Chemistry -...

1

Chemistr yfor Cambridge O Level

Derek McMonagle

Answer Book

2

Published byPEAK PUBLISHING LIMITEDLondonUK

© Peak Publishing Limited 2016Text © Derek McMonagle 2016

First published 2016

ISBN: 1 845222 13 X

All rights reserved.

No part of this publication may be reproduced, copied or transmitted save with written permission or in accordance with the provisions of the Copyright, Design and Patents Act 1988, or under the terms of any license permitting limited copying issued by the Copyright Licensing Agency, 90 Tottenham Court Road, London W1P 9HE.

Cambridge International Examinations bears no responsibility for the example answers to questions which are contained in this publication. The answers to exam-style questions and to Cambridge past paper questions in this book have been written by the author.

Any person who does any unauthorised act in relation to this publication may be liable to criminal prosecution and civil claims for damages.

Printed in Pakistan

3

Contents

1 Experimental chemistry ................................................................................ 4

2 Kinetic particle theory ...................................................................................5

3 Atomic structure ........................................................................................... 7

4 Materials and bonding .................................................................................. 9

5 Formulae, stoichiometry and the mole concept .........................................11

6 Elecrolysis ....................................................................................................13

7 Energy from chemicals ................................................................................14

8 Chemical reactions ...................................................................................... 16

9 Acid, bases and salts ................................................................................... 19

10 Two important industrial chemicals ammonia and sulfuric acid .................21

11 The Periodic Table ....................................................................................... 23

12 Metals ......................................................................................................... 24

13 Two important metals iron and aluminium ................................................ 26

14 Atmosphere and environment .................................................................... 27

15 Organic chemistry I .................................................................................... . 28

16 Organic chemistry I I ................................................................................... 30

4

Chapter 1: Experimental chemistry

Self – Assessment Answers

1. c 2. b 3. b 4. d 5. d6. b 7. b 8. a 9. c 10. b11. a) D b) C c) G d) H e) A12. Place the powder in a beaker and add water. Gently heat whilst stirring to ensure the

ammonium chloride dissolves. Filter the resulting mixture to obtain ammonium chloride solution as the filtrate and a mixture of carbon powder and manganese(IV) oxide as the residue.Place the ammonium chloride solution in an evaporating basin and gently heat to evaporate some of the water and concentrate the solution. Leave the solution to cool down overnight.

13. a) Chlorine b) Ammonia c) Hydrogen or ammonia d) Carbon dioxide, chlorine or oxygen e) Hydrogen, ammonia, oxygen, carbon dioxide, chlorine14. a) i) Ink contains dyes that would rise up the paper when the solvent reached them

and mix with the spots of colouring ii) A large spot would spread out over the paper and the colours would run into each

other iii) This concentrates the sample so the spots from it are easy to see iv) The colour spots would dissolve in the solvent before they rose up the paper b) The red spot has risen higher than the yellow spot because the red dye is more soluble

than the yellow dye. c) i) Purple – red and blue; green – blue and yellow

5

ii)

green purple brown

15. a) Substance X contains iron(II) ions Substance X does not contain chloride, bromide or iodide ions Substance X contains sulfate ions b) Substance Y contains ammonium ions Substance Y does not contain carbonate ions Substance Y contains chloride ions

Chapter 2: Kinetic particle theory


1. b 2. b 3. a4. b5. a6. a 7. b8. D9. C 10. d11. a) The size of the particles does not change b) The particles will move more quickly c) The frequency will increase d) The total energy of the particles increases because the average kinetic energy of the

particles increases

6

e) The pressure will increase because the particles will hit the walls of the container more frequently and with greater force

12. Water seeps through the porous clay from the inside to the outside of the pot. The water on the outside of the pot evaporates. Heat energy needed for evaporation. The evaporating water cools the pot which, in turn, cools the remaining water.

13. a) When steam comes into contact with skin it will be cooled and condense. When steam changes state to become water heat is given out. This heat will cause additional damage to skin.

b) The boiling point of a liquid varies with external pressure. The boiling point of water is only exactly 100°C when atmospheric pressure is exactly one atmosphere.

c) Gas particles are in constant random motion. Pressure in the tube is the result of gas particles colliding with the inner surface. When gas is heated the particles move more rapidly. The pressure in the tube increases as gas particles hit the surface of the tube more often and with more force. The tube will eventually break.

d) Wet clothing dries because water evaporates from it. Spreading washing out on a clothes line provides a much greater surface area than leaving wet clothes in a pile therefore evaporation will take place more quickly.

e) Energy is needed to change a solid into a liquid at its melting point. This is called the latent heat of fusion or melting. While the heat energy supplied is used to bring about this change of state there will be no increase in the temperature of the solid.

f) Particles diffuse as a result of colliding with other particles. The particles in a gas move much more quickly than those in a liquid. Particles of a substance will collide more often and with more energy when in a gas and therefore they will diffuse more quickly.

