.

If there are no materials to do the tests, a segment of the video episode shows what would be observed

when the tests using bromine water and an acidified solution of potassium permanganate are done.

1. Unsaturated hydrocarbons decolorize bromine water rapidly. In contrast alkanes

decolorize bromine water very slowly. 2. Unsaturated hydrocarbons decolorize an acidified aqueous solution of potassium

permanganate, KMnO4, to a colorless solution. No reaction is observed with alkanes.

CHEMISTRY IN ACTION

8

C

C C

HH

H

H

H

H

CH2

H2C CH2

CH3

Cyclic Hydrocarbons. Hydrocarbons may also form ring or cyclic structures, where the carbon atoms at both ends of a carbon chain may link and form a carbon-carbon bond. These cyclic hydrocarbons are called cycloalkanes. The general formula of cycloalkanes is CnH2n, which is 2 hydrogen atoms less than an aliphatic hydrocarbon. The simplest cycloalkane is a three-carbon ring called cyclopropane, C3H6, a compound used as an anesthetic. All the structures below are representations of cyclopropane. Expanded formula Condensed formula Line formula While the smallest ring structure is made of three carbon atoms, there is theoretically no limit to the size of a cycloalkane ring. Hence, cycloalkanes with rings made up of more than twenty carbon atoms can be found in nature. Notice that cycloalkanes are named by simply adding the prefix “cyclo-” to the name of the alkane containing the same number of carbon atoms as the cyclic compound. Hence, a five-carbon cycloalkane is cyclopentane and an eight-carbon ring is cyclooctane. Alkenes and alkynes also have cyclic analogs and are called cycloalkenes and cycloalkynes, respectively. Aromatic Hydrocarbons. The term “aromatic” was previously associated with sweet or spicy-smelling compounds. Through the years, many aromatic hydrocarbons were found not to be fragrant and were either odorless or have unpleasant odors. Today, an aromatic hydrocarbon is one that behaves chemically like benzene, C6H6, the parent aromatic hydrocarbon. Benzene and the other aromatic hydrocarbons have two important properties that set them apart from the aliphatic hydrocarbons, even with the presence of multiple bonds. First, benzene does not undergo addition reactions like the alkenes and alkynes such as in decolorizing bromine water. Second, benzene has an unexpected stability which may be the reason for its less reactive nature. This stability is observed in aromatic hydrocarbons, whether they are derivatives of benzene, such as toluene, naphthalene, and benzopyrene. From the structures of some aromatic hydrocarbons, including that of benzene that are shown below, we might be able to see what makes this group of hydrocarbons different. Benzene Toluene Naphthalene Benzopyrene

CHEMISTRY IN ACTION

9

The structures shown above for benzene and the other aromatic hydrocarbons are not sufficient to portray the observed properties of these compounds. Benzene, for example, does not have alternating single and double carbon bonds in the ring. Instead, all the carbon-carbon bonds of benzene are of the same length and strength and are found to be intermediate those of a single and a double bond – almost that of a one-and-one-half or 1.5 bonds. How can a bond be more than a single but less than a double bond? This happens when electrons are delocalized or shared by all six carbon atoms in the ring. How is electron delocalization in benzene illustrated? One way is to represent benzene by its two resonance structures: Resonance structures are correct Lewis structures of a molecule, but would not by any single one of these represent the true structure of the molecule. In other words, the properties indicated by any one of the structures would not be consistent with the observed properties of the molecule. What do these resonance structures mean? Benzene does NOT flip back and forth from one structure to another. Rather, the resonance structures tell us that the true structure of benzene is a contribution of the two structures. Benzene may also be represented by a ring with a circle inside to represent electron delocalization as in the structure below.

Geometry of Hydrocarbons. Methane, CH4, is the simplest hydrocarbon. We learned in Episode 29 – Binding Among Molecules that methane is a tetrahedral molecule. The hydrogen atoms are arranged in a tetrahedral fashion around the carbon atom as shown in the figure below. This is because there are four groups of electrons around carbon and the farthest that four repelling groups could position themselves to minimize repulsions is at the corners of a tetrahedron, according to the Valence Shell Electron Pair Repulsion (VSEPR) theory.

C

H

HHH

In butane, C4H10, the four carbon atoms are in a chain, CH3–CH2–CH2–CH3. What will be the positions of the carbon atoms relative to each other? If we use the VSEPR theory as our guide, we would consider each carbon atom as a center of a tetrahedron. The figure on the right shows the tetrahedral arrangement of the bonds around the third carbon atom. Can you see the other tetrahedral groups?

CHEMISTRY IN ACTION

10

CC

CCH

H H

H

H

H

H

H

H

H

CC

CC

The carbon-carbon bonds in the chain are at 109o from each other and not at 180o. That means they are not in a straight line! That is why our line structure for butane is a zig-zag pattern! Line structure for butane. Now, let us use the VSEPR theory to determine the bond angles around a carbon atom with a double bond in the alkene 2-butene, CH3CH=CHCH3. The bonds of the third carbon atom have been highlighted. How many groups of electrons are around this carbon atom? (Hint: a double bond is considered just one group). Yes, there are three groups and according to the VSEPR theory each group will be at 120o away from the others.

H3CC

CCH3

Look at the structure of 2-butyne and try to reason why the four carbon atoms are now truly in a straight line or the bond angles between the carbon-carbon bonds are 180o.

H3C C C CH3

180o?

In your future chemistry courses, you will meet another theory to explain the geometries around carbon atoms in hydrocarbons and in other carbon compounds. But the VSEPR theory should be sufficient in explaining geometries of simple hydrocarbons. VOCABULARY WORDS

1. Hydrocarbons - organic compounds that are made up solely of carbon and hydrogen.

2. Alkanes - open-chain aliphatic hydrocarbons with the general formula CnH2n+2; all the bonds present in the compound are single bonds.

3. Alkenes - hydrocarbons with at least one carbon-carbon double bond with a

general formula of CnH2n.

4. Alkynes – hydrocarbons with at least one carbon-carbon triple bond with a general formula of CnH2n-2.

CHEMISTRY IN ACTION

11

5. Cyclic hydrocarbons - hydrocarbons that form ring or cyclic structures, where the carbon atoms at both ends of a chain link up and form a carbon-carbon bond.

6. Saturated hydrocarbons - aliphatic hydrocarbons where all the bonds present

are single bonds. 7. Unsaturated hydrocarbons – hydrogen and carbon compounds with multiple

bonds (can be double or triple bonds or combinations of both) between carbon atoms.

8. Aromatic hydrocarbons - those that behave chemically like benzene, C6H6. 9. Structural isomers - compounds with the same molecular formula but differ in

the way the atoms are arranged and connected to one another. PRE- VIEWING ACTIVITIES

A. Present to your students a list of familiar organic substances with their formulas. These may include fuels like butane and acetylene, oil, sugar, acetic acid, formaldehyde, isopropyl alcohol, chloroform, acetone, etc. Let the students group the substances based on composition. Tell them that they will still classify these substances after completing the next lesson.

B. Pose the Guide Questions that the students will answer after viewing the episode.

Guide Questions/Answers

1. What elements compose hydrocarbons? The only elements that compose hydrocarbons are carbon and hydrogen. 2. Give the general formula for alkanes, alkenes, and alkynes. Alkanes CnH2n+2 Alkenes CnH2n Alkynes CnH2n-2 3. Describe one test used to differentiate saturated from unsaturated

hydrocarbons.

There are two tests that were shown in the video episode

that could differentiate saturated from unsaturated hydrocarbons:

CHEMISTRY IN ACTION

12

Test Expected Observation a) bromine

water test Unsaturated hydrocarbon: solution changes color from red brown to yellow very quickly Saturated hydrocarbon: very slow change in color

b) acidified KMnO4 test

Unsaturated hydrocarbon: purple color disappears fast Saturated hydrocarbon: no change in color

4. What are structural isomers? Give examples of hydrocarbons that are

structural isomers. Structural isomers are compounds with the same composition and formula but differ in structure and arrangement of the atoms. There are many possible examples of hydrocarbons that are structural isomers. One such pair is n-butane, CH3(CH2)2CH3 and isobutane or 2-methylpropane, (CH3)3CH.

5. Why are hydrocarbons insoluble in water? Hydrocarbons are non-polar. Following the rule “like dissolves like”, non-polar substances will not dissolve in a polar solvent like water.

6. What does electron delocalization mean?

Electron delocalization means that electrons are not situated between a fixed pair of atoms that are bonded together but is shared by more than two atoms in the molecule.

7. Who was the first to describe electron delocalization in benzene? Friedrich August Kekule was the first to describe delocalization of electrons among the carbon atoms in the benzene ring.

8. Name two natural sources of hydrocarbons. Hydrocarbons can be obtained from fossil fuels, natural gas, coal, and

petroleum. 9. What products are obtained from the combustion of hydrocarbons? When hydrocarbons burn, the products are carbon dioxide and water. 10. How do aromatic hydrocarbons differ from cyclic aliphatic hydrocarbons?

Aromatic and cyclic aliphatic hydrocarbons have carbon atoms forming rings, but the carbon-carbon bonds in cyclic aliphatic hydrocarbons are all single bonds. In aromatic hydrocarbons, carbon atoms share delocalized electrons within the ring.

CHEMISTRY IN ACTION

13

VIEWING ACTIVITIES POST-VIEWING ACTIVITIES

POST-VIEWING ACTIVITIES

Discuss the answers to the Guide Questions.

TEACHING TIPS

A. “Me and My Hydrocarbons”. To understand the terms and concepts learned in this lesson, let the students associate the terms given in the table below to related unique characteristics of their classmates. For example, the term “aromatic” may describe someone who always smells nice and fragrant.

Aromatic __________________

Non-polar __________________

Always miscible __________________

Saturated __________________

Forms double bonds __________________

Capable of delocalization ___________________

Organic in nature __________________

My isomer __________________

Very combustible ___________________

Each student will work with his/her own table and ask the classmate he/she identifies with the characteristic to sign on the space below the term. A student can sign in a table only once. After all the students have completed their tables, the teacher can ask some students to explain their choices.

B. Model-Making. Ask the class to form small groups and assign two or three

hydrocarbons to each group. You may even want to assign a group a set of isomers. Each group prepares a model for each compound showing the correct geometry and bond angles using balls and sticks or clay and sticks. Students should do some research and describe/report the following: § The geometry of the molecules. § The bond angles between bonds in the molecules. § The physical state of the compound at room temperature.

The video may be viewed in parts according to the lesson: (1) Nature of Organic Compounds at 3:34 – 5:02,

(2) General Classification of Organic Compounds at 5:03 – 5:48, (3) Alkanes at 6:02 – 12:20,

(4) Alkenes and Alkynes at 12:46 – 16:49, (5) Cyclic Aliphatic Compounds at 17:00 – 17:49, (6) Aromatic Hydrocarbons at 18:00 – 19:11, and

(7) Condensed Benzene Rings at 19:12- 19:54.

CHEMISTRY IN ACTION

14

CC

H

H

H

H

C

H

H

C

H

H

C

H

H

H

H

CC

H

H

H

H

C

H

C C

H

H

H

H

CH H

H

C

C

C

C

C

CHHH

H

H

H

H

H

H

H H

H

C

C

C

C

CH

H

H

H

H

C

H

H

H

H

H

CC

H

H

H C C

H

H

H

C. Hydrocarbons in Cars. Ask your students to know the process of burning

gasoline and how this makes cars run. You may also include the pollutants associated with using gasoline. Here are some questions you may ask with your students: § What is octane rating? § What pollutants are produced in burning gasoline? § What is the purpose of adding lead to gasoline? § How does burning of gasoline contribute to the greenhouse effect? You may

also want to ask your students what they can do to minimize the greenhouse effect.

ASSESSMENT

A. Complete the Table. Complete the table below by providing the condensed

and line structures of the hydrocarbons given in the first column.

Expanded formula Condensed formula Line formula

CHEMISTRY IN ACTION

15

a b

c

d

e

B. Hybridization. Identify the bond angles between the marked bonds in the

structure given below: C. Naming Hydrocarbons. Give the name of the following hydrocarbons:

1. _______________________________

2. _______________________________

3. _______________________________

4. _______________________________

D. Matching Type. Match the definitions/descriptions in Column A with the terms/concepts in Column B. Write only the letter on the space provided before each number. The items in Column B may be used more than once. Column A Column B

______ 1. Organic compounds that are composed of only carbon and hydrogen

A. Alkanes

______

2. Saturated hydrocarbons B. Alkenes

______ 3. A test to differentiate saturated from unsaturated hydrocarbons

C. Naphthalene

______ 4. Hydrocarbons with the general formula CnH2n

D. IUPAC

______ 5. Compounds with the same molecular formula but different structures

E. Heptane

______ 6. Aromatic hydrocarbon associated with mothballs

F. Hydrocarbon

CHEMISTRY IN ACTION

16

______ 7. Hydrocarbons with at least one carbon to

carbon triple bond G. 2-methyl hexane

______ 8. Alkane with seven carbon atoms

H. Structural isomers

______ 9. Isomer of heptanes I. Bromine water test

______ 10. Compounds found in fossil fuels J. Alkyne

E. Identifying Terms. Identify the term in each of the following numbers. Write

the letters of the word in the appropriate spaces and identify the mystery word inside the box. Define the mystery word.

Description of theTerms.

1. Class of hydrocarbons that consist of alkanes, alkenes, and alkynes. 2. Simplest alkyne. 3. Physical state at room temperature of hydrocarbons with more than 16

carbon atoms. 4. Halogen used in the test for differentiating unsaturated and saturated

hydrocarbons. 5. Compounds with the same formula but different structures. 6. Aliphatic hydrocarbon in a ring structure. 7. Parent compound is benzene. 8. Alkanes are ____________ hydrocarbons but alkenes nor alkynes are not. 9. Organic chemistry is the study of ________ and its compounds. 10. Combustion is a reaction of substances with this element.

11. Compound whose structure is represented by .

1. ___ ___ ___ ___ ___ ___ ___ ___ ___ 2. ___ ___ ___ ___ ___ ___ 3. ___ ___ ___ ___ ___ 4. ___ ___ ___ ___ ___ ___ ___ 5. ___ ___ ___ ___ ___ ___ ___ 6. ___ ___ ___ ___ ___ ___ 7. ___ ___ ___ ___ ___ ___ ___ ___ 8. ___ ___ ___ ___ ___ ___ ___ ___ ___ 9. ___ ___ ___ ___ ___ ___ 10. ___ ___ ___ ___ ___ ___ 11. ___ ___ ___ ___ ___ ___ ___

Mystery Word: __________________________________

CHEMISTRY IN ACTION

17

CC

H

H

H

H

C

H

H

C

H

H

C

H

H

H

H

CC

H

H

H

H

C

H

C C

H

H

H

H

CH H

H

CC

H

H

H C C

H

H

H

C

C

C

C

C

CHHH

H

H

H

H

H

H

H H

H

C

C

C

C

CH

H

H

H

H

C

H

H

H

H

H

CH2

HC

H2C

H2C

CH3

CH2

CH2CH CHCH3

CH3

CH3

CH2

CH2

CH2

CH

HC

CH2

a b

c

d

e

ANSWER KEY A. Complete the Table.

Expanded formula Condensed formula Line formula

CH3CH2CH2CH2CH3

CH3CºCCH3

B. Hybridization a. 120o b. 120o c. 109o d. 109o e. 180o

CHEMISTRY IN ACTION

18

C. Naming Hydrocarbons. Give the name of the following hydrocarbons.

a. 2,4-dimethyl hexane

b. 3-methyl pentene

c. 4,5-dimethyl-2-heptene

d. 1,2-dimethyl cyclohexane

D. Matching Type.

1. F 2. A 3. I 4. B 5. H

6. C

7. J

8. E

9. G

10. F

E. Identifying Terms.

1. A L I P H A T I C 2. E T H Y N E 3. S O L I D 4. B R O M I N E 5. I S O M E R S 6. C Y C L I C 7. A R O M A T I C 8. S A T U R A T E D 9. C A R B O N 10. O X Y G E N 11. B E N Z E N E

Mystery Word: HYDROCARBON

Definition: Organic compounds composed of carbon and hydrogen only.

CHEMISTRY IN ACTION

19

REFERENCES McMurry, J. (1998). Organic chemistry. (2nd ed.). FL: Brooks/Cole. Snyder, C.H. (1992). The extraordinary chemistry of ordinary things. (2nd ed.). NY:

John Wiley and Sons, Inc.

CHEMISTRY IN ACTION

20

Chapter 8: Organic Chemistry EPISODE 32: COMPOUNDS OF CARBON, HYDROGEN, AND OXYGEN

OVERVIEW

The previous episode deals with the simplest groups of organic compounds – the hydrocarbons. Replacing one or more of the hydrogen atoms attached to carbon atom produces a different set of organic compounds called derivatives of hydrocarbons.

This episode deals with oxygen-containing organic compounds namely alcohols, aldehydes and ketones, and carboxylic acids. The physical and chemical properties as well as the reactivity of these organic compounds are investigated and illustrations are presented for ease of understanding.

The sources and uses of oxygen-containing organic compounds are also presented, particularly those that we encounter every day. This episode will give us a better understanding of the chemistry behind metabolic actions in our body as well as diseases that may be associated with these organic compounds.

OBJECTIVES

At the end of this lesson, the student should be able to: 1. define functional groups; 2. determine the functional groups associated with alcohols, aldehydes, ketones

and carboxylic acids; 3. distinguish among alcohols, aldehydes, ketones and carboxylic acids based

on simple laboratory tests; 4. name systematically alcohols, aldehydes, ketones and carboxylic acids based

on IUPAC standards; 5. explain how alcohol, particularly ethanol, is metabolized in the body; 6. describe the effects of excessive use of alcohols in the body; 7. explain the oxidation reaction; 8. predict the products of the oxidation reactions of alcohols, aldehydes,

ketones and carboxylic acids; 9. identify the organic compounds responsible for the smell of some fruits,

animals and other commercial products; and 10. explain the uses of alcohols, aldehydes, ketones and carboxylic acids at home

and in the industry.

CHEMISTRY IN ACTION

21

INTEGRATION WITH OTHER LEARNING AREAS This episode is directly linked to the various episodes in Organic Chemistry: Episode 31 – Hydrocarbons, Episode 33 – Phenols, Ethers, and Esters, and Episode 34 – Hydrocarbon Derivatives Part III. Reactions of alcohols, aldehydes, ketones, and carboxylic acids as well as their occurrences and applications can be linked and integrated to various concepts of biological, biochemical, clinical, and environmental topics.

SCIENCE AND HEALTH IDEAS The alcohol ethanol in drinks of either low alcohol content (below 15%) or high alcohol content (over 30%) tend to be absorbed into the body more slowly. Our bodies are reasonably well–equipped to metabolize ethanol, making it less dangerous than methanol and isopropanol.

Distilled spirits (whiskey, brandy, rum, tequila, gin, etc.) contain no carbohydrates, no fats of any kind, and no cholesterol. However, alcohol abuse and alcoholism have been and remain persistent problems in the modern society.

Carbonyl compounds, particularly aldehydes are involved in the chemistry of vision. Carotenes and the compounds derived from them in our diets are cleaved at its central carbon-carbon bond to give vitamin A (retinol). Oxidation of retinol converts it to corresponding aldehyde, retinal, which reacts with the protein opsin to form the compound rhodopsin. Rhodopsin absorbs a photon of light and triggers a nerve impulse detected by the brain as a visual image.

Prostaglandins are prominent examples of naturally occurring carboxylic acids. More than 20 dozens prostaglandins have been identified as regulators of various biological processes and still continue to be an important focus of health care research. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring. They are mediators and have remarkable physiological effects including relaxation and contraction of bronchial tissues; dilation of blood vessels, lowering blood pressure, and offers promise as a drug to reduce the formation of blood clots. Two representative prostaglandins, known as PGE1 and PGF1a, are shown below.

Prostaglandin E1 (PGE1)

Prostaglandin F1a (PGF1a)

1

2

3

4

5

6

7

8

9

10

11 1213

14

15

16

17

18

19

20

CO2HO

OH

CH3

HO

1

2

3

4

5

6

7

8

9

10

11 1213

14

15

16

17

18

19

20

CO2H

OH

CH3

HO

HO

CHEMISTRY IN ACTION

22

SCIENCE PROCESSES

Communicating Hypothesizing Inferring

Modeling Predicting

VALUES

Holistic health Reverence and respect for life Environmental care Critical thinking Scientific orientation Personal discipline

Concern for common good Cooperation Creativity Goodwill Fairness

LIFE SKILLS

Active listening Giving and receiving feedbacks Empathy Cooperation and teamwork Decision making

Problem solving skills Critical thinking Setting goals Time management

IMPORTANT CONCEPTS

1. A functional group is the part of the molecules that determines the class to which the compound belongs. It also characterizes the chemical behavior of the organic compound.

2. The functional group present in alcohols, aldehydes and ketones, and carboxylic

acids are hydroxyl group (–OH), the carbonyl group (–C=O), and the carboxyl group (–COOH), respectively. The carbonyl group for aldehydes is terminal while that for the ketones are internal.

3. The systematic names of the alcohols, aldehydes, ketones, and carboxylic acids

are similar to parent alkane with the ending –e changed to –ol, –al, –one, and –oic acid, respectively.

4. Alcohols having small molecular masses are soluble in water because of the

presence of hydroxyl group. Alcohols having greater molecular masses are insoluble to water because of the long chain non-polar alkyl group.

CHEMISTRY IN ACTION

23

5. Carboxylic acids are acidic. Similar to inorganic acids, these organic acids can

change the color of blue litmus paper to pink or red. However, carboxylic acids and other organic acids are weak acids.

6. The oxidation reactions among oxygen-containing compounds differ. Alcohols

are readily oxidized to aldehydes and ketones. Aldehydes are oxidized to carboxylic acids. Ketones are slowly oxidized to lower acids upon heating. Carboxylic acids do not undergo oxidation reaction.

7. Alcohols, aldehydes, and ketones are flammable because these organic compounds are partially oxygenated. Carboxylic acids, on the other hand, are nonflammable because these compounds are fully oxygenated.

8. Ethanol could be obtained through fermentation. 9. Metabolism of ethanol in the body produces acetaldehyde which is further

oxidized to acetic acid and eventually to carbon dioxide and water. 10. A number of alcohols, aldehydes, ketones, and carboxylic acids occur in nature.

Alcohols and ketones are used mainly as solvents while aldehydes as flavoring agents, preservatives, and antiseptics. Carboxylic acids can be obtained from fruits and other foods.


This episode focuses on important oxygen-containing derivatives of hydrocarbons namely alcohols, aldehydes, ketones, and carboxylic acids. The properties, uses as well as reactivities of these groups of organic compounds are discussed in this episode. Each of the group of hydrocarbon derivatives can be distinguished from each other by a small structural part called the functional group. A functional group is a part of the molecule that allows us to classify it into a particular group. It is also the part of the molecule that gives the characteristic chemical behavior of the compound.

Alcohols. Alcohols have the general formula R–OH. The –OH is called the hydroxyl group and is the functional group for alcohols. Methyl alcohol and ethyl alcohol are common names. The systematic way of naming alcohols is similar to that of alkanes with the ending –e replaced by –ol. Examples are given below:

Methane

Methanol

C

H

HH

H

C

H

OHH

H

CHEMISTRY IN ACTION

24

For alcohols containing more than two carbons, the longest continuous chain must contain the hydroxyl group and the position of the hydroxyl group (as designated by a number) must be indicated. 1– Butanol along with 2–butanol and 2–propanol (or the isopropyl alcohol) is used to illustrate this:

1–Butanol

2–Butanol

2–Propanol

Some alcohols contain two to three hydroxyl groups. Examples are 1,2–ethanediol or commonly known ethylene glycol and 1,2,3–propanetriol, which is glycerin or glycerol. The former is used as antifreeze and the latter is a main component of fats and oils. The structures of these alcohols are shown below:

1,2–Ethanediol (Ethylene glycol)

1,2,3–Propanetriol (Glycerin or Glycerol)

The presence of the polar hydroxyl group in alcohols make low molecular mass alcohols soluble in water. However, high molecular mass alcohols are insoluble in water due to the very large non-polar portion of their molecules. Methanol. Many complicated alcohols occur in nature. An example would be menthol obtained from peppermint and citronella oil. Methanol, the simplest alcohol is also known as wood alcohol. This is because methanol can be obtained from the destructive distillation of wood. An illustration is shown in this episode. A piece of wood was wrapped with aluminum foil to eliminate any contact with air. Methanol is flammable. It burns with a non-luminous flame and like hydrocarbons, produces carbon dioxide and water when ignited. Methanol is poisonous. Around 30 mL ingested methanol can already cause blindness and in severe cases, death. Ethanol. A 100 percent ethanol is considered as absolute alcohol and is usually used as solvents in medicine, perfume, tinctures, and acrylics. Ethanol can be obtained from fermentation of molasses, a by-product of sugar refining. Ethanol is also the main component of beers and wine.

When the concentration of ethanol reaches 12 to 18 percent, fermentation stops. At this concentration, the enzymes used in the fermentation die. Distillation of the obtained ethanol could increase its concentration to 45 percent or 90 proof.

OH

1

2

3

4OH

1

2

3

4

OH

1 2 3

2

1HOOH

12

3HO OH

OH

CHEMISTRY IN ACTION

25

Denatured alcohol on the other hand, contains ethanol and small amount of methanol, benzene, pyridine, castor oil, and gasoline, making it unfit for drinking. Denatured alcohol is commonly used as solvents for lacquers and varnish. Three Classes of Alcohols. There are three types of alcohols based on the number of alkyl groups attached to the carbon bearing the hydroxyl group. The three classes of alcohols are primary, secondary, and tertiary alcohols. Primary alcohols contain only one alkyl group. Secondary alcohols and tertiary alcohols have two and three alkyl groups, respectively. The general formulas and examples are given below:

Class of Alcohol General Formula Example

primary (1°)

secondary (2°)

tertiary (3°)

In oxidation reactions, primary alcohols give aldehydes and secondary alcohols yield ketones. Tertiary alcohols do not undergo oxidation reaction. Aldehydes and Ketones. Aldehydes have the general formula RCHO. The structures as well as the systematic names of these compounds are shown below.

Common name: Formaldehyde Acetaldehyde IUPAC Name: Methanal Ethanal

The –C=O is called the carbonyl group and it is the functional group of aldehydes. Formaldehyde and acetaldehyde are common names. The systematic way of naming aldehydes is similar to alkane with the ending –e replaced by –al. The longest continuous chain must contain the aldehyde group. Thus, the systematic name of formaldehyde and acetaldehyde is methanal and ethanal, respectively.

C

H

OHR

H

HO

C

R

OHR

H

OH

C

R

OHR

R

OH

C OH

HC O

H3C

H

CHEMISTRY IN ACTION

26

Methanal. The preservation of fish through smoking is a common form of livelihood in the Philippines. Wood smoke contains methanol and this is the one responsible for fish preservation because of its bactericidal action. At room temperature, methanal is a gas. It is soluble in water and a 40 percent solution of methanal is commonly known as formalin. Formalin is used in preserving biological specimens and species and as an embalming fluid. Benzaldehyde. Another example of an aldehyde presented is benzaldehyde. Benzaldehyde, which is obtained from almond oil, has the carbonyl group attached to the benzene ring. It is mainly used as a flavoring agent.

Common name: Benzaldehyde IUPAC Name: Benzenecarbaldehyde

Acetone. Acetone is an example of a ketone. It is the smallest and simplest ketone. Like aldehydes, the carbonyl group is also the functional group in ketones. However, the carbonyl group for ketones is internal rather than terminal.

Common name: Acetone IUPAC Name: Propanone

Acetone is a common name. The systematic way of naming ketones is also similar to alkane with the ending –e changed to –one. For acetone, the systematic name is propanone. Acetone is commonly used as solvent for nail polish and dyes. In the body, an excess in ketone bodies including acetone causes ketoacidosis, and commonly occurs in acute diabetes, prolonged fasting and starvation. Since acetone is volatile, any excess amount can expelled through the lungs. Thus, people with ketoacidosis have strong acetone smell in their breath. Carboxylic Acids. Formic acid, the acid in ant bites and acetic acid, the main component of vinegar are the representatives of carboxylic acids. The general formula for the carboxylic acid is RCOOH. The functional group is –COOH, a carboxyl group. The systematic way of naming carboxylic acid is similar to alkanes with the ending –e replaced by –oic acid. The structures and IUPAC names of formic acid and acetic acid are given below. Carboxylic acids are weak acids as indicated by its ability to turn blue litmus to red. The general reaction illustrating the acidity of carboxylic acid is given below.

