YEAR 12 CHEMISTRY Preliminary Study Exam Question Pack

In this pack there are a series of exam questions which relate heavily to the A-Level chemistry topics you will study in year 1.

You should complete the packs for each of the following topics and correct your answers: Chemical Calculations Structure and Bonding Organic Chemistry Energy Changes

Page 1 of 56

Chemical Calculations

Year 12 Chemistry Preparation

Name: ________________________

Class: ________________________

Date: ________________________

Time: 47 minutes

Marks: 45 marks

Comments:

Page 2 of 56

Q1. (a) The formula for the chemical compound magnesium sulphate is MgSO4.

Calculate the relative formula mass (Mr)of this compound. (Show your working.)

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(2)

(b) Magnesium sulphate can be made from magnesium and dilute sulphuric acid.

This is the equation for the reaction.

Mg + H2SO4 → MgSO4 + H2

Calculate the mass of magnesium sulphate that would be obtained from 4g of magnesium. (Show your working.)

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Answer___________________ g

(2)

(Total 4 marks)

Q2. This question is about acids and alkalis.

(a) Dilute hydrochloric acid is a strong acid.

Explain why an acid can be described as both strong and dilute.

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(2)

Page 3 of 56

(b) A 1.0 × 10−3 mol/dm3 solution of hydrochloric acid has a pH of 3.0

What is the pH of a 1.0 × 10−5 mol/dm3 solution of hydrochloric acid?

pH = ___________________

(1)

A student titrated 25.0 cm3 portions of dilute sulfuric acid with a 0.105 mol/dm3 sodium hydroxide solution.

(c) The table below shows the student’s results.

Titration

1 Titration

2 Titration

3 Titration

4 Titration

5

Volume of sodium hydroxide solution in cm3

23.50 21.10 22.10 22.15 22.15

The equation for the reaction is:

2 NaOH + H2SO4 ⟶ Na2SO4 + 2 H2O

Calculate the concentration of the sulfuric acid in mol/dm3

Use only the student’s concordant results.

Concordant results are those within 0.10 cm3 of each other.

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Concentration of sulfuric acid = ___________________ mol/dm3

(5)

Page 4 of 56

(d) Explain why the student should use a pipette to measure the dilute sulfuric acid and a burette to measure the sodium hydroxide solution.

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(2)

(e) Calculate the mass of sodium hydroxide in 30.0 cm3 of a 0.105 mol/dm3 solution.

Relative formula mass (Mr): NaOH = 40

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Mass of sodium hydroxide = ___________________ g

(2)

(Total 12 marks)

Page 5 of 56

Q3. Citric acid is a weak acid.

(a) Explain what is meant by a weak acid.

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(2)

A student titrated citric acid with sodium hydroxide solution.

This is the method used.

1. Pipette 25.0 cm3 of sodium hydroxide solution into a conical flask.

2. Add a few drops of thymol blue indicator to the sodium hydroxide solution.

Thymol blue is blue in alkali and yellow in acid.

3. Add citric acid solution from a burette until the end-point was reached.

(b) Explain what would happen at the end-point of this titration.

Refer to the acid, the alkali and the indicator in your answer.

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(3)

(c) Explain why a pipette is used to measure the sodium hydroxide solution but a burette is used to measure the citric acid solution

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(2)

Page 6 of 56

(d) The table shows the student’s results.

Titration 1 Titration 2 Titration 3 Titration 4 Titration 5

Volume of citric acid solution in cm3

13.50 12.10 11.10 12.15 12.15

The equation for the reaction is:

C6H8O7 + 3 NaOH ⟶ C6H5O7Na3 + 3 H2O

The concentration of the sodium hydroxide was 0.102 mol / dm 3

Concordant results are those within 0.10 cm 3 of each other.

Calculate the concentration of the citric acid in mol / dm 3

Use only the concordant results from the table in your calculation.

You must show your working.

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Concentration = ____________________ mol / dm 3

(5)

(Total 12 marks)

Page 7 of 56

Q4. Aspirin tablets have important medical uses.

A student carried out an experiment to make aspirin. The method is given below.

1. Weigh 2.00 g of salicylic acid. 2. Add 4 cm3 of ethanoic anhydride (an excess). 3. Add 5 drops of concentrated sulfuric acid. 4. Warm the mixture for 15 minutes. 5. Add ice cold water to remove the excess ethanoic anhydride. 6. Cool the mixture until a precipitate of aspirin is formed. 7. Collect the precipitate and wash it with cold water. 8. The precipitate of aspirin is dried and weighed.

(a) The equation for this reaction is shown below.