14. a) i) C or D because A and B would both boil before the melting point of salicylic acid ii) The observer needs to be able to see through it b) i) Salicylic acid melts above the range of thermometer A ii) Thermometer C will give a more accurate reading as there will be more distance

between the graduations c) i) Melted at a higher temperature and melted over a narrower range ii) Melting over a wide range indicates a substance is impure. Recrystallising is a

method of removing impurities. d) It takes time for heat to pass from the oil to the thermometer. If the oil is heated too

quickly it will be hotter than shown on the thermometer15. a) The spreading of particles into the space available b)

Name of gas Relative molecular mass Time taken for the gas to diffuse /s

Carbon dioxide 44 25 Chlorine 71 33 Hydrogen 2 11 Methane 16 16 Oxygen 32 21 Sulfur dioxide 64 31

7

c)

d) The time taken for a gas to diffuses increases with the relative molecular mass of the gas

e) 29 s f) Ethyne g) i) X ii) Z h) i) Flushing the syringe several times ensures that none of the previous gas remains ii) Any anomalous or atypical results would has less effect if an average is taken.

Chapter 3: Atomic structure


1. b 2. a 3. c 4. b 5. d6. a 7. d 8. b 9. c 10. d

Time taken for the gas to diffuse /s

Rela

tive

mol

ecul

ar m

ass

0 10 20 30 40

10

20

30

40

50

60

70

80

8

11. a)

Element Proton number Number of neutrons Mass numberSodium (Na) 11 12 23Nitrogen (N) 7 7 14Sulfur (S) 16 16 32Magnesium (Mg) 12 12 24Aluminium (Al) 13 14 27

b)

12. a) Carbon b) Phosphorus c) Neon d) Silicon e) Potassium f) Beryllium13. a)

Particle Approximate

relative mass Charge Position in the atom

Proton 1 +1 In the nucleus

Electron 0 -1 Surrounding the nucleus

Neutron 1 0 In the nucleus

b) i) 13 ii) 14 c)

14. a) Statements 1 and 5 were found to be correct. b) Statements 2, 3 and 4 need some modification. i) Elements are made of small particles called atoms ii) Atoms cannot be created of destroyed during chemical reactions iii) All atoms of the same element have the same charge (atomic number) but may

vary slightly in mass (mass number) due to the presence of different isotopes iv) Atoms of different element have different charges (atomic numbers) v) Atoms combine in small whole numbers to form compounds15. a) X = electron, Y = neutron, Z = proton

2311Na 16

8O14

6C3717CI

2311Na 14

7N3216S

2412M

2713AI

9

b)

c) The chemical properties of an element are determined by its electronic configuration. The isotopes have the same electronic configuration.

d) 19.8 x 10 + 80.2 x 11 = 10.802 = 10.8 100

Chapter 4: Materials and bonding


1. d2. b3. b4. b5. b6. a7. c8. c9. a10. a11. a) 2, 8, 18, 8 b) Atoms c) An atom of krypton has a full outer shell of electrons and therefore does not need to

form bonds with other atoms d) As3-, Se2-, Br-, Rb+, Sr2+

12. a) i) 2.8.2 ii) 2.8 iii) 2.8.18.7 iv) 2.8.18.8 b)

MgBr Br Mg Br+ 2

2+ -

10

c) Mg + Br2 Mg2+ + 2Br-

13. a) D b) B c) E d) C e) A14. a)

delocalised valence electrons

metal cations

b) i) In a metal structure valence electrons are able to move and become delocalised in a lattice of positively–charged ions.

Electrons carry charge hence metals are able to conduct electricity. ii) In a metal structure layers of metal ions are able to slide over each other hence a

metal can be drawn into thin wires. c) Metallic bonds are the result of electrostatic forces of attraction between the

positively–charged metal ions in the metal lattice and the negatively–charged delocalised electrons. It requires a large amount of energy to overcome these forces.

15. a) i) Potassium: Z = 19; electronic configuration 2,8,8,1 Bromine: Z = 35; electronic configuration 2,8,18,7 ii)

Br KK Br

-

+

+

b) i) Carbon: Z = 6, 2, 4 Chlorine: Z = 17, 2, 8, 7

11

ii)

H

H

H H

H

Cx x

x

x

x

x

x

x

HH

H

C

c) Potassium exists as an ionic lattice in which each ion is surrounded by a number of oppositely charged ions. In order to melt potassium bromide a large amount of energy is needed to overcome the strong forces of attraction between oppositely charged ions.

Tetrachloromethane exists as a simple covalent compound. The forces of attraction between molecules are weak and therefore much less energy is needed to overcome them.

