Electrolysis

Question 1

Electrolysis

Answer 1

Electrolysis is the process that splits ionic compounds into the different elements that they are made of. Electrolysis happens using a solution that conducts electricity.

Question 2

cation

Answer 2

a positively charged ion, i.e. one that would be attracted to the cathode (negative electrode) in electrolysis.

Question 3

Electrolysis of aluminium

Answer 3

At the anode:
Carbon dioxide forms

At the cathode:
Aluminium forms

Question 4

At the cathode (negative electrode)

Answer 4

At the cathode (negative electrode)

What is formed at the cathode depends on the reactivity of the metal:
Hydrogen is produced if the metal is higher than hydrogen in the reactivity series.
The metal is produced if the metal is lower than hydrogen in the reactivity series.

Question 5

At the anode (positive electrode)

Answer 5

At the anode (positive electrode)

What is formed at the anode depends on if there are halide ions present:
If there are halide ions present, the respective halogen forms.
If there are no halide ions, oxygen forms.

Question 6

Explain what is meant by electrolysis.

Answer 6

decomposition (of
compound/substance
/electrolyte)(1)
• using (direct) current (1)

Question 7

Describe the test to show that a gas is chlorine.

Answer 7

(damp blue) litmus (paper)
(1)
• (turns red then) {bleaches
/ goes white} (1)

Question 8

(b) Dilute hydrochloric acid reacts with silver nitrate solution to form silver chloride
and nitric acid.
(i) Complete the sentence by putting a cross ( ) in the box next to your answer.
The reaction produces silver chloride as a precipitate.
In an equation this would be shown as
(1)
A AgCl(aq)
B AgCl(g)
C AgCl(l)
D AgCl(s)

Answer 8

D gCl(s)

Question 9

Chlorine is one of the products of the electrolysis.
The half-equation for the production of chlorine is
2Cl–
→ Cl2
+ 2e
Explain how the half-equation shows that chloride ions are oxidised.
(iii) Suggest why the solution remaining at the end of the electrolysis is alkaline.

Answer 9

Any one from
• it contains (excess)
{hydroxide/OH¯
} ions (1)
• {sodium/Na+} ions and
{hydroxide/ OH¯
} ions
remain (1)
• it is sodium
hydroxide/NaOH (1)
• {hydrogen/H+} ions have
been removed (at the
cathode) (1)

Question 10

When copper sulfate solution is electrolysed using inert electrodes, oxygen is
formed at the positively charged anode.
Explain how the oxygen is formed from ions in the solution.

Answer 10

Marking point 1
• {hydroxide/OH-
} ions
(from water) (1)
Marking point 2
• (ions) lose electrons /are
oxidised (1)