Alkanes power point

Overview of Organic Chemistry

Organic Compounds in Daily Life

Can you identify organic compounds from this picture?

1. Road surface (bitumen)

2. Fuel in car3. Tyres

Mr Friedrich WöhlerBorn: 31-Jul-1800

Birthplace: Eschersheim, GermanyDied: 23-Sep-1882

He changed the belief that organic compounds could only be made by living things.

Organic compounds are compounds that contain the element Carbon (C).

Most organic compounds also contain hydrogen (H).Organic compounds that contain only carbon and

hydrogen are called hydrocarbons.

Some Brief History

Question Time!Q: Do all compounds containing carbon considered as organic compounds?

A: No. Chemists consider carbonates and oxides

of carbon as INORGANIC compounds rather than organic.

Examples of inorganic compounds:

Some Real Life Incidents In Singapore (NE ISSUES)

Q: Why do you think Singapore imposed very harsh measure to control pollution of our air and the environment?

How Do We Classify Organic Compounds

Recall… On the topic of Periodic table..

We classified elements into families (group I, II ,III…). which had similar properties..

On the topic of Organic Chemistry..

We classify organic compounds into families known as the homologous series which have similar chemical properties within the series.


Definition:

A. A homologous series is a family of organic compounds with1. Similar chemical properties2. Similar functional group (reactive group)3. Same general formula

B. Organic compounds in the same homologous series have

1. Similar chemical properties because they have the same functional group

2. Different physical properties due to different chain length (number of carbon atoms per molecule)

Learning Point 1: As the number of carbon atoms increases, there is a gradual change in the physical properties.


The table below shows 4 homologous series, their functional groups and

their general formula we will learn in this topic of Organic Chemistry.

n refers to the number of carbon atoms

Naming Organic CompoundsThe table below shows 4 homologous series, their functional groups

and their general formula we will learn in this topic of Organic Chemistry.

Question Time 2!Q: Where do you use/find alkanes in everyday life?

Activity: Time To Use Your Creative Juices!Get into groups of 5 students each.

Complete this task in 2 minutes.

Your Group Task:As a group, come up with a mnemonic for memorizing the prefixes for the first four alkanes (methane, ethane, propane, butane).

My Version: Mike Eats Peanut Butter

Disclaimer: Best group will get a special present from me!

Interactive Activity:

ChemSketch Molecular Modelling

Time to learn more about the physical properties of alkanes!

ChemSketch Molecular Modelling Activity (30Mins)In your groups of 5, you are to:

1. Complete your individual worksheet by working together as a group to think about the questions and answering the

questions.

2. The complete worksheet must be submitted at the end of the lesson.

3. Follow the instructions in the worksheet.

4. Raise your hand to ask for assistance if your group encounters any problems or in doubt.

5. Have Fun!!

Reflection: ChemSketch Molecular Modelling Activity You have learnt 7 important concepts:

1) How to draw 2D structural formula for Alkanes (C1-C5) and Alkenes (C2-C4)

2) Derived the general formula of Alkanes CnH2n+2

3) Derived the general formula of Alkenes CnH2n

4) Alkanes are saturated (contains single C-C)5) Alkenes are unsaturated (contains C=C)6) As the no. of carbon atoms increases, the physical properties show

a gradual change (m.p., b.p., state at r.t.p.)7) Isomerism starts from butane, how to draw isomers of butane and

understand the term isomerism.

Chemical Properties of

Alkanes

Chemical Properties of AlkanesAlkanes are unreactive as their C-C and C-H bonds are very strong

and difficult to break.

They do not react with acids, alkalis, metals or oxidizing agents!

**Fun Fact: Alkanes used to be called paraffins ** In Latin Parum = little

Affinities = affinity

Named as such in the past because alkanes undergo few reactions

Reactions Of AlkanesAll alkanes have similar chemical properties because they belong

to the same homologous series.

Alkanes are rather unreactive; they not react with most chemicals.

However, they undergo 2 main types of reaction:

Combustion(Complete

& Incomplete)

Substitution Reaction

Alkanes

A. Combustion Reaction (2 Types)

1. Complete Combustion

2. Incomplete Combustion

Combustion(Complete)

(Incomplete)Substitution Reaction

Alkanes are called saturated hydrocarbons because they only have single bonds between carbon atoms (C-C).

Alkanes burn in a plentiful supply of air to release energy (this is why they are used as fuels).

Combustion (Complete)

Gas supplied here refers to Alkanes !!

Recall your

Bunsen Burner..


Substitution Reaction

Burning (properly called combustion) also produces :

1. Carbon dioxide (CO2)2. Water Vapour (H2O)3. Heat

Lets observe what happens when you light a bunsen burner!