C7H6O3 + C4H6O3 → C9H8O4 + CH3COOH salicylic acid aspirin

Calculate the maximum mass of aspirin that could be made from 2.00 g of salicylic acid.

The relative formula mass (Mr) of salicylic acid, C7H6O3, is 138

The relative formula mass (Mr) of aspirin, C9H8O4, is 180

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Maximum mass of aspirin = _______________ g

(2)

Page 8 of 56

(b) The student made 1.10 g of aspirin from 2.00 g of salicylic acid.

Calculate the percentage yield of aspirin for this experiment.

(If you did not answer part (a), assume that the maximum mass of aspirin that can be made from 2.00 g of salicylic acid is 2.50 g. This is not the correct answer to part

(a).)

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Percentage yield of aspirin = _______________ %

(2)

(c) Suggest one possible reason why this method does not give the maximum amount

of aspirin.

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(1)

(d) Concentrated sulfuric acid is a catalyst in this reaction.

Suggest how the use of a catalyst might reduce costs in the industrial production of aspirin.

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(1)

(Total 6 marks)

Page 9 of 56

Q5. Petrol is a mixture of hydrocarbons such as octane, C8H18

When petrol is burned in a car engine, a large amount of carbon dioxide is produced.

This car uses 114 g of petrol to travel one mile.

Calculate the mass of carbon dioxide produced when this car travels one mile.

Assume that petrol is octane and that combustion is complete.

(Relative atomic masses: H = 1; C = 12; O = 16)

The combustion of octane can be represented by this equation.

C8H18 + 12 O2 → 8CO2 + 9H2O

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Mass of carbon dioxide = ____________ g

(Total 3 marks)

Page 10 of 56

Q6. Limestone (CaCO3) is a raw material. On strong heating it is converted to calcium oxide which is a very useful substance.

(a) Calculate the formula mass (Mr) of calcium carbonate.

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Mr of calcium carbonate = ________________________

(2)

(b) About 60 million tonnes of calcium oxide is made in Britain each year. Calculate the mass of calcium carbonate needed to make this amount of calcium oxide.

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Mass of calcium carbonate needed = _______________ million tonnes

(4)

(c) Water is added to some of the calcium oxide produced in a process known as ‘slaking’. The product of this reaction is used to make plaster.

CaO(s) + H2O(1)→ Ca(OH)2(s)

(i) Give the chemical name of Ca(OH)2.

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(1)

(ii) What is the physical state of the Ca(OH)2 formed in the reaction?

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(1)

(Total 8 marks)

Page 11 of 56

Mark schemes

Q1. (a) Mg S O4

24 + 32 + 16 (×4) or 64 / evidence of all Ar’s

gains 1 mark

but (Mr) = 120

gains 2 marks 2

(b) evidence that 24(g) magnesium would produce 120(g) mapesiurn sulphate

gains 1 mark

or correct scaling by 1/6

but 20(g) magnesium sulphate

gains 2 marks [credit error carried forward from (a) with full marks in (b)]

2

[4]

Q2. (a) (strong because) completely ionised (in aqueous solution)

ignore pH

allow dissociated for ionised

do not accept hydrogen is ionising do not accept H+ are ionised

1

(dilute because) small amount of acid per unit volume

ignore low concentration 1

(b) 5.0

allow 5 1

(c) (titre): chooses titrations 3, 4, 5

1

average titre = 22.13 (cm3)

allow average titre = 22.13(3…) (cm3) allow a correctly calculated average from an incorrect choice of titrations

1

(calculation): (moles NaOH =

Page 12 of 56

allow use of incorrect average titre from step 2 1

(moles H2SO4 = ½ × 0.002324 =) 0.001162

allow use of incorrect number of moles from step 3

1

(concentration =

= 0.0465 (mol/dm3)

allow use of incorrect number of moles from step 4

1

alternative approach for step 3, step 4 and step 5

(concentration H2SO4 =)

= 0.0465 (mol/dm3) (1)

an answer of 0.046473 or 0.04648 correctly rounded to at least 2 sig figs scores marking points 3, 4 and 5

an answer of 0.092946 or 0.09296 or 0.185892 or 0.18592 correctly rounded to at least 2 sig figs scores marking points 3 and 5

an incorrect answer for one step does not prevent allocation of marks for subsequent steps

(d) pipette measures a fixed volume (accurately) 1

(but) burette measures variable volume

allow can measure drop by drop 1

(e) or 0.00315 (mol)

or

(mass per dm3 =) 0.105 × 40 or 4.2 (g)

