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Farr High School

NATIONAL 5 CHEMISTRY

Unit 2 Nature’s Chemistry

Question Booklet (UPDATED MAY 2017)

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Homologous Series 1. What is meant by a homologous series? A family of compounds with similar chemical properties and a general formula 2. What is the general formula for the alkanes? CnH2n+2 3. Copy and complete the table for the first 8 alkanes.

Name Molecular Formula

Full Structural Formula Shortened Structural

Formula

Methane CH4

CH4

Ethane C2H6

CH3CH3

Propane C3H8

CH3CH2CH3

Butane C4H10

CH3CH2CH2CH2CH2CH2 CH2CH3

Pentane C5H12

CH3CH2CH2CH2CH3

Hexane C6H14

CH3CH2CH2CH2CH2CH3

Heptane C7H16

CH3CH2CH2CH2CH2CH2CH3

Octane C8H18

CH3CH2CH2CH2CH2CH2CH2CH3

4. Why are alkanes described as saturated hydrocarbons?

Because no more atoms can be added to the molecule as there are no double bonds (all carbon atoms are singly bonded)

5. The following table gives the boiling points of the first six alkanes:

Alkane Boiling point (oC)

Methane -164

Ethane -89

Propane -42

Butane -1

Pentane 36

Hexane 69

a) Use the information in the table to draw a spike graph of boiling points against the number of carbon atoms in the molecules.

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b) Describe the trend in boiling points. As the number of carbon atoms increases, the boiling point increase c) Estimate the boiling points of i) heptane ii) octane 102°C 135°C 6. Crude oil contains a mixture of different alkanes. The alkanes can be separated into

useful products by the process shown below: a) What is the name of this process? Fractional distillation b) Which of the following physical properties is made use of when separating the

fractions in crude oil? A melting point B viscosity C boiling point D solubility c) State what is meant by the terms: (i) Flammability How readily a substance catches fire/the ease with which a chemical will burn (ii) Viscosity Used to describe the lack of fluidity of a substance

-200

-150

-100

-50

0

50

100

1 2 3 4 5 6

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Number of carbon atoms

No. of carbon atoms versus boiling point

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d) Which of the following statements is true for petrol. A It has a chain length of 1 – 4 and is a low boiling point liquid. B It has a chain length of 5 – 12 and is a low boiling point liquid. C It has a chain length of 5 – 12 and is a high boiling point liquid. D It has a chain length of 9 – 16 and is a low boiling point liquid. e) Place the fractions ‘diesel’, ‘fuel gas’, ‘bitumen’ and ‘petrol’ in order of: (i) ease of evaporation – easiest first Fuel gas – petrol – diesel - bitumen (ii) flammability – most flammable first Fuel gas – petrol – diesel - bitumen (iii) viscosity – most viscous first Bitumen – diesel – petrol – fuel gas f) Explain why petrol has a lower boiling point than lubricating oil.

Petrol is a smaller molecule than lubricating oil and therefore has smaller intermolecular forces holding them together which require less energy to break.

g) Explain why lubricating oil is less flammable than naphtha. Naptha contains smaller molecules than lubricating oil and therefore has smaller

intermolecular forces holding them together which require less energy to break and therefore it naptha is more volatile and easier to burn.

h) Explain why diesel is more viscous than naphtha. Naptha contains smaller molecules than diesel and therefore has smaller

intermolecular forces holding them together which means it is much more fluid. i) What two products are always made when hydrocarbons combust in a plentiful

supply of oxygen? Carbon dioxide and water

7. What is the general formula for the alkenes? CnH2n 8. Copy and complete the table for the first 7 alkenes.

Name Molecular Formula

Full Structural Formula Shortened Structural

Formula

ethene C2H4

CH2=CH2

propene C3H6

CH2=CHCH3

butene C4H8

CH2=CHCH2CH3

Pentene C5H10

CH2=CHCH2CH2CH3

hexene C6H12

CH2=CHCH2CH2CH2CH3

heptene C7H14

CH2=CHCH2CH2CH2CH2CH3

octene C8H16

CH2=CHCH2CH2CH2CH2CH2CH3

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9. Why are alkenes called unsaturated hydrocarbons?

They contain a carbon-to-carbon double bond and molecules can ‘add’ across the double bond

10. Describe the test and the result for an unsaturated hydrocarbon. An unsaturated hydrocarbon will decolourise bromine water rapidly 11. Complete the diagrams showing the addition reactions. Write word equations for the reactions.

12. Explain how hydrogenation is used to produce margarine from olive oil.

Hydrogen is added to olive oil which is an unsaturated hydrocarbon and this reduces the number of double bonds which allows the molecules to interact better and therefore increases the intermolecular forces between them which causes the compound to solidify.