Chapter 5: Formulae, stoichiometry and the mole concept


1. d2. b 3. b 4. c 5. c6. b 7. b 8. b 9. b 10. a11. a) Pb2+ + 2NO3

-(aq) + 2Na+(aq) + 2Br-(aq) → PbBr2(s) + 2Na+(aq) + 2NO3- (aq) Pb2+(aq) +

2Br-(aq) → PbBr2(s) b) Ba2+(aq) + 2Cl-(aq) + 2K+(aq) + SO4

2-(aq) → BaSO4(s) + 2K+(aq) + 2Cl-(aq) Ba2+(aq) + SO4

2-(aq) → BaSO4(s) c) Ag+(aq) + NO3

-(aq) + Na+(aq) + I-(aq) → AgI(s) + Na+(aq) + NO3- (aq) Ag+(aq) +

I-(aq) → AgI(s) d) Cu2+(aq) + SO4

2-(aq) + 2Na+(aq) + S2-→ CuS(s) + 2Na+(aq) + SO42- (aq)

12. a) Mg + Cl2 MgCl2

b) 2H2 + O2 2H2O

12

c) CuCO3 CuO + CO2

d) 2N2 + 3H2 2NH3

e) Ca + 2H2O Ca(OH)2 + H2

13. a) Ratio of carbon : hydrogen 85.7 : 14.3 = 1 : 2 12 1 Empirical formula is CH2

b) 56 / 14 = 4 Molecular formula is 4 x CH2 = C4H8

c) Compounds ii) and iv)14. a) 2Zn + O2 2ZnO b) 3.25 / 65 = 0.05 mol of zinc From the equation 2 moles of zinc react with 1 mole of oxygen molecules so 0.05

moles of zinc will react with ½ x 0.05 = 0.025 moles of oxygen molecules Mass of oxygen molecules = 0.025 x 32 = 0.8 g c) From the equation 2 moles of zinc produces 2 mole of zinc oxide so 0.05 moles of zinc

will produce 0.05 g of zinc oxide Mass of zinc oxide = 0.05 x (65 + 16) = 4.05 g Check that no mass has been gained or lost: 3.25 g + 0.8 g = 4.05 g15. a) CH2

b) i) 3 moles ii) 3 moles c) C3H6 + 9/2O2 3CO2 + 3H2O Or 2C3H6 + 9O2 6CO2 + 6H2O d) i) Ratio C : H = 85.71 : 14.29 = 7.14 : 14.29 = 1 : 2 12 1 The empirical formula is CH2

ii) The unknown compound has the same empirical formula as propene but it is not possible to identify it from the empirical formula alone. There are other compounds which have the same empirical formula.

16. a) 70.84 – 65.78 = 5.06 g b) 68.25 – 65.78 = 2.47 g c) 5.06 – 2.47 = 2.59 g d) Relative formula mass of MgSO4 = 24 + 32 + 64 = 120 Relative formula mass of xH2O = (2 + 16)x = 18x 2.47 = 2.59 120 18x x = 2.59 x 120 = 7 2.47 x 18 e) MgSO4.7H2O

13

Chapter 6: Elecrolysis


1. b2. c3. a4. c5. d6. d7. d8. b9. a10. b11. a) i) Na+, Cl-, H+, OH-

ii) Na+, Cl-

b) Anode: 2Cl-(l) Cl2(g) + 2ē Cathode: Na+(l) + ē Na(l)12. a) Improve appearance of taps; protect brass from corroding. b) Cr3+, SO4

2-

c) Make the tap the cathode of an electrolytic cell in which chromium(III) sulfate solution is the electrolyte. When the current flows the chromium ions are attracted towards the cathode where they are reduced to chromium metal. The chromium metal is deposited on the surface of the tap.

Cr3+(aq) + 3ē Cr(s)13. H+, OH-, K+, CrO4

2-, Cu(NH3)42+, SO4

2-

a) A yellow band will be seen moving towards the anode and a blue band will be seen moving towards the cathode.

b) The negative ions in the gel will be attracted to the anode while the positive ions will be attracted to the cathode. The yellow chromate ion carries a negative charge so it is attracted towards the anode. The blue tetraaminecopper(II) ion carries a positive charge so it is attracted to the cathode.

14. a) i) Copper ii) Magnesium b) Most reactive magnesium zinc iron tin copper silver c) i) 3.16 – 0.46 = 2.70 V ii) 1.56 - 0.46 = 1.1 V

14

15. a) i) B and D ii) A and C b) i) Oxygen ii) 4OH-(aq) O2(g) + 2H2O(l) + 4ē c) i) Electrode A is unchanged Electrode B is coated with an orange/brown solid The electrolyte is paler or more dilute ii) Electrode C is smaller Electrode D is larger The electrolyte is unchanged d) The following takes place during the electrolysis of copper(II) sulfate using active

electrodes. Copper atoms at the anode become copper ions in solution so the anode decreases in

size. Cu(S) Cu2+(aq) + 2ē Copper ions in solution become copper atoms at the cathode so the cathode increases

in size Cu2+(aq) + 2ē Cu(S)

Chapter 7: Energy from chemicals


1. c2. B3. a4. B5. c6. a7. d8. d9. b10. d11. a) Refinery gases b) Gasoline c) Kerosene d) Bitumen e) Fuel oil12. a) i) As the carbon content increases, the energy increases. ii) The oxidation of carbon to carbon dioxide is an exothermic process. When there is

more carbon to oxidise more heat is produced. b) 53 × 34 000 + 5 × 143 000 = 2 517 000 J = 2 517 kJ