1

= 0.126 (g) 1

an answer of 0.126 (g) scores 2 marks

an answer of 126(g) scores 1 mark

Page 13 of 56

an incorrect answer for one step does not prevent allocation of marks for subsequent steps

[12]

Q3. (a) produces H+ / hydrogen ions in aqueous solution

1

(but is) only partially / slightly ionised 1

(b) indicator changes colour 1

from blue to yellow

allow from blue to green 1

(when) the acid and alkali are (exactly) neutralised or (when) no excess of either acid or alkali

1

(c) pipette measures one fixed volume (accurately) 1

(but) burette measures variable volumes (accurately) 1

(d) 1

(mean titre =) 12.13(3) (cm 3) 1

(moles NaOH = conc × vol) = 0.00255 1

(moles citric acid = moles NaOH) = 0.00085 1

(conc acid = moles / vol) = 0.0701 (mol / dm 3)

allow ecf from steps 1, 2, 3 and / or 4

allow an answer of 0.0701 (mol / dm 3) without working for 1 mark only

1

[12]

Page 14 of 56

Q4. (a) 2.61 / range 2.5 to 2.7

correct answer with or without or with wrong working gains 2 marks

(accept answers between 2.5 and 2.7)

if answer incorrect moles of salicylic acid = 2/138 = 0.0145 moles ie 2/138 or 0.0145 gains 1 mark or (180/138) × 2 gains 1 mark

or 1 g → 180/138 = (1.304 g) gains 1 mark (not 1.304g alone)

2

(b) 42.1 range 40.7 to 42.3

accept correct answer with or without or with wrong working for 2 marks

ecf ie (1.1 / their answer from (a)) × 100 correctly calculated gains 2 marks

if answer incorrect percentage yield = 1.1 / 2.61 × 100 gains 1 mark

if they do not have an answer to part (a) or

they choose not to use their answer then:

• yield = (1.1 / 2.5) × 100 (1)

• = 44

accept 44 for 2 marks with no working 2

(c) any one from:

• errors in weighing

• some (of the aspirin) lost

do not allow ‘lost as a gas’

• not all of the reactant may have been converted to product

eg reaction didn’t go to completion

allow loss of some reactants

• the reaction is reversible

accept other products / chemicals

• side reactions

ignore waste products

• reactants impure

• not heated for long enough

• not hot enough for reaction to take place

Page 15 of 56

1

(d) any one from:

• use lower temperature

• use less fuel / energy

ignore references to use of catalyst

• produce product faster or speed up reaction

• more product produced in a given time (owtte)

• increased productivity

• lowers activation energy 1

[6]

Q5. 352 g gains 3 marks

(moles C8H18 = 114 / 114 = 1 mole) moles CO2 = 8 (1) mass CO2 = 8 × 44 (1) = 352 g (1)

1 mark for each point (ecf allowed between parts)

or

114 → 8 (1) × 44 (1)

114 → 352 g (1)

ecf allowed between parts

[3]

Q6. (a) 40 + 12 + (3 × 16) = 100

each for 1 mark 2

(b) Mr of CaO = 56

for 1 mark

mass required = 60 × 100/56

for 2 marks

= 107.1

for 1 mark 4

Page 16 of 56

(c) (i) calcium hydroxide 1

(ii) solid 1

[8]

Page 17 of 56

Structure and Bonding

Year 12 Chemistry Preparation

Name: ________________________

Class: ________________________

Date: ________________________

Time: 45 minutes

Marks: 45 marks

Comments:

Page 18 of 56

Q1. This question is about sodium chloride and iodine.

(a) Describe the structure and bonding in sodium chloride.

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(4)

(b) When sodium chloride solution is electrolysed, one product is chlorine.

Name the two other products from the electrolysis of sodium chloride solution.

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(2)

(c) Many people do not have enough iodine in their diet.

Sodium chloride is added to many types of food. Some scientists recommend that sodium chloride should have a compound of iodine added.

Give one ethical reason why a compound of iodine should not be added to sodium

chloride used in food.

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(1)

Page 19 of 56

(d) The bonding in iodine is similar to the bonding in chlorine.

(i) Complete the diagram below to show the bonding in iodine.

Show the outer electrons only.

(2)

(ii) Explain why iodine has a low melting point.

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(3)

(iii) Explain, in terms of particles, why liquid iodine does not conduct electricity.

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(2)

(Total 14 marks)

Page 20 of 56

Q2. The article gives some information about graphene.

Nanotunes!

Carbon can be made into nano-thin, strong sheets called graphene. A graphene sheet is a single layer of graphite. Graphene conducts electricity and is used in loudspeakers. The picture shows the structure of graphene.