13. What is the general formula for the cycloalkanes? CnH2n 14. Copy and complete the table for the first 6 alkanes.

Name Molecular Formula Structural Formula

cyclopropane C3H6

Cyclobutane C4H8

Cyclopentane C5H10

Cyclohexane C6H12

Cycloheptane C7H14

cyclooctane C8H16

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15. Propene and cyclopropane both have the formula C3H6. Describe a test that could be carried out to determine which chemical is which. Test for unsaturation - Add bromine water and the substance that decolourises the

bromine water rapidly must be propene as it is unsaturated 16. What word is used to describe chemicals with the same molecular formula but different

structural formula? isomers 17. Write the molecular formula and give the systematic names for the following chemicals:

a) C5H12 – 2-methylbutane b) C4H10 – 2,2-dimethylpropane c) C4H8 – but-1-ene d) C4H8 – but-2-ene e) C6H12 – hex-2-ene f) C6H12 – 4-methylhex-2-ene

18. Draw the structural formula for the following hydrocarbons:

a) pent-2-ene b) 2-methylpentane c) 2,3-dichlorohexane d) 2,3-dimethylpent-1-ene

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19. The names of some hydrocarbons are shown. A cyclobutane B cyclopentane C butane D propane E ethane F butene a) Identify the two isomers. A and F b) Identify the hydrocarbon that reacts quickly with bromine solution. F c) Identify the hydrocarbon which is a liquid at 25oC. You may wish to use the data booklet to help you. B

20. The grid shows the formulae for a number of hydrocarbons.

A

CH3 CH CH3

CH3

B

CH2

CH2 CH2

C

CH2 CH2

CH2 CH2

D

CH3 CH2 CH2 CH3

E

CH3 - C = CH2

CH3

F

CH2 =CH- CH2- CH2-CH3

a) Identify the two isomers of CH2=CH-CH2-CH3 C and E b) Identify cyclopropane. B c) Which box would be the product of box E reacting with hydrogen. A 21. Identify the homologous series each of the following molecules belongs to and name the compound shown. a) CH3CH2CH2OH b) CH3CH2CH3 c) CH3CH2CH2CH2CH2OH alcohols propan-1-ol alkanes propane alcohols pentan-1-ol d) CH3CH2COOH e) CH3CHCHCH3 f) carboxylic acids propanoic acid alkenes but-2-ene carboxylic acid ethanoic acid 22. The dienes are a homologous series of hydrocarbons which possess two carbon to carbon double covalent bonds per molecule of diene. The first three members of the diene series have the following molecular formulae:- C4H6 C5H8 C6H10 a) Are dienes, saturated or unsaturated molecules. Explain your answer. Unsaturated as they contain double bonds b) What would be the molecular formula of the diene with 7 carbon atoms? C7H12 c) What is general formula for the dienes? CnH2n-2

d) Draw a possible structural formula for the diene with formula C4H6

HC

O

OH

HC

O

OH

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23. The following reaction shows what happens to an alkene when it reacts with ozone.

a) Draw the structural formulae of the products you would expect from the following reaction.

+ ozone

b) Reaction with ozone and another alkene produces only one product. Draw the structural formula of the alkene which would react in this way.

24. Draw full structural formula for two isomers that have the molecular formula C4H8 and belong to two different homologous series. Give systematic names for the two isomers. But-1-ene

OR

But-2-ene

AND cyclobutane

C

H

H

H C

H

H

C

H

C

H

C

H

H

H

C

H

H

H C

H

H

C

H

C

H

C

H

H

H

+

ozone

C

H

H

H C

H

H

C

H

O

C

H

H

H C

H

H

C

H

O

+

O C

H

CH

H

H

O C

H

CH

H

H

ozone

C

H

H

H C

H

C

H

C

H

H

C

H

H

C

H

H

C

H

H

H

C

H

H

H C

H

C

H

C

H

H

C

H

H

C

H

H

C

H

H

H

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Everyday Consumer Products 1. Describe what happens during fermentation. Include the word equation and the chemical equation as part of your answer.

In fermentation, glucose reacts with water in the presence of yeast (enzyme) to produce alcohol and carbon dioxide.

Glucose + water → alcohol + carbon dioxide

C6H12O6 + H2O → C2H5OH + CO2 2. Describe how changing the temperature affects the efficiency of an enzyme.

As the temperature increases, the efficiency of the enzyme increases until it reaches its optimum at 37°C. Thereafter the efficiency decreases rapidly as the enzyme is denatured.

3. What process is used to increase the concentration of alcohol? distillation 4. Explain why alcohol and water can be separated in this way.

Alcohol has a lower boiling point (78°C) than water (100°C) and therefore it boils at a lower temperature which allows it to be separated from the water which requires a higher temperature to boil.

