Student Book Answers

Student book answers

Acids and alkalis

Making salts from metals or bases

Making salts from soultions

Electrolysis

Changes at the electrodes

The extraction of aluminium

Electrolysis of brine

Electroplating

Summary answers – Salts and electrolysis

AQA Examination-style answers – Salts and electrolysis

AQA Examination-style answers (continued) – Salts and electrolysis

AQA Examination-style answers – Unit 2 Chemistry

AQA Examination-style answers (Continued) – Unit 2 Chemistry

AQA Examination-style answers (Continued II) – Unit 2 Chemistry

AQA Examination-style answers (Continued III) – Unit 2 Chemistry

Chemistry C2 5.1 / Acids and alkalis
Answers to in-text questions
a Any soluble hydroxide, e.g. sodium hydroxide.
b A base is a substance that can neutralise acids.
c H+ ions/hydrogen ions
d OH-ions/hydroxide ions
e The substance is a solid.
Summary answers
1 a C b A c E d B e F f D
2 The paper would turn green in water (neutral), blue/purple in sodium hydroxide solution (strong alkali) and red/orange in citric acid solution (weak acid).
Chemistry C2 5.2 / Making salts from metals or bases
Answers to in-text questions
a A salt and hydrogen.
b The substance is a gas.
c A salt and water.
d zinc sulfate
e The substance is a liquid.
Summary answers
1 neutralisation, salt, water, metals, hydrogen
2 a Copper is not reactive enough to react with acid.
b Potassium is too reactive and would explode on contact with acid.
c Heat the solution in an evaporating basin on a water bath until the point of crystallisation. Then leave the liquid for a few days to allow the remainder of the water to evaporate off and the crystals to form.
Chemistry C2 5.3 / Making salts from soultions
Answers to in-text questions
a acid + alkali →salt  water
b ammonium nitrate/ammonium sulfate
Summary answers
1 acid (alkali), alkali (acid), water, neutralisation, indicator, insoluble, soluble, precipitation, solid, metal, polluted
2 a nitric acid + potassium hydroxide →potassium nitrate + water Use an indicator to find how much of each solution is required. Repeat with the correct quantities. Evaporate the solution to the point of crystallisation and then leave it for the rest of the water to evaporate off to get crystals of potassium nitrate.
b silver nitrate + a soluble chloride, e.g. sodium chloride →silver chloride + e.g. sodium nitrate Filter off the silver chloride precipitate, wash with distilled water and leave (or warm in an oven) to dry.
Chemistry C2 5.4 / Electrolysis
Answers to in-text questions
a Using an electric current to break down a substance.
b electrolyte
c negative electrode
d positive electrode
Summary answers
1 ions, move, solution, molten
2 a Zinc at -; iodine at +.
b Lithium at -; bromine at +.
c Iron at -; fluorine at +.
3 [Words/diagrams explain how ions carry charge.] If ions are not free to move (as they are not in a solid because they are held in position by strong electrostatic forces), no current can flow in the circuit.
Chemistry C2 5.5 / Changes at the electrodes
Answers to in-text questions
a Electron(s) are transferred from the ion to the electrode (electron loss).
b Electron(s) are transferred to the ion from the electrode (electron gain).
Summary answers
1 gain, reduced, lose, oxidised, less
2 a potassium at -, oxygen at +
b copper at -, chlorine at +
c hydrogen at -, oxygen at +
3 a 2Cl-→Cl2 + 2e-
b 2O2-→O2 + 4e-
c Ca2+ + 2e-→Ca
d Al3+ + 3e-→Al
e Na+ + e- →Na
f 2H+ + 2e-→H2
Chemistry C2 5.6 / The extraction of aluminium
Answers to in-text questions
a Aluminium is a good conductor of electricity and has a low density.
b Its ions must be free to move to the electrodes.
c Oxidised (ions lose electrons to become neutral atoms).
Summary answers
1 extraction, cryolite, energy, negative, positive, carbon, oxygen
2 a Aluminium ions (Al3+) are reduced (electrons gained); oxide ions (O2-) are oxidised (electrons lost).
b The carbon in the positive electrodes reacts with oxygen produced to give off carbon dioxide gas, burning the electrodes away: carbon + oxygen →carbon dioxide
3 At negative electrode: Al3+ + 3e- →Al;
At positive electrode: 2O2-→O2 + 4e-
Chemistry C2 5.7 / Electrolysis of brine
Answers to in-text questions
a Chlorine, hydrogen, sodium hydroxide solution.
b Water treatment, making bleach, making plastics (PVC).
c For example, making margarine.
d Making soap and paper, making bleach (with chlorine).
Summary answers
1 chlorine, hydrogen, hydroxide, bleach
2 With molten sodium chloride we would get sodium metal produced at the negative electrode and chlorine gas produced at the positive electrode. With sodium chloride solution we get hydrogen gas given off. With sodium chloride solution we also get a solution of sodium hydroxide formed in the electrolysis cell but not with molten sodium chloride.
3 a 2Cl-(aq) →Cl2(g) _ 2e- or 2Cl-(aq) – 2e-→Cl2(g)
b 2H+(aq) + 2e-→H2(g)
Chemistry C2 5.8 / Electroplating
Answers to in-text questions
a Chromium, tin, gold, silver (copper, nickel).
b At the positive electrode (atoms lose electrons).
c Nickel ions (Ni2+).