O

H

CH3H3C

O O

C

O

R OH+ H 2O C

O

R O- H3O

++

or

CHEMISTRY IN ACTION

27

Structures as well as occurrence and/or uses of some of the common carboxylic acids that we encounter everyday include:

Common Name

Structure IUPAC Name

Occurrences/Uses

1. Butyric acid

Butanoic acid

found in rancid butter, parmesan cheese, and

vomit, and has an unpleasant odor and acrid

taste 2. Caproic

acid

Hexanoic acid

compound responsible for the smell of goats and other

barnyard animals; found naturally in various

animals’ fats and oils 3. Caprylic

acid

Octanoic acid

found naturally in coconut and breast milk

4. Benzoic acid

Benzoic acid

Benzene carboxylic acid

main component of bathroom deodorants; its salts are normally used as food preservatives because they inhibit the growth of microorganisms in food

5. Citric acid

3–hydroxypropane– 1,3,5–tricarboxylic acid

obtained from citruses, a natural preservative; used to add an acidic (sour) taste to

foods and soft drinks; occurs in the metabolism of almost all living things; acts

as an antioxidant 6. Oxalic acid

Ethanedioic acid

abundantly present in many plants, most notably in

kamias; in edible foods such as star fruit (carambola), black pepper, parsley, poppy seed, amaranth, spinach, beets, cocoa,

chocolate, most nuts, most berries, and beans

OH

O

OH

O

OH

O

OH

O

HO OH

O O

OH

OHO

HOOH

O

O

http://en.wikipedia.org/wiki/Carambola

http://en.wikipedia.org/wiki/Black_pepper

http://en.wikipedia.org/wiki/Parsley

http://en.wikipedia.org/wiki/Poppy

http://en.wikipedia.org/wiki/Amaranth

http://en.wikipedia.org/wiki/Spinach

http://en.wikipedia.org/wiki/Beet

http://en.wikipedia.org/wiki/Cocoa

http://en.wikipedia.org/wiki/Chocolate

http://en.wikipedia.org/wiki/Nut_%28fruit%29

http://en.wikipedia.org/wiki/Berry

http://en.wikipedia.org/wiki/Bean

CHEMISTRY IN ACTION

28

7. Lactic acid

2–hydroxypropanoic acid

from sour milk; main component of skin

smoothers and feminine hygiene wash

Reactivity of Alcohols, Aldehydes, Ketones, and Carboxylic Acids. The flammability of the oxygen containing organic compounds is demonstrated using ethanol, ethanal, propanone, and ethanoic acid. Each sample was ignited with a match and the flammability was observed. Ethanol, ethanal, and propanone are all flammable and produced a characteristic blue flame, while ethanoic acid is nonflammable. Ethanoic acid did not burn because it is fully oxygenated while the other three samples are only partially oxygenated. Inter-Conversions of Alcohols, Aldehydes, Ketones and Carboxylic Acids Via Reduction-Oxidation Reactions. One of the most valuable reactions of alcohols, aldehydes, ketones, and carboxylic acids, both in the laboratory and industry is the reduction-oxidation reaction. In organic chemistry, reduction reaction [H], is the addition of hydrogen to an organic molecule or the removal of oxygen from it using reducing agents (RA). Oxidation reaction [O], on the other hand is the removal of hydrogen from an organic molecule or the addition of oxygen to it using oxidizing agents (OA) – either mild or strong.

General Reaction 1. Primary alcohols are oxidized either to their corresponding aldehydes or carboxylic acids depending on the nature of oxidizing agents chosen. The use of mild oxidizing agents (MOA) pyridinium chlorochromate (PCC) and pyridinium dichromate (PDC) in dichloromethane, CH2Cl2, solvent are the best method to prepare aldehydes from alcohols in the laboratory scale. However, the use of these MOA is too expensive for use in large scale industry.

Many strong oxidizing agents (SOA) such as CrO3, K2Cr2O7, Na2Cr2O7 and KMnO4 as aqueous acidic solutions, oxidize primary alcohols to carboxylic acids. Although

OH

O

HO

[O]with a MOA

(primary alcohol) (aldehy de) (carboxy lic acid)OHR

O

C

[O]with a SOA

[H]with a RA

HR H

OH

C C

O

R H

[O]with an OA

[H]with a RA

CHEMISTRY IN ACTION

29

aldehydes are intermediates in these oxidation reactions, they usually can’t be isolated because further oxidation reaction takes place too rapidly. Ketones, similar to aldehydes can be converted to carboxylic acids through oxidative cleavage using a very powerful oxidizing agent, acidified KMnO4. Aldehydes and carboxylic acids can be converted to their corresponding primary alcohols using reducing agents (RAs) such as: H2, with catalyst in CH3OH; sodium borohydride, NaBH4 in ethanol; and lithium aluminum hydride, LiAlH4 in ether. NaBH4 in methanol and H2, with catalyst in CH3OH is not nearly as potent a hydride donor as LiAlH4 and do not reduce carboxylic acids.

General Reaction 2. Secondary alcohols are oxidized to the corresponding ketones by the same reagents that oxidize primary alcohols. Moreover, ketones are reduced to the corresponding secondary alcohols by the same reagents that reduced aldehydes and carboxylic acids to primary alcohols.

Tertiary alcohols do not undergo oxidation reaction readily, but expect one under forcing conditions because of the absence of hydrogen on their hydroxyl-bearing carbon. Under certain special conditions, carboxylic acids can be oxidized further. Because it is already in a high oxidation state, further oxidation of carboxylic acids removes the carboxyl carbon as carbon dioxide. And, depending on the reaction conditions, the oxidation state of the remaining organic structure may be higher, lower or unchanged. The reactivity of these organic compounds to acidified potassium dichromate, K2Cr2O7 was presented in the video lesson. Addition of acidified K7Cr2O7 to the samples. show that ethanol and ethanal immediately turned the reagent to green, indicating that a chemical reaction took place. The green coloration is due to the formation of chromic ions. Propanone did not produce any immediate reaction. However, on standing, the sample also produced green solution. Ethanoic acid, on the other hand, did not react even on standing. To further confirm the reaction on acidified K2Cr2O7 with propanone and ethanoic acid, the samples were heated. With propanone, dichromate immediately turned to green while it did not change at all with ethanoic acid.

[O]with an OA C

O

R R'HRR'

OH

C

[H]with a RA

with an OA[O]

C

O

HO R'C

O

R OH+ C

OH

HHR

[H]with a RA

secodary alcohol ketone carboxylic acids primary alcohol

CHEMISTRY IN ACTION

30

The chemical reaction for the oxidation reactions of the samples is shown below:

Reaction 1: Reaction 2: Reaction 3:

The episode also showed that these reactions could also occur in our body. The foods that we eat are broken down into smaller molecules to be excreted or stored. Ethanol is used to illustrate this. Ethanol from alcoholic beverages is oxidized in the liver with the help of enzymes to become acetaldehyde. The acetaldehyde is further oxidized to acetic acid and eventually to carbon dioxide and water. If too much alcoholic beverages are ingested, the level of acetaldehyde in the body increases. This causes vomiting and dizziness associated with drunkenness. The legal intoxication is only 0.08 percent alcohol or 0.08 g/L of blood. If the alcohol level in the body exceeds 0.4 percent, stupor, coma or death can occur.

Additional Useful Information

The basic ingredients of the human body (average adult) are: water, protein, fats, carbohydrates, ions, salt, carbon dioxide, acids, bases, hydrogen peroxide, minerals, and vitamins. Oxygen, carbon, and hydrogen are three elements that make up most of the human body. Approximately the human body consists of oxygen (61 percent or 43 kg), carbon (23 percent or16 kg), and hydrogen (10 percent or 7 kg).

Alcohols. Ethanol or ethyl alcohol is the only alcohol fit for human consumption. Other than ethanol, the rest are fatal for human consumption even if ingested in small quantities.

Each molecule of alcohol is less than a billionth of a meter long and consists of a few atoms of oxygen, carbon, and hydrogen.

Along with methanol and ethanol, isopropanol or isopropyl alcohol is another important alcohol. Often containing fragrances and dissolved oils, isopropyl alcohol is the major component of rubbing alcohol. Industrially, it is prepared from petroleum by hydration of propene. Having a boiling point of 82°C, isopropyl alcohol quickly evaporates on the skin, producing a cooling effect. Since it possesses

OH K2Cr2O7

H3O+

OH

O

O K2Cr2O7

H3O+

OH

O

CH3C

H3C

O K2Cr2O7

H3O+

H3CC

O

OH+ C

O

H H

CHEMISTRY IN ACTION

31

weak antibacterial properties, it is normally used in the hospitals to maintain medical instruments in a sterile condition and to clean the skin before minor operations. Carboxylic Acids. Why does sugar rot your teeth? The truth is that it is not actually the sugar that rots your teeth. It is the plaque and sugar combination that does the dirty deed. Plaque is a collection of bacteria that adheres to your teeth and gets its energy by breaking down the sugars you eat. During sugar breakdown, many products are formed one of which is lactic acid which decreases the pH in your mouth. In an acidic environment, the hard enamel that protects your teeth dissolves which leaves your teeth vulnerable to decay and cavities. The saliva (average pH 6.8) in your mouth counteracts this decrease in pH by using buffers such as bicarbonate ion, HCO3

-, and the –COOH and –NH groups of proteins. However, the time it takes for the saliva to neutralize the acid depends on the amount of sugar that has been ingested. Therefore, the more sugar that is available, the more the bacteria multiply, the lower the pH in your mouth becomes, and the longer your teeth are susceptible to decay. Aldehydes and Ketones. Perfumes, fragrances, or scents are all part of our daily lives, often without us even knowing it – shampoos, soaps, detergents, and food all have scents associated with them. The sense of smell is very important as it helps us enjoy many experiences. Without the sense of smell, eating would be very bland because our taste buds can only detect four tastes: salt, sweet, bitter, and sour. The nose can detect seven primary odors: camphor-like, musky, floral, peppermint, ethereal, pungent, and putrid and can add to the taste of the meal. These fragrances are a result of volatile molecules which are given off and detected by the seven types of olfactory receptors in the nose that correspond to each of the primary odors. Many of the fragrances made into perfumes or scents originate from plants – from the flower (roses), seeds (cardamon), roots (angelica), wood (sandalwood), bark (cinnamon), and peels (orange). The fragrances are extracted from the plant in the form of essential oils. These essential oils contain a variety of molecules often in complicated mixtures. These molecules can have different structures that are combinations of varying functional groups which could be alcohols, ethers, aldehydes, ketones, esters, lactones, castor oil products, terpenes, paraffins, and heterocycles. Of these functional groups, aromatic aldehydes and ketones, along with heterocycles and terpenes are considered to be the most important.

VOCABULARY WORDS

1. Functional group - the part of the molecule that identifies the class to which a compound belongs; it also determines the characteristic chemical behavior of the compound.

CHEMISTRY IN ACTION

32

2. Alcohol - an organic compound whose functional group is the hydroxyl group

(–OH). 3. Aldehyde - an organic compound whose functional group is a terminal carbonyl

group (–C=O). 4. Ketone - an organic compound whose functional group is an internal carbonyl

group (–C=O). 5. Carboxylic acid – an organic compound whose functional group is the

carboxyl group (–COOH).

PRE-VIEWING ACTIVITIES

A. Demonstration. Iodine Test 1. Which is the apple and which is the potato? 2. Without smelling and touching, allow the students to distinguish a slice of

potato from the slice of apple. A drop of iodine is placed in both slices. [A blue coloration will occur in the potato while a brownish color will be observed from the apple.]

B. Introduce the video clip that deals with the different oxygen-containing organic

compounds and their properties as well as chemical reactions. C. Pose the Guide Questions that the students will answer after viewing the video

clips in the episode. Remind them from time to time to focus on finding the answers to the Guide Questions as they watch the video clips.

Guide Questions/Answers 1. What is a functional group?

A functional group is the part of the organic molecules that allows one to classify them to a certain group. It also characterizes the chemical behavior of the organic compound.

2. What are the oxygen-containing organic compounds presented and discussed in this episode? Give the general formula for each. The oxygen-containing compounds presented in the video clip are alcohols (ROH), aldehydes (RCHO), ketones (RCOR), and carboxylic acid, (RCOOH).

3. What is the functional group associated with each class of organic compounds given in question no. 2?

CHEMISTRY IN ACTION

33

The functional group for alcohol is the hydroxyl group (–OH). For aldehydes and ketones, it is the carbonyl group (–C=O). For carboxylic acids, it is the carboxyl group (–COOH).

4. Discuss the flammability of alcohols, aldehydes, ketones, and carboxylic acids. Alcohols, aldehydes, and ketones are flammable because these organic compounds are partially oxygenated. Carboxylic acids, on the other hand, are nonflammable because these compounds are fully oxygenated.

5. What is the oxidation product of aldehydes? The product of aldehyde oxidation is the carboxylic acid.

6. What is the oxidizing agent used in the episode? The oxidizing agent used in the presentation is the acidified potassium dichromate, K2Cr2O7.

7. Aldehydes and ketones contain carbonyl group. Differentiate the carbonyl group for aldehydes and ketenes. The carbonyl group of aldehydes is terminal while that of the ketone is internal.

8. Give the reaction showing the acidity of carboxylic acids.

9. What is the condition called when there is an excess of ketone bodies in one’s body? The condition wherein there is an excess of ketone bodies in the body is called ketoacidosis.

10. What is the final product of oxidizing ethanol in the body? The final oxidation product of ethanol is carbon dioxide and water.

VIEWING ACTIVITIES

C

O

OHR+ H2O C

O

O-R+ H3O

+

Let the students view the clips on: (1) Alcohol and Its Uses and Reactivity of Alcohols, at 2:80 – 9:34,

(2) Aldehydes and Ketones at 10:12 – 12:40, and (3) Carboxylic Acid at 12:49- 14:40.

CHEMISTRY IN ACTION

34

POST-VIEWING ACTIVITIES A. Discuss the answers to the Guide Questions. B. Mysterious Compound.

Objectives: § to be familiar with the characteristics of alcohols, aldehydes, ketones, and

carboxylic acids. § to appreciate the value of communication. Discussion: The class will be subdivided into six (6) groups with five (5) members each. Each group will be given six (6) envelopes. The first five (1st – 5th) envelopes contain pieces of a puzzle and the sixth (6th) envelop contains scrambled letters that will be needed in the finding the mystery compound. Using the first five envelopes, the group must be able to form five (5) equal sized squares. The group may only be given the sixth envelop once they have formed all the squares. The sixth envelop contains scrambled letters and a clue to what the compound is. Using the scrambled letters, spell out the mystery compound. Throughout the activity, no one is allowed to talk, write or make any sign language. They can only tap the group members to get a piece of the puzzle or position the letters of the mystery compound where they think it best fits. Marshals will be assigned to each group to make sure that the rules are strictly followed. Procedure: 1. Prepare the five equal sized squares as shown below:

2. Cut the outlined pieces. Get one piece of the puzzle from each square. Place

this in an envelop. Do the same for the rest of the puzzle until one envelop contains five unrelated pieces.

3. Obtain several pieces of square papers or cartolina. On each piece, write a letter corresponding to the mystery compound. Note that letters not included in the mystery word may be added.

Possible Mystery Compounds: CHOLESTEROL, ASCORBIC ACID, GLYCEROL, BENZOPHENONE, AND CINNAMALDEHYDE.

CHEMISTRY IN ACTION

35

C. Word Hunt.

Encircle the word described by the clues below. K E T O N E B O A T G A L A C E T O N E O L Z A L D E H Y D E Y T A C I D S R O F T G C T A D O I E D O H I E M R I R C E M R A A R E B D E K C T M N N O T O X I D A T I O N L H N H V I C Y C L O K A Y D R O C A R B O N N L A A L A O H O L U O E H Y D R O X Y L D L X Z Y B A D S W C C

1. the simplest ketone

2. have the general formula RCHO

3. carboxylic acids are weak __

4. reaction using acidic K2Cr2O7

5. functional groups for aldehydes and ketones

6. alcohol containing two –OH groups

7. ethylene glycol contains two ___ (–OH) groups 8. the acid in ant bite

9. alcohol obtained from molasses

10. also known as wood alcohol

D. Identifying Organic Compounds.

Given the following compounds, identify whether alcohol, aldehyde, ketone or carboxylic acid. Indicate the answer on the space provided opposite each structure.

CHEMISTRY IN ACTION

36

Compound Classification Compound Classification

1.

6.

2.

7.

3.

8.

4.

9.

5.

10.

E. Matching Type.

Match the systematic name given in Column A with the structures in Column B. Indicate the letter of the answer on the space provided before the number.

Column A Column B ____ 1. 2-Methyl-2-

pentanol

____ 2. Hexanal

A.

F.

____ 3. Pentanoic acid

____ 4. Benzoic acid

B.

G.

____ 5. Cyclobutanol

____ 6. 3-Methylbutanal

C.

H.

____ 7. 1-Propyl-1-cyclopentanol

____ 8. 3-Ethylpentanoic acid

D.

I.

O HO

OHHOO

COH

O

O OH

OH O

OO

O

OO O

OH

O

OH

OHHO

OH

OH

HO

O

OH

O

OH

CHEMISTRY IN ACTION

37

____9. 1,4-cylo- hexanediol ____10. 2,4-Dimethyl

-3-pentanone

E.

J.

F. Web Reaction.

Supply the missing organic molecule/s, the reaction condition/s and/or the reagent/s in the web reaction below. Write N.R. if the reaction is not feasible or there’s no appropriate reaction condition for the reaction to proceed.

ASSESSMENT Quiz. Choose the letter corresponding to the best answer.

1. This compound is commonly used as a flavoring agent in the preparation of cinnamon bread and other cinnamon-based products. The given compound is an example of __. A. alcohol . C. carboxylic acid. B. aldehyde. D. ketone.

2. More popularly known as undecylenic acid, 10-undecenoic acid, is used – in

combination of with zinc salts – to treat fungal infections such as athlete’s foot. The structure of this compound is __. A.

C.

1 2

4

5

6

78

9

10

K2Cr2O7 H3O

+KMnO4 H3O

+

OH

+

HO

O

LiAlH4 ether

3

O LiAlH4 ether

OH

O

O

OH

OO

OH

OH

OH

O

CHEMISTRY IN ACTION

38

B.

D.

3. The following undergo oxidation reaction with acidified KMnO4 at normal room condition EXCEPT __ A. butanal . C. butanoic acid. B. butanone. D. 2-butanol.

4. Better known as lactic acid, it is found sour milk and is also formed in the muscles during exercise. Give the IUPAC name of lactic acid. A. 1,2-dihydroxypropanoic acid C. 1-hydroxy-1-methylpropanoic acid B. 2-hydroxypropanoic acid D. 1,3-dihydroxypropanoic acid

5. The part of the molecules that determines the class to which the compound

belongs; also characterizes the chemical behavior of the organic compound. A. Functional group C. Parent B. Longest continuous carbon chain D. Substituent

6. It refers to the conversion of sugar and/or carbohydrates to alcohols or acids using yeast under anaerobic conditions. A. Acidification C. Oxidation B. Fermentation D. Reduction

7. If 2-methyl-1-butanol will be treated with acidified K2Cr2O7, which of the

following will be NOT be formed?

A. C.

B. D. Both A and B 8. The following organic molecules contain carbonyl group EXCEPT __

A. C.

O OH

HO

O O

O

OH

O

O

OH

O

OO

O-

O+

CHEMISTRY IN ACTION

39

B. D. Both A and C 9. Which of the following best describes why alcohols with higher molar masses

are immiscible in water? Alcohols with higher molar masses tend to be immiscible in water because of the __

A. absence of hydroxyl groups these alcohols are incapable of producing

hydrogen bonds with water. B. long chain of alkyl groups making the molecules non-polar. C. presence of the hydroxyl groups making these alcohols non-polar by nature. D. none of these.

10. Our bodies are reasonably well–equipped to metabolize ethanol. When

metabolized through our liver, the final products are A. aldehyde and ketone. C. carbon dioxide and water. B. aldehyde and carboxylic acid. D. ketone and carboxylic acid.

ANSWER KEYS

(Under Post-Viewing Activities)

C. Word Hunt.

K E T O N E B O A T G A L A C E T O N E O L Z A L D E H Y D E Y T A C I D S R O F T G C T A D O I E D O H I E M R I R C E M R A A R E B D E K C T M N N O T O X I D A T I O N L H N H V I C Y C L O K A Y D R O C A R B O N N L A A L A O H O L U O E H Y D R O X Y L D L X Z Y B A D S W C C

O

OH

CHEMISTRY IN ACTION

40

D. Identifying Organic Compounds.

1. ketone 6. alcohol 2. alcohol 7. ketone 3. carboxylic acid 8. carboxylic acid 4. aldehyde 9. aldehyde 5. ketone 10. aldehyde

E. Matching Type. 1. G 2. D 3. A 4. H

5. I

6. J 7. C 8. F 9. B 10. E

F. Web Reaction.

1.

6. K2Cr2O7, H3O+ / any strong OA

2.

7.

3. PCC, CH2Cl2

8. PDC or PCC in CH2Cl2

4.

9. NaBH4, etanol; or LiAlH4, ether

5. Na2Cr2O7, H3O+ / any OA 10. NaBH4, etanol; or LiAlH4, ether

O

O

OHHO

O

CHEMISTRY IN ACTION

41

(Under Assessment)

Quiz.

1. B 2. A 3. C 4. B 5. A

6. B 7. C 8. B 9. B 10. C

REFERENCES Atkins, R. C. & F. A. Carey. (2002). Organic chemistry: a brief course. (3rd ed.).

NY: McGraw-Hill, Inc. Goldberg, D. (1998). Fundamentals of chemistry. CA: McGraw-Hill, Inc. Magno, M. et al. (1991). Science and technology III. SEDP Series. QC: Book

Media Press. McMurry, John. (1998). Fundamentals of organic chemistry. (4th ed.). CA:

Brooks/Cole. Nueva España, R. et al. (1990). Science and technology III. QC: Abiva. Scott, W. H. (1996). Chemistry basic facts. Great Britain: Harper–Collins. Useful Websites _____. Alcohol Fun Facts. Accessed 26 October 2007. Postdam.edu Webpage. (http://www2.potsdam.edu/hansondj/index.html) ____. Perfume Chemistry. Accessed 25 October 2007. National Chemistry Week Web Page. (http://ncwsnc.cheminst.ca/articles/1997EC_perfume_e.html) ____. Why Sugar Rots Your Teeth? Accessed 25 October 2007. National Chemistry Week Web Page. (http://ncwsnc.cheminst.ca/trivia/index.html)

CHEMISTRY IN ACTION

42

Chapter 8: Organic Chemistry EPISODE 33: PHENOLS, ETHERS, AND ESTERS OVERVIEW

This episode deals with another group of oxygen-containing organic compounds: phenols, ethers, and esters. Phenols and ethers are structurally related to alcohols, while esters are products of hydrolysis reactions between alcohols and carboxylic acids. The physical and chemical properties as well as the uses of these compounds are introduced. Their reactivity is also compared with other related compounds through simple laboratory tests. Finally, the episode also shows how esters and ethers can be synthesized in the laboratory.

OBJECTIVES

At the end of this lesson, the student should be able to: 1. identify the functional groups of phenols, ethers, and esters; 2. compare the reactivity of alcohols and phenols; 3. account for the difference between the rates of reaction of benzene and phenols; 4. explain the difference in solubility between high molecular weight alcohols

and phenols; 5. identify the type of compound responsible for the odors associated with

certain fruits and flowers; 6. state the importance of temperature in some synthesis reactions; 7. explain the need to purify compounds obtained from synthesis; 8. explain the necessary precautions in the preparation and use of phenols and

ethers; 9. demonstrate how to synthesize esters in the laboratory; and 10. explain how soap works as a cleansing agent.


Viewing Episodes 31 – Hydrocarbons and 32 – Compounds of Carbon, Hydrogen, and Oxygen, would greatly facilitate the viewer’s comprehension of this episode which tackles a more complex group of organic compounds.

CHEMISTRY IN ACTION

43

SCIENCE PROCESSES

Communicating Hypothesizing Inferring

Modeling Predicting

VALUES

Holistic health Reverence and respect for life Environmental care Critical thinking Scientific orientation Personal discipline

Concern for common good Cooperation Creativity Goodwill Fairness

LIFE SKILLS

Active listening Giving and receiving feedbacks Empathy Cooperation and teamwork Decision making

Problem solving skills Critical thinking Setting goals Time management

IMPORTANT CONCEPTS

1. Phenols, like alcohols, have the hydroxyl group as its functional group.

2. Phenols are weakly acidic, much weaker acid than carboxylic acids. 3. In terms of reactivity, phenols are more reactive than benzene. The increase in

reactivity is due to the presence of the hydroxyl group. 4. Ethers are relatively unreactive to oxidizing agents, reducing agents, acids or

bases. 5. Phenols are partially soluble in water. The solubility of phenol is due to the

formation of hydrogen bonds with water. 6. Esters are derivatives of carboxylic acids. They are produced from the reaction

of alcohol with carboxylic acid in the presence of mineral acid. The reaction is called esterification.

CHEMISTRY IN ACTION

44

7. The characteristic scent of flowers and fruits is due to the presence of esters. BACKGROUND INFORMATION/EPISODE CONTENT

Three (3) vials containing different samples are introduced at the start of the episode, each containing a representative compound

for phenols, ethers, and esters. Based on the representative compounds, the properties, reactivity and uses of

these groups of compounds are investigated. Phenols. Phenol is a colorless solid with a characteristic strong odor similar to that of Lysol. This compound is very corrosive. Its vapor can burn nasal passages and it can cause painful burns on the skin on contact. The functional group of phenols is a hydroxyl group, -OH. It is the same functional group in alcohols but in phenols, it is attached to an aromatic ring. Phenols, therefore, are organic compounds with a hydroxyl group attached to an aromatic ring. Shown below is the structure of phenol in Figure 1.

All other compounds with the structure of phenol as the parent structure are classified collectively as phenols. Examples of phenol derivatives are given in Figure 2. Catechol is used in dye processing while resorcinol is used in tanning and in the manufacture of resins.

Ortho-chlorophenol Cathecol Resorcinol (2-Chlorophenol) (1,2-Benzenediol) (1,3-Benzenediol)

Figure 2. Examples of phenols.

Phenols and alcohols have the hydroxyl group as their functional group. Since they are structurally related, is it possible for them to have similar properties?

A comparison of the solubility in water of phenol and 1-hexanol is shown in the video lesson.

OH

Figure 1. Structure of phenol.

OH

OH

OH

OH

OH

Cl

CHEMISTRY IN ACTION

45

Phenol and 1-hexanol are both six-carbon compounds and contain a hydroxyl group. When 1-hexanol is added to water, the mixture forms two layers, indicating that this alcohol is immiscible with water. We learned in the previous episode that the length of the carbon chain affects the solubility of the alcohol and solubility in water drops sharply when the carbon chain is four carbon atoms in length. For phenol, a 2% mass by volume of phenol and water still results in a solution but a 10% mixture results in a cloudy mixture, indicating that phenol is only partially miscible with water. The slight solubility of phenol is due to the ability of the hydroxyl group to form hydrogen bonds with water, shown as dotted lines in Figure 3. The hydroxyl group of 1-hexanol is also capable of hydrogen bonding but the long nonpolar carbon chain prevents the alcohol from forming a solution with water.

OH

H

OH

OH

OH

H

A dilute aqueous solution of phenol is commonly known as carbolic acid which veterinarians use as an antiseptic. Unlike alcohols which are generally non-acidic, phenols are weakly acidic. The Ka values for phenols are in the range of 10-10 and are weaker acids compared to carboxylic acids whose Ka values are about 10-5 for acetic acid and benzoic acid. Reactivity of Phenols. Phenols are also structurally related to benzene. The reactivity of the two compounds was compared by reacting both with acidic potassium permanganate, KMnO4, a very strong oxidizing agent.

Table 1. Comparison of reactivities of benzene and phenol.

Reagent added Effect on Benzene (pure)

Effect on Phenol (2% solution)

Acidic KMnO4 (purple solution;

strong oxidizing agent)

No reaction

Mixture turned brown

Bromine, Br2 in water (red-brown solution)

No immediate reaction Reagent decolorized; formation of white precipitate of 2,4,6-

tribromophenol

Figure 3. Hydrogen bonding between phenol and water.

CHEMISTRY IN ACTION

46

In addition, phenols can easily be oxidized even just by exposure to light to quinone or semiquinones. This is why phenols are stored in dark colored bottles. On the basis of these observations, we can say that phenol is more reactive than benzene. The greater reactivity of phenol compared to benzene is due to the presence of the hydroxyl group. The hydroxyl group is an activating group because of its electron donating effect through resonance. The activating effect of phenols is most pronounced in the ortho or para positions as can be seen in the resonance structures given in Figure 4.

OH OH OH OH

Figure 4. Resonance structures of phenol.

Ethers. Diethyl ether or simply ether is a common topical anesthetic. Ethers have the general formula R – O – R’. The R groups stand for alkyl groups, and R and R’ may be the same or different alkyl groups. Common names of ethers contain the names of the alkyl groups attached to oxygen followed by the word “ether”. The simpler alkyl group is named first. The IUPAC system of naming ethers attaches the suffix “-oxy” to the simpler alkyl group, which then becomes a substituent of the more complex alkyl group that serves as parent alkane. Examples of these two ways of naming ethers are given in Table 2.

Table 2. Examples of ethers and their common and IUPAC names.