15

c) Anthracite because it gives out the most heat per unit mass13. a) In a fuel cell the reactants are supplied from an external source whereas in an

electrochemical cell the reactants are contained within the cell. b) Electric Current

Fuel in

Excess

AnodeElectrolyte

Cathode

fuel

Air inē

ē

ē

ē

H2

O2

H2O

H+

H+

H2O

Unusedgasesout

c) Hydrogen arrives at the anode and splits to form hydrogen ions and electrons. The hydrogen ions pass through the cell to the cathode while the electrons flow externally to the cathode creating an electric current.

At the cathode hydrogen ions, electrons and oxygen combine to form water. d) i) Palladium hydride does not have a definite composition or formula but contains

hydrogen within the metallic lattice. ii) Palladium can absorb up to 900 times its own volume of hydrogen at r.t.p. iii) Palladium is too expensive for widespread use.14. a) Bond Number

C-H 5H-O 1C-C 1C-O 1O=O 3

b) Bond Number

C=O 4H-O 6

c) An exothermic reaction is a process that gives of heat to the surroundings. When ethanol is used as a fuel, following energy is required to break the bonding:

Bond energy /kJ mol-1 Total energy needed / kJ mol-1

413 413 x 5 = 2065464 464 x 1 = 464

16

347 347 x 1 = 347358 358 x 1 = 358498 498 x 3 = 1494

The following table shows the energy release during the reactions when bonds are formed:

Bond energy /kJ mol-1 Total energy needed / kJ mol-1

805 805 x 4 = 3220464 464 x 6 = 2784

15. a) 0.1 x 40 x 4.2 = 16.8 kJ b) i) 86 ii) 0.43 / 86 = 0.005 iii) 16.8 / 0.005 = 3360 kJ c) It is likely that the experimental answer will be less than the calculated answer. Not

all of the heat produced by burning the hexane will be transferred to the water. Some heat energy will be lost heating the apparatus and heating the surrounding air.

d) C6H14(l) + 19/2O2(g) 6CO2(g) + 7H2O(g) e)

C6H14+ 19/20 2

ΔH=- 3360 kJ mol-1

Ener

gy

Time

6CO2+ 7H2O

Chapter 8: Chemical reactions


1. c2. b3. A4. A5. d6. a7. B

17

8. D9. a10. a) Reaction 1 is a redox reaction because zinc changes oxidation state from 0 to +2 while

hydrogen changes oxidation state from +1 to 0. Reaction 2 is not a redox reaction since zinc has an oxidation state of +2 in both ZnO and ZnCl2, and hydrogen has an oxidation state of +1 in both HCl and H2O.

b) Oxidation: Zn(s) Zn2+(aq) + 2ē Reduction: 2H+(aq) + 2ē H2(g)11. a) Y b) X c) X d) Z e) Y12. a) Time less, volume of hydrogen the same – more acid particles so more effective

collisions per unit time. Rate increases. b) Time less, volume of hydrogen the same – total surface area of iron greater so more

effective collisions per unit time. Rate increases. c) Time more, volume of hydrogen the same – total surface area of iron less so less

effective collisions per unit time. Rate decreases. d) Time less, volume of hydrogen the same – more acid particles per unit volume so more

effective collisions per unit time. Rate increases. e) Time more, volume of hydrogen the same – particles moving more slowly so less

effective collisions. Rate decreases13. There are a number of ways of doing this activity. Here is one possible answer: a) Balance, conical flask, bung and delivery tubing, measuring cylinder, large beaker,

stopwatch b) Constant – mass of magnesium carbonate, volume of dilute hydrochloric acid. Procedure – add dilute hydrochloric acid to magnesium carbonate in conical flask,

quickly place bung and delivery tube into the flask and bubble gas into water in a beaker.

Repeat for powder and lumps with cold and warm acid – 4 times in total. c) Measure the time taken for each reaction to go to completion i.e. when no more carbon dioxide gas is evolved. d) The reaction with the fastest rate will be the one which is the quickest to go to completion. e) Expect warm hydrochloric acid on powdered magnesium carbonate. Warm acid –

hydrogen ions moving more quickly in solution. Powder – greater surface area for collision with hydrogen ions. This combination will provide more effective collisions and thus the fastest reaction.

14. a)

Time / minutes Mass of reaction vessel and contents / g Total mass lost / g

0.0 190.45 0.000.5 189.89 0.561.0 189.49 0.96

18

1.5 189.22 1.232.0 189.01 1.442.5 188.87 1.583.0 188.73 1.723.5 188.63 1.824.0 188.53 1.924.5 188.43 2.025.0 188.36 2.095.5 188.31 2.146.0 188.27 2.186.5 188.26 2.197.0 188.25 2.207.5 188.25 2.208.0 188.25 2.20

b)

c) 2.20 g d) 6.75 minutes e) 1.25 minutes

2.82.42.32.22.12.01.91.81.71.61.51.41.31.21.11.0

.9

.8

.7

.6

.5

Time / minutes

Tota

l mas

s los

t / g

.