Summary answers
1 plating, nickel, oxidised, negative, electrons, reduced, atoms, deposited
2 The plating process itself will cost money in terms of energy and chemicals. However, in jewellery this will still make it cheaper than an object made of a pure precious metal. Plating metals to protect them from corrosion or damage again costs money but the object will need replacing less frequently.
3 Ni2+(aq) + 2e- →Ni(s) then Cr3+(aq) + 3e-→Cr(s)
Chemistry C2 5.1 – C2 5.8 / Summary answers – Salts and electrolysis
1 a i zinc oxide/zinc hydroxide
ii zinc oxide + sulfuric acid →zinc sulfate + water
or
zinc hydroxide + sulfuric acid →zinc sulfate + water
b Add zinc oxide/zinc hydroxide to the acid. Warm the mixture and stir. Filter to remove the excess zinc oxide/zinc hydroxide from the zinc sulfate solution. Heat the
solution in an evaporating basin on a water bath until the point of crystallisation. Then leave the liquid for a few days to allow the rest of the water to evaporate off and the crystals to form.
2 a 2KOH(aq) _ H2SO4(aq) →K2SO4(aq) _ 2H2O(l)
b ZnO(s) _ 2HNO3(aq) →Zn(NO3)2(aq) _ H2O(l)
c Ca(s) _ 2HCl(aq) →CaCl2(aq) _ H2(g)
d Ba(NO3)2(aq) _ Na2SO4(aq) →BaSO4(s) _ 2NaNO3(aq)
3 a B
b A
c B
d A
e B
f A
4 Negative electrode: sodium, calcium, zinc, aluminium. Positive electrode: iodide, fluoride, oxide, bromide.
5 A chlorine gas, B hydrogen gas, C sodium hydroxide solution
6 a 2H2O →2H2 _ O2
b Negative electrode (_): 2H_ _ 2e_ →H2
Positive electrode (_): 4OH_ →O2 _ 2H2O _ 4e_
c 1 mole.
d The power supply.
7 a K+ + e-→K
b Ba2+ + 2e-→Ba
c 2I-→I2 + 2e-
d 2O2-→O2 + 4e
8 Description should include the object to be plated as the negative electrode in a solution containing metal ions (e.g. CuSO4 solution for copper plating). To keep the
concentration of metal ions in solution constant, a positive electrode made of the metal to be plated should be used. Half equation: Cu2+ + 2e- →Cu
Chemistry C2 5.1 – C2 5.8 / AQA Examination-style answers – Salts and electrolysis
1 a B (1 mark)
b 1 (1 mark)
c i alkali (1 mark)
ii neutralisation (1 mark)
iii sodium chloride (1 mark)
2 a A white precipitate or a white solid. (1 mark)
b lead nitrate _ sodium chloride →lead chloride _ sodium nitrate (reactants for one mark, products for one mark) (2 marks)
c Add sodium chloride or any other soluble salt that will give a precipitate with lead ions or a named alkali; allow to settle or filter. (2 marks)
3 There is a clear and detailed scientifi c description of how to prepare copper(II) sulfate solution from copper(II) oxide and dilute sulfuric acid and how to obtain crystals from the solution.The answer shows almost faultless spelling, punctuation and grammar. It is coherent and in an organised, logical sequence. It contains a range of appropriate and relevant specialist terms used accurately. (5–6 marks)
There is a scientific description of the preparation of copper(II) sulfate. There are some errors in spelling, punctuation and grammar. The answer has some structure and organisation. The use of specialist terms has been attempted but not always accurately. (3–4 marks)
There is a brief description of the reaction of copper(II) oxide with an acid or of crystallisation of a solution of copper(II) sulfate. The spelling, punctuation and grammar are very weak. The answer is poorly organised with almost no specialist terms and/or their use demonstrating a general lack of understanding of their meaning. (1–2 marks)
No relevant content. (0 marks)
Examples of chemistry points made in the response:
• Use dilute sulfuric acid.
• Place acid in a beaker.
• Warm the acid.
• Add copper(II) oxide.
• In small amounts.
• Until in excess or there is no further reaction.
• Filter (to remove excess copper(II) oxide).
• Heat filtrate/solution to evaporate some water.
• Allow solution to cool and crystallise or allow to evaporate slowly at room temperature.
• Remove/filter crystals from remaining solution.
Chemistry C2 5.1 – C2 5.8 / AQA Examination-style answers (continued) – Salts and electrolysis
4 a Ions can move in solution, silver ions are positive and are attracted to the negatively charged spoon. (2 marks)
b gaining, electron (2 marks)
c Any sensible suggestion – e.g. better appearance; less toxic; less likely to corrode; less expensive than solid silver. (1 mark)
5 a i Sensible suggestion – e.g. high melting point; strong; can be shaped; holds (hot) liquid, does not react with liquid (magnesium chloride/magnesium); low cost, at high temperature carbon electrode would burn with oxygen from the air to produce carbon dioxide. (1 mark)
ii Sensible suggestion – e.g. does not react with chlorine; high melting point; low cost (but do not accept if low cost already allowed in i). (1 mark)
b i Less heat/energy needed or lower cost of energy (accept less heat lost). (1 mark)
ii Less fossil fuel burned (for heat/energy) so less pollution; less global warming; resources conserved; less mining (must be linked) or less thermal; heat pollution.
(1 mark)
c i Mg2+ + 2e-→Mg (1 mark)
ii Cl-→Cl2 + 2e- (1 mark)
Chemistry C2 1 – C2 5 / AQA Examination-style answers – Unit 2 Chemistry
