Oxford Revise AQA GCSE Chemistry | Chapter 10 answers

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Answers

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Mark

AO / Specification reference

01.1

hydrogen

1

AO2

4.4.3.4

01.2

2Cl⁻ (aq) → Cl₂(g) + 2e⁻

one mark for formulae and state symbols of reactants

one mark for formulae and state symbols of reactants

or

one mark for correct formulae

one mark for correct state symbols

one mark for balancing

3

AO2

4.4.3.5

01.3

independent – concentration of sodium chloride solution dependent – current

1

1

AO2

01.4

distance between electrodes or size of electrodes or volume of solutions

1

AO3

01.5

Graph of ‘concentration of sodium chloride solution in g/dm3’(horizontal axis) against ‘current in amps’ (vertical axis)

Points plotted at (0.2,0.2), (0.4,0.33), (0.6,0.43), (0.8, 0.47), (1.0, 0.52)

one mark for plotting three points one mark for plotting all points one mark for line of best fit

3

AO2

AO3

01.6

as concentration increases, the current also increases

as concentration increases, more ions are present to carry the charge

1

1

AO3

4.4.3.1

02.1

cathode/negative

1

AO1

4.4.3.1

02.2

chlorine zinc

1

AO2

4.4.3.2

02.3

in solid zinc, chloride ions are not free to move so cannot conduct electricity

and move to the electrodes

1

1

1

AO1

4.4.3.1

02.4

ZnCl₂(l) → Zn(s) + Cl₂(g)

1

AO1

4.4.2.2

03.1

too reactive to extract by reduction (with carbon)/reacts with carbon

1

AO1

4.4.3.3

03.2

cathode/negative

1

AO1

4.4.3.2

03.3

lots of energy needed to melt potassium sulfate

2

AO3

4.4.3.3

03.4

cathode: 2H⁺ (aq) + 2e⁻ → H₂(g)

anode: 4OH⁻(aq) → O₂(g) + 2H₂O(l) + 4e⁻

6

AO2

4.4.3.3

03.5

potassium metal is not produced in the electrolysis of potassium solution of potassium would react with the water/is too reactive

1

AO3

4.4.3.3

04.1

aluminium is above carbon in the reactivity series

1

AO1

4.4.3.3

04.2

carbon/graphite

1

AO1

4.4.3.3

04.3

carbon reacts with oxygen produced at the anode, forming carbon dioxide which burns away the anode

1

AO1

4.4.3.3

04.4

(liquid) aluminium oxide and cryolite

accept ‘bauxite’ instead of ‘(liquid) aluminium oxide’

1

1

AO1

4.4.3.3

04.5

Al³⁺(aq) + 3e⁻ → Al(l)

one mark for formulae and state symbols of reactants

one mark for formulae and state symbols of reactants

or

one mark for correct formulae

one mark for correct state symbols

one mark for balancing

3

AO2

4.4.3.5

04.6

large amounts of energy are required for the electrolysis/to keep the aluminium liquid

1

AO1

4.4.3.3

05.1

unreactive/does not react

conductor that carries an electric current into a liquid or solution

1

1

AO1

4.4.3.1

05.2

PbBr₂

1

AO2

4.2.1.2

05.3

Level 3: The description, explanation and names of the products are correct. The account is clearly written and well-structured.

5-6

AO1

4.4.3.1

4.4.3.5

Level 2: The description, explanation and names of the products are mainly correct, although there might be one or two errors. The account

is written fairly clearly, but is somewhat disorganised.

3-4

Level 1: The description, explanation and names of products are partly correct, but there are several errors and the account lacks detail. The account is not written clearly, and consists of isolated facts rather than

one flowing piece of work.

1-2

No relevant content.

0

Indicative content

• the current causes the ions to move to the electrodes
• positive lead ions move to the negative electrode/cathode
• negative bromide ions move to the positive electrode/anode
• at the positive electrode, positive lead ions gain electrons, so lead atoms are formed
• at the negative electrode, negative bromide ions lose electrons, so bromine is formed
• cathode: Pb²⁺ + 2e⁻ → Pb
• anode: 2Br⁻ → 2e⁻ + Br₂

06.1

higher temperatures are required to melt the salts

1

AO3

06.2

to collect any gases given off at the electrodes

1

AO1

4.4.3.4

06.3

the cathode will become pink-brown

1

AO2

4.4.3.4

06.4

if lit splint goes out with a squeaky pop, then the gas is hydrogen/H₂ if glowing splint relights, then the gas is oxygen/O₂

1

1

AO1

4.4.3.4`

06.5

some water molecules break down to make hydrogen ions and hydroxide ions

the hydrogen ions are attracted to the cathode

where they gain electrons, as shown in the half equation below

2H⁺(aq) + 2e⁻ → H₂(g)

1

1

3

AO1

4.4.3.4

4.4.3.5

07.1

row one: does not conduct because ions not free to move

row two: positive sodium ions move to the negative electrode, where they pick up electrons to make sodium metal

negative chloride ions move to the positive electrode, where they donate electrons to make chlorine gas

1

1

1

AO2

4.2.2.3

07.2

2H⁺ (aq) + 2e⁻ → H₂(g)

one mark for formulae and state symbols of reactants

one mark for formulae and state symbols of reactants

or

one mark for correct formulae

one mark for correct state symbols

one mark for balancing

3

AO2

4.4.3.5

07.3

Level 3: The explanation is correct. The account is clearly written and

well-structured.