0 1 2 3 4 5 6 7 8

19

f) CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) g) Molar mass of carbon dioxide = 12 + 2 x 16 = 44 g Volume of carbon dioxide = 24 000 x 2.20 = 1200 cm3

44 h) Molar ratio of calcium carbonate and carbon dioxide is 1:1. Amount of carbon dioxide produced = 2.20 = 0.05 mol 44 Molar mass of calcium carbonate = 40 + 12 + 3 x 16 = 100 g Mass of calcium carbonate = 100 x 0.05 = 5.00 g i) Molar ratio of calcium carbonate to hydrochloric acid is 1:2. Moles of acid needed = 2 x 2 x 0.05 = 0.20 mol Volume of 2M acid needed = 1000 x 0.2 = 100 cm3

2.0

Chapter 9: Acid, bases and salts


1. d2. a3. c4. d5. a6. b7. b8. c9. a10. d11. a) 7 b) An indicator would remain in the lithium sulfate as an impurity but this is not a problem when a pH meter was used c) Reactants get more thoroughly mixed so more accurate end point d) 2OH-(aq) + 2H+(aq) 2H2O(l)12. a) The temperature of the mixture increases therefore heat is being given off b) Neutralisation c) 20 cm3; the temperature starts to decrease after this so heat is no longer being given

off as a result of a chemical reaction d) The dilute hydrochloric acid is more concentrated as a smaller volume is needed to

neutralise the potassium hydroxide solution e) KOH + HCl KCl + H2O f) universal indicator or a pH meter turns green / shows pH = 7 so mixture neutral

20

13. a) Acidity / alkalinity b) Reacts to form a salt, water and carbon dioxide c) i) 2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.04.5 5.0 5.5 6.0

final pH of soil

Mas

s of l

ime

need

ed to

raise

pH

of so

il to

6.5

in k

g m

-2

ii) Least for sandy soil and most for clay soil iii) The lower the initial pH the more lime needed d) i) 0.98 x 200 = 196.0 kg ii) 1.12 x 200 = 224.0 kg14. a)

b) Some time between 5 and 10 minutes because it is over this period that the pH of the saliva drops below 5.5.

c) From about 7 – 20 minutes i.e. 13 minutes d) This is not good for the teeth. Additional acid will increase decay. e) This is good for the teeth. The cheese is alkaline and neutralises the acidic saliva

Time in minutes

pH o

f sal

iva

40 5 10 15 20 25 30

5

6

7

21

stopping tooth decay. f) It returns to starting value of 6.5. g) Weakly alkaline, e.g. pH 8, to neutralise any acidity as the teeth are being cleaned.15. a) A solution that is neither acidic nor alkaline b) It would be impossible to use equal masses of the different remedies because the

tablets would be different masses/sizes. A powder dissolves in water more quickly than a tablet. c) An indicator / probe from pH meter d) Improve accuracy / reduce chances of atypical result e) i) Weak alkali ii) e.g. Magnesium hydroxide iii) e.g. Mg(OH)2(aq) + 2HCl(aq) MgCl2(aq) + 2H2O(l) f) Y. It needed the largest volume of dilute hydrochloric acid to neutralise it therefore it

would neutralise the most acid in the stomach

Chapter 10: Two important industrial chemicals ammonia and sulfuric acid


1. a2. D3. a4. c5. d6. c7. b8. c9. a10. b11. a) Nitrogen – the air; hydrogen – natural gas b) Finely divided iron c) Oxidation d) Neutralisation e) e.g. fertiliser12. a) NH3(g) + HNO3(aq) NH4NO3(aq) b) Number of moles of nitric acid = 5 x 2 = 10 mol Number of moles of ammonia needed = 10 mol At r.t.p. one mole of ammonia occupies 24 dm3

Volume of dry ammonia needed = 24 x 10 = 240 dm3

c) Amount of ammonium nitrate produced = 10 mol

22

Mass of 1 mol of ammonium nitrate = 4 x 1 + 2 x 14 + 3 x 16 = 80 g Mass of ammonium nitrate produced = 80 x 10 = 800 g d) Calcium hydroxide is a base and will react with the ammonium ion releasing ammonia

gas. This will create an unpleasant smell and the crop will not have the benefit of the nitrogen which is lost as ammonia.

13. a) Initially, the addition of more fertiliser to the soil increases the yield of crops but after reaching a maximum, addition of more fertiliser results in a fall in yield.

b) The concentration of ammonium nitrate in the soil becomes too high and interferes with the mechanism by which the plant roots absorb nutrients from the soil. The result is that the plants absorb less nutrients, causing a fall in yields.

c) The use of excess fertiliser results in a fall in yield so the farmer will grow less on his/her land and earn less from it.