1 a CaF2 (1 mark)
b calcium ion with 2,8,8 electrons on three circles square bracket with 2+ charge outside top right chloride ion with 2,8,8 electrons on three circles square bracket with - charge outside top right (4 marks)
c The (electrostatic) forces/bonds between oppositely charged ions are strong, and there are many bonds/ forces or it has a giant structure/lattice, and so a large amount of energy is needed to break the bonds so that ions can move freely. (3 marks)
2 a 183.5 or 184 (2 marks)
(if answer incorrect, correct working 63.5 or 64 + 56 + 32 × 2 gains one mark).
b 34.6 or 34.8 or 34.78 (2 marks)
(if answer incorrect (63.5 or 64 × 100) ÷ (183.5 or 184) gains one mark).
c Any one from: contains a higher percentage (accept greater amount or more) of copper; contains no iron or fewer impurities. (1 mark)
d i Diagram showing any three from: spoon as negative electrode; pure copper as positive electrode; in (beaker/container) copper(II) sulfate solution; power supply or battery or cell symbol or electrodes labeled + and -. (3 marks)
ii Copper ions are positively charged and so are attracted to or move to the negative electrode, where they gain electrons or are reduced, forming copper atoms which are deposited on the spoon. (3 marks)
3 a There is a clear, logical and detailed scientific description of how to do paper chromatography. The answer shows almost faultless spelling, punctuation and grammar. It is coherent and in an organised, logical sequence. It contains a range of appropriate and relevant specialist terms used accurately. (5–6 marks)
There is a brief description of how to do paper chromatography with. The spelling, punctuation and grammar are very weak. The answer is poorly organized with almost no specialist terms and/or their use demonstrating a general lack of understanding of their meaning. (1–2 marks)
No relevant content. (0 marks)
Chemistry C2 1 – C2 5 / AQA Examination-style answers (Continued) – Unit 2 Chemistry
Examples of chemistry points made in the response:
• Draw a pencil line on paper (close to bottom).
• Mark/label starting points (in pencil).
• Put spots of colours/samples onto starting points.
• Put paper into solvent/water.
• Solvent/water below (pencil) line/spots.
• Use cover/lid on beaker/container.
• Allow solvent to run to (near to) top of paper.
• Remove from solvent/allow paper to dry.
• Any other technical detail, e.g. use capillary tube for sample spots.
b Any three from: drink contains two colours; one colour in drink is C2; one colour in drink is unknown (allow not permitted); drink does not contain C1 and/or C3.
(3 marks)
c i To separate the (flavour) compounds (allow to show how many flavours/
compounds there are). (1 mark)
ii To identify the compounds (allow to find the Mr or relative masses of the compounds). (1 mark)
4 a 2.61 (g) (2 marks)
If the answer is incorrect then correct working, e.g. 2/138 or (180/138) × 2 or 1 g →180/138 gains one mark.
b 42.1 (per cent) (2 marks)
If answer incorrect then or (1.1/ecf from a) × 100 correctly evaluated gains two marks, or correct working, e.g. (1.1/2.61) × 100 gains one mark.
c Any one from: errors in weighing; some (of the aspirin) lost; not all of the reactant may have been converted to product or reaction didn’t go to completion; the reaction
is reversible; side reactions; reactants impure; not heated for long enough; not hot enough for reaction to take place. (1 mark)
Chemistry C2 1 – C2 5 / AQA Examination-style answers (Continued) – Unit 2 Chemistry
Examples of chemistry points made in the response:
• Draw a pencil line on paper (close to bottom).
• Mark/label starting points (in pencil).
• Put spots of colours/samples onto starting points.
• Put paper into solvent/water.
• Solvent/water below (pencil) line/spots.
• Use cover/lid on beaker/container.
• Allow solvent to run to (near to) top of paper.
• Remove from solvent/allow paper to dry.
• Any other technical detail, e.g. use capillary tube for sample spots.
b Any three from: drink contains two colours; one colour in drink is C2; one colour in drink is unknown (allow not permitted); drink does not contain C1 and/or C3.
(3 marks)
c i To separate the (flavour) compounds (allow to show how many flavours/
compounds there are). (1 mark)
ii To identify the compounds (allow to find the Mr or relative masses of the compounds). (1 mark)
4 a 2.61 (g) (2 marks)
If the answer is incorrect then correct working, e.g. 2/138 or (180/138) × 2 or 1 g →180/138 gains one mark.
b 42.1 (per cent) (2 marks)
If answer incorrect then or (1.1/ecf from a) × 100 correctly evaluated gains two marks, or correct working, e.g. (1.1/2.61) × 100 gains one mark.
c Any one from: errors in weighing; some (of the aspirin) lost; not all of the reactant may have been converted to product or reaction didn’t go to completion; the reaction
is reversible; side reactions; reactants impure; not heated for long enough; not hot enough for reaction to take place. (1 mark)
Chemistry C2 1 – C2 5 / AQA Examination-style answers (Continued II) – Unit 2 Chemistry