© 7immy/iStock

(a) Use the picture and your knowledge of bonding in graphite to:

(i) explain why graphene is strong;

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(3)

(ii) explain why graphene can conduct electricity.

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(2)

Page 21 of 56

(b) Graphite is made up of layers of graphene.

Explain why graphite is a lubricant.

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(2)

(Total 7 marks)

Q3. Glass is made from silicon dioxide.

© Velirina/iStock/Thinkstock

(a) Silicon dioxide has a very high melting point.

Other substances are added to silicon dioxide to make glass. Glass melts at a lower temperature than silicon dioxide.

Suggest why.

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(1)

(b) Sodium oxide is one of the substances added to silicon dioxide to make glass.

(i) Sodium oxide contains Na+ ions and O2– ions.

Give the formula of sodium oxide.

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(1)

Page 22 of 56

(ii) Sodium oxide is made by heating sodium metal in oxygen gas.

Complete the diagram to show the outer electrons in an oxygen molecule (O2).

(2)

(c) Glass can be coloured using tiny particles of gold. Gold is a metal.

Describe the structure of a metal.

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(3)

(Total 7 marks)

Page 23 of 56

Q4. The picture shows a copper kettle being heated on a camping stove.

Copper is a good material for making a kettle because:

• it has a high melting point

• it is a very good conductor of heat.

(a) Explain why copper, like many other metals, has a high melting point. You should describe the structure and bonding of a metal in your answer.

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(4)

Page 24 of 56

(b) An aeroplane contains many miles of electrical wiring made from copper. This adds to the mass of the aeroplane.

It has been suggested that the electrical wiring made from copper could be replaced by lighter carbon nanotubes.

The diagram shows the structure of a carbon nanotube.

(i) What does the term ‘nano’ tell you about the carbon nanotubes?

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______________________________________________________________

(1)

(ii) Like graphite, each carbon atom is joined to three other carbon atoms.

Explain why the carbon nanotube can conduct electricity.

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(2)

(Total 7 marks)

Page 25 of 56

Q5. (a) The diagram shows part of the ionic lattice of a sodium chloride crystal.

(i) Complete the spaces in the table to give information about both of the ions in

this lattice.

Name of ion Charge

__________________________ __________________________

__________________________ __________________________

(2)

(ii) When it is solid, sodium chloride will not conduct electricity. However, molten sodium chloride will conduct electricity. Explain this difference.

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(2)

(iii) Complete the sentence.

Sodium chloride conducts electricity when it is molten and when it is

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(1)

Page 26 of 56

(b) The symbol for a calcium atom can be shown like this:

(i) What is the mass number of this atom?

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(1)

(ii) What information is given by the mass number?

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(1)

(c) Calcium burns in oxygen with a brick-red flame. The product is a white solid. It is calcium oxide and its formula is CaO.

(i) Balance the chemical equation for the reaction.

Ca(s) + O2(g) → CaO(s)

(1)

(ii) Describe, in terms of electrons, what happens to a calcium atom when it becomes a calcium ion.

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(2)

(Total 10 marks)

Page 27 of 56

Mark schemes

Q1. (a) lattice / giant structure

max 3 if incorrect structure or bonding or particles 1

ionic or (contains) ions 1

Na+ and Cl-

accept in words or dot and cross diagram: must include type and magnitude of charge for each ion

1

electrostatic attraction

allow attraction between opposite charges 1

(b) hydrogen

allow H2

1

sodium hydroxide

allow NaOH 1

(c) any one from, eg: • people should have the right to choose • insufficient evidence of effect on individuals • individuals may need different amounts.

allow too much could be harmful

ignore religious reasons

ignore cost

ignore reference to allergies 1

(d) (i) one bonding pair of electrons

accept dot, cross or e or − or any combination, eg

1

6 unbonded electrons on each atom 1

(ii) simple molecules

max 2 if incorrect structure or bonding or particles

accept small molecules

accept simple / small molecular structure 1

Page 28 of 56

with intermolecular forces

accept forces between molecules

must be no contradictory particles 1

which are weak or which require little energy to overcome − must be

linked to second marking point

reference to weak covalent bonds negates second and third marking points

1

(iii) iodine has no delocalised / free / mobile electrons or ions 1

so cannot carry charge

if no mark awarded iodine molecules have no charge gains 1 mark

1

[14]

Q2. (a) (i) giant lattice

allow each carbon atom is joined to three others 1

atoms in graphene are covalently bonded

max. 2 marks if any reference to wrong type of bonding 1

and covalent bonds are strong or need a lot of energy to be broken

allow difficult to break 1

(ii) because graphene has delocalised electrons

allow each carbon atom has one free electron 1

which can move throughout the structure

do not accept just electrons can move. 1

(b) because there are weak forces between molecules

allow no bonds between the layers 1

so layers / molecules can slip / slide. 1

[7]