Artificial fertilisers are expensive to buy and take time to spread on the soil. Using excess fertiliser wastes both money and time.

All nitrates are very soluble in water. Excess fertiliser will be washed out of the soil by rain and will accumulate in water courses where it may cause environmental problems, such as eutrophication, and may get into drinking water.

14. a) Nitrogen – air; hydrogen – natural gas b) In the forward reaction 4 moles of gas go to 2 moles so high pressure pushes

equilibrium to the right. c) i) Increases the rate of reaction by lowering the activation energy. ii) The iron(III) oxide is reduced by hydrogen: Fe2O3(s) + 3H2(g) 2Fe(s) + 3H2O(g) iii) No effect d) Solubility – pass the reaction mixture through water: ammonia will dissolve while the

unreacted nitrogen and hydrogen will largely pass through without dissolving. Boiling point – cool the reaction mixture to below –33°C: the ammonia will condense

and form a liquid which can be collected while the unreacted nitrogen and hydrogen will remain as gases.

15. a) i) e.g. Crude oil refining; metal sulphide ore extraction ii) S(s) + O2(g) SO2(g) iii) Sulfur dioxide turns acidified potassium dichromate(VI) from orange to green b) i) There would be less sulfur trioxide in the equilibrium mixture ii) There would be more sulfur trioxide in the equilibrium mixture c) i) The reaction is highly exothermic and results in a mist of sulfuric acid that cannot

be condensed. ii) The sulfur trioxide is first reacted with 98% sulfuric acid to form oleum, to which

water is subsequently added. SO3 + H2SO4 H2S2O7

H2S2O7 + H2O 2H2SO4

23

Chapter 11: The Periodic Table


1. d2. b3. a4. c5. d6. a7. c8. b9. b 10. d11. a) Similarities in the chemical reactions of the elements b) i) Li, Na, K or Be, Mg, Ca ii) All other ‘groups’ except the above c) Some of the elements were placed in groups with others exhibiting similar chemistry;

however there were too many instances where elements with obviously different chemistry were grouped together in order to make the elements appear to fit the pattern.

12. a) Neon b) Hydrogen, sulfur, neon c) Chromium and nickel d) Magnesium and sulfur e) Potassium f) Sulfur g) Neon h) Nickel13. a)

11 12 13 14 15 16 17 18

23 24 27 28 31 32 35.5 40Na Mg Al Si P S Cl Ar

b) Top number: atomic number which is the number of protons in an atom of the element.

Atomic symbol is the short-hand way of representing the element. Bottom number: relative mass number is the number of protons + average number of

neutrons in an atom of the element. c) i) Phosphorus, sulfur, chlorine, argon ii) Sodium, magnesium, aluminium iii) Silicon14. a) Halogens

24

b) By gaining a single electron to form the X- ion c) Fluorine Chlorine Bromine Iodine d) i) Fluorine and chlorine as gases, bromine is a liquid and iodine is a solid. ii) Colour becomes darker iii) Reactivity decreases15. a) They have complete outer shells of electrons. b) Krypton hexafluoride, KrF6 and xenon hexafluoride, XeF6. c) In the clathrates the noble gas atoms have no chemical bonds with other atoms but

exist as single atoms simply trapped in a lattice. d) When they heated the clathrates noble gases were driven off. This appeared to be

similar to the thermal decomposition of compounds like carbonates. e) Xenon hexafluoroplatinate: Xe + PtF6 XePtF6

Chapter 12: Metals


1. d2. c3. c4. c5. a6. b7. d8. B9. c10. b11. a)

Metal Compound(s) commonly providing ore

Method of extracting metal

copper sulfide and carbonate heating in air

iron oxideschemical reduction of molten oxide using carbon monoxide

lead sulfide heating in air

sodium chloride electrolysis of molten chloride

b) i) Sodium

25

ii) It cannot be obtained by chemical reduction using reducing agents like carbon and carbon monoxide. It was only isolated after electricity was discovered.

c) i) A metal that exists in the ground actually as metal and not a metal compound. ii) Gold, silver, copper12. a) Metal X is grey but the deposits at the bottom of the beaker are brown. The colour of

the solution in the beaker has changed from blue to green. b) Displacement reaction c) Iron. Iron is above copper in the reactivity series and iron forms solutions of

compounds which are green. d) Cu2+(aq) + Fe(s) Cu(s) + Fe2+(aq) e) i) Silver is below copper in the reactivity series so would not displace copper ions

from solution. ii) Magnesium is a Group II metal and Group II metal compounds form colourless

solution.13. a) A more reactive metal will displace the ions of a less reactive metal from a solution of a

salt of the less reactive metal. b) Copper, cobalt, chromium, magnesium c) Mg(s) + Cu2+(aq) Mg2+(aq) + Cu(s) d) i) To remove any outer layer of oxide and ensure a good contact with the electrolyte ii) Magnesium iii) Magnesium14. a) Malleability b) The layers aluminium atoms are able to slide over each other very easily. c)