5 a Diamond is very hard because it has a giant (covalent) structure/lattice, in which each carbon atom forms four (covalent) bonds, and so there are many strong (covalent) bonds to break. (Covalent must be mentioned at least once for full marks.)
(3 marks)
b There is a clear, logical and detailed scientific description of the structure and bonding in graphite correctly explaining both of the properties. The answer shows
almost faultless spelling, punctuation and grammar. It is coherent and in an organised, logical sequence. It contains a range of appropriate and relevant specialist terms used accurately. (5–6 marks)
There is a scientific description of the structure and bonding in graphite and some explanation of at least one the properties. There are some errors in spelling,
punctuation and grammar. The answer has some structure and organisation. The use of specialist terms has been attempted, but not always accurately. (3–4 marks)
There is a brief description of the structure and bonding in graphite and an attempt at an explanation of one the properties. The spelling, punctuation and grammar are
very weak. The answer is poorly organised with almost no specialist terms and/or their use demonstrating a general lack of understanding of their meaning.
(1–2 marks)
No relevant content. (0 marks)
Chemistry C2 1 – C2 5 / AQA Examination-style answers (Continued III) – Unit 2 Chemistry
Examples of chemistry points made in the response:
• Each carbon/atom joined/bonded to three other carbon/atoms. or Each carbon forms three bonds.
• In layers.
• Only weak forces (of attraction)/bonds between layers.
• Layers/atoms can slide over each other.
• One electron on each carbon is not used for bonding.
• Electrons delocalised or electrons free.
• Electrons carry the charge/current.
• Giant structure/lattice.
• Covalent (bonds).
• Strong bonds or a lot of energy needed to break bonds.
• Diagrams could be used: to show layered structure, to show that each carbon is bonded to three other carbon atoms, to show giant structure (at least three rings required).
c i Hexagons of carbon atoms or rings of six carbon atoms. (1 mark)
ii Any two correct reasons, e.g. they have special properties as they are nanoparticles; can form nanotubes; can be used for drug delivery; as catalysts; as lubricants; for reinforcing materials; or any other specific correct use. (2 marks)

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