Oxford Revise AQA GCSE Combined Science Foundation | Chapter C7 answers

Question

Answers

Extra information

Mark

AO / Specification reference

01.1

A – Cathode

B – Anode

C – Electrolyte

3

AO1

5.4.3.2

01.2

A – sodium

B – chlorine

1

1

AO2

5.4.3.2

01.3

ions are not free to move in solid sodium chloride

1

AO1

5.4.3.2

01.4

bulb lights up

1

AO3

5.4.3.2

02.1

independent variable is potential difference

dependent variable is rate of bubbles

1

1

AO2

5.4.3.4

02.2

1V–5V

units (at least once) are needed for the answer; 4 v is not correct

1

AO2

5.4.3.4

02.3

chlorine gas is toxic

too much released at high voltage

1

1

AO3

5.4.3.4

02.4

measure volume of gas/collect in measuring cylinder

1

AO3

5.4.3.4

03.1

aluminium and oxygen

1

AO1

5.4.3.3

03.2

arrow drawn pointing to correct place on bottom right

1

AO1

5.4.3.3

03.3

carbon/graphite

1

5.4.3.3

03.4

carbon/graphite electrodes react with oxygen

forms carbon dioxide

therefore, electrode wears away

1

1

1

AO1

5.4.3.3

03.5

B

1

AO1

5.4.3.3

03.6

lower the melting point

less energy needed for electrolysis

electrolysis is cheaper to run

1

1

1

AO1

5.4.3.3

04.1

ionic

1

AO1

5.4.3.4

04.2

anode

1

AO1

5.4.3.4

04.3

chlorine gas

1

AO3

5.4.3.4

05.1

aluminium is too reactive/more reactive than carbon

1

AO1

5.4.3.3

05.2

carbon or graphite

1

AO1

5.4.3.3

05.3

aluminium oxide must be molten for electrolysis to take place

cryolite reduces the melting point of the mixture

therefore, reducing the cost of the electrolysis

1

1

1

AO1

AO2

5.4.3.3

05.4

aluminium ions have a positive charge

so they are attracted to the negatively charged cathode

1

1

AO1

5.4.3.3

05.5

because of the high temperatures involved

oxygen reacts with the carbon to form carbon dioxide

1

1

AO1

5.4.3.3

06.1

cathode/negative electrode

anode/positive electrode

1

1

AO1

5.4.3.2

06.2

bromine and lead

1

AO2

5.4.3.4

06.3

bubbles

or brown gas produced

1

AO3

5.4.3.1

07.1

Level 3: Full detailed method that describes how to produce the electrolyte and how to set up the circuit. Diagram provided with anode, cathode, and electrolyte labelled. Circuit should include a battery symbol.

5-6

AO1

5.4.3.4

Level 2: Method provided that describes how to produce the electrolyte or how to set up the circuit. Diagram provided but some labels missing.

3-4

Level 1: Attempt at a method provided but no detail on how to produce the electrolyte or how to set up the circuit. No diagram, or unlabelled/incorrectly labelled diagram provided.

1-2

No relevant content.

0

Indicative content:

• dissolve potassium sulfate in water
• pour electrolyte/potassium sulfate solution into a beaker
• attach electrodes to a (DC) power supply
• connect the electrodes in a series circuit/with the negative terminal attached to the cathode and the positive terminal attached to the anode
• insert electrodes into the potassium sulfate solution
• ensure electrode to not touch each other
• switch the power supply onto a low voltage
• Labelled diagram of electrolysis set-up

award a maximum of 5 marks if students use a method that involves molten potassium sulfate, as the melting point is too high for a student to carry out in a lab.

07.2

bubbles

because oxygen gas produced

1

1

AO2

AO3

5.4.3.4

07.3

electrolysis of potassium sulfate: observe gas given off

electrolysis of copper sulfate: (brown-coloured) metal/copper coating the electrode

copper less reactive than hydrogen, so metal formed

potassium is more reactive than hydrogen, so hydrogen gas formed

1

1

1

1

AO2

AO3

5.4.3.4

08.1

MgCl₂

1

AO2

08.2

• magnesium nitrate
• most salts in solution will produce hydrogen gas at the cathode
• as magnesium is more reactive than hydrogen
• so need to electrolyse molten salt
• melting point of magnesium chloride and magnesium phosphate significantly higher than magnesium nitrate
• so more energy needed/process would be more expensive

AO2

5.4.3.2

5.4.3.3

5.4.3.4

08.3

cathode

accept negative electrode

1

09.1

cathode

accept negative electrode

1

AO1

5.4.3.1

09.2

chlorine zinc

1

AO2

5.4.3.2

09.3

in solid zinc, chloride ions are not free to move

so cannot conduct electricity

and move to the electrodes

1

1

1

AO1

5.4.3.1

09.4

ZnCl₂(l) → Zn(s) + Cl₂(g)

1

AO1

5.2.2.2

10.1

a rock that has enough metal in it to be worth economically worth extracting

1

AO1

5.4.3.3

10.2

potash

accept potassium ore

1

10.3

both require heat

in catalytic cracking, the vapour is passed over a hot catalyst

in steam cracking, the vapour is mixed with steam before heating

1

AO3

5.4.3.3

11.1

separate mixtures

identify substances

1

1

AO1

4.8.1.3

11.2

chromatogram with dot at bottom for sample and solvent line above

three different dots above solvent line

1

1

AO2

4.8.1.3

11.3

fractional distillation/crystallisation

1

AO1

4.1.1.2

11.4

substance would melt/boil at one specific temperature

because a pure substance is made of only a single element or compound

1

1

AO1

4.8.1.1