atoms of other metals

atoms of aluminium

d) Harder because it will be more difficult for layers of atoms to slide over each other e) e.g. strong, low density, doesn’t corrode15. a) i) Add water to each metal Add dilute hydrochloric acid to each metal ii) Calcium will react with water but the others do not • Add dilute hydrochloric acid magnesium, iron and zinc • Magnesium reacts rapidly with most bubbles of gas • Zinc reacts but more slowly that magnesium • Iron reacts but more slowly than zinc iii) Calcium, magnesium, zinc, iron b) i) Displacement ii) Soluble salts of magnesium, zinc and metal M, such as nitrates iii) Metal M would have no reaction with magnesium nitrate. Metal M would displace zinc ions from zinc nitrate

26

Chapter 13: Two important metals iron and aluminium


1. c2. b3. d4. b5. a 6. d7. C8. a9. c10. D11. a) i) Reaction with sodium hydroxide solution ii) Reaction with dilute hydrochloric acid iii) Amphoteric b) i) Sodium aluminate ii) Al2O3(s) + 2NaOH(aq) + 3H2O(l) 2NaAl(OH)4(aq) c) Impure aluminium oxide or bauxite contains impurities like iron(III) oxide that must be

removed before electrolysis12. a) A reaction in which both reduction and oxidation take place b) Reduction is the gaining of electrons while oxidation is the loss of electrons c) Oxygen gas is reduced to oxide ions while iron atoms are oxidised to iron(III) ions. d) Reduction: Al3+ + 3ē Al Oxidation: 2O2- O2 + 4ē13. a) Cell potential is positive for metals above iron and negative for metals below iron in

the reactivity series. b) Value between -0.38 V and -0.59 V c) Magnesium d) Copper would not protect iron from rusting. The metals would form a cell in which iron

was the anode and would be oxidised.14. a) i) 3+

ii) 2-

b) i) Pure aluminium oxide has a much higher melting point therefore it would require much more energy / cost to carry out the electrolysis.

ii) Al3+ + 3ē Al iii) The oxygen produced at the anodes reacts with them to form carbon dioxide

therefore the anodes are slowly eroded away.15. a) Fe2O3, C, CaCO3

b) Carbon monoxide C + O2 CO2

CO2 + C 2CO c) Burning coke to form carbon dioxide is a highly exothermic reaction.

27

d) It does not decompose at high temperatures; it is a poor conductor of heat. e) In the blast furnace limestone breaks down to calcium oxide and carbon dioxide. CaCO3 CaO + CO2

Calcium oxide reacts with acidic impurities, such as silicon dioxide, that would attack the furnace lining, and converts them to slag which can be removed from the furnace.

CaO + SiO2 CaSiO3

Chapter 14: Atmosphere and environment


1. c2. b3. d4. b5. a6. a7. c8. d9. c10. d11. a) 1000

Carbonmonoxide

Nitrogenoxides

Sulfurdioxide

Particles

Atmospheric pollutant

Mas

s per

yea

r / m

illlio

ns o

f ton

nes

900

800

700

600

500

400

300

200

100

0

b) Nitrogen oxides and sulfur dioxide c) The flue gases are passed through a slurry of powdered limestone. Limestone is

calcium carbonate. Sulfur dioxide dissolves in the water to form an acid which is then neutralised by the calcium carbonate to form calcium sulfate.

12. a) A thin layer of rhodium or other catalyst on a ceramic matrix

28

b) carbon dioxide

water

nitrogen

carbon monoxide

hydrocarbons

nitrogen oxides

c) Oxidised – carbon monoxide, hydrocarbons Reduced – nitrogen oxides13. a) To measure the proportion by volume of oxygen in air. b) Oxygen c) 2Cu(s) + O2(g) 2CuO(s) d) Pink-brown copper turns to black copper(II) oxide. Volume of air in the syringes decreases. e) 39 – 40 cm3

14. a) Mercury oxide b) Oxidation / redox reaction c) The amount of red particles (mercury oxide) appeared to remain the same d) 16.7% oxygen and 83.3% nitrogen e) The volumes were the same15. a) i) Fluoride ii) F-

b) Fluorine, chlorine, iodine c) Nitrate, NO3

-

d) i) 429.3 mg ii) 0.4293 g e) These ions dissolve in rain water as it passes over and through rocks. In different

places the ions present in the rocks will be different and/or be present in different proportions.

f) The ions in spring water will interfere in reactions. For example, if such tap water is used to make up silver nitrate solution the halide ions present will cause the precipitation of silver halides.