Formula Common Name IUPAC Name

CH3CH2–O–CH2CH3 diethyl ether ethoxyethane

CH3–O–CH2CH3 methyl ethyl ether methoxyethane

Many ethers occur naturally but one can also synthesize ethers in the laboratory. A demonstration of the synthesis of diethyl ether from ethyl alcohol in the presence of concentrated sulfuric acid is shown in the video lesson. The equation for the reaction is given below.

2CH3CH2OH145oC

H2SO4 CH 3CH 2 O CH2CH3 + H2O

The mixture is refluxed in an air-tight set-up to prevent the ether, a volatile and flammable substance, from escaping. It is also necessary that temperature is maintained at about 140oC since a change in temperature of about 30oC may result in other dehydration mechanisms and yield other products.

CHEMISTRY IN ACTION

47

ethene

2CH3CH2OH170oCH2SO 4 CH 2 CH 2 + H2O

2CH3CH2OH100oCH2SO 4 CH 3CH 2 + H2O

OSO 3H Ethers are relatively unreactive toward any oxidizing agent, reducing agent, acids or bases. However, on standing, they are easily converted to hydroxyperoxides, which can be explosive. Ethers are also flammable and should not be used when there is an open flame in the vicinity. In the past, diethyl ether found large scale use as an anesthetic. It was easy to prepare, easy to administer, and it causes excellent muscle relaxation. However, it is no longer used as an anesthetic because it can cause nausea and irritation to the nasal passages and as mentioned above, is highly flammable. An example of a naturally occurring substance with an ether linkage is vanillin which is obtained from vanilla beans. Vanillin is not only an ether but also a phenol and an aldehyde as well. Esters. Esters are compounds that often have pleasing and desirable odors that make them useful as additives to foods and beverages. These substances are derivatives of

carboxylic acids and have the characteristic functional group - COOR or C

O

OR. An ester can be prepared from the reaction of a carboxylic acid and an alcohol, using a strong acid such as H2SO4, as catalyst.

R C O

O

H + H O R'H+

+ H2Ocarboxylic acid alcohol ester

R C O

O

R'

The reaction is called esterification and an – OH group is lost from the carboxylic acid and a – H atom is lost from the alcohol and water is formed as one of the products. The net effect of this reaction is that the – OR’ group of the alcohol substitutes for the – OH group in the carboxylic acid. We can view a demonstration of the synthesis of ethyl acetate from ethyl alcohol and acetic acid in the presence of sulfuric acid. Ethyl acetate is the ester sample in the third vial shown in the video; it is the compound with the smell of plastic balloon and nail polish.

ethyl bisulfate

CHEMISTRY IN ACTION

48

H3C C O

O

H + H O CH2-CH3H+

+ H2Oacetic acid ethyl alcohol ethyl acetate

H3C C O

O

CH2-CH3

The synthesis of esters, as with other organic compounds, yields impure products since they are mixed with other reaction products and may be other original substances in the reaction mixture. To get pure esters, you need to do some purification steps, but if you wish to experience the process of synthesizing an ester, you may follow the scaled-down amounts presented in the video. Even without purification, the smell of ethyl acetate should be detectable after 20 minutes of reflux in water bath. Esters are named according to the common and the IUPAC system of nomenclatures. The key to naming esters is to identify the carboxylic acid part and the alcohol part in the structure! The name of the alcohol part of the ester appears first and is followed by a separate word giving the name of the acid part. The name for the alcohol part is simply the R group present. On the other hand, the name for the acid part is obtained by dropping the -ic acid ending and replacing this by the suffix -ate. Consider the example given below:

CH3-CH2 C O

O

CH3 acid part alcohol part

System Acid parent Alcohol parent Name of ester Common Propionic acid Methyl alcohol Methyl propionate IUPAC Propanoic acid Methanol Methyl propanoate

Esters are responsible for many flavors and fragrances of fruits and flowers. Usually, a natural flavor is a mixture of esters, with one being fairly dominant. Esters present in some common fruits and flowers are given in Table 4.

Table 4. Esters associated with some common fruits and flowers.

Fruit/Flower Structure Name

Ilang-ilang O

O

Linalool acetate

Sampaguita C O

O

(CH2)4CH3

OH

Amyl salicylate

CHEMISTRY IN ACTION

49

Banana CH3 C O

O

(CH2)4CH3

Pentyl ethanoate

Orange CH3 C O

O

(CH2)7CH3

Octyl ethanoate

Apple CH3CH2CH2 C O

O

CH3

Methyl butanoate

Pineapple CH3CH2CH2 C O

O

CH2CH3

Ethyl butanoate

Some esters have medicinal uses, the most common of which are aspirin and oil of wintergreen. These are esters of salicylic acid, an aromatic hydroxy acid, the same parent acid of amyl salicylate, an ester found in sampaguita. Oil of wintergreen, also called methyl salicylate, is used in skin rubs and liniments to help relieve the pain of sore muscles. Aspirin is a drug that has the ability to relieve pain (analgesic), lower body temperature (antipyretic), and reduce inflammation (anti-inflammatory). It is also used as a blood thinner and increase the time it takes for blood to coagulate. Saponification. The reverse reaction of esterification is the hydrolysis of an ester. In this reaction, the ester is converted back to the component alcohol and carboxylic acid with the addition of water. A very common hydrolysis reaction is that of triglycerides, esters of glycerol and fatty acids. The reaction is catalyzed by a base, such that the carboxylic acid recovered is neutralized by the base and the salt of the fatty acid, which is essentially soap, is obtained. Hence the reaction is called saponification. Soap is the salt of the anion of the carboxylic or fatty acids in triglycerides. The fatty acids are carboxylic acids of long, usually unbranched chain of hydrocarbons, 12 to 26 carbon atoms in length. The cleaning action of soap is directly related to the structure of this carboxylate anion: a long non-polar hydrocarbon chain, and polar end where the carboxylate anion is located.

O

O

non-polar body polar head The structure of the soap anion is like a contradiction: it has a water-loving head but its body does not dissolve in water. So the soap anions form tiny spherical groups called micelles, where their non-polar parts are hidden inside and the polar ends are at the outer part, in contact with water molecules. Dirt, grease, and oils are non-polar and dissolve inside the micelles. The micelles do not aggregate into larger groups because their surfaces are negatively charged, but they remain dissolved in water because their surfaces attract the positive ends of the polar water molecules.

Figure 5. An ion of

soap.

CHEMISTRY IN ACTION

50

The micelles are subsequently rinsed away, taking with them the soil and dirt that have dissolved inside them.

Figure 6. A soap micelle.

VOCABULARY WORDS

1. Phenols - are organic compounds with a hydroxyl group attached to an aromatic ring.

2. Ethers - organic compounds with the general formula R – O – R’, where the R groups stand for alkyl groups.

3. Esters - derivatives of carboxylic acids with the characteristic functional group - COOR; compounds that often have pleasing and desirable odors that make them useful as additives to foods and beverages.

4. Esterification – the reaction of an alcohol with a carboxylic acid in the presence of a mineral acid forming an ester and water.

5. Saponification – based catalyzed hydrolysis of triglycerides in which the

products obtained are glycerol and soap.

6. Micelle – the structure formed when soap anions aggregate into tiny spheres with their non-polar parts hidden inside and the polar ends are exposed in contact with water molecules.

PRE-VIEWING ACTIVITIES A. Introduce the lesson using examples of phenols, ethers, and esters that your

students may have heard. Examples are Vitamin E, BHA (a food antioxidant), thymol and vanillin (flavoring agents), catechol (skin irritant) for phenols; diethyl ether was used in the past as an inhalation anesthetic for ethers, while acetyl salicylic acid (aspirin), methyl salicylate (oil of wintergreen), and many plant and fruit odors are esters.

B. You may illustrate to the class how liquid SOSA (a NaOH solution) is able to unclog sinks of fatty deposits through the saponification reaction.

grease

CHEMISTRY IN ACTION

51

C. Pose the Guide Questions that the students will answer after viewing the episode. Ask them to focus their attention on finding answers to the guide questions as they watch the video episode.

Guide Questions/Answers 1. What is the similarity between phenols and alcohols?

Alcohols and phenols have the hydroxyl or –OH group. [However, because the –OH group in phenols is bonded directly to a benzene ring, it behaves differently from that of alcohols.]

2. Compare the solubility of phenol and 1-hexanol in water. Phenol is partially soluble in water while 1-hexanol is immiscible in water.

3. Give the general formula of ethers. The general formula of ethers is R – O – R’.

4. Compare the reactivity of phenol and benzene toward acidic KMnO4. Phenols readily react with acidic KMnO4 while benzene is unreactive.

5. What will happen to phenols if left in clear reagent bottles? Phenols will undergo oxidation to produce quinone.

6. In the preparation of ethers from alcohols, what side reaction can happen if the reaction temperature goes above 145oC? Above 145oC, the major product will not be ether but rather alkenes.

7. Give the general equation for the esterification reaction.

ROH + RCOOH RCOOR + HOH

8. What functional groups are present in aspirin? The functional groups present in aspirin are the carboxyl group and the ester group.

9. Define saponification. Saponification is a base-catalyzed hydrolysis reaction. It is the reverse of esterification. The products obtained in the reaction are soap and glycerol.

10. What type of base is used in saponification reactions? Strong bases such as NaOH are used in saponification reaction.

acid

CHEMISTRY IN ACTION

52

VIEWING ACTIVITIES



TEACHING TIPS

Suggested Activities A. Chem Bingo. Objectives:

1. To enjoin students to become familiar with the basic concepts associated with phenols, ethers, and esters.

2. To help students identify the esters associated with familiar fruits and flowers.

3. To recall some of the common reactions undergone by phenols, ethers, and esters.

Procedure: 1. Preparation of the bingo card. 2. The bingo card will have five columns and each column is assigned five

different words. The words that the columns may contain are given below:

B I N G O Phenol Ether Ester Alcohol Carboxylic acid

Soluble Immiscible Oxidized Flammable Unreactive

Ethyl acetate Aspirin Sulfuric acid Quinone Methoxy pentane

Esterification Saponification Oxidation Resonance Alkene

Carbolic acid Perfume Topical anesthetic Peroxides Acetaminophen

View the following segments: (1) 2:48 - 7:23 for Phenols,

(2) 7:28 – 11:30 for Ethers, and (3) 11:53 - 23:00 for Esters.

CHEMISTRY IN ACTION

53

3. Prepare different combinations of the words depending the size of the class. One such combination is given below:

B I N G O

Ether Flammable Sulfuric acid

Saponification Topical anesthetic

Ester Oxidized Methoxy pentane

Alkene Acetaminophen

Alcohol Soluble Aspirin Resonance Peroxides Phenol Immiscible Quinone Oxidation Carbolic acid Carboxylic acid

Unreactive Ethyl acetate

Esterification Perfume

4. Prepare questions whose answers are the terms in the bingo card. 5. Write each letter-word combination on small balls, disks or tiles. These

pieces will be drawn during the game, similar to the usual bingo game.

Playing the game: 1. Each student will be given a bingo card. 2. Before the game starts, inform the class the pattern being sought, whether

horizontal, vertical or diagonal. 3. When a ball is drawn, announce the letter but not the word. Ask the class the

question corresponding to the word. If the students give the correct answer, then they can block off the letter-word combination.

4. The game continues until a student declares a “Bingo”.

B. Which Does Not Belong? Choose the word that does not belong to the group. Write your answer on the space before the number.

_____ 1. hydroxyl group

quinone resonance micelle

_____ 2. carbonyl oxy antiseptic explosive _____ 3. alcohol oxidation sulfuric acid carboxylic acid _____ 4. KMnO4 phenol acidic ether _____ 5. ester phenol benzene ether

CHEMISTRY IN ACTION

54

C. Scrambled Letters. Arrange the letters to identify the compound and draw the correct structure. A clue for each compound is given below.

1 L H A M E O E E H Y T T N A T 2 L N P O E H 3 T Y E M A B E H O N T X U 4 E N N U I Q O 5 L C H T E O A C 6 T O Z A E E B T L N H E Y 7 O E N E P X A H T T Y E N 8 O N R L I S C E O R 9 L T E T E C T H A Y E A

10 R C D I C C A B O A L I

1. an ester 6. an ester with a benzene ring 2. contains a hydroxyl group bonded to a benzene ring

7. an ether

3. an ether 8. used in tanning 4. oxidation product of phenol 9. present in plastic balloon 5. used in dye processing 10. dilute solution of pheno

D. Multiple Choice. Choose the letter that corresponds to the best answer.

1. The following organic compounds contain oxygen EXCEPT

A. alcohol. C. ether. B. benzene. D. ester.

2. Which of the following describes a phenol? A. It is aromatic. C. It is completely soluble in water. B. It contains two hydroxyl groups. D. It is a strong acid.

3. The correct IUPAC name of

OCH2CH3

. A. Ethylcyclopentyl ether C. Cyclopentylethyl ether B. Cyclopentoxyethane D. Ethoxycyclopentane

4. The alcohol used in the preparation of butylhexanoate is

A. butanol. C. hexane. B. hexanol. D. butane.

CHEMISTRY IN ACTION

55

CH3CHCH2OH

CH3

+ CH3CHCH2COH

CH3 OH3O+

heat

CH2CHCH3

CH3

CH3CHCH2C

CH3 O

OCH2CHCH3

CH3

CH3CHCH2C

CH3

CH2CHCH3

CH3

CH3CHCH2CH2

CH3

OH

OCH2CHCH3

CH3

CH3CHCH2C

CH3 O

For items 5 and 6, select the structure for each given name. Refer to the choices below:

A. O C.

HO

NO3

B. C

O

O

D.

O

5. Butylbutanoate 6. Propoxycyclobutane

7. The products for the reaction:

are H2O and A.

C.

B.

D.

8. Esters can be used as component of the following EXCEPT

A. tanning agent. C. solvent. B. perfume. D. flavoring.

9. The base-catalyzed hydrolysis of an ester will produce A. an ester and water. C. glycerol and soap. B. alkene and water. D. aldehydes and ketones. C.

10. Which of the following will produce peroxides on standing?

A.

CO

O

B.

O

C.

O

D.

CHEMISTRY IN ACTION

56

O

O

OH

OH

CO O

E. Modified True or False. Write TRUE if the name given to the compound whose structure is shown is correct. If the name is incorrect, give the correct name on the space provided before the number. Indicate the functional group of the compound on the blank at the right hand side.

_________1. Propylcyclopentylether________________

O

_________2. Propyl-2 methylpentanoate_____________

_________3. 1,3-Phenyldion_______________________

_________4 . Propylcyclohexyl ether________________

O

_________5. Phenylmethanoate____________________

ANSWER KEYS B. Which Does Not Belong?

1. micelle 2. carbonyl 3. H2SO4 4. ether 5. benzene D. Scrambled Letters.

1. Methyl ethanoate 6. Ethyl benzoate 2. Phenol 7. Ethoxypentane 3. Methoxybutane 8. Resorcinol 4. Quinone 9. Ethyl acetate 5. Cathecol 10. Carbolic acid

E. Multiple Choice. 1. B 2. A 3. D 4. A 5. B

6. D 7. A 8. A 9. C 10. C

CHEMISTRY IN ACTION

57

F. Modified True or False.

1. Propoxycyclopentane ether Ether 2. True Ester 3. 1,3-benzenediol Phenol 4. Propoxycyclohexane Ether 5. Methyl benzoate Ester

REFERENCES McMurray, John. (1998). Organic chemistry. (2nd ed.). FL: Brooks/Cole. Snyder, Carl H. (1992). The extraordinary chemistry of ordinary things. (2nd ed.).

NY: John Wiley & Sons, Inc.

CHEMISTRY IN ACTION

58

Chapter 8: Organic Chemistry EPISODE 34: HYDROCARBON DERIVATIVES PART III

OVERVIEW

Episode 33 showed that hydrogen, carbon, and oxygen can combine to form a large variety of organic compounds. This episode introduces another two groups of derivatives of hydrocarbons: the alkyl halides and amines. Alkyl halides are formed by replacing one or all of the hydrogen atoms in the alkanes with a halogen. Amines are derivatives of ammonia, replacing one or all of the hydrogen atoms with an alkyl group. The physical and chemical properties of alkyl halides and amines are discussed and some are illustrated using simple laboratory tests. Examples of naturally occurring and synthetic alkyl halides and amines are given. The uses and harmful effects of these compounds are likewise discussed.

OBJECTIVES

At the end of this lesson, the student should be able to: 1. describe the reactions involved in the preparation of alkyl halides; 2. define free radicals; 3. enumerate the many uses of alkyl halides in the synthesis of other organic

compounds; 4. explain the harmful effects of some halogenated hydrocarbons; 5. identify primary, secondary, and tertiary amines; 6. explain the solubility of amines; 7. show the acid-base reaction of amines; 8. explain the uses of amines in medicine; 9. identify naturally occurring amines found in plants and animals; and 10. explain the action of some nitrogen-containing compounds in the body.

INTEGRATION WITH OTHER LEARNING AREAS This episode can be linked with Episode 23 - Please Pass the Protons: Acids Bases and Episode 38 - The Atmosphere.

SCIENCE PROCESSES

Predicting Controlling variables

CHEMISTRY IN ACTION

59

VALUES

Usefulness of synthetic vs naturally occurring pesticides

Care for the environment

LIFE SKILLS Critical thinking Creative thinking

Decision-making

IMPORTANT CONCEPTS

1. Alkyl halides are halogenated hydrocarbons, the halogens being chlorine, bromine, fluorine, and iodine. They are useful intermediates in the synthesis of other organic compounds such as ethers, carboxylic acids, and amines.

2. Some halogenated compounds though offer some benefits are known to have harmful effects like Freon and DDT.

3. Amines are derivatives of ammonia obtained by replacing one or more of its

hydrogen atoms with an alkyl group. 4. Some examples of naturally occurring amines include adrenaline or epinephrine

and also some alkaloids. BACKGROUND INFORMATION/EPISODE CONTENT Alkyl Halides. Alkyl halides are halogenated hydrocarbons, the halogens being chlorine, bromine, fluorine, and iodine. The general formula of alkyl halides is RX, where X stands for the halogen and R is any simple alkyl or substituted alkyl group. We have encountered some reactions that produce alkyl halides. In Episode 31, we saw that bromine-water reacted very slowly with alkenes. However, the reaction occurred faster when exposed to light. The chemical equation for the bromine test is as follows:

Alkynes also react with bromine-water as shown in the equation below.

Similarly, alkanes react with halogens to produce alkyl halides. Methane is used to show the reaction in the production of carbon tetrachloride (CCl4):

CH2 CH2Br2uv

2 CH2 CH2

Br

Br

CH CHBr22uv HC CH

Br

Br

Br

Br

CHEMISTRY IN ACTION

60

Naming Alkyl Halides. Alkyl halides are named as alkanes with the halogens considered as substituents. The modifications for the names of the halogens in the alkyl halides are as follows:

Bromine - Bromo Chlorine - Chloro

Iodine - Iodo Fluorine - Fluoro

Common names may also be used in naming alkyl halides. Examples of IUPAC names and common names of alkyl halides are given below:

Structure IUPAC name Common name

2-bromopentane pentylbromide

2-chloropentane pentylchloride

Iodocyclopentane cyclopentyliodide

2-bromo-2-methylpropane isobutylbromide

1,1-dichlorocyclohexane cyclohexyldichloride

Preparation of Alkyl Halides. The mechanism for the preparation of alkyl halides involves the formation of free radicals. Free radicals contain odd electrons or unpaired electrons and are very reactive. Once started, the reaction continues until all the hydrogen atoms in the alkane are replaced by a halogen. A detailed mechanism of the reaction is illustrated in the next page. Free radical reactions are not easily controlled in the laboratory and are therefore not commonly used in the preparation of alkyl halides. The most common synthesis of alkyl halides is the one that uses alcohol as the starting material. The general reaction is:

CH4Cl2uv CH3Cl

Cl2uv CH2Cl2

Cl2uv CHCl3 CCl4

Cl2uv

Br

Cl

I

Br

ClCl

CHEMISTRY IN ACTION

61

Cl - Cl 2 Cl .uvInitiation step:

free radicals

Propagation step:

C

H

H

H

H.. .ClH.

.

ClC

H

H

H

+

Termination step:

The chlorine free radical can continue to react until methane is fully halogenated.

The termination step can be any or all of the following:

Cl + Cl - Cl

CH3CH3

CH3

+

+.Cl.

Cl... CH3CH3

CH3Cl

ROH HCl/ZnCl2 RCl.

Alkyl halides are useful intermediates in the synthesis of other organic compounds such as ethers, carboxylic acids, and amines. Halogenated compounds are known to have harmful effects. An example is dichlorofluoromethane (CCl2F2) or commercially known as Freon 12. Freon is an odorless and stable compound. It is non-corrosive and nonflammable and is ideal for use in aerosols and as refrigerants and foaming agents. However, its stability has certain setbacks. Freon 12 can stay for a long time in the atmosphere because of its stability. But in the stratosphere, it is converted to free radicals and reacts with the ozone layer, thus causing its depletion. Another example is dichlorodiphenyltrichloroethane or DDT. The structure of DDT is:

CHEMISTRY IN ACTION

62

This compound was previously used as an effective insecticide. However, its low solubility in water allows it to accumulate in water runoffs. Plants absorb DDT residues which are transferred to animals and eventually to humans through the food chain. Since it is insoluble in water, DDT accumulates in the body and interferes with calcium metabolism. Amines. Amines are derivatives of ammonia, replacing one or more of its hydrogen atoms with an alkyl group (e.g., methyl, -CH3). There are three types of amines based on the number of alkyl groups attached to the nitrogen atom: primary (10), secondary (20), and tertiary (30) amines. A comparison of the three types of amines is shown below with the corresponding examples:

Type of Amine Formula Example

1o amine

2o amine

3o amine

The solubility of amines in water is demonstrated in this episode with diethylamine and aniline as the samples. It was observed that diethylamine, a low molecular weight amine, is soluble in water. The solubility of low molecular weight amines is due to the formation of hydrogen bonds between the amino group and water. The formation of hydrogen bonds is shown below:

Naming of Amines. Amines have common as well as IUPAC names. The common name is obtained by identifying the alkyl group(s) attached to the amino group. The simpler alkyl group is named first followed by the more complex alkyl group and the word amine. Examples used in the episode are shown below:

NH2R NH2CH3

NHR2 NHH3C

H3C

NR3N CH3

H3C

H3C

N HH

R HO

H

O HHH-bonding

The alkyl group is methyl. Therefore, the common name of the amine is

methylamine.

H3C N H

H

methyl

CHEMISTRY IN ACTION

63

The IUPAC name of amines uses the more complex alkyl group as the parent amine and the simpler alkyl group as the substituent. The two examples above are named methanamine and N-methylethanamine. The N- before the word methyl indicates that the alkyl group is attached to nitrogen. It can be observed that the common names are simpler to use than the IUPAC names. Methanamine, a primary amine, is responsible for the characteristic smell of fish. Aromatic amines also exist and they are derivatives of aniline. Some examples of aromatic amines are shown below:

Reactivity of Amines. The episode introduces a teaching technique called probex: predict, observe, and explain. This technique allows more student participation inside the classroom. To demonstrate the reactivity of amines, aniline was allowed to react with a strong acid such as HCl. The reaction was analyzed using the probex technique.

PREDICT § Nitrogen belongs to Group 5A and therefore contains five valence

electrons. Three covalent bonds are formed together with lone pair electrons.

§ The lone pair can be donated to an electron deficient compound making aniline act as a Lewis base.

§ Reaction with HCl will therefore be an acid base reaction.

OBSERVE § An experiment was performed to determine the validity of the prediction.

§ HCl was added to a sample of aniline. The formation of a white precipitate was observed.

§ The white precipitate was characterized by determining its solubility in water.

§ The white crystals obtained readily dissolved in water.

NH2

Br

NH2

O2N

NH2

m-methyl aniline p-bromo aniline 2-ethyl-5-nitro aniline

The simpler alkyl is methyl and must be named first

followed by the more complex alkyl, ethyl, and then the word amine.

The name of the amine is methylethylamine.

H3C N H

CH2CH3

methyl(simpler alkyl)

ethyl(more complex alkyl)

CHEMISTRY IN ACTION

64

EXPLAIN § Aniline acted as a Lewis acid by donating its lone pair of electrons as shown below:

§ The crystal observed is . The compound is ionic will therefore dissolve in water.

§ The crystals were further reacted with a strong base, NaOH. The reaction is shown below:

§ The reaction reverts back to the original amine.

The acid base reactions described above showed that insoluble amines could be made soluble by converting it to an ionic compound. This implies that the solubility of the amine can be controlled by the pH of the medium. The ability of amines to act as solubility switch enables them to be useful in extraction procedures, synthesis, and even in medicine. Natural Amines. Some examples of naturally occurring amines include adrenaline or epinephrine, synthesized in the adrenal medulla. In cases of heart failure, adrenaline is administered as an IV solution of epinephrine chloride. Other naturally occurring amines include alkaloids. Alkaloids are basic, nitrogen-containing compounds that have physiological effects. Examples of common alkaloids include caffeine, obtained from coffee and tea, morphine, an analgesic, and quinine, an anti-malarial agent. The structures of these compounds are shown below:

NH2

HCl

NH3+Cl-

base

acid

salt

NH3+Cl-

NH2ClH + - NH2

Na+ -OH+ H2O + NaCl

CHEMISTRY IN ACTION

65

Caffeine Morphine Quinine

Additional Useful Information

1. DDT is deposited and stored in the fatty tissues of animals. DDT is considered as endocrine disrupters, that is, they are chemicals that affect the hormonal system.

2. Alkaloids usually contain one or more cyclic carbon chains in which nitrogen is part of the cyclic group.

3. Calcium which is stored in the bones is important in several body functions such as muscle contractions, nerve conduction, and enzyme function.

4. Calcium metabolism involves the mechanism that maintains adequate calcium levels. Defects in the mechanism can lead to hypercalcemia or hypocalcemia.

5. Amines are essential to life because they are the main constituents of amino acids.

6. Aromatic amines are used in the synthesis of dyes. 7. Heterocyclic amines have nitrogen atom within the ring. 8. The high melting point of alkyl halides compared to alkanes is due to the polar

bond between carbon and the halogen.

VOCABULARY WORDS

1. Halogenated compounds – compounds that contain halogen atoms; the halogens being chlorine, bromine, fluorine, and iodine.

2. Amines - derivatives of ammonia as a result of replacing one or more of its hydrogen atoms with an alkyl group.

3. Alkaloids - basic, nitrogen-containing compounds that have physiological

effects like caffeine, obtained from coffee and tea, morphine, an analgesic, and quinine, an anti-malarial agent.

4. Free Radicals – species that contain odd electrons or unpaired electrons and are very reactive.

PRE-VIEWING ACTIVITIES Pose the Guide Questions which the students will answer after viewing the episode. Ask them to focus on finding the answers to the Guide Questions as they watch the video.

N

N

O

N

N

CH3H3C

Oo OH

N

H N

CH3O

N

H

HO0

CHEMISTRY IN ACTION

66

Guide Questions/Answers

1. Give the formula of Freon 12. CCl2F2

2. Why is Freon 12 a good material for refrigerants and aerosols? Freon 12 is stable. 3. What happens with Freon when it is released in the atmosphere?

Freon reacts with light to form free radicals. The free radicals in turn react with the ozone layer, slowly depleting it.

4. What is DDT?

DDT stands for dichlorodiphenyltrichloroethane and it is used as a pesticide.

5. Why is DDT harmful to animals, humans, and the environment? Since DDT is insoluble in water it accumulates in water runoffs. DDT is then absorbed by plants which can later be transferred to animals and humans. In the body, DDT interferes with calcium metabolism.

VIEWING ACTIVITIES



TEACHING TIPS Suggested Activities A. Slum Book. For a deeper understanding of some alkyl halides and amines, ask

the students to prepare a Slum Book for the following compounds: Freon 12, DDT, morphine, and caffeine. The student may choose any of these compounds. The students may also use the research materials they gathered before viewing the episode. The format of the Slum Book is given in the next page.

Show video clip on Application and Effects of Halogenated Compounds

at segments 6:25 - 8:25 as set induction activity.

CHEMISTRY IN ACTION

67

B. Epitaph Writing. Tell the students to write an epitaph for the compound of their

choice. They may use the information gathered from their research materials. They are to be creative in writing the epitaph. At the end of the class, each student will be asked to read his/her prepared epitaph.

Me and My Slum Note

E E E E E E E E E E E E E E E E E E E

Getting to know you Name: ________________________________________________________ Nickname: ________________________________________________________ Date of Birth: ________________________________________________________ Place of Birth: ________________________________________________________ Address: ________________________________________________________ Name of Parents: ________________________________________________________ Likes: ________________________________________________________ Dislikes: ________________________________________________________ Favorite Color: ________________________________________________________ Chums: ________________________________________________________ Enemies: ________________________________________________________ Hobbies: ________________________________________________________

CHEMISTRY IN ACTION

68

Let’s Get Personal Favorite Crush: ________________________________________________________ First Love: __________________________________________________________ Describe your ideal man/woman: __________________________________________________________ Ambition: __________________________________________________________

Dedication

ASSESSMENT

A. Crossword Puzzle. Complete the crossword puzzle.

1 2 3 1 2 3 5 4 6 5 6

CHEMISTRY IN ACTION

69

Across Down

1. dichlorodifluoromethane 2. root word for iodine 3. amines are Lewis _______ 4. halogenated hydrocarbons 5. reagent used in bromine test 6. alkaloid present in coffee

1. amine with one R group 2. element found in amine 3. related to heart attack 4. amine containing benzene 5. insecticide 6. derivatives of NH3

B. Complete the Table. Complete the table below by providing the necessary information:

Structure Name Alkyl Halide or Amine?