5. What is the general formula for alcohols? CnH2n+1OH 6. Name and draw the functional group for alcohols. -OH Hydroxyl 7. Describe how ethanol can be made from ethene. Dehydration of ethanol using concentrated sulfuric acid 8. Give the names of the following alcohols :

a) ethanol b) propan-1-ol c) pentan-3-ol d) heptan-3-ol 9. Draw the full structural formulae of the following alcohols and give their names.

a) CH3CH2OH ethanol b) CH3CH(OH)CH3 propan-1-ol c) CH3CH2CH2CH2OH butan-1-ol d) CH3CH(OH)CH2CH2CH3 pentan-2-ol

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10. Draw the shortened structural formulae for : a) butan-1-ol b) hexan-3-ol c) octan-2-ol CH3CH2CH2CH2OH CH3CH2CH(OH)CH2CH2CH3 CH3CH(OH)CH2CH2CH2CH2CH2CH3

11. Two isomeric straight chain alcohols, each having 4 carbon atoms, are known. Draw a structural formula for each of these alcohols and write the name. butan-1-ol butan-2-ol 12. Besides alcoholic beverages, give two uses of alcohols. Fuel and solvent 13. Give the general formula for carboxylic acids. CnH2n+1COOH 14. Name and draw the functional group for carboxylic acids. Carboxyl group 15. Draw the full structural formula for the following: a) ethanoic acid b) pentanoic acid c) heptanoic acid 16. Give 3 uses for carboxylic acids. Treat limescale, preserve foods and vinegar. 17. Carboxylic acids are weak acids. What does this mean? They do not fully dissociate.

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18. The table below shows the boiling points for some carboxylic acids.

Acid Formula mass Boiling point oC

Methanoic acid 46 101

Ethanoic acid 60 118

Propanoic acid 74 141

Butanoic acid 88 164

a) Present this information as a bar graph.

b) Predict the boiling point of pentanoic acid. 181-187°C 24. From the list of chemicals below, identify a) the alcohols E, I, J b) the carboxylic acids C, G, K

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20

40

60

80

100

120

140

160

180

methanoic acid ethanoic acid propanoic acid butanoic acid

Bo

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Carboxylic acid

Carboxylic Acids

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Energy From Fuels 1. Write balanced equations for the combustion of: a) methane CH4 + 2O2 → CO2 + 2H2O

b) propane C3H8 + 5O2 → 3CO2 + 4H2O

c) methanol CH3OH + 3

2O2 → CO2 + 2H2O

2. The formula for measuring enthalpy change is Eh = c x m x ∆T Write down what each of the symbols in the equation stands for and the units that they

are measured in. Eh = enthalpy of combustion (kJ) c = specific heat capacity of water (kJ kg-1 °C-1) m = mass of water (kg) ΔT = change in temperature (°C) 3. Complete the sentences below using the following words:

endothermic exothermic lost reactants negative joules surroundings

The symbol for enthalpy change is Eh and the units are joules. In an exothermic

reaction energy is lost to the surroundings. When the products have more energy than

the reactants, the reaction is endothermic. It will take in energy from its surroundings.

Combustion reactions are exothermic so Eh is negative.

4. Calculate the heat required to raise the temperature of:

a) 1 kg of water by 15 oC. 62.7kJ b) 8 kg of water by 37 oC. 1237.28kJ c) 250 cm3 of water by 20 oC. 20.9kJ d) 500 cm3 of water by 55 oC. 114.95kJ e) 100 cm3 of water by 13 oC. 5.43kJ

5. When some ethane was burned, it heated 200 g of water from 15.5 oC to 37.0 oC.

a) Write a balanced symbol equation for the reaction.

C2H6 + 7

2O2 → 2CO2 + 3H2O

b) Calculate Eh. 17.97kJ

6. In an experiment burning propanol a pupil heated 100g of water using a spirit burner. The resulting change in temperature was from 10.5oC to 42.5oC.

a) Write a balanced symbol equation for the reaction.

C3H7OH + 9

2O2 → 3CO2 + 4H2O

b) Calculate Eh. 13.38kJ 7. C2H4 + 3O2 2CO2 + 2H2O What mass of water vapour is produced on burning 7g of ethene? 9g

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8. 2H2 + O2 H2O What mass of water vapour is produced on burning 1g of hydrogen? 4.5g 9. 2CO + O2 2CO2 What mass of carbon monoxide must be burned to give 4.4g of carbon dioxide? 2.8g 10. What mass of carbon dioxide is produced on burning 8 g of methane (CH4) completely in oxygen? CH4 + 2O2 → CO2 + 2H2O 22g 11. What mass of carbon dioxide is produced on burning 2.3 g of ethanol (C2H5OH) completely in oxygen? C2H5OH + 3O2 → 2CO2 + 3H2O 4.4g