Chapter 15: Organic chemistry I


1. d2. b3. c4. a5. b6. c7. a8. c9. b10. d

29

11. a) A series of related chemical compounds that have the same functional group but differ in formula by the number of CH2 groups in the carbon chain. Members of an homologous series show a gradation of physical properties and have similar chemistry.

b) Indicates that a carbon chain contains 4 atoms. c) A group of atoms that is responsible for the characteristic chemistry of a compound. d) The functional group –C=C– present in an alkene. e) Compounds with the same molecular formula but different structural formulae.12. a) C4H6

b) Ethyne c) C2H2 + 5/2O2 2CO2 + H2O d) Prop + yne = propyne e) H

H

HCCCH

f) Expect the chemistry of alkynes to resemble alkenes because they are unsaturated and able to undergo addition reactions

13. a) 14.3% b) 85.7/12 : 14.3/1 = 7.14 : 14.3 ≅ 1 : 2 Empirical formula CH2

c) 42 / 14 = 3 Molecular formula C3H6

d) Alkenes14. a)

Number of carbon atoms in alkane

Heat

giv

en o

ut in

kJ/

mol

0 1 2 3 4 5 6 7

1000

2000

3000

4000

5000

30

b) i) 1550 kJ mol-1 (from graph) ii) 3510 kJ mol-1 (from graph) c) C2H6 + 7/2O2 2CO2 + 3H2O d) 5 x 22.4 = 112 dm3

15. a) i) Mixture of carbon-carbon single bonds and some carbon- carbon double bonds ii) All carbon-carbon single bonds. b) i) Sunflower oil ii) Beef fat c) R-CH=CH-COOH + I2 R-CHI-CHI-COOH d) The greater the level of unsaturated, the greater the amount of iodine that reacts with

the lipid and the less unreactive iodine remains. e) Iodine value = (18.55 – 2.60) x 1.269 / 0.158 = 128.1 Most likely to be a vegetable oil – far too high for an animal fat

Chapter 16: Organic chemistry II


1. c2. d3. a4. a5. b6. D7. a8. B9. c10. D11. a) Alkene, ester b) Addition polymerisation c) HH

H

C C

C

OCH3

O

d) e.g. Drawing instruments, in windows as a substitute for glass12. a) Fermentation converts sugars, such as glucose, into ethanol and carbon dioxide. C6H12O6 2C2H5OH + 2CO2

The reaction is carried out at around 25 – 35 °C and normal atmospheric pressure in

31

the presence of yeast. Ethanol may also be obtained from the hydration of ethene using steam.

CH2=CH2 + H-OH C2H5OH The reaction is carried out at 300°C and 6-7 MPa. b) Fermentation gives an aqueous solution of about 15% by volume of ethanol. The

ethanol solution must be distilled and the ethanol dried before it can be used a s a solvent. Hydration of ethene produces a pure product and for this reason it is the preferred.

13. a) H H H H H H

H Cl H Cl H Cl

C C C C C C

b) ii, iii, vi c) e.g. Electrical insulation, clothing14. a) –OH, hydroxyl and –COOH, carboxylic acid b) Condensation polymerisation c) H O

CH 3

O C C

d) Relative molecular mass of the repeating unit is 3 x 12 + 4 x 1 + 2 x 16 = 72 Number of repeating units = 162 000 / 72 = 2250 units15. a) CH3CH2CH2COOH + CH3OH CH3CH2CH2COOCH3 + H2O b) 88 c) Relative molecular mass of methanol = 32 1.6 g is 1.6 / 32 = 0.05 mol Reactants react in the ratio of 1 : 1 Mass of 0.05 mol of butanoic acid = 88 x 0.05 = 4.4 g d) Acts as a catalyst e) Heated while connected to a vertical condenser. This prevents the reactants and any

product formed from boiling off into the air. f) To neutralise the sulfuric acid in the reaction mixture g) Pouring the two layers into a separating funnel and pouring off the unwanted lower

aqueous layer to leave the top layer of product. h) Butyl methyl butanoate i) Relative molecular mass of butyl methyl butanoate = 102 Expected yield = 102 x 0.05 = 5.1 g Percentage yield = 1.7 x 100 / 5.1 = 33.3%

32

Chemistr yfor Cambridge O Level

Chemistry for Cambridge O Level has been written to provide up-to-date coverage of the material required for the latest Cambridge International Examinations O Level Chemistry syllabus 5070. Important features include:• A comprehensive text covering all of the material needed for Cambridge O Level

Chemistry• Full colour illustrations, engaging photographs and clear diagrams• Learning objectives at the start of each chapter to get the student thinking about

the chapter content• Definitions of key terms• Chapter summaries in the form of ‘Key Points’ to help students review their

learning and identify where additional work might be needed• ‘Check your Understanding’ exercises within the text that are focused on

particular parts of the chapter content• ‘How to do it’ boxes giving worked examples of different chemical calculations • A full range of practical activities covering all the requirements of the syllabus• Cambridge O Level style questions at the end of each chapter to allow students

to check their understanding as they work through the book.• Past examination papers at the end of each chapter show the students how they

might expect the chapter content to be examined

Derek McMonagle is a highly experienced teacher, examiner and consultant on Science curriculum. He has been writing science learning and teaching materials for over 30 years.

Chemistry -...

Documents

Transcript of Chemistry -...