C. Classifying Amines. Encircle the amino group in each of the following

compounds and identify whether it is a 10, 20 or 30 amine:

Compound Classification

1.

2.

Cl

I

N

Br

F

NH2

CH2 CH NH2

CH3

CH2 CH NH

CH3

CH3

CHEMISTRY IN ACTION

70

3.

4.

5.

D. Identification. Identify the term(s) that best describe(s) the statements. Write the

answer on the space provided before each number: ____________________ 1. Halogenated hydrocarbons ____________________ 2. Amines with three alkyl groups ____________________ 3. An amine wherein the amino group is directly

attached to the benzene ring ____________________ 4. Type of reaction between an amine and a strong

acid ____________________ 5. Destroys the ozone layer ____________________ 6. Lewis bases donate _____________ ____________________ 7. Which is more soluble in water, methylamine or

trimethylamine? ____________________ 8. Valence electrons of nitrogen ____________________ 9. The mechanism for the synthesis of alkyl halide

in the presence of UV light involves the formation of ______________.

____________________ 10 An amine responsible for the distinct odor of fish

CH

CO O CH3

NH

CH CH NH2

CH3OH

CHEMISTRY IN ACTION

71

ANSWER KEYS A. Crossword Puzzle. 1 P 2N 3A

1 F R E O N 2I O D O

I T R

M R E

3B A S E O N

R 5D G A 4A L K Y L H 6A L I D E L

N M T N I

I 5B R O M I N E N

L N E

I 6C A F F E I N E

N S

E B. Complete the Table. Complete the table below by providing the necessary information:

Structure Name Alkyl Halide or Amine?

2-chloro-2-methylpentane Alkyl halide

2-butyl-1-iodocylcyclohexane Alkyl halide

N-ethylbutanamine Amine

2-bromo-2-fluoropentane Alkyl halide

Cl

I

N

Br

F

CHEMISTRY IN ACTION

72

m-methylaniline Amine

C. Classifying Amines. Encircle the amino group in each of the following

compounds and identify whether it is a 10, 20, or 30 amine:

Compound Classification

1.

Primary amine

2.

Secondary amine

3.

Secondary amine

4.

Primary amine

5.

Secondary amine

D. Identification. Write the word(s) that best describe(s) the statement in each of

the following numbers:

Alkyl halides 1. Halogenated hydrocarbons Tertiary amine 2. Amines with three alkyl groups Aromatic amine 3. An amine wherein the amino group is directly

attached to the benzene ring Acid-base reaction 4. Type of reaction between an amine and a strong

acid Freon 12 5. Destroys the ozone layer Electron pair 6. Lewis bases donate _____________ Methyl amine 7. Which is more soluble in water, methylamine or

trimethylamine?

NH2

CH2 CH NH2

CH3

CH2 CH NH

CH3

CH3

CH

CO O CH3

NH

CH CH NH2

CH3OH

CHEMISTRY IN ACTION

73

Five 8. Valence electrons of nitrogen. Free radicals 9. The mechanism for the formation of alkyl halide

in the presence of UV light involves the formation of ______________.

Methanamine 10 An amine responsible for the distinct odor of fish REFERENCES

McMurry, J. (1998). Organic Chemistry. (2nd ed.). FL: Brooks/Cole. Snyder, C.H. (1992). The extraordinary chemistry of ordinary things. (2nd ed.). John

Wiley & Sons, Inc. Useful Websites http://www.3dchem.com/molecules.asp?ID=90 http://www.pan-uk.org/pestnews/Actives/ddt.htm http://www.chw.org/display/PPF/DocID/22678/router.asp http://en.wikipedia.org/wiki/Calcium_metabolism http://hyperphysics.phy-astr.gsu.edu/hbase/organic/amine.html

http://www.3dchem.com/molecules.asp?ID=90

http://www.pan-uk.org/pestnews/Actives/ddt.htm

http://www.chw.org/display/PPF/DocID/22678/router.asp

http://en.wikipedia.org/wiki/Calcium_metabolism

http://hyperphysics.phy-astr.gsu.edu/hbase/organic/amine.html

CHEMISTRY IN ACTION

74

Chapter 9: Organic Chemistry EPISODE 35: POLYMERS: THE GIANT MOLECULES

OVERVIEW

Polymers make up an important class of compounds that widely exist in nearly every aspect of our lives. Things we use at home (from carpets, upholstery, sheets, furniture to kitchenware), the parts of our cars (seats, tires, ceiling, dashboards, steering wheel), the clothes we wear (polyester, rayon, etc.), the toys children play with, the appliances we use, foods that we eat and even the molecules in our body are made up of polymers. This lesson focuses on the diversity in the chemical forms of polymers. The different classes of polymers, their basic chemical formulas, properties and uses are discussed here. Specific examples of polymers are cited. The corresponding video for this lesson includes a visual presentation of processes such as polymerization, vulcanization and other chemical reactions involved in the synthesis of certain polymeric compounds. Charles Goodyear’s accidental discovery of vulcanization, the search for synthetic rubber and textile fibers such as nylon are also presented in this episode.

OBJECTIVES

At the end of this lesson, students should be able to: 1. define monomer and polymer; 2. describe the types of polymers and name some examples; 3. differentiate polymers according to their properties; 4. differentiate between addition and condensation polymerization reactions; 5. identify monomers that form specific polymers; 6. draw structural formulas for polymers made from given monomers; and 7. identify the good and bad effects of using plastics to human beings and the

environment.


Episodes 31 – Hydrocarbons, 32 – Compounds of Carbon, Hydrogen and Oxygen, 33 – Phenols, Ethers and Esters, and 34 – Hydrocarbon Derivatives Part III, serve as foundations of this episode. On the other hand, Episodes 36 – Polymers: The Giant Molecules and 37 – Molecules of Heredity: DNA and RNA are directly related to this episode, biomolecules being natural polymers.

CHEMISTRY IN ACTION

75

SCIENCE AND HEALTH IDEAS

Environmental science Ecological balance Trivia: § Limonene is being studied as a substance that aids in the biodegradability of § polymers. § The solid parts of all plants are made up of polymers. These include cellulose,

lignin, and various resins. § Wood resins are polymers of a simple hydrocarbon, isoprene.

SCIENCE PROCESSES

Experimenting Identifying

Classifying Predicting

VALUES

Environmental awareness Environmental concerns

Social responsibility

LIFE SKILLS

Creative thinking Critical thinking Decision-making

Problem-solving Productivity Entrepreneurial skills

IMPORTANT CONCEPTS

1. Polymers are large molecules, also called macromolecules or giant molecules,. that are made up of smaller ones (monomers) that are linked by covalent bonding.

2. Addition polymerization is formation of polymers from unsaturated monomers joined together without the loss of atoms from the reacting molecules.

3. Condensation polymerization is polymerization using monomers that are bi-functional or have two functional groups that are joined together with the simultaneous elimination of atoms or groups of atoms, usually H2O.


Polymers (poly = “many” and mer from Greek meros = “part”) are large molecules that are made up of smaller molecules that are linked by covalent bonding. Polymers

CHEMISTRY IN ACTION

76

are also called macromolecules or giant molecules. The small molecular units making up a polymer are called monomers. There are many naturally occurring polymers. Proteins in our bodies, cellulose in plants, rubber from rubber tree, silk from silkworm cocoon, and piňa fibers from the piňa plant are some examples of natural polymers. Synthetic polymers are those that are synthesized in the laboratory for some intended use. Some materials that are made up of synthetic polymers are nylon fabric, polyvinyl chloride (PVC) pipes, plastics, and polyurethane foams.

Monomers are the building blocks or the repeating units of polymers. These building blocks may come from the different classes of organic compounds. A polymer may have from hundreds to millions of these monomers. If a polymer contains only one type of monomer, it is called a homopolymer. When two or more types of monomers are contained in the chain, a copolymer is obtained. The properties of a polymer are quite different from the properties of its monomer units. The table below shows a comparison of some properties of the polymer polyethylene and its monomer ethylene or ethene.

Table 1. Comparison of ethylene and polyethylene.

Property Ethylene Polyethylene Molar mass 8 g/mole 1,000,000 g/mole

State at room temperature

gas solid

Reaction reactive unreactive, stable When writing the formula for the polymer product, the repeating monomer unit is placed inside the bracket with bonds extending on both directions. The subscript n refers to the number of times the monomer units are repeated in the full structure of the polymer. The formula for polyethylene is:

CH2 CH2 n .

Polymerization. The reaction involved in the formation of a polymer is called a polymerization reaction. The process involves the formation of covalent bonds between the monomers. The two general types of polymerization are addition and condensation. Addition Polymerization. In this type of polymerization, unsaturated monomers join together without the loss of atoms from the molecules. Examples of addition polymers are polyethylene, polystyrene, Teflon, poly(vinyl chloride), & polypropylene

CHEMISTRY IN ACTION

77

The polymerization reaction proceeds in three steps: 1. Free-radical formation. A free radical is a molecule with an atom that has an

unpaired electron. The unpaired electron makes a free radical very reactive and can catalyze or initiate many addition polymerizations. Organic peroxides (ROOR) are frequently used for this purpose.

2. Propagation of polymeric chain. 3. Termination. These steps are illustrated below in the formation of polyethylene.

Step 1: Free-radical formation. The peroxide splits into free radicals: RO:OR ® 2 RO�

Step 2: Propagation of polymeric chain. The initial free radical adds to ethylene to form a new free radical. The chain continues to elongate (polymerize) as long as free radicals continue to add to ethylene:

RO� + CH2=CH2 ® RO-CH2-CH2� ROCH2CH2� + CH2=CH2 ® ROCH2CH2CH2CH2� ROCH2CH2CH2CH2� + CH2=CH2 ® RO(CH2CH2)n�

Step 3: Termination. Polymerization stops when the free radicals are used up by combining with other free radicals to form a stable compound. Two possible routes are shown below:

RO� + RO(CH2CH2)n� ® RO(CH2CH2)nOR or

RO(CH2CH2)n� + RO(CH2CH2)n� ® RO(CH2CH2)n (CH2CH2)nOR Condensation Polymerization. In this process, monomers are bifunctional or have two functional groups, and these join together with the simultaneous elimination of atoms or groups of atoms, usually H2O. Examples of condensation polymers are proteins, polysaccharides, nucleic acids, polyesters, polyamides (nylons), and polyurethanes. Shown below as Figure 1 is the condensation reaction involved in the formation of Nylon 66, a synthetic fiber made from the monomers adipic acid (a six-carbon acid) and hexamethylenediamine (a six-carbon amine). Notice the water molecule removed (in box of dotted sides) during the formation of a bond between the carbon atom of adipic acid and the nitrogen atom of hexamethylenediamine.

CHEMISTRY IN ACTION

78

Adipic acid Hexamethylenediamine

n

The table below lists some common condensation polymers and their uses.

Table 2. Some common condensation polymers and their uses. Condensation

Polymer Monomers Applications

Polyethylene terephthalate

Terephthalic acid and ethylene glycol

Tire cord, permanent-press clothing and magnetic tape for tape recorders and

computers KevlarTM Terephthalic acid and

p-phenylenediamine Bullet-proof vests

NomexTM Isophthalic acid and m-phenylenediamine

Parts for electrical fixtures, flame-resistant clothing for race-car drivers and firefighters,

and flame-resistant building materials. Silicone Dimethyl siloxane Breast implants, hydraulic oils and lubricants,

antifoaming agents for frying potato chips, components of suntan oil, car polish, digestive

aids and make-up, space suits, dentures, contact lenses, artificial skin, etc.

Nylon-66 1,6-diaminohexane and 1,6-hecanedioic

acid

Carpeting, tire cord, fishing lines, textiles, gears, bearings, and zippers

Natural Polymers. Many natural materials are polymers. Examples of naturally-occurring polymers are given below. Biomolecules such as: § polysaccharides are polymers made up of sugar units. Starch and cellulose are

both made up of glucose molecules, § proteins are copolymers made up of amino acids, § nucleic acids are chains of purine and pyrimidine bases.

COH

O

(CH 2 ) 4 C

O

OH

N

H

H

(CH 2 ) 6 N

H

H

C

O

(CH 2 ) 4 C

O

N

H

(CH 2 ) 6 N

H

-H 2 O

Figure 1. Formation of Nylon 66

CHEMISTRY IN ACTION

79

Natural rubber is a polymer of isoprene or 2-methyl-1,3-butadiene, hence it is also called polyisoprene. It is obtained from the rubber tree plant Evea gracilensis. Rubber is a soft, sticky material when warm and a hard, brittle material when cold. It can be coiled, twisted and intertwined. The polymer chains can be straightened when rubber is stretched but if overly done, they may slip past each other and not return to their original position. Charles Goodyear discovered in 1839 the process of vulcanization when he accidentally dropped some natural rubber containing sulfur on a hot stove. The process has improved the elasticity of rubber. Vulcanization creates sulfur cross links between the isoprene chains. The sulfur bonds prevent the chains from slipping past each other when the rubber is stretched. Thus, the added cross links make the rubber harder and stronger. Materials that act in this stretchable way and recover their original shape after a deforming force has been applied on them are called elastomers. Synthetic Polymers. While most natural polymers play key roles in the basic functioning of living organisms, we have increasingly become dependent on synthetic polymers which can be “tailor-made” to suit particular purposes. Polyethylene is the simplest of the synthetic polymers. It is produced cheaply and has the largest production volume among polymers. It is a homopolymer made from a chain of alkene called ethane or ethylene, CH2=CH2. It is familiar to us either as soft, lightweight plastic bags used for packaging fruits and grocery items. Substituted polyethylenes may also come as hard, tough molded items used at home such as toys, tables, and cabinets. The polymerization of ethylene is represented by the following reaction: Under conditions of high pressure and temperature and in the presence of a catalyst, these unsaturated hydrocarbons are made to join together in long chains producing a new compound. During polymerization, the unsaturation is lost; one pair of electrons from the double bond is used to form a covalent bond with each of two other molecules of ethylene, thereby producing a fully saturated product.

H2C CH2 -CH2CH2-CH2CH2-CH2CH2-CH2CH2-

H2C CH2

catalyst-(CH2CH2)-nn

ethylene polyethylene

ethylene unit

CHEMISTRY IN ACTION

80

Two principal kinds of polyethylene that differ in the arrangement of the polymer chains are produced depending on the catalysts and conditions used during manufacture. These are the following:

High Density Polyethylene (HDPE) § Linear chains are arranged in an ordered crystalline structure. § The molecules have greater rigidity and higher tensile strength. § These materials melt at 135oC. § These products are colored, opaque, and are formed in molds. § They are used for making beer cases, toys, television cabinets, and bottle

caps.

Low Density Polyethylene(LDPE) § Chains are branched, cross-linked ethylene monomer units. § They are waxy, transparent or translucent, semi-rigid bendable plastics with

a melting point of 110oC. § These are used to make plastic bags, plastic films, squeezable soft drink

bottles, and electric wire insulations. Some familiar polymers are related to polyethylene in that the monomer units have one or more of the hydrogen atoms in ethylene substituted by other elements or group of atoms. These are sometimes called substituted polyethylenes. Teflon or polytetrafluoroethylene is a tough, unreactive nonflammable material with low friction and high melting point. Teflon is widely used as a non-stick coating for frying pans and other cooking utensils. Electrical tapes and tapes for water pipe connections are also made of Teflon. The monomer unit in Teflon is tetrafluoroethylene, CF2=CF2. This monomer is formed when all the hydrogen atoms in ethylene are replaced by fluorine. Polyvinyl acetate is a derivative of Teflon which makes chewing gums chewy and gummy. This material becomes brittle at low temperature thus, a good way of removing chewing gums on clothes is by applying ice on the gum. Polypropylene (PP) is made from the monomer propylene, which is produced by replacing one of the hydrogen atoms in ethylene by a methyl group. This polymer is a tough material that is made into fibers used in making rice sacks, candy wrapping, and plastic adhesives. Polyvinyl Chloride (PVC) comes from the monomer chloroethene or vinyl chloride which is formed when one of the hydrogen atoms of ethylene is replaced with a chlorine atom. PVCs are used as hard plastic in floor tiles, water pipes and in soft forms like raincoats that are tough as leather-like materials. PVCs are transformed into softer

CHEMISTRY IN ACTION

81

and flexible materials by adding plasticizers like polychlorinated biphenyls (PCB) and dibutyl phthalate (DBP).

What is a plasticizer? Plasticizers are compounds that are added to the polymer to soften it. It is believed that the plasticizer molecules insert themselves between chains of the polymer through intermolecular forces of attraction, causing some disorder in the arrangement of the chains, making them soft and pliable. The plasticizers escape from the polymer with time through evaporation and diffusion, making the plastic crack or become brittle. Polystyrene is produced from the monomer styrene, which has a benzene ring substituting for one of the hydrogen atoms in ethylene. This polymer is used in making disposable cups and utensils. It is also used in making rigid foam for styrofoam, styropor, ice chests, and packing materials for shipping instruments and appliances. Styrene-butadiene rubber (SBR) is one of the most important synthetic rubbers today that serve as a cheaper substitute for natural rubber. It is a copolymer of styrene (25%) and butadiene (75%) and the presence of butadiene removes the brittleness of polystyrene and imparts elasticity to this copolymer. It is widely used in the production of rubber tires. Polyurethanes comprise a class of synthetic resinous, fibrous, or elastomeric compounds made by the reaction of diisocyanates (organic compounds containing two functional groups of structure –NCO) with other difunctional compounds such as glycols. These elastomers are used as flexible foams for padding in cushions, mattresses, and furniture. As rigid foams, they are used for such lightweight structural elements as cores for airplane wings. Polyacrylonitriles are a class of resinous, fibrous, or rubbery substances belonging to the family of organic polymers based on acrylonitrile. Almost all polyacrylonitrile resins are copolymers made from mixtures of monomers, with acrylonitrile usually making up the major portion; other monomers often present include butadiene, styrene, vinylidene chloride or other vinyl compounds. Polymer Fibers. Textile fibers used in our clothes are made from a combination of natural fibers such as natural cotton, linen, silk and wool plus synthetic fibers like nylon, acrylon, and dacron. Nylon was discovered by DuPont chemist Wallace Carothers. The original compound was named Polymer 66 because of its two different monomer units 1,6-hexadiamine and adipic acid, both having 6 carbon atoms.

CHEMISTRY IN ACTION

82

The polymerization involves the reaction of a carboxyl group of the adipic acid and the amino group of 1,6-hexadiamine producing water molecule and an amide linkage. Nylon is used in making stockings, various outer and undergarments.

Dacron is a polyester made from ethylene glycol and terepthalic acid. The hydroxyl groups in ethylene glycol react with the carboxylic groups in terepthalic acid to produce long chains held together by ester linkages. These polyester molecules are useful fibers for wash-and-wear clothes. When blended with cotton, the textile product is lightweight, durable and has a natural feel. When Dacron is formed as a magnetic film, it is called Mylar and it is used in making audio and video tapes.

Plastics. Plastics are synthetic or semi-synthetic materials that are used to manufacture objects of industrial or commercial use. Many of these are colorful, lightweight, strong, easy to clean, and inexpensive polymer-made materials. The term “plastic” actually refer to the property of a material to be cast, set or pressed into molds or shapes at certain conditions, and this property is exhibited by many polymers. Naturally occurring substances were used as plastic materials long before the first synthetic plastics were made. These materials include gutta-percha from the sap of certain trees and shellac from the secretions of small scale insects and horns of animals. Today, synthetic plastics have found use in almost all aspects of our lives because of the variety of properties that they exhibit. Plastic products have been developed to conduct electricity ,as shield against electromagnetic radiation, as plastic electrodes in conducting paints, inks, fibers, and flooring materials.

terephathalic acid

ethylene glycol

OHHO

+

COOH

HOOC

O

O

O O

npolyester

CHEMISTRY IN ACTION

83

The first synthetic plastic was celluloid, a product of plant material cellulose and nitrate. However, the discovery of Bakelite, the first plastic entirely made from synthetic materials by Leo H. Baekeland marked the true beginning of the plastic industry. Most plastics are now made from the breakdown products of petroleum and coal. Demand for the materials grew so rapidly that many of the most important plastics entered into commercial production. Types of Plastics. Plastics are grouped into two main types based on their properties. 1. Thermoplastics are plastics that can be repeatedly softened or melted by heating

then shaped into new products. Polymers that belong to this group are polyethylene, polystyrene (Styrofoam), polyvinyl chloride (PVC), and nylon.

Thermoplastics are made up of long, thin, covalently bonded monomers that

form tangled chains. Relatively weak electrostatic forces hold the chains together. These forces can be easily destroyed by heat. When the plastic is warmed, the chains begin to move against each other making the polymer stretch and flex easily. It melts at low temperatures and does not decompose.

2. Thermosets are plastics that cannot be softened by heating, hence their shape can

no longer be changed. Examples are Bakelite and polyurethanes. Thermosets are made up of cross-linked chains. Strong covalent bonds both within and between the chains form a random three-dimensional network with rigid bonds which inhibit the chains from moving in relation to one another. When they are heated, the bonds are stretched or compressed. The covalent bonds between the chains develop as the thermosetting polymers are cured, usually by heating, after they are molded and shaped. Once the bonds form between the polymer chains, the plastics become rigid and hard. Their shapes cannot be changed and they burn or char before they melt.

Plastic Production. Most of the plastics produced are of the thermoplastics type, while thermosets account for less than 15% of plastic production. The production of plastic makes use of different processes such as extrusion either by blow-molding, calendaring, and foaming. Extrusion is the predominant plastic-forming process used in the industry today. In this process, a heated thermoplastic solution is forced continuously through fine holes in a die made in a desired shape. Extrusion may be compared to squeezing toothpaste from a tube that produces a long, narrow, continuous product. Calendaring is a process that involves a melted mass of polymer passed over and through a series of heated rollers to form a sheet. It is used to produce semi-finished goods such as coverings, flooring, and plastic sheets for use in wrapping.

CHEMISTRY IN ACTION

84

Foaming is done by mixing compressed air or gas into the melted polymer mass. As the process goes on, a gas is released as foaming agent to expand the polymer. The expanded polymers can be made into products ranging from egg boxes and drinking cups to sponges. Plastic Wastes. Most plastics are not biodegradable. Scientists and environmentalists are searching for methods in dealing with plastic waste disposal. Recycling some of these wastes is one way of reducing plastic rubbish while others can be ground up then reprocessed into new products. The effects of plastics on the environment, however, go beyond the issue of recycling. Chemicals like chlorofluorocarbons, CFCs, are used as foaming agents in the manufacture of some plastic products but CFCs contribute to ozone depletion. Thus, there is a growing call for the plastic industry to drastically cut its production. Misconception about Polymers.

Misconception: Polymers are restricted to monomers of the same chemical composition or molecular weight and structure.

Correction: As mentioned in the concept, some natural polymers are

composed of one kind of monomer. However, most natural and synthetic polymers are made up of two or more different types of monomers.

VOCABULARY WORDS 1. Monomers - the building blocks or the repeating units of polymers.

2. Polymers - large molecules that are made up of smaller units linked by covalent

bonding. 3. Plastics - synthetic or semi-synthetic materials that are used to manufacture

objects of industrial or commercial use. 4. Plasticizers - compounds that are added to soften polymers. 5. Thermoplastics - plastics that can be repeatedly softened or melted by heating

then shaped anew. 6. Thermosets - plastics that cannot be softened by heating hence their shape can

no longer be changed.

CHEMISTRY IN ACTION

85

7. Extrusion - plastic-forming process where a heated thermoplastic solution is

forced continuously through fine holes in a die to transform the material into some desired shape.

8. Calendaring - a process where a melted mass of polymer is passed over repeatedly through a series of heated rollers to form a sheet.

9. Foaming - mixing compressed air or gas into the melted polymer mass to make

it expand.

10. Vulcanization – the cross linking of isoprene chains via the sulfur bonds to make rubber harder and stronger.


A. Let the students make a list of things made out of polymers. Tell them to give their reasons for classifying these things as such. Discuss some of the applications and examples of polymers given in the previous concepts.

B. Introduce the study of polymers as one of the important and updated discipline

of the new generation through the video episode. C. Pose the Guide Questions that the students will answer after viewing the

episode. Tell them to focus on finding the answers on the video they are going to watch.

Guide Questions/Answers 1. What are polymers? How are they classified?

Polymers are long chains of carbon atoms made of several repeating units called monomers. Polymers are classified based on their sources and types of polymerization.

2. What are the different types of polymers?

Polymers may be natural or synthetic. They may either be a homopolymer or a copolymer. They may also be addition or condensation polymer.

3. How do we write the structures of polymers?

A shortcut notation is used in representing a polymer. The monomer is placed inside brackets. Hyphens (-) or tildes (~) symbols can be placed on both sides of the monomer which means that the repeating units may extend in both directions. The notation n indicates how many times a monomer is repeated in the full structure of the polymer.

CHEMISTRY IN ACTION

86

4. Cite the different polymers seen in the video. Give their properties and uses.

The different polymers are: a. Polyethylene – its monomer is the alkane ethane. They are the common

plastics either as soft, lightweight, plastic bags or hard, tough, plastic moldings.

b. Polypropylene – the monomer is the alkene propene. Rice sacks, plastic adhesives, cigarette and candy wrappers are made of these.

c. Polyvinylchloride – the monomer is chloroethene. It is used as tough plastic in floor tiles and water pipes. The softer forms are used as raincoats imitating leather materials.

d. Polystyrene – a benzene containing polymer. It is used in making rigid foams such as styrofoam and packing materials.

e. Polyurethane – a polyester compound used in making mattresses and foams.

f. Polytetrafluoroethylene – commonly known as Teflon. A polymer with low friction and a high melting point, making it ideal as nonstick coating for frying and cooking pans.

g. Polyvinyl acetate – a gummy polymer that becomes brittle at low temperatures. It is used in chewing gums and other gummy products.

h. Nylon – a copolymer of two monomers, 1,6-hexadiamine and adipic acid, joined by an amide linkage. It is used as a substitute textile fiber and commonly used in stockings and undergarments.

i. Dacron – a polyester made from ethylene glycol and terephthalic acid. This polyester fiber is blended with cotton and wool to make lightweight, durable wash-and-wear clothes with a natural feel.

j. Polyacrylonitrile – commonly known as arlon or acrylon, it is another popular synthetic fiber used in sweaters and carpets.

5. What is polymerization? Polymerization is the process by which polymers are produced. It occurs in the presence of a catalyst and under a certain pressure and temperature.

6. Explain how vulcanization can make elastomers more rigid and stronger.

Vulcanization creates sulfur cross links between hydrocarbon chains. These sulfur bonds prevents the chains from slipping past each other when elastomers are stretched.

7. Explain how tough plastics like PVCs can be transformed into softer

materials. The addition of plasticizers such as polychlorinated biphenyls, PCBs, or dibutyl phthalate, DBP, makes tough plastics softer. Plasticizers are liquids of low volatility but with time this is lost through evaporation making the plastic crack or become brittle.

CHEMISTRY IN ACTION

87

8. Describe the different synthetic fibers cited in the video.

These are nylon, dacron, mylar, and arlon or acrylon.

9. Differentiate HDPE from LDPE. High density polyethylenes are linear-chained polymers that are closely packed forming an ordered crystalline structure characterized by high rigidity and tensile strength. Low density polyethylenes are branched chain, cross-linked polymers that are waxy, semi-rigid, and transparent.

10. What is the main problem posed by polymers on the environment? How do

we counteract these bad effects of polymers on the environment? Plastic waste disposal is the main problem since plastics are non-biodegradable and tend to accumulate. Reusing and recycling are possible counteraction to these bad effects.

VIEWING ACTIVITIES



TEACHING TIPS

Suggested Activities:

A. Creating Models of Polymers. Let students create a fragment model of

polymers using materials such as beads and strings or clay balls and wooden sticks. Bring out the creativity of the students by encouraging them to make use of different colors to represent the different atoms making up the molecule.

B. Contest in the Identification of Polymers. To test whether the students have

gained mastery of polymer structures, ask them to identify the repeating units given a fragment of the molecules or to write the structure of the polymer given the monomer. A few examples are presented below: 1. What is the repeating unit in PVC? 2. What is the repeating unit in polyacrylonitrile? 3. Give the structure of the polymer made from vinyl fluoride. Show at least

four repeating units.

Segments 2:33 – 12:15 may be viewed to get a general idea of the nature of polymers,

but if time permits, full video viewing may be done for added information.

CHEMISTRY IN ACTION

88

4. Give the structure of the polymer made from vinylidene chloride. Give at

least four repeating units.