Page 29 of 56

Q3. (a) weaker bonds

allow (other substances) react with the silicon dioxide

or

fewer bonds

ignore weaker / fewer forces

or

disruption to lattice

do not accept reference to intermolecular forces / bonds 1

(b) (i) Na2O

do not accept brackets or charges in the formula 1

(ii)

electrons can be shown as dots, crosses, e or any combination

2 bonding pairs

accept 4 electrons within the overlap 1

2 lone pairs on each oxygen

accept 4 non-bonding electrons on each oxygen 1

(c) lattice / regular pattern / layers / giant structure / close-packed arrangement 1

(of) positive ions or (of) atoms 1

(with) delocalised / free electrons

reference to incorrect particles or incorrect bonding or incorrect structure = max 2

1

[7]

Page 30 of 56

Q4. (a) any four from:

max 3 marks if any reference made to covalent / ionic bonding / molecules or intermolecular forces or graphite / diamond or forces of attraction between electrons and then ignore throughout

• giant structure / lattice

ignore layers

• positive ions

• sea of electrons or delocalised / free electrons

ignore electrons can move

• awareness of outer shell / highest energy level electrons are involved

• (electrostatic) attractions / bonds between electrons and positive ions

• bonds / attractions (between atoms/ ions) are strong

allow hard to break for strong

ignore forces unqualified

• a lot of energy / heat is needed to break these bonds / attractions

ignore high temperature 4

(b) (i) that they are very small

accept tiny / really small / a lot smaller / any indication of very small

eg microscopic, smaller than the eye can see

or

1–100 nanometres or a few (hundred) atoms

ignore incorrect numerical values if very small is given 1

(ii) any 2 from:

• one (non-bonded) electron from each atom

• delocalised / free electrons

allow sea of electrons

ignore electrons can move

• electron carry / form / pass current / charge

ignore carry electricity 2

[7]

Page 31 of 56

Q5. (a) (i) sodium........ positive or +

both required 1

chloride... negative or –

both required

do not credit chlorine 1

(ii) ions not free (to move) in solid crystal / lattice

ions are free to move when sodium chloride is molten 1

or ions are mobile

do not credit when ions are molten

allow 'particles' for ions (1) mark

do not credit electrons etc 1

(iii) dissolved in water

or in aqueous solution

accept in solution

accept in water

or when a gas/ vapour or solid it will not 1

(b) (i) 40 1

(ii) (total) number of protons and neutrons (in the nucleus) 1

(c) (i) 2Ca + O2 -+ 2CaO

accept any 2n : n : 2n ratio

do not credit if any other change has been made 1

(ii) any two from

electron(s) is / are lost

from the outer shell / orbit / ring

or from the shell furthest the nucleus

or from the 4th shell

two / both (electrons are lost)

accept two electrons are lost for (2)marks

accept both electrons are lost from the

atom for (1) mark 2

Page 32 of 56

Organic Chemistry

Year 12 Chemistry Preparation

Name: ________________________

Class: ________________________

Date: ________________________

Time: 35 minutes

Marks: 34 marks

Comments:

Page 33 of 56

Q1. The diagram shows a reaction which takes place in an oil refinery.

(a) X, Y and Z are all examples of which type of compound?

___________________________________________________________________

(1)

(b) What type of chemical reaction takes place when compound X is converted into compounds Y and Z?

___________________________________________________________________

(1)

(c) Compounds Y and Z are both useful substances.

Compound Y is unsaturated. Compound Z is saturated.

(i) Suggest one use for compound Y.

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(1)

(ii) Suggest one use for compound Z.

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(1)

(Total 4 marks)

Page 34 of 56

Q2. Known crude oil reserves are being used up rapidly. Crude oil is used to produce many useful fuels, such as petrol. One way to conserve crude oil reserves would be to increase the production of bio-fuels.

(a) Ethanol can be produced for use as a bio-fuel. Cars can be powered by ethanol or ethanol–petrol mixtures.

Sugar cane can be fermented to give a mixture of water (boiling point 100 °C) and ethanol (boiling point 78 °C).

(i) How can ethanol be separated from water?

______________________________________________________________

______________________________________________________________

(1)

(ii) Ethanol, C2H5OH, burns to release heat energy.

Complete the balanced symbol equation by writing in the formulae of the two products.