5-6

AO2 × 3

AO3 × 3

4.4.3.4

Level 2: The explanation is mainly correct. The account is written fairly

clearly, but is somewhat disorganised.

3-4

Level 1: The explanation is partly correct, but there are several errors

and the account lacks detail and clarity.

1-2

No relevant content

0

Indicative content

• in the solution, water molecules break down producing hydrogen ions and hydroxide ions
• sodium and chloride ions are also present in the solution
• the current causes the ions to move to the electrodes
• positive sodium and hydrogen ions move to the negative electrode/cathode
• negative chloride and hydroxide ions move to the positive electrode/anode
• at the positive electrode, positive hydrogen ions gain electrons, so hydrogen is formed
• hydrogen gas makes a lit splint give a squeaky pop
• at the negative electrode, hydroxide ions react to make oxygen gas
• oxygen gas relights a glowing splint
• both chlorine and oxygen are formed because of the relatively low concentration of chloride ions in the dilute solution
• also, at the negative electrode, chloride ions react to make chlorine gas, which has a characteristic smell

08.1

too reactive/reacts with carbon/more reactive than carbon

1

AO1

4.4.3.3

08.2

carbon/graphite

1

AO1

4.4.3.3

08.3

aluminium oxide must be molten for electrolysis to take place cryolite reduced the melting point of the mixture

therefore, reducing the cost of the electrolysis

1

1

1

AO1

AO2

4.3.3.3

08.4

aluminium ions have a positive charge

so they are attracted to the negatively charged cathode

1

1

AO1

4.4.3.3

08.5

because of the high temperatures involved

oxygen reacts with the carbon to form carbon dioxide

1

1

AO1

4.4.3.3

09.1

copper

1

AO2

4.4.3.4

09.2

hydrogen

1

AO1

4.4.3.4

09.3

placing lit splint in collected gas gives a squeaky pop

2

AO1

09.4

brown liquid resulting from the formation of bromine from bromide ions

2Br⁻ (aq) → Br₂(aq) + 2e⁻

bubbles (of colour) gas resulting from the formation of oxygen

4OH⁻ (aq) → O₂(g) + 2H₂O(l) + 4e⁻

1

3

1

3

AO2 x 6

AO3 X 2

4.4.3.4

4.4.3.5

09.5

two from:

• smaller quantity of solution required (so cheaper / less waste to dispose of)
• easier to make observations at electrodes
• bromine is toxic/ harmful so safer to generate small amounts

one mark for each correct answer

2

AO3

10.1

only partially ionised in aqueous solution

1

AO1

4.4.2.6

10.2

3Mg(s) + 2H₃PO₄(aq) → Mg₃(PO₄)₂(aq) + 3H₂(g)

1

AO2

4.3.1.1

10.3

oxidised: magnesium

reduced: hydrogen

1

1

AO2

4.4.2.1

10.4

Na₃PO₄

3NaOH(aq) + H₃PO₄(aq) → Na₃PO₄(aq) + 3H₂O(l)

one mark for Na₃

one mark for one PO₄

accept a balanced equation for the salt provided

2

1

AO3

4.4.2.2

10.5

moles of  H₃PO₄ = 0.5 × \( \frac{{25}}{{1000}}\)

= 0.0 125

moles of NaOH = 0.0 125 × 3 = 0.0 375

= 0.25 dm³ or 250 cm³

1

1

1

1

1

AO2

4.3.4

11.1

2 Mg(NO₃)₂(s) → 2 MgO(s) + 4 NO₂(g) + O₂(g)

one mark for formulae and state symbols of reactants

one mark for formulae and state symbols of reactants

or

one mark for correct formulae

one mark for correct state symbols

one mark for balancing

3

AO2

4.3.1.1

11.2

calcium carbonate

1

AO1

11.3

M_r of CaCO₃ = 40 + 12 + (3 × 16)

= 100

1

1

AO2

4.3.1.2

11.4

50 kg – 22 kg

= 28 kg

1

1

AO2

4.3.1.2

12.1

two spots drawn at different heights

do not award mark if a spot for water is provided

1

AO2

4.1.1.2

12.2

D

1

AO2

4.1.1.2

12.3

water will release vapours before its boiling point or boiling points of water and this substance are quite similar

in fractional distillation, these vapours will condense on the glass beads and drop back into the mixture

whereas the substance vapours will only evaporate in the condenser so will collect in a separate vessel

1

1

1

1

1

AO2

4.1.1.2

13.1

increases

1

AO1

4.1.2.6

13.2

Group 1 – reactivity increases down group

Group 7 – reactivity decreases down group

1

1

AO1

4.1.2.5

4.1.2.6

13.3

sodium hydroxide

hydrogen

1

1

AO1

4.1.2.5