C. Polymer List. Ask students to make a list of plastic objects or parts of objects that they encounter every day. Ask them to identify the kinds of polymers used in making the items. Let them compare their lists with those made by their classmates.

D. Active Debate. Pose to the class the statement “An environmental activist states

that all plastics should be banned”. Divide the class into two debating teams. Assign the “pro” and “con” positions. Ask each debating group to develop arguments for its assigned positions or provide an extensive list of arguments that they might discuss.

At the end of a brief discussion, let them select 2-3 spokespersons. Arrange the two debating teams so that they are facing each other. Have the spokespersons of each team to occupy the front seats and the remaining students behind them.

Begin the debate by having the spokespersons present their views. After all the opening arguments have been heard, stop the debate and reconvene the teams. Ask them to strategize how to counter the opening arguments of the opposing side. Resume the debate. As the debate continues, encourage other students to pass notes to their spokespersons with suggested arguments or rebuttals. Urge them to cheer the arguments of their spokespersons. Then end the debate when it is appropriate. Reconvene the whole class and hold a discussion on what the students learned about the issue from the debate experience. Ask them to identify what they thought were the best arguments raised by both sides.

E. Litter Inventory. Let the students survey one area and make a list of the litter they see or find. Let them critically determine to what extent plastics contribute to the litter problem in their community. Encourage them to defend their position on this.

F. Recycling Materials. Encourage students to collect and recycle materials

considered to be a trash. Ask them to submit a project of recycled product. Organize an exhibit showcasing all these recycled products. Remind students that there is money in this trash.

CHEMISTRY IN ACTION

89

G. Plastics Display. Let the students research on Plastic Recycling Codes. Tell

them to gather samples of plastics for each code. Encourage them to make a creative and informative display of the actual products with their codes.

ASSESSMENT A. Identification. Identify what is being described in the following: __________ 1. The simplest, least expensive, and highest-production volume

synthetic polymer. __________ 2. The process by which monomers are converted to polymers. __________ 3. Branch-chained, cross-linked polyethylene that are waxy,

transparent, and generally melts at low temperatures. __________ 4. A compound that is added to soften polymers. __________ 5. A process which creates sulfur cross-links between hydrocarbon

chains to make rubber harder and stronger.

B. Matching Type. Match the different types of plastics listed in Column A with their indicated use listed in Column B. Write the letters that correspond to your answer. These letters will form a message. Column A Column B ___1. Mylar UG. Chewing gums ___2. Polyvinyl chloride HE. Non-stick coating for cooking pans ___3. Nylon EF. Mattresses and foams ___4. Dacron LP. Disposable cups ___5. Polyurethanes ND. Carpets and sweaters ___6. Polyvinyl acetates EA. Rice sacks ___7. Polypropylene DI. Water pipes ___8. Polyacrylonitrile GO. Magnetized video and audio films ___9. Polytetrafluoroethylene YR. Wash-and-wear clothes ___10.Polystyrene SM. Stockings and undergarments Message: ________________________________________________________

C. Complete the Table.

Monomer Polymer Structural Formula 1) polyethylene [~CH2-CH2~]n propylene 2) [~CH3-CCH3=CH2~]n styrene polystyrene 3) 4) teflon 5)

CHEMISTRY IN ACTION

90

ANSWER KEYS A. Identification.

1. Polyethylene 2. Polymerization 3. Low density polyethylene 4. Plasticizer 5. Vulcanization

B. Matching Type. 1. GO 2. DI 3. SM 4. YR 5. EF 6. UG 7. EA 8. ND 9. HE 10. LP

Message: God is my Refuge and Help.

C. Complete the Table. 1. 2. 3. 4. 5.

ethylene

polypropylene

[~CH2-CH~]n

tetrafluoroethylene F F [~C-C~]n F F

REFERENCES

Ash, M. (1992). Handbook of plastics, compounds, elastomers, and resins. NY: Grolier.

Britannica Micropaedia Ready Reference (Volume 9). (1997). Morgan, N. (1995). Chemistry in action. NY: Oxford University. Tan, E. (1992). Science and technology III. A compilation of instructional materials

for special science classes. QC: SEI, DOST.

CHEMISTRY IN ACTION

91

Chapter 9: Polymer Chemistry and Biochemistry EPISODE 36: THE MOLECULES OF OUR FOOD

OVERVIEW

This episode deals with the polymers of living things – carbohydrates, lipids, and proteins. The monomers of these molecules are in themselves already complex. It is not surprising to find the structures, compositions, and reactions of the molecules of our food even more variable and definitely more intricate. Carbohydrates, lipids, and proteins are important because these are the molecules which form the major part of a person’s diet. An account of what happens to these biomolecules inside the body and how these are converted to nutrients and energy and tackled in this episode.

OBJECTIVES

At the end of this lesson the student should be able to: 1. identify the structure, understand the properties, and describe the functions of three biomolecules – carbohydrates, lipids, and proteins; 2. differentiate the different types and give examples of carbohydrates, lipids,

and proteins; 3. discuss the role played by enzymes in digestion of food; 4. explain what happens to carbohydrates, lipids, and proteins upon digestion in

the body; and 5. describe the process of energy production from the by-products of

carbohydrates, lipids, and protein digestion.


Episodes 31- Hydrocarbons, 32 – Compounds of Carbon, Hydrogen, and Oxygen, 33 – Phenols, Ethers, and Esters, and 34 – Hydrocarbon Derivatives Part III on Organic Chemistry and Episode 35 on Polymers: The Giant Molecules are foundations for the better appreciation of this episode.

SCIENCE AND HEALTH IDEAS Malnutrition Obesity and its risks SCIENCE PROCESSES

Observing Experimenting

Computing Inferring

CHEMISTRY IN ACTION

92

Classifying Predicting

VALUES

Taking care of one’s health

LIFE SKILLS

Self-control Valuing one’s resources

Health consciousness

IMPORTANT CONCEPTS

1. Metabolism is the sum total of all biochemical reactions in our system. It can be subdivided into two general processes: catabolic and anabolic reactions.

2. Metabolism involves three important biomolecules which are sourced by the body from its food intake. These are carbohydrates, lipids, and proteins. They are the molecules that sustain our life and are called as macronutrients.

3. Carbohydrates may either be monosaccharides, disaccharides or

polysaccharides. 4. Lipids are biomolecules that are water-insoluble but soluble in organic solvents

of very diverse in nature and serve as energy source for the body.

5. Proteins are linear polymers of amino acids joined by amide bonds also called as peptide bonds.

6. Proteins perform many functions in the body among them: (1) as structural components, (2) for transport, (3) for defense ,(4) as hormones, and (5) as enzymes.


The three important biomolecules making up our food are carbohydrates, lipids, and proteins. They are the molecules that sustain our life and are called as macronutrients. Carbohydrates. Carbohydrates literally mean “hydrates of carbon”. They are aldehydes or ketones with multiple hydroxyl groups. Monosaccharides are known as simple sugars and they serve as building blocks of other carbohydrates. Two of the most important monosaccharides are glucose and fructose.

CHEMISTRY IN ACTION

93

Monosaccharides. Glucose, also known as dextrose or blood sugar, is the most important monosaccharide. It has six carbon atoms with an aldehyde group at carbon one and hydroxyl groups on the rest of the carbon atoms. Figure 1 illustrates the linear structure of glucose, which is known as a Fischer projection structure. Glucose is more accurately referred to as D-glucose, where “D” stands for dextral or right, that is the hydroxyl group at the second to the last carbon (known as the reference carbon) is located to the right. In fact, all the common monosaccharides are said to be “right-handed”.

Glucose undergoes a reversible reaction leading to the formation of a six-membered cylic structure called the glucopyranose ring as shown in Figure 2. Glucose and other monosaccharides exist in two different isomers which only differ in the position of their hydroxyl group at carbon one. When the hydroxyl group at carbon one is pointing upward, the isomer is known as the alpha, α, isomer or more completely as α-D-glucopyranose. Meanwhile, if the hydroxyl group is pointing downward, the isomer is known as the beta, β, isomer or more completely as β-

D-glucopyranose.

Fructose is the sugar found in fruits and honey. Like glucose it also has six-carbon atoms but instead it has a ketone group at carbon two and hydroxyl groups on the rest of the carbon atoms. Figure 3 shows the linear and cyclic structures of D-fructose.

CH2OH

HH

H

H H

HO OH

O

OH

OH

a-D-Glucose

CH2OH

HH

H

H

HHO

OHO

OH

OH

b-D-Glucose

HH

H

HOH

H

OH

OH

CH2OH

HOH2CHOH2C

HO

O

H

OH

CH2OHO

HOH

HH OH

OH

O

CH2OH

CH2OH

HO

D-fructose a-D-fructofuranose b-D-fructofuranose

Figure 1. Linear structure of D-glucose.

Figure 2. Cyclic structures of D-glucose.

COH

OH

HO

CH2OH

OH

OH

H

H

H

H

CHEMISTRY IN ACTION

94

Figure 3. Linear and cyclic structures of D-fructose.

Disaccharides. Disaccharides are formed by joining two monosaccharides via a glycosidic bond. A glycosidic bond is formed by condensation of two hydroxyl groups from each monosaccharide to form an ether bond with accompanying loss of water as illustrated in the formation of maltose in Figure 4. Maltose, also known as malt sugar, is formed from two α-D-glucose units joined by an α1-->4 glycosidic bond.

Sucrose, which is used as table sugar, is made up of glucose and fructose units joined by an α1-->β2 glycosidic bond as shown in Figure 5.

Figure 5. Formation of sucrose from glucose and fructose units.

Polysaccharides. Polysaccharides are known as complex carbohydrates because they are made up of multiple monosaccharide units. The three major polysaccharides are cellulose, starch, and glycogen. Cellulose is the major structural carbohydrate of the plant’s cell wall. It is made up of linear chains of β-D-glucose joined by β1-->4 glycosidic bonds as shown in Figure 6. The linear structure of cellulose makes it suitable for compaction into fibers that are stabilized by H-bonds. Furthermore, cellulose is combined with various cementing materials like gums and pectins that further strengthen the fibers.

+

CH2OH

HH

H

H H

HO OH

O

OH

OH23

4

5

6

1

CH2OH

HH

H

H H

HO OH

O

OH

OH 1

23

5

6

4

CH2OH

HH

H

H H

HO

O

OH

OHO

CH2OH

HH

H

H H

OH

O

OH

OH1 4

a-D-Glucose a-D-Glucose Maltose

Figure 4. Formation of maltose from two glucose units.

CHEMISTRY IN ACTION

95

Figure 6. Structure of cellulose. Starch is the storage form of glucose in plants. Starch is a mixture of amylose and amylopectin. Amylose is a linear chain α-D-glucose joined by α1-->4 glycosidic bonds. Amylose forms a helical structure in water and iodine can fit through the core of this helix to form a bluish-black complex, thus iodine test is a useful qualitative test for starch. Meanwhile, amylopectin has a1-->6 branches about every 30 glucose residues of the a1-->4 glucose backbone. Figure 7 illustrates the structures of amylose and amylopectin.

Figure 7. Structures of amylose and amylopectin.

Glycogen is the storage form of glucose in animals and humans. Glycogen is primarily synthesized and stored in the liver, the largest internal organ of our body. In fact, about two-thirds of the liver is stored glycogen and can be readily mobilized during fasting or strenuous exercise. The muscles can also synthesize and store glycogen. The structure of glycogen is similar to that of amylopectin except that it is more highly branched since the a1-->6 branches occur at about every 10 glucose residues of the a1-->4 glucose backbone. Each end of the “branches” is said to be a reducing end because it is where the hydrolysis of glucose units occur during glycogen mobilization.

O

O

OH

OH

OH

O

OH

OH

HO

HO

14

O

O

OH

OH

HO

14

O

O

OH

OH

OH

HO

14

Amylose.

Amylopectin.

CHEMISTRY IN ACTION

96

Lipids. Lipids are biomolecules that are water-insoluble but soluble in organic or non-polar solvents. Lipids are rather diverse and come in the form of fats, oils, cholesterol compounds, and fat soluble-vitamins. Lipids serve as energy source, components of the cell membrane, and hormones. Fatty Acids. Fatty acids are long-chain carboxylic acids that have even number of carbon atoms. Fatty acids can be either saturated or unsaturated. Saturated fatty acids have only carbon-carbon single bonds, C-C, while unsaturated fatty acids have at least one carbon-carbon double bond, C=C. Table 1 enumerates the common fatty acids. For unsaturated ones, the symbol delta (Δ) states the position of the double bond.

Table 1. Common fatty acids.

Saturated Carbon Atoms

Unsaturated Carbon Atoms

Lauric acid C12 Oleic acid C18 D9 Myristic acid C14 Linoleic C18 D9,12 Palmitic acid C16 Linolenic C18 D9,12,15 Stearic acid C18 Arachidonic C20 D5,8,11,14

Lauric acid is the major component of coconut oil. Studies have shown that lauric acid is beneficial to human health because of its antimicrobial properties, ability to strengthen the immune system, and ability to lower blood cholesterol level. Meanwhile linoleic acid, together with linolenic acid, is considered as essential fatty acid (EFA). EFAs are commonly added in infant milk formula and are touted as a key nutrient for a brighter child. This claim has a scientific basis because EFAs are essential components of plasma membrane in general and the neuronal membrane in particular. The unsaturation in EFAs makes them more flexible and fluid, allowing faster membrane response during the rapid development of the brain throughout the childhood years. The structures of lauric acid and linoleic acid are shown in Figure 8.

Figure 8. Structures of lauric acid and linoleic acid.

CHEMISTRY IN ACTION

97

Fats and Oils. Fats and oils are triesters of glycerol and fatty acids hence are known as triacylglycerols or triglycerides. Their general structure is shown in Figure 9. Fats are solid at room temperature because they mostly contain saturated fatty acids, hence, are more compact in structure. They serve as energy reserves, as insulation against heat loss, and as cushioning of internal organs in animals and humans. Oils are liquid at room temperature because of the presence of significant amount of unsaturated fatty acids. The C=C bond renders a bend in the structure of the fatty acids hence they are less compact in structure. They serve as energy reserve in plants.

Phospholipids. Phospholipids have a phosphate group attached to one of the hydroxyl groups of the glycerol and fatty acids on the other two hydroxyl groups. A phospholipid is said to be amphipathic in nature because it contains a “polar head” and two “nonpolar tails” as shown in Figure 10.

They serve as the primary components of the cell membrane. The representation of the cell membrane is said to be a fluid mosaic model. It is fluid because the phospholipid bilayer is capable of flowing laterally. It is mosaic in appearance because it has embedded proteins that serve as transporters of polar substances through the non-polar lipid bilayer as illustrated in Figure 11.

Figure 9. General structure of

triglycerides.

Figure 10. General structure of phospholipid.

CHEMISTRY IN ACTION

98

Figure 11. Fluid mosaic model of a cell membrane. Proteins. Proteins are linear polymers of amino acids joined by amide bonds which are called as peptide bonds. Amino Acids. Amino acids are the building blocks of proteins. They have an amine and carboxylic acid group attached to a common carbon atom known as the α-carbon. The acid donates the proton to the amino group to form a zwitterionic structure which contains both positive and negative charges but the net charge is zero as illustrated in Figure 12.

There are twenty standard amino acids and they differ in the structure of the side chain or R group that is also attached to the α-carbon. The identity and nature of the amino acids are therefore determined by its R group. Table 2 gives the structure and nature of some amino acids.

Table 2. Examples of amino acids.

Name Structure Nature Leucine

Aliphatic amino acid that contains an alkyl side chain. Non-polar and

neutral in net charge.

Phenylalanine

Aromatic amino acid that contains a benzene ring. Non-polar and


H3N+ C COO-H

CH2

CHH3C CH3

H

COO-CH3N+

CH2

H3N+ C COO-H

R

H2N C COOH

H

R

formal structure zwitterionic structure

Figure12. General structure of

an amino acid.

CHEMISTRY IN ACTION

99

Serine

Alcoholic amino acid that contains a hydroxyl group. Polar and


Cysteine

Sulfur-containing

Glutamate

Acidic amino acid that contains an extra carboxylic acid. Polar and

negative in net charge.

Lysine

Basic amino acid that contains an extra amino group. Polar and

positive in net charge.

Peptides. Amino acids are linked by an amide bond that is formed from the amine group of one amino acid and the carboxylic acid of another amino acid. This is an example of condensation reaction with water as a byproduct. This amide bond is called a peptide bond and the resulting molecule is called a peptide. Proteins are polypeptides with at least 50 amino acids. Proteins serve many functions in our body including (1) structural components (such as collagen in connective tissues and keratin of the hair), (2) transport (such as hemoglobin, the oxygen transporter of the red blood cells), (3) defense (such as immunoglobulins or antibodies in the blood plasma), (4) hormones (such as insulin which lowers blood glucose level), and (5) speeding up of biochemical reactions (such as the various enzymes). Enzymes. Enzymes are proteins that hasten or speed up the rate of a biochemical reaction, hence are called as biocatalysts. Many enzymes catalyze the digestion of the food that we eat. In the mouth, salivary amylase breaks down amylose to maltose and oligosaccharides at a neutral pH condition. In the stomach pepsin cuts the peptide bonds of proteins forming smaller oligopeptide chains under acidic condition. Most of the enzymatic digestion of food occurs at the small intestines under basic conditions. Oligopeptides are broken down into amino acids by trypsin, chymotyrpsin, and other peptidases. The breakdown of oligosaccharides and maltose from starch is continued by pancreatic amylase and maltase respectively into glucose. The enzyme lipase breaks down the ester linkage of triglycerides into glycerol and fatty

H

COO-CH3N+

CH2

OH

HCOO-CH3N+

CH2

SH

HCOO-CH3N+

CH2

CH2

COO-

H

COO-CH3N+

CH2

CH2

CH2

CH2

NH3+

CHEMISTRY IN ACTION

100

acids. These monomers of biomolecules are absorbed by the intestinal microvilli which are finger-like projections that increase the surface area for nutrient absorption.

Some of the food that we eat remains undigested by our body because we lack specific enzymes that can degrade them. A specific example is cellulose which can only be broken down by the enzyme cellulase. Only ruminants like cow, horse, and goat have this enzyme along with termites. However, cellulose along with other dietary fiber is still beneficial to our health because it provides roughage for smooth elimination of undigested food, absorbs toxins and cholesterol, and promote the growth of “good bacteria” in our digestive system.

Metabolism. Metabolism is the sum total of all biochemical reactions in our system. It can be subdivided into two general processes: catabolic and anabolic reactions. Catabolic reactions result in the breakdown of complex molecules into simpler ones such as the digestion of food biomolecules into their molecular building blocks. Meanwhile, anabolic reactions result to the synthesis of complex molecules from their molecular building blocks. The products of food digestion are processed either way. Anabolic Reactions. Anabolic reaction is the synthesis of larger molecules from smaller building blocks. The mentioned products of food digestion are used by our body to synthesize the biomolecules that we need. Glucose are joined together to form glycogen by the enzyme glycogen syntase. Fatty acids are processed to form fats, phospholipids, and cholesterol. Excess glucose is also converted to fats. Amino acids are used to synthesize new proteins for growth and repair of body tissues. Some amino acids are also used for the synthesis of nitrogeneous bases which serve as components of the nucleic acids DNA and RNA.

Catabolic Reactions. Catabolic reaction is the breakdown of large complex molecules into smaller ones. Our body needs a continuous supply of energy and this energy is supplied by catabolism of carbohydrates, lipids, and proteins. Carbohydrates, particularly glucose, are the primary sources of energy in our body under normal conditions. A glucose molecule undergoes a series of reactions to yield energy in the form of adenosine triphosphate or ATP. The overall reaction of glucose is:

C6H12O6 (aq) + O2 (g) ---> 6CO2 (g) + 6H2O (l) + 36-38 ATP

The glucose reserve of our body in the form of glycogen can only last for 24 hours if used without replenishing. After which, fats are mobilized as energy source by our body. Fats yield twice the amount of energy equivalent to the same amount of carbohydrates. This is because fats are more reduced hence yield more ATP during

CHEMISTRY IN ACTION

101

energy metabolism. Proteins serve as last resort for energy source. The depletion of body proteins particularly that of the muscle is typical for prolonged starvation and severe malnutrition. Proteins contain equal amount of energy per gram as carbohydrates. The units used in expressing the amount of energy derived from food are joule (J) and calorie (c):

1 calorie = 4.18 J Majority of the processed food products have nutritional labels that state the amount of energy the product contains per serving and the amounts of other important micronutrients. The amount of energy is expressed in Calorie (C):

1 Calorie = 1,000 calorie = 1 kilocalorie An average person requires 2,000 to 3,000 Calories per day to maintain normal body functions. The excess amount of energy is stored in the body as fats and excessive fat accumulation leads to obesity. Obesity is now a great health concern worldwide because of the increasing percent of obese people. Obesity increases the risk of developing life-threatening diseases such as diabetes, cardiovascular diseases, arthritis, and even cancer by at least 30%. The body mass index or BMI is used to determine whether a person is obese or not. BMI is the ratio of weight to the height of an individual:

BMI = weight in kg / height in m2 A BMI of less than 18 is considered as underweight; the ideal weight is between 18 to 24; greater than 24 is overweight; 30 is obese and over 35 is very obese. Around 3,500 Calories is equivalent to one pound or 0.45 kilogram of body weight. This is the amount a person should take or lose from the basal caloric requirement to gain or lose one pound. The best way to lose weight is a proper combination of regular exercise and dietary plan. VOCABULARY WORDS

1. Metabolism - the sum total of all biochemical reactions in our system.

2. Anabolic reaction - the synthesis of larger molecules from smaller building blocks.

3. Catabolic reaction - results in the breakdown of complex molecules into

simpler ones.

4. Body mass index – BMI, index for obesity; the ratio of weight to the height of an individual.

5.

CHEMISTRY IN ACTION

102

6. Carbohydrates - literally means “hydrates of carbon”; they are aldehydes or

ketones with multiple hydroxyl groups.

7. Monosaccharides - known as simple sugars that serve as building blocks of other carbohydrates.

8. Disaccharides – sugars formed by joining two monosaccharides via a glycosidic

bond. 9. Polysaccharides - complex carbohydrates made up of multiple monosaccharide

units.

10. Fats and oils - triesters of glycerol and fatty acids hence are known as triacylglycerols or triglycerides.

11. Fatty acids - long-chain carboxylic acids that have even number of carbon atoms.

12. Proteins - linear polymers of amino acids joined by amide bonds which are

called as peptide bonds.

13. Amino acids are the building blocks of proteins. They have an amine and carboxylic acid group attached to a common carbon atom known as the α-carbon.

14. Zwitter ion – structure of amino acids which contains both positive and negative

charges but the net charge is zero.

15. Peptides - structure formed when amino acids are linked by an amide bond that is formed from the amine group of one amino acid and the carboxylic acid of another amino acid.


A. Show different pictures of foodstuff. Group the students and have them classify the examples as to sources of proteins, carbohydrates, and lipids.

B. Write the vocabulary words on the board and have each group to get the meaning of these words from the video.

CHEMISTRY IN ACTION

103

VIEWING ACTIVITIES

POST-VIEWING ACTIVITIES A. Discussion.

Part I: Carbohydrates

1. Check if the students have correctly listed the examples of foodstuff that are sources of carbohydrates. 2. Have the students write the meaning of carbohydrates, monosaccharides, glucose, fructose, disaccharides, glycosidic bond, maltose, sucrose, polysaccharides, cellulose, starch, amylose, amylopectin, and glycogen on the board. 3. Discuss the structure, functions, and classification of carbohydrates in reference to what the students have written on the board. Show the structures of each example of carbohydrates from the video.

Part II: Lipids 1. Check if the students have correctly listed the examples of foodstuff that are sources of lipids. 2. Have the students write the meaning of lipids, fatty acids, fats, oils on the board. 3. Discuss the structure, functions, and classification of lipids in reference to

what the students have written on the board. Show the structures of each example of lipids from the video.

Part III: Proteins 1. Check if the students have correctly listed the examples of foodstuff that are sources of proteins. 2. Have the students write the meaning of amino acids, zwitterion, peptides, peptide bond, proteins, hemoglobin. 3. Discuss the structure, functions, and classification of proteins in reference to

what the students have written on the board. Show the structures of each example of amino acids and proteins from the video.

The video is best viewed by parts. Stop the video after watching a part

then proceed to the suggested post-viewing activities for each. (1) 0:00 - 6:32 on Carbohydrates,

(2) 6:33 - 9:09 on Lipids, (3) 9:09 - 11:12 on Proteins,

(4) 13:09 - 16:29 on Enzymes, and (5) 16:30 - 23:00 on Metabolism.

CHEMISTRY IN ACTION

104

Part IV: Enzymes 1. Have the students write the meaning of enzymes, amylase, maltase,

peptidase, cellulase. 2. Discuss the structure, functions, and classification of enzymes in reference to

what the students have written on the board. Show the structures of each example of amino acids and proteins from the video.

Part V. Metabolism 1. Have the students write the meaning of metabolism, anabolic reaction, catabolic reaction. 2. Summarize on a table the building blocks of each type of biomolecule and

the enzymes needed to digest and synthesize them. B. Experiment 1: Starch Decomposition. Procedure:

1. Prepare 20 mL of a 10% starch solution. 2. Carefully pour 5 mL of this starch solution in a test tube. Add 1 drop of

iodine solution. Observe the color change. 3. Obtain three clean test tubes labeled A, B and C. Pour 5 mL of starch

solution on each test tube. 4. Add 1 mL of water of test tube A, 1 mL of 6 M HCI to test tube B, and 1 mL

of saliva to test tube C. 5. Let the setup stand for at least 30 minutes. Add 1 drop of iodine to each of

the three test tubes. Observe and record what happens to the three test tubes. Questions:

1. What is the color reaction of starch to the iodine test? 2. Which of the three test tubes indicates starch decomposition? Why?

C. Experiment 2: Identifying Biomolecules. Perform standard confirmatory test for the presence of carbohydrates (Iodine Test), fats (Acrolein Test), and proteins (Xanthoproteic Test). Results of these tests serve as control. § Iodine Test: Add a drop of iodine solution to 2 mL of starch solution.

Observe the color change. § Acrolein Test: Place 2 to 3 drops of coconut oil in a tin can. Heat until it

starts giving off fumes. Note the odor of the fumes. § Xanthoproteic Test: Measure of 5 mL of egg white in a test tube. Add 2

drops of concentrated nitric acid to the test tube. Heat the solution until it boils. Let it cool and add a drop of ammonium hydroxide solution to make the mixture slightly basic. Note the color changes.

CHEMISTRY IN ACTION

105

Procedure: 1. Perform the test for carbohydrates, fats, and proteins in food samples. Follow

the procedure above to test the following food samples: flour, potato, ripe banana, rice washing, paste, peanut, and milk.

2. The iodine test can be done directly on the original samples. 3. In testing for fats and proteins, solid food samples should be macerated in

water using the mortar and pestle. Filter. Use the filtrate in performing the tests.

Data: Write down your observations by filling up the table below:

Observations

Sample Starch Fats Protein

Flour

Milk

Banana

Peanut

Rice washing

Potato

Questions:

1. What did you observe when starch solution is tested with iodine? 2. Describe the odor of the fumes when coconut oil was heated. 3. Describe what happens to egg white after treating with nitric acid? With

ammonium hydroxide solution? 4. Which of the food samples tested positive for the presence of starch, fats, and

proteins? Why?

TEACHING TIPS

Challenge. 1. Let each student calculate his/her body mass of index (BMI) from the given

formula in the text. On the board, summarize the BMI equivalent of the class by determining how many are underweight, normal in weight, overweight, and obese. Have the students calculate the calorie that they need to gain or lose to maintain their ideal weight. Refer to the Background Information for the formula.

CHEMISTRY IN ACTION

106

2. Let the students research by group the following topics. a. Different disorders that results from malnutrition in protein, carbohydrate, or

lipid requirements. b. Proper ways of gaining weight. c. Obesity and its risks. d. Proper ways of gaining weight.

ASSESSMENT

A. Multiple Choice. Choose the letter corresponding to the best answer.

1. Which of the following links two sugar molecules in a disaccharide?

A. Amino bond C. Peptide bond B. Ether bond D. Carboxyl bond

2. Which of the following is NOT TRUE of lipid molecules?

A. Lipids are molecules which are generally insoluble in organic solvents. B. Lipids occur in the body in the form of triglycerides. C. The living membrane is made up of an assembly of bilayered lipid molecules. D. The main molecules of lipids are associated with fatty acids made up of

straight chains of carboxylic acids. 3. Which of the following is the building block of protein molecules?

A. ATP C. Amino acids B. Hexose D. Fatty acids

4. Which of the following is the storage form of carbohydrates in animals?

A. Cellulose C. Glycogen B. ATP D. Starch

5. Which of the following are not products of food digestion in the body?

A. Amino acids C. Glucose B. Fatty acids D. Sugar

B. Morse Type. Below are two columns of phrases and terms. The first column consists of phrases which may or may not be related to those in the second column which are numbered I & II. Write A if the term in the 1st column is related to I only in the second column, B if it is related to II only, C if it is related to both I & II and D if the item is neither related to I nor II.