C2H5OH + 3O2 2_____ + 3_____

(2)

(b) The cost of producing a bio-fuel, such as ethanol, by fermentation, is at least three times higher than the production cost of petrol. It costs less to produce ethanol from alkanes. In the production, the vapour of an alkane is passed over a hot catalyst.

Ethene is then converted into ethanol.

(i) What has happened to the hexane to produce ethene?

______________________________________________________________

(1)

(ii) Complete the structural formula for ethene, C2H4.

C C

(1)

Page 35 of 56

(iii) Name the compound that is added to ethene to produce ethanol, C2H5OH.

______________________________________________________________

(1)

(c) As explained in parts (a) and (b), ethanol can be made using either sugar or alkanes as the starting material.

Evaluate the advantages and disadvantages of using these two starting materials to produce ethanol.

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(4)

(Total 10 marks)

Page 36 of 56

Q3. This question is about polymers.

(a) Polyesters are produced when monomers join together and lose a small molecule.

Name the small molecule lost.

___________________________________________________________________

(1)

(b) Poly(propene) is produced from propene.

Complete the structure of poly(propene) in the equation.

(3)

(c) Carpets are made from:

• poly(propene)

• wool

• a mixture of poly(propene) and wool.

Poly(propene) wears out more slowly than wool.

A mixture of poly(propene) and wool to make carpets is more sustainable than using just poly(propene) or just wool.

Suggest why.

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(2)

Page 37 of 56

Polymer fibres are used to make firefighter uniforms.

The table below shows some properties of two polymer fibres.

Polymer fibres

Property Poly(propene) Polyester

Density in g/cm3 0.90 1.38

Melting point in °C 165 260

Flame resistance Poor Good

Water absorption Low High

(d) Evaluate the suitability of poly(propene) and polyester for firefighter uniforms.

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(4)

(Total 10 marks)

Page 38 of 56

Q4. This question is about organic compounds.

(a) Ethanol is an alcohol. One use of ethanol is in alcoholic drinks.

Give two other uses of ethanol.

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___________________________________________________________________

(2)

(b) Which gas is produced when sodium reacts with ethanol?

Tick ( ) one box.

Carbon dioxide

Carbon monoxide

Hydrogen

Oxygen

(1)

(c) Ethanoic acid (CH3COOH) can be produced from ethanol (CH3CH2OH).

(i) What type of reaction produces ethanoic acid from ethanol?

______________________________________________________________

(1)

(ii) Complete the displayed structure of ethanoic acid.

(1)

Page 39 of 56

(iii) Solutions of ethanoic acid and hydrochloric acid with the same concentration have different pH values.

Explain why the solution of ethanoic acid has a higher pH than the solution of hydrochloric acid.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(2)

(d) Ethanol and ethanoic acid react in the presence of a catalyst to form an ester.

(i) Name the ester made from ethanol and ethanoic acid.

______________________________________________________________

(1)

(ii) What type of chemical is used as a catalyst in this reaction?

______________________________________________________________

(1)

(iii) Esters are used in perfumes because they smell pleasant and are volatile.

What does volatile mean?

______________________________________________________________

(1)

(Total 10 marks)

Page 40 of 56

Mark schemes

Q1. (a) hydrocarbon

1

(b) thermal decomposition / cracking 1

(c) (i) making polymers / poly(e)thene

accept plastic (bags) 1

(ii) fuel 1

[4]

Q2. (a) (i) by (fractional) distillation

accept a description of the distillation process (heat and how separation works) eg heat and condense accept boil / vapourise etc for heat

or

fractionation 1

(ii) CO2

note the order of these products must be correct 1

H2O

wrong way round = 1 mark 1

(b) (i) (hexane) has been broken down (into smaller hydrocarbons / molecules) 1

accept (thermal) decomposition / cracked / split / broken up owtte

(ii) H H │ │ C = C │ │ H H

accept CH2 = CH2

1

(iii) water / hydrogen oxide / steam

accept H2O 1

Page 41 of 56

(c) candidates must include both sugar cane and crude oil in their evaluation and both an advantage and a disadvantage to gain full marks.

if they do not then the maximum mark is three

any four from:

advantages of using sugar

• country has no wealth to buy (large quantities of) crude oil

not ‘expensive’ alone

• country has limited technological development

or

underdeveloped / third world country

• able / suitable climate to grow sugar cane

• enough land to grow sugar cane / land cannot be used to grow food / deforestation

• sugar is a renewable source

or

crude oil is a non-renewable resource / finite resource / limited resources

• CO2 / carbon neutral

advantages of using alkanes:

• economic costs are low

• continuous process

• country has large oil resources

• country has oil refineries / cracking plants

• very pure product

• faster process 4

[10]