Substitution ReactionCombustion (Complete)

Lets break it down frame by frame:



1. Methane gas (CH4) exits from the mouth the Bunsen Burner and mixes with the oxygen gas (O2) in the atmosphere

2. A flame is placed near the mouth of the Bunsen Burner.

Lets break it down frame by frame:



3. Methane gas (CH4) burns in oxygen gas (O2) in the surrounding atmosphere (process: combustion)

4. The products of the combustion are CO2 and H2O.5. Complete combustion Blue, non-luminous flame !



Writing A Balanced Equation : Complete Combustion of Methane

Word Equation: Methane(g) + Oxygen(g) Carbon dioxide(g) + Water(l) + Heat

Chemical Equation: Step 1: CH4(g) + O2(g) CO2(g) + H2O(l) [Write the chemical equation]

Step 2: CH4(g) + O2(g) CO2(g) + 2H2O(l) [Balance the equation]

Note: Heat is always evolved from the combustion. In the following equations, I will omit it for clarity.

How to Balance Combustion Reactions:

1.Balance the carbon atoms2.Balance the hydrogen atoms3.If you need an odd number of Oxygens, double all coefficients

_____ C4H10 + _____O2 __4___CO2 + _____H2O_____ C4H10 + _____O2 __4___CO2 + ___5__H2O

Need 13 oxygen atoms – so give O2, coefficient of 13 and double all other coefficients

___2__ C4H10 + __13___O2 __8___CO2 + __10___H2O



Some Important Pointers on Complete Combustion

Heat is always produced during combustion of hydrocarbons exothermic reaction always.

General Equation: CxHy(g) + (x + y/4) O2(g) x CO2(g) + (y/2) H2O(l)

*Only applies for COMPLETE COMBUSTION OF ALKANES + ALKENES*

Combustion(InComplete

)Substitution ReactionCombustion (InComplete)

Some Important Pointers on Complete Combustion

When there is insufficient oxygen gas, incomplete combustion occurs.Note: Incomplete combustion also occurs for larger alkanes

(e.g candle wax C25H52)

Its means that the alkanes is not burnt completely and gives a more sooty flame (orange-yellow in colour) !

The black soot is carbon and the yellow flame comes from glowing carbon atoms

Think Tank Time : Can you suggest some products produced by the incomplete

combustion besides CO2 & H2O?

Carbon Monoxide (CO) Soot (unburnt carbon particles)

Combustion(InComplete

)Substitution ReactionCombustion (InComplete)

What Happens If There Is Insufficient Oxygen ?

The possible balanced chemical equation for the incomplete combustion of methane gas is :

CH4(g) + O2(g) → C(s) + 2H2O(g) [Carbon Only]

2CH4(g) + 3O2(g) → 2CO(s) + 4H2O(g) [Carbon Monoxide Only]

4CH4(g) + 5O2(g) →2CO(s) + 2C(s) 8H2O(g) [Mixture of Both]

B. Substitution Reaction

1. Substitution Reactions of Methane (CH4) and Chlorine (Cl2)


(Incomplete)Substitution Reaction

Combustion Substitution ReactionSubstitution Reaction

What Is It About?

Alkanes react with halogens, such as chlorine and bromine, in the presence of ultraviolet light (UV light)

For example:Methane reacts with chlorine to form chloromethane

and hydrogen chloride gas.CH4(g) + Cl2(g) CH3Cl(g) + HCl(g)

This is substitution reaction. The hydrogen atom in methane is replaced by chlorine atom.

UV light

chloromethane


How does the reaction look like?

C HH

HH

Cl-Cl C ClH

HH

H-Cl+UV

light

chloromethane

+

More hydrogen atoms can be replaced with chlorine atoms to produce a mixture of four organic compounds!!


Writing Out The Entire Sequence Of Reaction..

More hydrogen atoms can be replaced with chlorine atoms to produce a mixture of four organic compounds!!

SummaryToday you have learnt about the first part of Organic Chemistry:

Today’s Lesson: Part 1- Alkanes (saturated molecules)

1. Naming Organic Compounds

2. Homologous Series

3. Structural/ Condensed Formula of Alkanes

4. Physical Properties of Alkanes

5. Chemical Properties of Alkanes

6. Uses of Alkanes and its substituted derivatives

Next lesson: Part 2- Alkenes (unsaturated molecules)

Bunsen Burner Shockwave Flash Animation and Pictures:http://msbeaker.blogspot.com/2010/11/burnt-toast.html Pictures from Slides 5:

http://teamseagrass.blogspot.com/2010/05/massive-oil-spill-off-changi-east.html

Pictures from Slides 6: http://library.thinkquest.org/3616/chem/periodic.gif Pictures from Slides 8 & 9: ‘O’ Level Science Chemistry by Tan Yin Toon pg. 193Pictures from Slide 10:http://hexen.fushyumang.com/en/promotions/assests/shell.jpg Pictures from Slide 31:http://images.amazon.com/images/P/0300075979.01.LZZZZZZZ.jpg

References

http://msbeaker.blogspot.com/2010/11/burnt-toast.html



http://library.thinkquest.org/3616/chem/periodic.gif

http://hexen.fushyumang.com/en/promotions/assests/shell.jpg

http://images.amazon.com/images/P/0300075979.01.LZZZZZZZ.jpg

Date post:	16-Jan-2017
Category:	Education
Upload:	lerangeline
View:	18,657 times
Download:	0 times

Alkanes power point

Education