CHEMISTRY IN ACTION

107

Set A Column 1 Column 2 1. Dextrose I. Carbohydrates 2. Linked by and ether bond II. Lipids

3. Enzymes for digestion 4. Polymers of sugar molecules

5. Hydrocarbon

Set B

Column 1 Column 2 1. A protein molecule I. Enzymes

2. With amino acid as its building block

II. Glucose

3. A fuel for body cells 4. Specific in action

5. An assembly of fatty acids

Set C Column 1 Column 2 1. Aspartic acid I. Proteins 2. Found in living membrane II. Lipids

3. Yields blue color with iodine test 4. Flat, extended or fibrous

5. With a peptide bond

ANSWER KEY

A. Multiple Choice. 1. B 2. A 3. C 4. C 5. D

B. Morse Type.

Set A 1. A 2. A 3. D 4. A 5. C

CHEMISTRY IN ACTION

108

Set B

1. A 2. A 3. B 4. A 5. D Set C

1. A 2. C 3. D 4. A 5. A

REFERENCES

Brown, T.L., LeMay, H.E. & B.E. Bursten. (2004). Chemistry: the central science. NJ: Prentice Hall, Inc.

McKee, T. & J. R. McKee. (2003). Biochemistry: the molecular basis of life. NY: McGraw-Hill, Inc.

CHEMISTRY IN ACTION

109

Chapter 9: Polymer Chemistry and Biochemistry EPISODE 37: MOLECULES OF HEREDITY: DNA and RNA

OVERVIEW

From one-celled plants and animals to humans, the living state includes some highly complex forms of matter. In addition to water, which is the most abundant compound in living organisms, the next important constituents are lipids, carbohydrates, proteins, and nucleic acids. These four types of macromolecular substances are collectively known as biomolecules. Biomolecules are polymers of several basic building blocks or monomers. This episode is about nucleic acids, which are also known as the molecules of heredity, and the what, how, and why of the genetic processes.

OBJECTIVES

At the end of this lesson the student should be able to: 1. identify the structure, understand the properties, and describe the functions of the biomolecules of heredity – DNA and RNA; 2. describe the double helix structure of DNA; 3. state the basis for and importance of specific base-pairing of the nitrogenous bases; 4. explain the process of gene expression by replication, transcription, and translation; and 5. describe the basic process used in genetic engineering and its applications.


Episodes 31-34 on Organic Chemistry and Episode 36 which is on The Molecules Of Our Food are good preparations before viewing this episode.

SCIENCE AND HEALTH IDEAS

Genetic basis of diseases: sickle-cell anemia

SCIENCE PROCESSES

Observing Inferring Comparing

Contrasting Predicting Reasoning

CHEMISTRY IN ACTION

110

VALUES

Self-acceptance Self-appreciation

LIFE SKILLS

Information decoding

IMPORTANT CONCEPTS

1. Gene expression refers to the flow of genetic information from the DNA to protein. Three processes are involved in the transfer of the information from the DNA to protein, namely: replication, transcription, and translation.

2. The genetic code is a list of the different amino-acids called for by a combination of three nucleotides (hence called a triplet but more technically referred to as codon) in the process of protein synthesis.

3. Biotechnology is the use of living organisms to produce pharmaceutical,

agricultural, food, and industrial products. 4. Recombinant DNA technology is the insertion of a foreign gene into the DNA

of a host cell and allowing the host to express that foreign gene.


Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the biomolecules of heredity. Genes are specific sequences of nitrogeneous bases in our DNA that determine particular traits like the shape of your nose or the color of your skin. Genes actually encode for a particular protein or enzyme that interact with environmental factors and affect a particular trait. For example, the color of our skin, hair, and eyes are determined by the synthesis of the pigment molecules called melanin which is a protein. Melanin is a brown-black pigment that colors our skin, hair, and eyes and serves to protect us from harmful ultraviolet or UV rays from the sun. The critical enzyme that catalyzes the process is called tyrosinase. Melanin synthesis is increased by exposure to sunlight resulting to a tanning effect. In this chapter you will learn about the structure of nucleic acids and the biochemical process by which genetic information in the DNA is expressed. Nucleotides. The building blocks of nucleic acids are the nucleotides. It has three basic components: sugar, phosphate, and nitrogenous bases. Depending on the identity of the components present, nucleic acids can either be deoxyribose nucleic acid, DNA, or ribonucleic acid, RNA.

CHEMISTRY IN ACTION

111

The sugar and phosphate groups serve as the backbone for nucleic acids. The sugar in nucleic acid is based on the five-carbon sugar ribose. DNA has the sugar 2-deoxyribose while that of RNA is ribose as shown in Figure 1.

Figure 1. Structures of sugar moieties of DNA and RNA. The term “2-deoxyribose” in DNA means that oxygen was removed from the 2nd carbon atom leaving hydrogen atoms only. Take note that the numbering of the sugar is given a prime sign (e.g. 1’) to distinguish it from the numbering of the nitrogeneous bases. The phosphate group attaches to carbon-5 (5’) of the sugar to form a nucleoside as shown in Figure 2. The bond between the sugar and phosphate is called a phosphoester bond.

Figure 2. Formation of nucleosides. The nitrogeneous bases or N-bases in nucleic acids are of two general types: purine and pyrimidine. The purine bases are adenine (A) and guanine (G), which are made up of conjugated five- and six-membered rings that contain two nitrogen atoms each. The pyrimidine bases cytosine (C), uracil (U), and thymine (T), which are all made up of a six-membered ring only with two nitrogen atoms. Figure 3 below illustrates the structure of the N-bases.

Adenine (A) Guanine (G) Cytosine (C) Thymine (T) Uracil (U)

O

H

HOH

OH

H

OH

HH

2-Deoxyribose Ribose

1'

2'3'

4'5'CH2 CH2

5'4'

3' 2'

1'

H

O

H

OHOH

OH

H

OH

H

P-O O-

O

O-

+

O

H

HOH

C

H

OH

HH

5'HOH2 OH2P-O

O

O-

H

O

H

HOH

C

H

OH

H

Phosphate 2-Deoxyribose 2-Deoxyribonucleoside

NH

NH

O

O

CH3

N

NH

NH

N

NH2

O

NH

NH

O

O

CHEMISTRY IN ACTION

112

Figure 3. Structures of nitrogeneous bases found in nucleic acids. Nitrogeneous bases attach to C1 atom (1’) of the sugar in a nucleoside to form nucleotides. The purine bases attach via its N9 atom to form a C1-N9 glycosidic bond. Meanwhile, the pyrimidine bases attach via its N1 atom to form a C1-N1 glycosidic bond as illustrated in Figure 4.

Figure 4. Formation of nucleotides.

Nucleic Acids. Nucleic acids are formed when two nucleotides are joined together via a phosphodiester bond as illustrated in Figure 5 below:

Figure 5. Formation of nucleic acid.

Deoxyribonucleic Acid (DNA). DNA is made up of deoxyribonucleotides that are joined by 3’ to 5’ phosphodiester bonds. DNA serves as repository of genetic materials. The eukaryotic DNA is a double-stranded helix formed by two complimentary and antiparallel strands. The complementary nature of the two strands is due to the specific base pairing between a purine and pyrimidine: guanine pairs with cytosine and adenine with thymine. The base pairs are stabilized by three and two H-bonds, respectively.

N

N N

N

NH2

O

H

HOH

C

H HH

OH2P-O

O

O

1'

9

Adenosine

1'OH2P-O

O

O-

H

O

H

HOH

C

H H

NH2

ON

N

1

Cytosine

Cytosine

1 ON

N

NH2

O

H

HO

C

H HH

OH2P-O

O 1'

9

1'OH2P-O

O

O

H

O

H

HO

C

H H

N

N N

N

NH2

Adenosine

CHEMISTRY IN ACTION

113

N

N

NH

N

NH2

NH

NH

O

O

CH3

Adenine Thymine

N

NH

NH

N

NH2

O

Guanine Cytosine

N

NHO

H2N

The antiparallel characteristic of the DNA means that one of the chain runs in 5’ to 3’ direction while the other one runs at the opposite direction of 3’ to 5’. There are 10 base pairs per turn of the helix and the distance per turn is 34 nm. This feature of the DNA double helix was discovered by Francis H.C. Crick and James D. Watson in 1953. Figure 6 illustrates the base-pairing and double-helical structure of the DNA.

Figure 6. Base-pairing and double-helical structure of DNA. Ribonucleic Acid (RNA). RNA is made up of ribonucleotides that are also joined by 3’ to 5’ phosphodiester bonds. RNA is transcribed from a DNA template and is directly involved in the synthesis of proteins. RNA forms a single-stranded helix in contrast to double-helical DNA. The sugar moiety of RNA is ribose and instead of thymine, uracil is the pyrimidine in RNA that pairs with adenine.

There are three types of RNA: ribosomal RNA (rRNA), messenger RNA (mRNA), and transfer RNA (tRNA). Ribosomal RNAs associate with proteins in the cytoplasm to form ribosomes which become the sites for protein synthesis in the cell. Messenger RNAs serve as templates for protein synthesis. Transfer RNAs are involved in bringing amino acids from the cytoplasm to the ribosomes during protein synthesis. Gene Expression. Gene expression refers to the flow of genetic information from the DNA to protein. A parent DNA is copied to form two identical daughter DNAs during

Sugar-phosphate backbone

5’ 3’

Base pairs

10 base pairs per turn (34 nm distance)

3’ 5’

CHEMISTRY IN ACTION

114

replication. The DNA is used as the template for the synthesis of RNAs during transcription. The RNA in turn is used as the template in the synthesis of protein during the translation process:

Replication. Replication is the synthesis two identical double-stranded DNA from a parent DNA. This occurs inside the nucleus. The mode of replication is semi-conservative in nature because each strand of the parent DNA is used as template for synthesis. The resulting product is two daughter DNAs each with an old strand and a new strand. Replication is a complex process that requires several enzymes and proteins to facilitate the synthesis. DNA polymerase (DNA Pol) is the multi-subunit enzyme that catalyzes the polymerization of deoxyribonucleotides. DNA replication can be subdivided into initiation, elongation, and termination stage. During initiation, the DNA double-helix is unwounded to expose the nitrogeneous bases. Each strand is then made as template for DNA synthesis by DNA Pol during the elongation phase. Complementary base pairing between G-C and A-T is followed so is the anti-parallel orientation of the strands. Lastly, upon complete replication of the template, the process is terminated which results to two daughter DNAs as shown in Figure 7.

Figure 7.

DNA replication.

DNA RNADNA ProteinReplication Transcription Translation

CHEMISTRY IN ACTION

115

Transcription. Transcription is the synthesis of complementary RNA strand from the DNA template. This occurs at specific region in the nucleus called the nucleolus. It is catalyzed by the enzyme RNA polymerases (RNA Pol).

The process is also subdivided into initiation, elongation, and termination stages. During initiation, the DNA double-helix is unwounded to expose the nitrogeneous bases. Only one strand (the 3’-->5’ strand) is used as template for RNA synthesis by RNA Pol during the elongation phase. RNA has uracil instead of thymine so the complementary base pairing between G-C and A-U. The anti-parallel orientation of the DNA-RNA hybrid strands is followed. Lastly, upon complete transcription of the template, the process is terminated which results to the formation of a single strand RNA as shown in Figure 8. Translation. Translation is the synthesis of protein from the mRNA transcript. It involves the participation of the rRNA and tRNA. This occurs at the ribosomes in the cell’s cytoplasm. The base sequence of the mRNA is read as triplets called codons which make up the genetic code. Since there are four N-bases, there is a total of 64 codons (43 = 64). However, only 61 codons encode a particular amino acid. The remaining three codons (UAA, UAG, and UGA) do not encode for any amino acid and are known as the stop codons since they signal the termination of the translation process. The genetic code is shown in Table 1. The first, second, and third bases in a codon are read from the left, to the top, then to right respectively. For example, the codon UCG encodes for serine (S). However, other codons also code for serine (UCU, UCC, UCA, AGU, and AGC) which illustrates the degeneracy of the genetic code, that is several codons can encode for the same amino acid.

Figure 8. Transcription

of RNA from

DNA.

CHEMISTRY IN ACTION

116

Table 1. The genetic code.

U C A G

U Phenyalanine (F) Phenyalanine (F)

Leucine (L) Leucine (L)

Serine (S) Serine (S) Serine (S) Serine (S)

Tyrosine (Y) Tyrosine (Y)

Stop Stop

Cysteine (C) Cysteine (C)

Stop Tryptophan (W)

U C A G

C Leucine (L) Leucine (L) Leucine (L) Leucine (L)

Proline (P) Proline (P) Proline (P) Proline (P)

Histidine (H) Histidine (H)

Glutamine (Q) Glutamine (Q)

Arginine (R) Arginine (R) Arginine (R) Arginine (R)

U C A G

A Isoleucine (I) Isoleucine (I) Isoleucine (I)

Methionine (M)

Threonine (T) Threonine (T) Threonine (T) Threonine (T)

Asparagine (N) Asparagine (N)

Lysine (K) Lysine (K)

Serine (S) Serine (S)

Arginine (R) Arginine (R)

U C A G

G Valine (V) Valine (V) Valine (V) Valine (V)

Alanine (A) Alanine (A) Alanine (A) Alanine (A)

Aspartate (D) Aspartate (D) Glutamate (E) Glutamate (E)

Glycine (G) Glycine (G) Glycine (G) Glycine (G)

U C A G

Translation is also subdivided into initiation, elongation, and termination stages. During initiation, the mRNA and ribosomes are assembled to form the initiation complex. The tRNA carries the amino acid to the mRNA-ribosome complex. The first AUG codon (for methionine) serves as the start codon for translation. During elongation the next codon is read and encoded to equivalent amino acid. Peptide bond is then formed between the amino acids as catalyzed by peptide synthethase enzyme. The process of elongation continues until a stop codon is encountered. This signal the termination process where the protein is released to the cytoplasm and the mRNA-ribosome complex is dissociated. The process is illustrated in Figure 9.

Figure 9. Translation of protein from RNA. Biotechnology. Biotechnology is the use of living organisms to produce pharmaceutical, agricultural, food, and industrial products. The advent of modern Biotechnology is associated with the development in recombinant DNA technology

CHEMISTRY IN ACTION

117

in the 1970s. The advancements in Biotechnology have resulted to great benefits in the fields of agriculture, medicine, environmental engineering, and pharmaceutical industry. Recombinant DNA technology is the insertion of a foreign gene into the DNA of a host cell and allowing the host to express that foreign gene. The process starts with the cleaving of the gene of interest and the host genome with a restriction endonuclease. Restriction endonuclease cleaves DNA at specific recognition sites which are palindromic sequences of four to eight bases. The term palindromic means that the base sequence is the same whether read forward or backward. For example, EcoR1 (Eischerischia coli strain 1) cleaves the palindromic 5’-GAATTC-3’ sequence as shown in Figure 10.

Figure 10. Recognition site for the restriction endonuclease, EcoR1. The foreign DNA fragment is then hybridized with the host’s genome using DNA ligase. The host is usually a species of bacteria like Escherichia coli that contains circular extra-chromosomal DNA known as plasmids. The cells are then transformed by heat shock and/or adding specific chemicals so that the foreign gene can be fully integrated to host’s genome. The cells are then cultured and the colonies formed are selected to identify the recombinants. Selection is done by integrating probes into the host such as an antibiotic resistance gene that allows the recombinants to survive in a selecting medium while killing the non-recombinants. The isolated recombinants are then cultured to obtain the recombinant DNA and/or the protein product of the inserted gene. Recombinant DNA has been successfully used in the production of insulin using E. coli. Before, insulin is obtained from the pancreas of cadavers or animals like pig or horse, making it a scarce and expensive medication. In addition, insulin obtained from animals can trigger allergic responses in the recipient. Mass production of insulin through biotechnology has lowered the cost and risks of insulin medication for type I diabetic patients. Another application of this technology is the production of genetically modified organisms (GMOs), particularly crops (corn, rice, sorghum, and tomato) that have desirable characteristics such as pest resistance, drought resistance, higher yield, and higher nutritional value. However, the use of this technology is not without potential health and environmental risks. Therefore, strict monitoring and testing

5' G A A T T C 3'5'C T T A A G3'

CHEMISTRY IN ACTION

118

need to be done in fully harnessing the benefits of this technology with minimal detrimental impacts.

VOCABULARY WORDS 1. Double-stranded helix - two complimentary and anti-parallel strands of

nucleotides.

2. Ribosomal RNA - (rRNA), that which associates with proteins in the cytoplasm to form ribosomes.

3. Messenger RNA – (mRNA), it serves as template for protein synthesis. 4. Transfer RNA – (tRNA) it is involve in bringing amino acids from the

cytoplasm to the ribosomes during protein synthesis. 5. Replication – process when a parent DNA is copied to form two identical

daughter DNAs. 6. Transcription - . the process when a DNA is used as the template for the

synthesis of RNAs. 7. Translation - the process when an RNA in turn is used as the template in the

synthesis of protein. 8. RNA polymerase - (RNA Pol), the enzyme that catalyzes the synthesis of

complementary RNA strand from the DNA template during transcription.

9. DNA polymerase - (DNA Pol), the multi-subunit enzyme that catalyzes the polymerization of deoxyribonucleotides.

10. Codon - the combination of three nitrogenous bases ( hence called a triplet) that determines the amino acid that the mRNA chooses in the synthesis of protein.

11. Stop codon – that which signals the termination of the translation process. 12. Palindromic sequence – a genetic code whose base sequence is the same

whether read forward or backward.

CHEMISTRY IN ACTION

119


A. Tell the students to list what physical traits/characteristics that they have are very similar to that of their mother or father.

B. Have two or more students write on the board their list of similar physical traits to their parents. Discuss what influences the color of our skin, hair, and eyes as written in the background information.

VIEWING ACTIVITIES


A. Part I & II: Nucleotides and Nucleic Acids. 1. Ask the students what nucleotides are and their components. 2. Discuss the process of nucleic acid assembly from its components using the video or related visual aids. 3. Ask the students what the two kinds of nucleic acids are. Write a table on a

piece of manila paper and have the students compare and contrast the components and functions of DNA versus RNA.

4. Discuss the structure of DNA and RNA using the video or related visual aids.

B. Part III: Gene Expression. 1. Ask the student what is meant by replication, transcription, and translation. 2. Discuss the process of replication to students and show how a DNA is

replicated (refer to Figure 7). 3. Let the student answer the challenge on DNA replication. 4. Discuss the process of transcription to students and show how a RNA is

transcribed from DNA template (refer to Figure 8). 5. Let the student answer the challenge on DNA replication. 6. Discuss the process of translation to students. Post the genetic code table on the board or give each student or group of students a copy of the table. Show how protein is transcribed from DNA template (refer to Figure 9). 7. Let the student answer the challenge on DNA replication.

The video is best viewed by parts. Stop the video after watching a part

then proceed to the suggested post-viewing activities for each. (1) 2:25 - 11:24 on Nucleotides and Nucleic Acids and

(2) 11:39 - 22:57 on Gene Expression.

CHEMISTRY IN ACTION

120

TEACHING TIPS

A. Gene Expression.

1. Replication. a. Determine the sequence of the complementary DNA (cDNA) strand of

the given DNA template: 5’-GATTACATTCGACGTAGGCAATCAGTAGCCTTACAGTATAGCAGAC-

3’

b. Calculate the percentages of other bases in the given double-strand DNA samples.

Sample A G T C

1 22% 2 35%

2. Transcription. Determine the sequence of the mRNA transcript from the given DNA template:

5’-TACTAAGACTATTTCCTCACGGTGCTTTACAUC-3’ 3. Translation. “Da Vinci Hidden Genetic Code” From the determined mRNA transcript in #2, determine the amino acid of the

peptide that can be translated from it. Write the one letter symbol of the amino acid sequence and removed the first amino acid to reveal the “Da Vince Hidden Genetic Code”. (Note: You can make these activities into a three-stage group contest with “exciting prize(s)” for the group(s) that will get the highest score(s) at the fastest time.)

B. Biotechnology. Let the students research by group and report to the class the basic principles and

applications of the following topics on Biotechonology. 1. Recombinant DNA Technology 2. DNA Fingerprinting 3. Genetically Modified Plants 4. Genetically Modified Animals

CHEMISTRY IN ACTION

121

REFERENCES Brown, T. L., LeMay, H. E. & B.E. Bursten. (2004). Chemistry: The central science.

NJ: Prentice Hall, Inc. McKee, T. & J. R. McKee. (2003). Biochemistry: the molecular basis of life. NY:

McGraw-Hill, Inc.

CHEMISTRY IN ACTION

122

Chapter 10: Environmental Chemistry EPISODE 38: THE ATMOSPHERE

OVERVIEW

The episode focuses on the atmosphere, its layers and the chemical nature of each layer. The role of the atmosphere in maintaining the heat balance of the earth is discussed. The different components of the air and the changes that occur in the atmosphere are also shown.

OBJECTIVES

At the end of this lesson, the student should be able to: 1. enumerate the gaseous components of air in the atmosphere and their

abundances; 2. cite the significance of water vapor in the air; 3. discuss the five zones or layers of the atmosphere, and their roles in the

atmosphere; 4. identify the major air pollutants and their sources; 5. recognize the importance of ozone in the atmosphere and how to prevent its

further depletion; 6. explain the greenhouse effect and identify the gases that aggravate it; 7. discuss the concept of global warming; 8. recognize the key role that science literacy plays in helping people promote

environmental protection; and 9. demonstrate self-awareness, critical–thinking, and decision-making skills to

maintain the cleanliness of air.


This episode links up indirectly with Episodes 7 - Phases of Matter and 8 - Kinetic Molecular Theory and more directly to Episodes 39 – Soil, Its Chemistry and Pollution and 40 – Our Water Resources. SCIENCE PROCESSES

Identifying and classifying layers of the atmosphere Using space-time relationships

Predicting the effect of increasing amount of air pollutants to global warming

CHEMISTRY IN ACTION

123

VALUES

Care for the environment Scientific orientation Personal discipline Concern for common good

Cooperation Social responsibility Accountability

Consider Chapter 1 Section 1 and 2 of the Clean Air Act. REPUBLIC ACT NO. 8749 PHILIPPINE CLEAN AIR ACT OF 1999 Chapter 1 General Provisions Article One Basic Air Quality Policies

SECTION 1. Short Title. - This Act shall be known as the “Philippine Clean Air Act of 1999.”

SECTION 2. Declaration of Principles. - The State shall protect and advance the right of the people to a balanced and healthful ecology in accord with the rhythm and harmony of nature.

The State shall promote and protect the global environment to attain sustainable development while recognizing the primary responsibility of local government units to deal with environmental problems.

The State recognizes that the responsibility of cleaning the habitat and environment is primarily area-based.

The State also recognizes the principle that “polluters must pay”.

Finally, the State recognizes that a clean and healthy environment is for the good of all and should, therefore, be the concern of all.

http://www.chanrobles.com/philippinecleanairact.htm

The students can be asked to prepare a slogan

on how they can contribute or help in the implementation of the Clean Air Act.

http://www.chanrobles.com/philippinecleanairact.htm

CHEMISTRY IN ACTION

124

LIFE SKILLS

Self-awareness and realization Critical and creative thinking Effective communication

Cooperation and team-work Decision making

IMPORTANT CONCEPTS

1. The atmosphere is the protective layer of gases above the earth’s surface, extending up to about 500 kilometers. It is composed of different gases with nitrogen and oxygen having the highest percentages.

2. The atmosphere is divided into four layers or zones based on temperature variations as follows: the troposphere, stratosphere, the mesosphere, and the ionosphere or thermosphere.

3. The greenhouse effect is the process of warming the surface and the lower

atmosphere of the earth by absorption of solar radiation and the reemission of infrared radiation by atmospheric gases.


Components of the Atmosphere. The atmosphere is the protective layer of gases above the earth’s surface, extending up to about 500 kilometers. Fifty percent of the mass of the atmosphere can be found in the lower 5.6 kilometers. The atmosphere is composed of different gases with nitrogen and oxygen having the highest percentage of 78.09% and 20.94% respectively. The remaining 1% consists of trace gases like argon, carbon dioxide, and ozone. Water vapor is also present but the percentage of which varies depending on particular areas such as the desert and above the ocean. Figure 1 shows the distribution of the gases in the atmosphere.

Figure 1. Distribution of

gases in the atmosphere.

CHEMISTRY IN ACTION

125

The amount of oxygen dissolved in the waters is about 4%, which is extremely important in sustaining marine life. Nitrogen, though relatively inert, acts significantly as a diluent for oxygen in the air. If the oxygen in the atmosphere were not diluted, combustion will become so abundant that fires would break out all around us. Oxidation processes will happen many times faster than normal if this were so. Nitrogen can be split up by the energy coming from lightning, jet aircrafts, and automobile engines. It reacts with oxygen to produce nitrogen dioxide, NO2, which is a precursor for nitric acid (HNO3) when it reacts in the atmosphere with oxygen and water vapor, contributing to acid rain. The chemical equations involved are shown below.

N2 + O2 + heat ® 2NO

2NO + O2 ® 2NO2 2NO2 + ½ O2 + H2O ® 2HNO3

Other gases and water vapor make up less than 1% of the atmosphere. Other gases in the atmosphere are present in low concentrations: carbon dioxide (355 ppm), neon (18 ppm), helium (5.2 ppm), krypton (1.0 ppm), xenon (0.08 ppm), ozone (1.0-1.5 ppm). Free hydrogen, methane, nitrous oxide (N2O), nitrogen dioxide, and sulfur oxides (SOX2) are also present but only in trace amounts. One very important component of the air in the atmosphere is water vapor. It keeps the temperature near the surface within a habitable range. It absorbs excess heat when the temperature is high, and it releases heat when the temperature is low. Because of this, the atmosphere acts as a heat engine. It converts the energy coming from the sun into other forms. Otherwise, it would simply get hotter and hotter as the years go by. Climatological data, however, indicates that there is no net increase or decrease in the average global temperature. The Layers of the Atmosphere. The atmosphere is divided into four layers or zones based on temperature variations as the altitude increases. The four zones are the troposphere, stratosphere, the mesosphere, and the ionosphere or thermosphere. Table 1 shows the four layers of the atmosphere with the corresponding characteristics and Figure 1 gives an illustration of the layers of the atmosphere.

CHEMISTRY IN ACTION

126

Table 1. Layers of the atmosphere.

Layer

Altitude (from the Earth’s surface)

Temperature

Other Characteristics

Troposphere

20 km

15oC – 25oC

- chemical species are dispersed which is why contaminated air in one country can reach locations thousands of miles away from it

Stratosphere

20-50 km

-60oC freezing point

- layer where ozone lies - supersonic and jet aircrafts normally

navigate here since there is less turbulence as compared to the troposphere

- short-wavelength ultraviolet radiation (200 to 320 nm) enters here, which is readily absorbed by the O2 and O3 present in the layer

Mesosphere

50 to 85 km

- decrease in the amount of energy absorbing species such as ozone

- UV radiation converts O2 and NO to O2

+ and NO+, respectively

Thermosphere

85 or km

extending to about 500 kilometers

200 K at 100 km to 500 K at 300 km

- penetrated by 100 nm radiation, converting O2 to O2

+, and NO to NO+ - together with the mesosphere, they

comprise what is called the ionosphere, which plays an important role in long distance communications

Exosphere 900 kilometers - outermost layer where the molecules of the atmosphere merge with space

Figure 2. Layers of the atmosphere.

http://www.ucar.edu/learn/1_1_1.htm


CHEMISTRY IN ACTION

127

Air Pollutants. Air pollution may be caused by nature. Erupting volcanoes release hydrogen sulfide, sulfur dioxide, and carbon monoxide. Decaying plants and animals give off methane, ammonia, and hydrogen sulfide. Forest or grass fires emit CO and CO2. Lightning produces N2O, NO2, and NO. All these circulate within the atmosphere until they are precipitated onto the surface of the Earth by rain, snow or hail.

Humans may also bring about pollution. Sulfur oxides (SOx), nitrogen oxides (NOx), CO, hydrocarbons, and particulates are the major pollutants. Sulfur oxides normally come from industrial plants that burn coal as fuel while nitrogen oxides are produced by factories, power-generating plants, and vehicle exhausts. These compounds are the major ingredients for acid rain and are the key components in the production of photochemical smog. A simplified scheme for photochemical smog formation is shown below.

Ground level ozone is also an indication of smog formation. Ozone itself is quite toxic, even at a low concentration of less than 0.5 ppm. Carbon monoxide, hydrocarbons, and particulates mainly come from automobiles due to the burning of fuels. Carbon monoxide is a toxic gas while hydrocarbons and particulates including lead cause damage to lungs and kidneys. Knowing the sources of these pollutants, it is possible to prevent further aggravation by passing and implementing strict anti-pollution laws. The Ozone Layer. The ozone, as mentioned earlier, is important because it is the only substance in the atmosphere that absorbs harmful radiation in the 200-300 nm range. The depletion of the ozone layer poses a serious threat to all living organisms. The reactions below show how CFCs destroy the ozone layer.

NO2 + UV NO + O.O.