Page 42 of 56

Q3. (a) water

allow H2O 1

allow hydrogen chloride or HCl 1

(b) single C‒C bond and nothing added to the trailing bonds 1

3 × H and CH3 correct

must be four single bonds 1

n at bottom right 1

must be fully correct to score all 3 marks

an answer of

scores 3 marks

(c) any two from:

• poly(propene) comes from a non-renewable source

allow poly(propene) will run out

• poly(propene) requires a lot of energy to make

• poly(propene) is not biodegradable

• a wool carpet needs replacing more often

must refer to the carpet, not just the fibre

• wool requires the use of large areas of land (which could be used to grow food crops)

ignore references to cost ignore pollution ignore landfill

allow converse arguments 2

Page 43 of 56

(d) any four from:

advantages of polyester • better flame resistance (so burns less easily)

allow good flame resistance so protects the firefighter

• higher melting point (so melts less easily)

allow high melting point so uniform is not damaged

• absorbs water so less likely to ignite

disadvantages of polyester: • high density so uniform is heavy • absorbs water so firefighter gets wet • absorbs water so uniform becomes heavy

• justified conclusion 4

allow converse arguments throughout.

max 3 marks if only advantages or only disadvantages of one type of fibre

[10]

Q4. (a) any two from:

• fuel

allow source of energy

• solvent

allow perfume / aftershave

• antiseptic

allow antibacterial 2

(b) Hydrogen 1

(c) (i) oxidation

do not allow redox 1

(ii) correct structure 1

(iii) ethanoic acid is a weak / weaker acid

it = ethanoic acid 1

because it does not completely ionise.

allow because it does not completely dissociate

allow it has a lower concentration of hydrogen ions

allow converse for hydrochloric acid

Page 44 of 56

do not allow ionising 1

(d) (i) ethyl ethanoate 1

(ii) acid

allow any strong acid

allow correct formulae 1

(iii) evaporates easily / quickly

allow low boiling point

do not allow flammable 1

[10]

Page 45 of 56

Energy Changes

Year 12 Chemistry Preparation

Name: ________________________

Class: ________________________

Date: ________________________

Time: 31 minutes

Marks: 30 marks

Comments:

Page 46 of 56

Q1. This question is about the reaction of ethene and bromine.

The equation for the reaction is:

C2H4 + Br2 → C2H4Br2

(a) Complete the reaction profile in Figure 1.

Draw labelled arrows to show:

• The energy given out (ΔH)

• The activation energy.

Figure 1

(3)

(b) When ethene reacts with bromine, energy is required to break covalent bonds in the molecules.

Explain how a covalent bond holds two atoms together.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

Page 47 of 56

(c) Figure 2 shows the displayed formulae for the reaction of ethene with bromine.

Figure 2

The bond enthalpies and the overall energy change are shown in the table below.

C=C C–H C–C C–Br Overall energy change

Energy in kJ / mole 612 412 348 276 −95

Use the information in the table above and Figure 2 to calculate the bond energy for

the Br–Br bond.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Bond energy _________________________ kJ / mole

(3)

Page 48 of 56

(d) Figure 3 shows the reaction between ethene and chlorine and is similar to the reaction between ethene and bromine.

Figure 3

“The more energy levels (shells) of electrons an atom has, the weaker the covalent bonds that it forms.”

Use the above statement to predict and explain how the overall energy change for the reaction of ethene with chlorine will differ from the overall energy change for the reaction of ethene with bromine.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(6)

(Total 14 marks)

Page 49 of 56

Q2. Methanol (CH3OH) can be made by reacting methane (CH4) and oxygen (O2) in the presence of a platinum catalyst. The reaction is exothermic.

An equation that represents the reaction is:

2CH4 + O2 → 2CH3OH

(a) The energy level diagram for this reaction is given below.

(i) Use the diagram to explain how you know that this reaction is exothermic.

______________________________________________________________

______________________________________________________________

______________________________________________________________

(1)

(ii) Explain, in terms of the energy level diagram, how the platinum catalyst increases the rate of this reaction.

______________________________________________________________

______________________________________________________________

(1)

Page 50 of 56

(b) The equation can also be written showing the structural formulae of the reactants and the product.

(i) Use the bond energies given in the table to help you to calculate the energy change for this reaction.

Bond Bond energy in kJ

C –– H 435

O = O 498

C –– O 805

O –– H 464

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

Energy change = ___________________ kJ

(3)

(ii) In terms of the bond energies, explain why this reaction is exothermic.

______________________________________________________________

______________________________________________________________

(1)

(Total 6 marks)

Page 51 of 56

Q3. Hydrogen chloride is made by reacting hydrogen with chlorine.