+ HC

+ O2 O3

O. RCH

O

O3 + HC RCH

O

HC + O2 + NO2 RCOONO2

O

+ other products

CHEMISTRY IN ACTION

128

Prior to the Montreal Protocol-Copenhagen Revision, which banned the use of chlorofluorocarbons, CFCs, and 1,1,1-trichloroethane in 1989, these CFCs used as propellants were a major cause of ozone depletion. Although CFC levels have not increased anymore due to the use of new ozone-friendly products such as hydrofluorocarbons, HFCs, and hydrochlorofluorocarbons, HCFCs, the already-present CFCs will contribute to ozone depletion well into the next century. Greenhouse Effect. The greenhouse effect is the process of warming the surface and the lower atmosphere by absorption of solar radiation and the reemission of infrared radiation by atmospheric gases. The more greenhouse gases there are in the atmosphere, the more energy is bounced around and redirected back toward the surface. This increases the temperature near the surface. Figure 3 shows the percentages of greenhouse gases in the atmosphere.

Figure 3. Percentages of

greenhouse gases in the

atmosphere.

The concentration of carbon dioxide in the atmosphere increased from 275 ppm during the pre-industrial era to 355 ppm today. The increase is mainly due to the fossil fuel-burning, which greatly contributes to what is called the greenhouse effect. Together with the other greenhouse gases such as methane, CFCs, and nitrogen oxides, carbon dioxide traps the heat coming from the sun’s radiation.

CFCl3uv

CFCl2 + Cl

Cl + O3 ClO + O2

+ O

O2 + Cl

+ NO2

ClNO2O

+ NO

NO2 + Cl

CHEMISTRY IN ACTION

129

Some studies predict a 2 to 3oC rise in global temperature due to the greenhouse effect. Consequently, polar ice caps would melt, causing floods. Generally, any changes in the climate would also greatly affect our food supply as plant production becomes more and more difficult.

VOCABULARY WORDS 1. Troposphere – the layer immediately over the earth’s surface where pollutants

are dispersed which is why contaminated air in one country can reach locations thousands of miles away.

2. Stratosphere – the ozone layer; layer that absorbs harmful radiation in the 200-300 nm range.

3. Mesosphere – the layer generally marked by a decrease in the amount of energy

absorbing species like ozone. 4. Thermosphere - together with the mesosphere, these layers comprise what is called

the ionosphere, which plays an important role in long distance communications. 5. Exosphere - outermost layer where the molecules of the atmosphere merge with outer

space.

Additional Useful Information.

1. Acid rain and global warming are not related. (http://www.kare11.com/cs/forums/1350/ShowPost.aspx)

2. The use of aerosol spray cans do not contribute to climate change. The main

contributor to climate change is carbon dioxide which is produced from the burning of coal, oil, and gas. (http://www.gcrio.org/gwcc/misconceptions.html)

3. The composition of the troposphere is 70% N2 and 21% O2. All weather

phenomena take place in this layer. 4. The top of the troposphere is called the tropopause and the temperature at this

region does not change with an increase in altitude. 5. The ocean is the main source of water vapor in the atmosphere. 6. The chemical reactions in the ionosphere at thermosphere are as follows: In the ionosphere: O + hv ® O+ + e-

N + hv ® N+ + e-

In the thermosphere: N + O2 ® NO + O

http://www.kare11.com/cs/forums/1350/ShowPost.aspx

http://www.gcrio.org/gwcc/misconceptions.html

CHEMISTRY IN ACTION

130

N + NO ® N2 + O O + O ® O2

7. The gases present in the mesosphere includes O3, O2, NO, H, and OH. The

chemical reactions that occur in this layer include:

H2O + hv ® OH + H H2O2 + O ® OH + OH

8. Ozone is produced from the photochemical reaction of sunlight on NO2 and

volatile organic compounds, VOCs, from vehicles. This may cause eye irritation,

difficulty in breathing, and increase susceptibility to infection.


A. Group the class into four. Instruct each group to draw a picture that will depict common sources of air pollutants.

B. Tell the students to classify the pollutants as natural or man- made. VIEWING ACTIVITIES


A. Confirm answers of students in the previewing activity based on the video clip presented.

B. Task the students to look for news articles that focused on a particular factory or an activity or event that contributed to air pollution.

C. Layers of the Atmosphere.

I. Let the students to bring the following materials: colored sand (five different colors), long, transparent glass bottle , ruler, marking pen.

2. Instruct the students to use the colored sand and glass bottle to represent the layers of the atmosphere. They should make their own scale to show the relative thicknesses of the different layers of the atmosphere.

Show the video clip on natural and man-made pollutants at segments 10:29 – 16:00.

CHEMISTRY IN ACTION

131

3. The students may report in class and discuss his/her work.

ASSESSMENT A. Multiple Choice. Choose the letter corresponding to the best answer.

1. What percentage of dry air in the atmosphere is nitrogen? A. 78% C. 4%

B. 21% D. 1% 2. Which of the following gases is present in trace amounts in the air? A. CO2 C. Ne

B. N2O D. O3 3. Water vapor is an important component of air because it

A. absorbs the oxides to form acid. B. blocks ultraviolet radiation. C. helps in the transmission of electronic communication signals. D. helps in regulating the temperature in the atmosphere. 4. This zone/layer in the atmosphere is where supersonic and jet aircrafts

normally navigate. A. Troposphere C. Mesosphere

B. Stratosphere D. Thermosphere

5. All weather phenomena take place in this zone/layer. A. Troposphere C. Mesosphere

B. Stratosphere D. Thermosphere 6. In what range are the ultraviolet radiations that ozone absorbs?

A. 100-200 nm C. 300-400 nm B. 200-300 nm D. 400-500 nm 7. Which of the following is identified as a major ozone depletor? A. Hydrofluorocarbons C. Hydrochlorofluorocarbons B. Hydrocarbons D. Chlorofluorocarbons 8. This phenomenon describes the trapping of infrared radiation within the

Earth’s atmosphere,causing global warming. A. Meissner effect C. Greenhouse effect B. Doppler effect D. Common-ion effect 9. Which of the following pollutants is nontoxic by nature? A. Carbon monoxide C. Nitrogen oxide B. Carbon dioxide D. Ozone

CHEMISTRY IN ACTION

132

10. The ionosphere is a layer in the atmosphere composed of the A. Troposphere and stratosphere. C. Mesosphere and thermosphere. B. Stratosphere and mesosphere. D. Troposphere and mesosphere.

B. Modified TRUE or FALSE. Study the statements below then write:. TT if statements A and B are TRUE. TF if statement A is TRUE and statement B is FALSE. FT if statement A is FALSE and statement B is TRUE. FF if statements A and B are FALSE.

1. A. The percentage of oxygen in the air is 21%. B. Water vapor keeps the temperature near the surface within a

habitable range.

2. A. The turbulence in the mesosphere allows cold air to go down to replace the warm air below it to continuously regulate temperature.

B. Ground level ozone is nontoxic.

3. A. The greenhouse effect is the process of warming the surface and the lower atmosphere by absorption of solar radiation and reemission of infrared radiation by atmospheric gases.

B. Depletion of the ozone layer is not a threat to living organisms.

4. A. Sulfur oxides are produced from forest or grass fires. B. Carbon monoxide is a toxic gas.

5. A. The Montreal Protocol-Copenhagen Revision bans the use of CFCs

and 1,1,1-tricholoethane. B. CFCs contribute to the increase in ozone layer.

ANSWER KEY

A. Multiple Choice.

1. A 2. B 3. D 4. B 5. A 6. B 7. D 8. C 9. B 10. C

B. Modified TRUE or FALSE. 1. TT 2. FF 3. TF 4. FT 5. TF

CHEMISTRY IN ACTION

133

REFERENCES American Chemical Society. (2000). Chemistry in context. (3rd ed.). NY: McGraw-

Hill, Inc. Chang, R. (1998). Chemistry. (6th ed.). NY: McGraw-Hill, Inc. Snyder, C. (1992). The Extraordinary chemistry of ordinary things. (2nd ed.). NY:

John Wiley & Sons, Inc. Useful Websites http://www.science.uwaterloo.ca/~cchieh/cact/applychem/atmosphere.html http://www.ucar.edu/learn/1_1_1.htm http://www.aeat.co.uk/netcen/airqual/kinetics/ http://www.gcrio.org/gwcc/misconceptions.html

http://www.science.uwaterloo.ca/~cchieh/cact/applychem/atmosphere.html


http://www.aeat.co.uk/netcen/airqual/kinetics/

http://www.gcrio.org/gwcc/misconceptions.html

CHEMISTRY IN ACTION

134

Chapter 10: Environmental Chemistry EPISODE 39: SOIL: ITS CHEMISTRY AND POLLUTION

OVERVIEW

In Episode 38, we discussed about the atmosphere. The lithosphere is the solid part of the Earth. In this episode, we will tackle the most important part of the lithosphere - the soil. The first part of this episode investigates the composition and properties of soil. The second part deals with fertilizers that restore and increase soil fertility. Also discussed are the factors that my decrease soil fertility.

OBJECTIVES

At the end of this lesson, the student should be able to: 1. recognize the important role that soil plays for us and our environment; 2. identify the component soil; 3. relate soil composition and soil fertility; 4. cite the functions of organisms in soil; 5. identify the micronutrients present in soil necessary for plant growth; 6. explain pH and ion exchange properties of soil; 7. describe different methods of maintaining soil fertility; 8. identify soil pollutants and their sources; 9. recognize the significance of understanding soil chemistry in the promotion

of conservation of the environment; and 10. demonstrate decision-making and critical-thinking skills in using concepts on

soil chemistry as a responsible member of community.


This episode can be integrated with Episode 38 – The Atmosphere, before this one, and the next one Episode 40 – Our Water Resources since changes in the atmosphere and the water resources would in one way or another also affect the soil.

SCIENCE PROCESSES

Experimenting Interpreting data

CHEMISTRY IN ACTION

135

VALUES

Proper care for nature Care for the environment Scientific orientation Personal discipline Concern for common good

Affection for family and friends Cooperation Social responsibility Accountability

LIFE SKILLS Self-awareness and realization Critical and creative thinking Effective communication


IMPORTANT CONCEPTS

1. The soil is a non-renewable resource that is found in the interface between the earth, the air, and the water. It serves as a platform for human activities and so all changes on the soil can have both socio-economic and environmental impact on life.

2. Soil composition may vary depending on the location, climate, and vegetation.

3. Insects, earthworms, and burrowing animals that hasten the decomposition of

small rocks, mineral deposits, and organic matter enhance the fertility of the soil.

4. The nutrients in soil may not always present in the desired abundance. This is when fertilizers are used – sometimes natural and at other times synthetic.

5. Aside from fertilizers, there are also other substances known as pesticides that

are necessary to ensure plant health. Like fertilizers when used indiscriminately, they pollute the soil as they accumulate.

6. Other soil pollutants are industrial wastes, corroding metals such as tin, iron, and

aluminum, plastics, and by-products of strip mining operations and acid-mine drainage.


Introduction. The soil is a non-renewable resource that is found in the interface between the earth, the air, and the water. The importance of soil lies on the fact that it is what plants rely on for survival and nourishment. Animals, in turn, rely on these plants for their survival. The absence of soil or the unhealthy condition of soil poses food supply problem for us. The soil also serves as a platform for human

CHEMISTRY IN ACTION

136

activities. The varied functions of the soil have both socio-economic and environmental importance and as such there is a need to protect it. Soil. Soil is a mixture of loose sedimentary rock fragments and minerals. Decaying plants and animals are also found in the soil. The formation of soil takes place when air, water, plant life, animal life, and rocks interact. It serves as anchorage for plants as well as filter for groundwater. Generally, soil is composed of 45% mineral matter, 25% water, 5 % organic matter, and 25% air. However, soil composition may vary depending on the location, climate, and vegetation. The mineral particles that are present in soil are essentially silicon dioxide (SiO2) in the form of sand, silt, or clay. Table 1 gives the difference in diameter size of sand, silt, and clay.

Table 1. Diameter size of sand, silt, and clay.

Diameter Size Range Sand 2 to 1/16 mm Silt 1/16 to 1/256 mm Clay 1/256 mm

The organic matter on the other hand is usually made up of the decaying bodies of plants and animals, and animal manure. These serve as food to fungi, worms, and bacterial microorganisms, whose metabolisms release products that can be used by other organisms. Humus composes the bulk of organic matter in soil. It is a dark-colored, formless mass that is water insoluble and results from the partial decomposition of plant and animal matter. Humus contributes to soil fertility to a large extent in that it helps keep soil particles together while being porous enough to allow flow of water and air for plant root growth. The moisture holding capacity of humus keeps the soil from drying up. Moreover, humus also retains nutrients such as nitrogen, phosphorus, and potassium for plant nourishment. Soil Composition. The relationship between soil composition and fertility was demonstrated. Table 2 shows the soil composition of two samples and the observations obtained from the demonstration.

Table 2. Data for soil composition and soil fertility.

Sample Soil Composition Observation Sand 80% sand

10% silt 10% clay

-Water drained effectively -allowed airflow -very low water-holding capacity

Loam 50% silt 25% sand

-water drained slow -airflow is slow

CHEMISTRY IN ACTION

137

25% clay -store significant amount of water Clay 60% clay

20% sand 20% silt

-poor drain ability -poor airflow -absorbs more water

The results illustrated that the soil texture should be somewhat loose as it plays an important role in airflow, water drain, and water retention. Living Organisms in Soil. Organisms in soil also provide for a healthy soil. Insects, earthworms, and burrowing animals hasten the decomposition of small rocks, mineral deposits, and organic matter. This enhances the fertility of the soil. The decaying excreta and dead bodies of these organisms are useful in providing nutrients to the soil. Finally, they aid in “fixing” or converting nitrogen to the more easily absorbed ions such as NO2

-, NO3-, and NH4

+ salts shown in Figure 1.

Figure 1. Nitrogen fixing scheme.

http://images.google.com.ph/imgres?imgurl=http://www.hort.purdue.edu/rhodcv/hort640c/nuse/nfert.gif&imgrefurl=http://www.hort.purdue.edu/rhodcv/hort640c/nuse/nu00006.htm&h=375&w=483&sz=8&hl=tl&start=3&um=1&tbnid=uJ_xDu5qrccJPM:&tbnh=100&tbnw=129&prev=/images%3Fq%3Dnitrogen%2Bfixing%26svnum%3D10%26um%3D1%26hl%3

Dtl%26sa%3DN

Soil Nutrients. Plants need more than just water, carbon dioxide, and sunlight to survive. They need other nutrients for nourishment. Aside from carbon, hydrogen, and oxygen, elements such as nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur, should be available in relatively large amounts. These are called macronutrients. Other elements such as iron, manganese, boron, molybdenum, copper, zinc, cobalt, and chlorine are also essential but in smaller amounts as micronutrients. However, the plants do not easily absorb these. They have to be made available in the form of water-soluble ions such as Ca+2, SO3

-2, and SO4-2. These have to be present in the

soil in proper quantities and proportions since too much or too small may be harmful. Chemical Properties of Soil. Ion exchange is a process where plants are able to take up nutrients by exchanging some of the ions present in the root system for the nutrient ions in soil. This is the mechanism by which K, Ca, Mg, and other nutrients are made available to plants. For example, Ca+2 are absorbed via release of H+ ions.

http://images.google.com.ph/imgres?imgurl=http://www.hort.purdue.edu/rhodcv/hort640c/nuse/nfert.gif&imgrefurl=http://www.hort.purdue.edu/rhodcv/hort640c/nuse/nu00006.htm&h=375&w=483&sz=8&hl=tl&start=3&um=1&tbnid=uJ_xDu5qrccJPM:&tbnh=100&tbnw=129&prev=/images%3Fq%3Dnitrogen%2Bfixing%26svnum%3D10%26um%3D1%26hl%3Dtl%26sa%3DN




CHEMISTRY IN ACTION

138

The pH also determines how much of a certain nutrient can be taken up by the plants since it affects the solubility of the ions. The typical pH conducive for plant nourishment is 4.0 to 8.5. A very low soil pH means that the soil is too acidic and may lead to lost of nutrients by cation exchange with H+. A high soil pH on the other hand will make some micronutrients insoluble and in some cases may also be damaging to plants. However, different plants require narrower ranges for optimum growth. Tomatoes and corn, for example, grow best when the pH of the soil is from 6.2 to 7.0. Use of Soil Fertilizers. The nutrients are not always present in the desired abundance. Crop removal, erosion, and leaching are some of the reasons why soil needs to be enriched occasionally as nitrogen, phosphorus, and potassium are depleted. This is where fertilizers come in. Between the two types (natural and synthetic), synthetic fertilizers are normally more efficient since the nutrients are already in the forms that are available for uptake. Natural fertilizers such as animal manure have to be processed first. Care must be taken when using these fertilizers since excessive use may lead to a high runoff of nitrates and phosphates from the fields to the water bodies, causing eutrophication. Eutrophication is the enrichment of water bodies by dissolved nutrients. This results to growth of aquatic plant life and the eventual depletion of oxygen in the water body. Fertilizer bags contain three or more numbers to indicate the amount of each nutrient it contains. The first number indicates the nitrogen content measured as %, the second number indicates the phosphorus content measured as %P2O5, and the third number indicates the potassium content measured as %K2O. Additional numbers may indicate the level of other nutrients and these must be specified. This method is internationally accepted and is used in choosing the correct fertilizer that is needed. For example, if the soil is deficient in phosphorus, then the second number, which is %P2O5, must be high. That is the fertilizer formula must be 12.24.12 and not 26.0.26. The fertilizer formula also allows you to compare fertilizers. One bag of urea (46.0.0) for instance would provide more than twice the amount of nitrogen compared to a bag of ammonium sulfate (21.0.0)

http://www.gov.nf.ca/agric/pubfact/Fertility/soilclimate.html http://www.dnagardens.com/whatissoilfertility.html Februalry 2003

Soil Pollutants. Aside from fertilizers, there are also other substances known as pesticides that are necessary to ensure plant health. It is believed that without these, 90% of the crops will be lost. Chlorinated hydrocarbons used as pesticides are extremely toxic and therefore hazardous to animals and humans. They pollute the soil as they accumulate.

http://www.gov.nf.ca/agric/pubfact/Fertility/soilclimate.html

http://www.dnagardens.com/whatissoilfertility.html

CHEMISTRY IN ACTION

139

Other soil pollutants are industrial wastes, corroding metals such as tin, iron, and aluminum, plastics and by-products of strip mining operations and acid-mine drainage. ADDITIONAL INFORMATION

Soil salinity can affect plant growth.

Conductivity (mmho/cm) Interpretation Less than 2 -Low accumulation of salt

-No effect on plant growth 2-4 -Moderate accumulation of salt

-Plant growth will not be restricted but frequent irrigation is needed

4 or above -Very high salt accumulation -May affect plant growth

http://soils.tfrec.wsu.edu/mg/chemical.htm Nutrients in the Soil. 1. The macronutrients in soil can be divided into two groups; the primary and the

secondary nutrients.

Category Nutrients Primary Nitrogen

Phosphorus Potassium

Secondary Cadmium Magnesium

Sulfur

2. If the soil is too acidic, lime can be added to lower the acidity. Lime also provides additional calcium and magnesium for plant use. Moreover, lime improves the physical property of the soil by increasing water and air movement.

3. The high acidity in soil results to an increase in the amount of aluminum which

is harmful to plants. 4. Below is a chart on nutrient availability based on pH:

CHEMISTRY IN ACTION

140

http://soils.tfrec.wsu.edu/mg/chemical.htm 5. The cation exchange capacity of the soil or CEC is dependent on three factors;

amount organic matter, amount of clay, and type of clay

VOCABULARY WORDS

1. Humus - composes the bulk of organic matter in soil that contributes to soil fertility to a large extent in that it helps keep soil particles together.

2. Eutrophication - the enrichment of water bodies by dissolved nutrients resulting in the growth of aquatic plant life and the eventual depletion of oxygen in the water body.


Divide the class into several groups and have them conduct research/interview on the type of crops that can be planted in a certain area in relation to the type of soil. Give them at least one week to do this before the actual discussion on soil. If possible, ask the students to bring soil samples where the crops are planted. Let the groups take turns reporting their “findings” while the rest of the class critiques.

http://soils.tfrec.wsu.edu/mg/chemical.htm

CHEMISTRY IN ACTION

141

VIEWING ACTIVITIES


A. Study the soil samples brought by the students. Note the physical properties of the soil.

B. Test the pH of the soil using pH paper and classify them as acidic and basic. C. Relate the physical properties of the soil and the pH with the type of crops

grown. Make generalizations.

ASSESSMENT

Quiz. Multiple Choice. Choose the letter corresponding to the best answer. 1. How much mineral matter is usually present in soil? A. 45% C. 5%

B. 25% D. 15% 2. Which substance makes up mineral matter? A. Si C. SiO2 B. SiO D. SiO3 3. Decaying plants, animals, and animal manure are examples of A. mineral water. C. inorganic matter. B. humus. D. organic matter. 4. The dark-colored, formless, and water-insoluble component of soil is A. sand. C. clay. B. humus. D. silt. 5. All of the following are macronutrients EXCEPT: A. C. C. K. B. H. D. Co. 6. Loam soil is characterized by a large percentage of A. sand. C. clay. B. silt. D. water. 7. Which factor greatly affects the availability of nutrient ions for plants? A. pH C. Humidity B. Color D. Hardness

Show the video clip on Chemical Properties of Soil at segments 11:55 – 14:08.

CHEMISTRY IN ACTION

142

8. All of the following are reasons why soil needs to be enriched occasionally EXCEPT A. crop removal. C. leaching. B. erosion. D. presence of worms. 9. The fertilizer formula of 10.24.14 contains A. 10% N, 24% P2O5, and 14% K2O. B. 10% P2O5, 24% N, and 14% K2O. C. 10% N, 24% K2O P2O5, and 14% P2O5. D. 10% K2O, 24% P2O5, and 14% N. 10. Among the widely used substances for ensuring plant health, these are

considered as potentially the most hazardous pollutants A. manure. C. chlorinated hydrocarbons. B. NPK fertilizers. D. humus. ANSWER KEY

Quiz.

1. A 2. C 3.D 4. B 5. D 6. B 7. A 8.D 9. A 10. C

REFERENCES

American Chemical Society (2000). Chemistry in context. (3rd ed.). NY: McGraw-Hill, Inc.

Chang, R. (1998). Chemistry. (6th ed.). NY: McGraw-Hill, Inc. Snyder, C. (1992). The extraordinary chemistry of ordinary things. (2nd ed.). NY:

John Wiley & Sons, Inc.

CHEMISTRY IN ACTION

143

Useful Websites http://ec.europa.eu/environment/soil/index_en.htm http://www.agroservicesinternational.com/Education/Fert4.html http://www.dnagardens.com/what_is_soil_fertiliy.html http://www.gov.nf.ca/agric/pubfact/Fertility/soilclimate.html http://library.thinkquest.org/J003195F/definiti.htm http://www.agr.state.nc.us/cyber/kidswrld/plant/nutrient.htm http://soils.tfrec.wsu.edu/mg/chemical.htm

http://ec.europa.eu/environment/soil/index_en.htm

http://www.agroservicesinternational.com/Education/Fert4.html

http://www.dnagardens.com/what_is_soil_fertiliy.html

http://www.gov.nf.ca/agric/pubfact/Fertility/soilclimate.html

http://library.thinkquest.org/J003195F/definiti.htm

http://www.agr.state.nc.us/cyber/kidswrld/plant/nutrient.htm

http://soils.tfrec.wsu.edu/mg/chemical.htm

CHEMISTRY IN ACTION

144

Chapter 10: Environmental Chemistry EPISODE 40: OUR WATER RESOURCES

OVERVIEW

This episode focuses on the various water resources and the different ways we obtain and make use of this valuable resource. It also discusses the different processes water undergoes during treatment. In addition, various water pollutants and their sources are investigated.

OBJECTIVES

At the end of this lesson, the student should be able to: 1. discuss the distribution of the Earth’s water supply; 2. evaluate water purity; 3. explain why water is an excellent solvent; 4. identify the sources of fresh water supply for the city dwellers; 5. describe the processes that water undergoes prior to consumption; 6. identify the sectors that demand for water; 7. classify the various water pollutants and their sources; 8. define biological oxygen demand (BOD); 9. differentiate aerobic from anaerobic decomposition; 10. cite methods for clean-up of oils spills; 11. recognize the diminishing availability of clean water and appreciate how

scientific understanding may improve man’s ability to sustain such; and 12. demonstrate awareness, problem solving skills, and responsibility for the

preservation of a reliable and safe water supply for the community.


This episode is directly linked to the previous episodes concerning Environmental Chemistry: Episode 38 – The Atmosphere, and Episode 39 – Soil: Its Chemistry and Pollution. Topics on solutions and solubility as well as the nature and polarity of molecular compounds – specifically that of the compound water, can likewise be integrated in this episode. Regarding the initial steps in the purification process, particularly the sedimentation process, in water purification done in treatment plants, the formation of colloidal particles can be linked with this video clip as well as with cleaning oil spills. Issues concerning environmental awareness such as fresh water pollution in the form of eutrophication, the increase in the pH of water in lakes or other bodies water in a local community, may be also be integrated in the discussion. Health and medical

CHEMISTRY IN ACTION

145

related issues concerning pollutants - organic or inorganic, present in water in the alarming levels may also be brought out. Finally, the fundamental concepts in biology such forms of life in the different ecosystems, biodiversity, and biological magnification are appropriate topics that can be integrated in this episode.

SCIENCE PROCESSES

Observing Collecting data Science modeling Measuring

Organizing and analyzing data Inferring Communicating

VALUES

Care for the environment Scientific orientation Personal discipline Concern for common good

Cooperation Social responsibility Accountability

LIFE SKILLS

Self-awareness and realization Critical and creative thinking Effective communication


IMPORTANT CONCEPTS 1. We have two sources of water: (1) underground wells and aquifers and (2) lakes

and rivers. 2. Water treatment consists of several steps including sedimentation, flocculation,

filtration, chlorination, and aeration. 3. There are three sectors in the society that demand for water: the municipal,

industrial, and agricultural sectors.


Water Facts of Life. § Nearly 97 percent of the world's water is salty or otherwise undrinkable. Another

2 percent is locked in ice caps and glaciers. That leaves just 1 percent for all of

CHEMISTRY IN ACTION

146

humanity's needs - all its agricultural, residential, manufacturing, community, and personal needs.

§ There is the same amount of water on Earth as there was when the Earth was formed. The water from your faucet could contain molecules that dinosaurs drank.

§ Water regulates the Earth's temperature. It also regulates the temperature of the

human body, carries nutrients and oxygen to cells, cushions joints, protects organs and tissues, and removes wastes.

§ Water is part of a deeply interconnected system. What we pour on the ground

ends up in our water and what we spew into the sky ends up in our water. § There are more than twenty anomalous behaviors that water exhibits, among

these is the fact that water expands while cooling from 4 °C to 0 °C. Water expands by 9 percent when it freezes. Frozen water (ice) is lighter than water which is why ice floats in water.

§ The human brain is 75 percent water and 75 percent of a living tree is water. § A person can live about a month without food, but only about a week without

water. § Water is an excellent solvent for ionic and polar substances. § There are many existing technologies for the purification of water such as

reverse osmosis and ultraviolet treatment but there is no single method that works best. The best purification method would have to be a combination of the current technologies already available.

§ Due to the discoveries of various chlorination byproducts in drinking water,

epidemiological studies have found that risks for bladder cancer, colon cancer, and rectal cancer increases with the length of lifetime once drinks chlorinated waters.

§ Among so many threats to our water resources, oil spills may have the most

immediate and significant effects. § Water is such a valuable commodity due to its ever-increasing demand. As the

supply steadily dwindles and as pollution becomes more prevalent, this demand is all the more exaggerated.

§ Bird flu or avian influenza is an infectious disease of birds ranging from mild

to severe form of illness. All birds are thought to be susceptible to bird flu,

CHEMISTRY IN ACTION

147

though some species are more resistant to infection than others. Some forms of bird flu can cause illness to humans. Philippine birds can get the infection when they share water supply with wild birds and use a water supply that might be contaminated by infected dropping.

Sources of Water. Of all the water on Earth, 97 percent are found in the oceans and seas, and 2 percent are frozen in icecaps or glaciers. This leaves us with only about 1 percent as our potential source of fresh water supply. Our country is very rich in water resources; we have about 400 rivers, 58 lakes, and 100 000 hectares of freshwater swamps. Rainwater is an essential add-on to this supply. Although, theoretically distilled, rainwater is never free from contamination as it falls onto the ground. It is fact that no water on Earth is absolutely free of impurities. Being a polar compound, water is an excellent solvent for ionic and polar substances since it exhibits a strong dipole interaction with other molecules. This interaction is known as hydrogen bonding. Because it is such a good solvent, there is much salt dissolved in seawater (around 3 to 3.5 percent inorganic solutes). This is why seawater is described as saline (consisting of or containing salt). Where do we get our water? There are two sources: (1) underground wells and aquifers; and (2) lakes and rivers. For those who live in major cities, water companies acquire water from lakes outside the metropolitan area. Water Treatment. The water that comes out of our faucets had to undergo several treatments. Untreated water from lakes is stored in dams and is allowed to settle so that sedimentation takes place. After this, it is treated with calcium hydroxide, Ca(OH)2 and aluminum sulfate, Al2(SO4)3 so that the aluminum hydroxide, Al(OH)3 that subsequently forms can adsorb the impurities via a process called flocculation. Then, the supernatant liquid is passed through several chambers of gravel and sand for further filtration. Next, it is treated with chlorine to get rid off of much of the bacteria, after which the water is finally aerated so that the excess chlorine gas escapes. The water by this time is relatively cleaner, rendering it safe for human consumption. Demand for Water. Because water is such a necessity, there is a huge and growing demand for it. We can classify the demands are coming from three user sectors: municipal; industrial and agricultural. The municipal sector includes houses, hospitals, restaurants, hotels, offices and other relatively small-scale establishments where the water is typically used for drinking and hygienic purposes. The industrial sector includes factories and manufacturing plants that use water as either raw material or as coolant fro heat generating machines. Finally, the agricultural sector, which happens to exert the biggest demand for this precious commodity among the three, requires water for irrigation.

CHEMISTRY IN ACTION

148

Water Pollutants. After use, much of the water goes to the sewers, where it eventually ends up in streams, rivers, seas, and oceans, with only very little disposed of in household septic tanks. It is interesting to note that the wastewater that goes into the rivers and streams are those that are usually able to get back into water supply. Theoretically, there is no problem with this. But, studies show that the quality of water is steadily deteriorating. This may be attributed to high amount of water pollutants. For example, there are high levels of pesticide residues in runoffs from farmlands. This eventually causes the concentration of dissolved oxygen in water bodies to decrease to a level that it is unable to support marine life. Pollutants may be classified into two general types: inorganic and organic pollutants. Common inorganic pollutants are mineral acids, inorganic salts, metal and its compounds, some of which are radioactive. Mineral acids cause dramatic change in the acidity of water, while inorganic salts dictate the level of salinity. Metals such as mercury, aluminum, lead, iron, copper and zinc and some of their compounds are toxic. Lead poisoning, for example is similar to mercury poisoning. These metals are usually brought about by mine tailings. Organic compounds are especially harmful to the water in a sense that they are usually oxygen-demanding compounds. They are normally carried in the form of domestic sewage, industrial wastes from food processing plants, or as effluents from slaughterhouses and meatpacking establishments. In the process of breaking these compounds down, oxygen is used up by the bacteria that cause the degradation, thus casing the level of dissolved oxygen in the water to go down. Dissolved oxygen concentration of less than 6 mg/L renders the water polluted and unsuitable for marine life. Biological Oxygen Demand, BOD. This requirement of bacteria to decompose organic matter in water expressed in terms of quantity known as Biological Oxygen demand, BOD. The BOD is a measure of the oxygen used in meeting the metabolic needs of microorganisms in water that is rich in organic matter. For nearly pure water, the BOD is one part per million (1 ppm). If the BOD is 5 ppm, the water is said to be of doubtful purity. Products of aerobic decomposition are CO2, HNO3 and NH3 and H3PO4 and H2SO4. Their counterparts in aerobic decomposition are CH4, NH3 and amines, PH3 and H2S, respectively. Synthetic organic compounds that are toxic such as heptachlor, DDT, and chlordane employed as pesticides are also of particular interest since they become part of agricultural runoff. Agricultural runoff, in turn promotes the growth of algae in waterways. Since these algae used up oxygen, fish may suffocate in the water.

CHEMISTRY IN ACTION

149

Oil Spills. Among so many threats to our water resources, oil spills may have the most immediate and significant effects. Nonetheless, technology has given us the capability of remedy them. Some employ mechanical methods, while others use chemical means such as emulsification. Now, there is also an emerging technology where oil slicks can be degraded biologically by certain organisms. Is Your Drinking Water Safe? In the 1800’s and centuries before, cholera and other outbreaks of water-borne illness were common. Epidemics often killed the weakest members of the society first, children, the elderly, and those already suffering some illness. Even before, it was understood that microorganisms in water could cause illnesses, connections had been made between epidemics and the public water supply. In one famous case, a cholera epidemic was halted in London, England by a physician who removed the handle of the Broad Street Pump, a public watering hole suspected to be the source of the disease. For wide spread, killer epidemics of water-borne origin, chlorination seems a safe means to control the spreading. However, it was found that cryptosporidium and giardia cysts can survive chlorination and cause death in persons with weak immune system who contacted them. In 1993, more than 400 000 people developed gastrointestinal illness when a water treatment plant in Milwaukee, Wisconsin failed to control the turbidity of a water source believed to be highly contaminated with cryptosporidium cysts. Metals can contaminate the water at any point, from the source all the way down to the pipes in the consumer’s very own home. Once the water leaves the treatment plant, it can travel many miles, move through various storage systems and pipes before reaching your cup and pot. Along the way, it can pick up lead, mercury, and other metals. Water coming from the tap can have higher levels of unwanted metals than the water from one pipeline inspected at the treatment plant. Volatile organic chemicals, VOCs, can reach the water supply from agriculture, industry, lawns and gardens. Two of the many examples are the herbicide atrazine and the pesticide lindane. Public water system treatments are generally ineffective for these VOCs. These kinds of compounds can be both carcinogenic and estrogenic, contributing to cancer and hormone malfunction. One wonders how water treatments intended to kill bacteria can be completely harmless to humans and animals. Large organisms like humans/animals are actually collections of cooperating cells, each individually taken is not any different from the bacteria.

CHEMISTRY IN ACTION

150

One of the benefits of this condition is, of course, that many other cells have the means to survive even if some cells suffer assaults, which would have easily brought single-celled bacteria to extinction. But is the presence of bacteria killer be a good thing to drink when we take/drink some friendly bacteria to colonize our bowels, to help us digest our foods, and metabolize essential vitamins? Does not one negate the other? There is cause to worry about the chlorination of water that scientific investigations are trying to substantiate. Findings tend to show that trihalomethanes: chloroform, bromodichloromethane, dibromocloromethane, bromoform, and haloacetic acids form in water when both chlorine and organics are present. And organics are impossible to eliminate from public water systems as they come from plants and animals. In the United States, chloroform is found in nearly every public water system. Epidemiological studies tend to show that risks for bladder cancer, colon cancer, and rectal cancer increases with the length of time one has been drinking chlorinated waters. Bladder and rectal cancer risks correlate with trihalomethane levels. Colon cancer risk correlates with length of time drinking of chlorinated water, not with trihalomethanes levels – but some other some other chlorination byproducts still to be identified. (Source: http://www.cfsn.com/water.htm; February 2003). In the report Drinking Water Source and Chlorination Byproducts I. Risk of Bladder Cancer (Epidemiology, January 1998, Vol 9:1, pp 21–28; KP Cantor, CF Lynch, ME Hildesheim, M Dosemeci, J Lubin, M Alaanja, G Craun), the authors write in the discussion: “Chlorination byproducts were discovered in drinking water in 1974, and numerous evaluations since have identified much higher levels in chlorinated surface area than in chlorinated ground water, owing to higher levels of precursor chemicals in the former. A large body of evidence from laboratory studies have shown that the byproduct mixtures, and many component chemicals identified to date, are mutagenic and/or carcinogenic.

… many people are unaware of the source of their community drinking water, and most are unaware of the hypothesis of a link between water source and cancer risk.” In the report Drinking Water Source and Chlorination Byproducts II. Risk of Colon and Rectal Cancers (Epidemiology, January 1998, Vol 9:1, pp 21–28; KP Cantor, CF Lynch, ME Hildesheim, M Dosemeci, J Lubin, M Alaanja, G Craun), the authors write in the introduction:

CHEMISTRY IN ACTION

151

“Chlorination byproducts result from the disinfection of drinking water with chlorine. The practice of adding chlorine to raw water supplies became widespread at the turn of the twentieth century, but it was not until the mid-1970s that Rook and Beller, et al. independently observed that chlorine reacts with naturally occurring organic matter to form trihalogenated methanes (THMs).

Subsequently, a US Environmental Protection Agency survey reported that chloroform, the most ubiquitous of the THMs, could be found in almost every treated drinking water supply.” In references to the differences in correlation between colon and rectal cancers, the authors write: “Our findings of differences in risk patterns for colon and rectal cancers associated with chlorination byproducts are consistent with suggestions of different etiologies for these tumors.” In conclusion to this paper the authors remark: “Recent evidence indicates that certain classes of byproducts, such as brominated compounds, halogenated acetic acids, and chlorinated hydroxyfuranones maybe more harmful than the THMs.”

VOCABULARY WORDS

1. Inorganic pollutants - mineral acids, inorganic salts, a metal and its compounds, some of which are radioactive.

2. Flocculation – when water in dams is treated with calcium hydroxide, Ca(OH)2

and aluminum sulfate, Al2(SO4)3 so that the aluminum hydroxide, Al(OH)3 that subsequently forms can adsorb the colloidal impurities.

3. Biological oxygen demand - BOD, a measure of the oxygen used in meeting

the metabolic needs of microorganisms in water that is rich in organic matter. 4. Sedimentation – when suspended particles in untreated water from lakes that is

stored in dams are allowed to settle down.


A. Bring to class three different types of bottled water (i.e. distilled, mineral, and spring water) and ask the class which among these is the “purest.” Instruct the students to give explanations for their criteria for “pure” water. Tell them to compare water from the tap against the first three samples.

CHEMISTRY IN ACTION

152

B. Introduce the video clip that deals with our water resources. C. Pose the Guide Questions that the students will answer after viewing the video

clip in the episode. Remind them from time to time to focus on finding the answers to these questions as they watch the video clip.

Guide Questions/Answers 1. How much of the Earth’s water can be our source of freshwater supply?

Of all the water on Erath, only about 1 percent can be tapped as potential source of freshwater supply. The bulk of the water is found in the oceans and seas (97 percent) and some are locked up in polar ice caps or glaciers (2 percent).

2. Is there such a thing as “absolutely pure water” on Earth?

No. all water would carry to a certain extent some amount of “impurities.” Purified water is the terminology used for water that has undergone one or several purification treatments. But since all of these methods have limitations, the water that comes out of every treatment cannot be 100 percent pure.

3. Why is water considered as an excellent solvent? Water is an excellent solvent, especially for ionic salts, due to its ability to establish strong dipole interactions with other molecules or particles. This is the reason why there is so much salt in seawater (saline).

4. What are the two sources of freshwater supply? For us, urban dwellers, we depend on nearby lakes and rivers or underground wells or aquifers as sources of freshwater supply.

5. What steps does water from these sources undergo prior to consumption? The water management agencies see to it that the water coming out of our faucets is sufficiently clean and safe. This is why they first treat the water from the sources prior to distribution. This treatment involves several stages: sedimentation, flocculation, filtration, chlorination and aeration.

6. List the three major water-demanding sectors. Which has the highest demand? The three sectors are: municipal, industrial and agricultural. Among these, the agricultural sector has by volume, the greatest demand for water, primarily for irrigation purposes.

CHEMISTRY IN ACTION

153

7. How are the freshwater supply sources contaminated?

Freshwater supply sources become contaminated when the wastewaters end up going to the bodies of water where they came from. In many cases also, pollutants are simply washed off into the water sources.

8. What are the different types of water pollutants? Give a few examples for each. Pollutants are of two types: inorganic and organic. Inorganic pollutants include mineral acids, inorganic salts and metals. Organic pollutants include domestic sewage, and industrial wastes from food-processing plants, among others.

9. What is biological oxygen demand (BOD)? Biological oxygen demand (BOD) is the quantity that expresses the amount of oxygen needed by bacteria to decompose organic matter in water. For nearly pure water, the BOD is 1 mg/L or 1 ppm. A BOD of 5 ppm is considered of doubtful purity already.

10. Differentiate the effect of aerobic decomposition from those of anaerobic decomposition in water. Bacteria may decompose organic matter either with the presence of oxygen (aerobic) or the absence or lack of oxygen (anaerobic). Aerobic decomposition byproducts are: CO2, HNO3 and NH3 and H3PO4 and H2SO4. Their anaerobic counterparts are: CH4, NH3 and amines, PH3 and H2S.

11. How are oils spills remedied? With the current technologies available, oil spills may be remedied mechanically, chemically or even biologically. Chemical methods include the widely used emulsification. Biological methods, meanwhile, involve decomposition of oil slicks by the action of certain organisms.

VIEWING ACTIVITIES

Viewing Activities:

Let the students watch the clips on:

(1) The Water in Our Environment at 2:42 – 3:30, (2) How is Water Purified for Use? at 4:48 – 6:48,

(3) The Uses of Water at 7:00 – 8:30, (4) Wastewater Disposal at 8:41 – 10:05, and

(5) Inorganic & Organic Pollutants at 10:49 – 14:30 and 14:31 -20:00.

CHEMISTRY IN ACTION

154


Discuss the answers to previously posed Guide Questions. TEACHING TIPS

Suggested Activities

A. Demonstration Activity: Build Your Own Watershed. Objectives: 1. to illustrate the basic properties of a watershed: how water flows from higher

elevations to lower elevations and how watersheds are interconnected. 2. to understand how the placement of buildings, roads, and parking lots can be

important to watershed runoff, and how careless use and disposal of harmful contaminants can have a serious effect on downstream watershed inhabitants.

3. to discuss the pollution as a local and global problem. 4. to give suggestions to fix the problems on pollution.

Duration: 1 laboratory class period.

Materials: (per class) § 1 large plastic bowl container (about 1.5 in ´ 3 in ´ 1 in) § 1.0 kg of modeling clay § 1.5 kg of sand (any type of sand will do) § 2.0 kg aquarium gravel § 1 roll of wax paper or plastic wrap § ¼ cup cocoa mix § iced tea mix (other flavored drink mix) § 1 spray bottle or bucket full of water

Background: The land we live on is divided into watersheds. A watershed is a land area whose runoff drains into any river, stream, lake, or ocean. Small watersheds, such as the watershed for the creek behind your house, or the watershed for the pond down the road, drain into small bodies of water, and cover small land areas. The runoff from small watersheds joins together, and their combined areas become a new, larger watershed. Large watersheds drain into large bodies of water, and cover immense land areas. Despite their differences in sizes, all watersheds share common properties. They all perform the same function of transporting water over the Earth’s surface. The watersheds encompass suburban lawns, parking lots and city streets. Water seeps down through the soil to aquifers, which are underground formations in rock and soil that contain enough ground water to supply wells and springs.

CHEMISTRY IN ACTION

155

Many human activities have an effect on watersheds. Construction projects like dams can limit the flow of water; construction of roads and buildings can divert and even increase the flow of water. Agricultural fertilizers can run off of crop fields and inadvertently fertilize harmful microorganisms in rivers and lakes, having an adverse effect on water quality and marine life. The irresponsible disposal of household and industrial chemicals can be harmful because these chemicals travel through the watershed, poisoning life and damaging natural ecosystems. Watersheds can also have an effect on humans. Many communities use rivers, streams, and aquifers as their source of drinking water. Water treatment prepares this water for human consumption, but if the water is laden with chemicals and microorganisms, it can be difficult to treat effectively. Floods are one of the major events in a watershed. Homes built on flood plains, low lying areas adjacent to rivers, are susceptible to flooding conditions when heavy precipitation exceeds the watershed’s capacity to absorb water. Rivers, streams, and lakes overflow, threaten human lives, and damage or destroy roads, buildings, and flood control measures. Watersheds can also become dry, causing water shortages for those who depend on their lakes and rivers for drinking water. It is clear that humans have a close relationship with watersheds. The responsible planning of watershed use and development is important to ensure that the ecosystems sustained by the watersheds are not destroyed, and to protect the health and safety of our communities.

Pre-Lesson Instructions/Activities: 1. Prior to the demonstration, the teacher should engage the students in

activities involving identification of a local watershed. Maps can be used to facilitate this activity and a field trip to a local river or pond can serve to demonstrate the concept of a watershed.

2. Ask students to identify where the water is coming from. How far does the

watershed extend? For a small stream, the answer may be several hundred feet; but for a lake or river, the watershed may be much larger.

3. Assign students or group the students to bring the necessary materials to be used for the activity, at least a day before the demonstration proper.

Lesson/Activity Proper: 1. Wash the aquarium gravel carefully to remove any powdery residue that may

add cloudiness to the water. Fill the container to about 2 inches from the bottom with the gravel. Slope the gravel slightly so, that at one end (down slope), the gravel is only about ½ inch deep and, at the other end (upslope), the gravel is about 3 inches deep. This gravel layer will represent the aquifer.

CHEMISTRY IN ACTION

156

2. Mix the clay and the sand. The consistency of this mixture should be gritty,

with slightly more clay than sand. This mixture should allow water to run freely over it, but if left standing, the water should slowly permeate the surface. Add this mixture to the container carefully, so as not to disturb the slope of the aquifer already placed. The slopes should be similar, with about 2 inches of sand/clay mix overlying the gravel already placed, and on the downhill end there should be about 3 inches of gravel left exposed.

3. Carve a channel in the middle of the clay/sand layer, about ½ inch deep and about 1 inch wide. This channel will represent the main river of the watershed. Near the top of the slope, split the channel into two or three separate channels to represent tributaries. You may wish to add other tributaries along the main branch of the “river” to further illustrate other watersheds.

4. With some extra clay/sand mix, build little hills between the tributaries. These hills separate the smaller watersheds, but when looked at as a whole, the entire “river” system is one watershed. You may also wish to add some small model trees or green felt to represent forests or fields. Buildings can be represented with small blocks of wood.

5. Along the main river, flatten out an area that is about 8 inches by 3 inches. Cut out a piece of wax paper to be about 4 inches by 3 inches in size. Stick this down onto the clay sand mix, sloping it slightly towards the river. If necessary, use some clay to hold the edges down. Explain to students that this wax paper represents the impervious surface of a parking lot.

6. Fill the bottom of the aquarium up to about 2 inches from the bottom with water. The water should fill all of the aquarium gravel “aquifer” area, and should just reach up to the lowest extent of the clay/sand mixture. Explain to students that the aquifer captures and transports water that seeps down through the soil.

7. Using the spray bottle, simulate rain over the flattened soil area and the parking lot. Tell the students to note that the “rain” soaks through the soil, but runs off the parking lot to the river. Ask them what the effect would be if the entire watershed was “paved”.

8. Sprinkle some cocoa mix over the sides of one of the smaller watersheds. Tell the students that the cocoa represents pollution. Over one of the unpolluted “watersheds,” cause some rain with the spray bottle (*it may be necessary to cause more rain by pouring water). Note that the runoff from the rain is clean. Now, make it rain over the polluted area. Ask the students to note how the pollution travels down through the watershed, contaminating all downstream areas.

9. Discuss why the pollution is a problem and what can be done to fix the problem.

CHEMISTRY IN ACTION

157

Extensions:

1. What are some possible sources of watershed pollution in your community? 2. What other impervious surfaces besides parking lots can cause excessive

runoff in a watershed? 3. What can be done to reduce our impact on watersheds and their

environment? 4. Using a map of the area around your house, identify where the runoff from

your driveway will end up. Can you track the path of potential pollution to a large body of water (i.e., ocean or bay)?

5. There are four major watersheds in the Philippines: the Makiling Forest Reserve; Angat Watershed; Ambuklao-Binga Watershed; and the Pantabangan-Carrangalan Watershed. Why should these watersheds be protected? How should the Philippine government protect these watersheds?

B. The Hydrologic Cycle.

(Source: http://media.nasaexplores.com/lessons/02-054/9-12_2.pdf)

Objective: to construct a model of the hydrologic cycle. Duration: 1 laboratory class period. Materials: § student working sheets § 3 empty 1.5 L soft drink bottles with caps (per group) § 60 cm of heavy cotton string or wick (per group) § clear film container (per group) § tap water § cubes of ice § soil § plant seedlings § scissors § clear tape § knife § tapered reamer § poke (or other tools that could be used to punch a hole in one of the bottle

tops)

Pre-Lesson Instructions: 1. Gather the materials and have them laid out for the students to use at stations. 2. Divide class into groups of three or four students.

Lesson/Activity Proper: 1. Discuss water purification and how nature purifies water. 2. Distribute and discuss the Student Sheets.

CHEMISTRY IN ACTION

158

3. Monitor student progress as they work through the stations to build their

models of the hydrologic cycle.

Discussion/Wrap –Up: 1. Let the students draw a detailed diagram of their hydrologic cycle model. Be

sure to have them label all parts and tell what each part represents in nature. 2. Go over the following terms with the class.

a. Capillary action: the action by which the surface of a liquid is elevated or depressed, depending on the relative attraction of the molecules of the liquid for each other or for those of a solid, where it is in contact with a solid (as in a capillary tube)

b. Condensation: (1) the process of changing from a vapor to a liquid; (2) a liquid obtained by the coming together of a gas or vapor

c. Evaporate: to pass off in vapor or in invisible minute particles (to cause evaporation)

d. Precipitation: water droplets or ice particles condensed from atmospheric water vapor that fall to the Earth’s surface, such as rain or snow

e. Transpiration: process in which water absorbed by the root systems of plants moves up through the plants, passes through pores (stomata) in their leaves or other parts, and then evaporates into the atmosphere as water vapor; the passage of water vapor from a living body through a membrane or pores.

f. Water vapor: water in a gaseous (vapor) form and diffused as in the atmosphere

Extensions: Have each group create a poster to represent the hydrologic cycle that occurred in their models.

Student Work Sheets:

The Hydrologic Cycle

Name: _____________________________ Date Performed: _____________ Section: ____________________________ Date Submitted: ___________

CHEMISTRY IN ACTION

159

Background Information:

CLASS SETTING:

OUTER SPACE STATION; STUDENTS WILL ACT LIKE ASTRONAUTS

The astronauts on the International Space Station (ISS) must recycle their water. This includes respiration, perspiration, shower and shaving water, and even urine. These wastewaters will be purified and then used as drinking water.

Biological treatments are used to purify water on Earth. The microorganisms used in this process destroy contaminants in the water. The ISS will use physical and chemical processes to remove contaminants. The Urine Processor will remove volatile components in the urine using distillation (heat disinfection used to prevent microbial growth). Volatile components will remain as liquid brine, which will be returned to Earth and disposed.

The ISS will also use filtration and temperature sterilization to ensure the water is safe to drink. Water will be checked often to ensure it meets the water quality requirements and monitored closely for bacteria, pollutants, and proper pH (a measure of the acidity or alkalinity in the solution). The pH scale ranges from 0 to 14. Substances with a pH value of 7 are neither acidic nor basic. Pure water has a pH value of 7. The recycled water on the ISS is almost sterile and much better than tap water from home or school. There is no odor or bad taste.

For Space Shuttle missions, it is not necessary to recycle the water or waste products. The Shuttle fuel cells produce water as a byproduct; however, water recycling will be imperative for long-duration missions such as on the Space Station or possible missions to Mars. There are no fuel cells on the Space Station; therefore, water will not be produced. In addition, a spacecraft on a lengthy trip to Mars would be limited to the amount of water it could carry because of weight restrictions.

Here on Earth, Mother Nature recycles of water. This activity will show you how water is naturally recycled here on Earth.

Materials: § Student working sheets § 3 empty 1.5 L soft drink bottles with caps / group § 60 cm of heavy cotton string or wick / group § Clear film container / group § tap water § cubes of ice § soil § plant seedlings

CHEMISTRY IN ACTION

160

§ scissors § clear tape § knife § tapered reamer and poke (or other tools that could § be used to punch a hole in one of the bottle tops)

Procedure:

PART A

1. Remove labels from three bottles. Hold it about 6 inches away from the

bottle and move it rapidly up and down so that the air warms the seam of the label.

2. Cut bottle A just below the curve at the top of the bottle, so a straight edge remains on the bottle.

3. Cut bottles B and C just above the bases, so the bottles have straight sides. 4. Poke a hole in one cap. Insert a loop of string (about 40 centimeters) so that

about 5 cm hangs down from the cap. Place this cap on bottle B. 5. Place a cap with no hole on bottle C. Tie about 20 cm of string around the

bottle neck so one end hangs down about 7 cm.

CHEMISTRY IN ACTION

161

PART B

1. Wet both wicks thoroughly. This will bring a constant source of water from

the reservoir to the plants. 2. Add about 150 milliliters of water to bottle A. This is the water source for

the cycle. Place bottle B upside down into bottle A. Be sure that the ends of the string hang into the water in bottle A.

3. Fill bottle B with about 1 cup of pre-moistened soil to cover the loop of the string. The string wick should run up into the soil and not be pressed against the side of the bottle.

4. Plant two or three seedlings of a fast-growing plant, such as Chinese cabbage or turnip, in the soil around the perimeter of bottle B. When bottle C isn’t being used, leave it off bottle B so that air circulates and the seedlings are better able to grow.

5. Place the third bottle top upside down in the center of the soil in bottle B. Carefully place bottle C upside down into bottle B. Be sure the wick hangs into the upside down bottle cap. The bottle cap will be your “rain gauge.” Also, be sure not to smash the plants.

6. Use clear tape to seal the seams between all three bottles. This will seal the cracks and keep the bottles in place.

7. Fill bottle C with ice water. Be sure there is more ice than water. 8. Study your model for a few minutes. Is anything happening? Draw a detailed

diagram of your model of the hydrologic cycle. Be sure to label all parts, and state what they represent in nature.

9. Define the following terms: capillary action, condensation, evaporation, precipitation, transpiration, and water vapor.

10. After a few hours, check the upside down bottle cap in bottle B. What do you see?

C. Investigative Project.

One interesting and relevant activity for the students is to make them form research groups and investigate the different brands and types of bottled water available in the market. They can evaluate which of the brands or types is/are better or safer. They should be able to carry out a well-designed study with plausible criteria. This may take the form of term-long investigative project.

D. Water Consumption Monitoring.

The students may task to monitor the amount of water they consume in their households on a daily basis for one week. This would help them realize how much of this precious resource they are using up. They may also include data on how much of this consumption is allotted for relatively unnecessary uses.

CHEMISTRY IN ACTION

162

E. Diagram of Water Flow.

The students may also be asked to draw a diagram showing the flow of wastewater in their community or neighborhood. This would be of use for future reference for studies regarding the possible contamination of water supply sources by the community.

ASSESSMENT

Quiz. Choose the letter corresponding to the best answer. 1. Of all the water on Earth, how much is available as potential freshwater supply?

A. 1 percent C. 50 percent B. 2 percent D. 97 percent

2. Absolutely, pure water exists ONLY in theory.

A. False. C. Either true or false. B. True. D. Cannot be determined.

3. In the Philippines, freshwater supply may come from the following EXCEPT:

A. aquifers. C. seas. B. lakes. D. underground wells.

4. Water undergoes through the following purification steps at the municipal level

EXCEPT _ A. aeration. C. sedimentation. B. flocculation. D. ultraviolet treatment.

5. Water for household use falls under which category of water-demanding sector?

A. Agricultural C. Municipal B. Industrial D. Either A or B

6. Metal and its compounds are examples of _ pollutants. A. Inorganic C. Synthetic organic B. Natural organic D. All of these

7. The amount of oxygen required by bacteria to decompose organic matter in water is expressed in a quantity known as _

A. BOD. C. BCD. B. COD. D. NID.

CHEMISTRY IN ACTION

163

8. If CO2 is a product of aerobic decomposition, what is its counterpart in aerobic

decomposition? A. CH4 C. NH3 B. H2S D. PH3

9. Water exhibits an anomalous behavior at which temperature range? A. 0 – 4 °C C. 4 – 10 °C B. 0 – 10 °C D. 10 – 14 °C

10. This intermolecular force of attraction is responsible for the excellent solvent qualities of water. A. Dipole-induced dipole C. Dispersion forces B. Dipole-dipole D. Hydrogen bonding

ANSWER KEY

Quiz.

1. A 2. B 3. C 4. D 5. C 6. A 7. A 8. A 9. A 10. D

REFERENCES

American Chemical Society. (2000). Chemistry in context. (3rd ed.). NY: McGraw-Hill, Inc.

Chang, R. (1998). Chemistry. (6th ed.). NY: McGraw-Hill, Inc. Snyder, C. (1992). The extraordinary chemistry of ordinary things. (2nd ed.). NY:

John Wiley & Sons, Inc.

CHEMISTRY IN ACTION

164

Useful Websites ___. Water Resources. Accessed 18 September 2007. NASA Explorer Web Page. (http://www.nasaexplores.com/show2_912a.php?id=04-209&gl=912) ___. Build Your Own Watersheds. Accessed 18 September 2007. US Environmental Agency Web Page. (http://www.epa.gov/safewater/kids/activity) ___. Water Resources. Accessed 18 September 2007. Department of Health, Republic of the Philippines Web Page. (http://www.doh.gov.ph/faqs) ___. Water Facts of Life. Accessed 18 September 2007. City of Rockford, Illinois Web Page. (http://www.ci.rockford.il.us/)

Date post:	21-Jan-2016
Category:	Documents
Upload:	marc-celis
View:	107 times
Download:	0 times

Chem Volume 3

Documents