H2(g) + Cl2(g) → 2HCl(g)

Bond Bond energy in kJ

H – H 436

Cl – Cl 242

H – Cl 431

Is the reaction between hydrogen and chlorine exothermic or endothermic? Use the bond energies to explain your answer.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

(Total 3 marks)

Page 52 of 56

Q4. Methane and oxygen react together to produce carbon dioxide and water.

The methane gas will not burn in oxygen until a flame is applied, but once lit it continues to burn.

(a) Explain why energy must be supplied to start the reaction but it continues by itself once started.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(4)

(b) Sketch an energy level diagram for the reaction and indicate on the diagram the nett energy released.

(3)

(Total 7 marks)

Page 53 of 56

Mark schemes

Q1. (a) line goes up before it goes down

1

energy given out correctly labelled 1

activation energy labelled correctly 1

(b) electrostatic force of attraction between shared pair of negatively charged electrons 1

and both positively charged nuclei 1

(c) bonds formed = 348 +4(412) + 2(276) = 2548 kJ / mol 1

bonds broken − bonds formed = 612 + 4(412) + (Br-Br) − 2548 = 95 kJ / mol 1

Alternative approach without using C-H bonds

For step 1 allow = 348 + 2(276) = 900 kJ / mol

Then for step 2 allow 612 + (Br-Br) − 900 = 95 kJ / mol

193 (kJ / mol) 1

accept (+)193 (kJ / mol) with no working shown for 3 marks

−193(kJ / mol) scores 2 marks

allow ecf from step 1 and step 2

(d) Level 3 (5–6 marks): A detailed and coherent explanation is given, which demonstrates a broad understanding of the key scientific ideas. The response makes logical links between the points raised and uses sufficient examples to support these links. A conclusion is reached.

Level 2 (3–4 marks):

An explanation is given which demonstrates a reasonable understanding of the key scientific ideas. A conclusion may be reached but the logic used may not be clear or linked to bond energies.

Level 1 (1–2 marks):

Simple statements are made which demonstrate a basic understanding of some of the relevant ideas. The response may fail to make logical links between the points raised.

0 marks:

No relevant content.

Indicative content

Size and strength • chlorine atoms have fewer electron energy levels/shells

Page 54 of 56

• chlorine atoms form stronger bonds • Cl–Cl bond stronger than Br–Br • C–Cl bond stronger than C–Br

Energies required • more energy required to break bonds with chlorine • more energy given out when making bonds with chlorine • overall energy change depends on sizes of energy changes

Conclusions • if C−Cl bond changes less, then less exothermic • if C−Cl bond changes more, then more exothermic • can’t tell how overall energy change will differ as do not know which

changes more. 6

[14]

Q2. (a) (i) energy / heat of products less than energy of reactants

owtte

allow products are lower than reactants

allow more energy / heat given out than taken in

allow methanol is lower

allow converse

allow energy / heat is given out / lost allow ΔH is negative 1

(ii) lowers / less activation energy

owtte

allow lowers energy needed for reaction

or it lowers the peak/ maximum

do not allow just ‘lowers the energy’ 1

(b) (i) bonds broken: (2 × 435) + 498 = 1368

allow: (8 × 435) + 498 = 3978 1

bonds made: (2 × 805) + (2 × 464) = 2538

allow: (6 × 435) + (2 × 805) + (2 × 464) = 5148 1

energy change: 1368 – 2538 = (–)1170

allow: 3978 – 5148 = (–)1170

ignore sign

allow ecf

correct answer (1170) = 3 marks 1

(ii) energy released forming new bonds is greater than energy needed to break existing bonds owtte

allow converse

do not accept energy needed to form new bonds greater

Page 55 of 56

than energy needed to break existing bonds 1

[6]

Q3. exothermic does not gain any credit

1

reactants: bond breaking (436 + 242 =) 678 (kJ) 1

products: bond making (2 × 431 =) 862(kJ)

so overall 184 (kJ) released / –184(kJ) 1

[3]

Q4. (a) idea that

existing bonds must first be broken

for 1 mark

(credit molecules / atoms more likely to react when they collide)

energy is released when new bonds form

gains 1 mark

but more energy is released when new bonds form

gains 2 marks

or overall reaction exothermic

this breaks more bonds so the reaction continues

for 1 mark max 4

(b) • reactant level higher than product level (names of reactants and products not required)

• indication that activation energy required (i.e. the “hump”)

• any correct indication of nett energy change

(i.e. between product and reactant levels even if other marks not gained)

for 1 mark each 3

[7]