Edexcel IGCSE Chemistry electrolysis

Practise electrolysis questions by predicting electrode products, explaining observations and writing half-equations for ion discharge.

Exam points

Explain conductivity in ionic melts or solutions by referring to mobile ions.
Identify electrode products and observations for molten salts or aqueous solutions.
Write or interpret half-equations, including electron gain for reduction at the cathode.

Covered syllabus points

1.55C Covalent compounds and conductivity 1.56C Ionic compounds and conductivity 1.57C Anions and cations 1.58C Electrolysis experiments 1.59C Electrolysis half-equations 1.60C Electrolysis practical

[Maximum number: 5]

Iron metal was discovered several thousand years ago. Iron is produced industrially from iron(III) oxide by extraction using carbon.

Sodium is a metal in Group 1 of the Periodic Table. Sodium was discovered by Sir Humphrey Davy in 1807. It is produced industrially by the electrolysis of sodium chloride.

(a)

The diagram shows a simplified version of the Downs cell, which can be used to produce sodium industrially. The electrolyte is molten sodium chloride.

Figure for Question (a) — Edexcel IGCSE Chemistry

[ 5 ]

(i)

Explain why the molten electrolyte conducts electricity.

[ 2 ]

(ii)

What is the formula of the cation in the electrolyte?

Figure for Question (ii) — Edexcel IGCSE Chemistry

[ 1 ]

(iii)

Give ionic half-equations for the reactions at the anode and cathode.

anode……

cathode……

[ 2 ]

M1 (anode) $2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_{2}+2 \mathrm{e}^{(-)}$

M2 (cathode) (2) $\mathrm{Na}^{+}+(2) \mathrm{e}^{(-)} \rightarrow(2) \mathrm{Na}$

ACCEPT $2 \mathrm{Cl}^{-}-2 \mathrm{e}^{(-)} \rightarrow \mathrm{Cl}_{2}$

both half-equations correct but order reversed scores 1

[Maximum number: 8]

A scientist reacts lead(II) nitrate solution with sodium bromide solution.

This is the equation for the reaction.

\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{NaBr}(\mathrm{aq}) \rightarrow \mathrm{PbBr}_{2}(\mathrm{~s})+2 \mathrm{NaNO}_{3}(\mathrm{aq})

(a)

The scientist electrolyses molten lead(II) bromide using this apparatus.

[ 6 ]

(i)

Explain why lead(II) bromide needs to be molten rather than solid for electrolysis to occur.

[ 3 ]

(ii)

The electrolyte is at a temperature of $400^{\circ} \mathrm{C}$ .

Explain a suitable material for the electrodes.

[ 2 ]

(iii)

Give the half-equation that occurs at the negative electrode.

[ 1 ]

$\mathrm{Pb}^{2+}+2 \mathrm{e}^{(-)} \rightarrow \mathrm{Pb}$

IGNORE state symbols even if incorrect

(b)

Bromine forms at the positive electrode.

This is the half-equation for the reaction at the positive electrode.

2 \mathrm{Br}^{-} \rightarrow \mathrm{Br}_{2}+2 \mathrm{e}^{-}

[ 2 ]

(i)

State what is observed at the positive electrode.

[ 1 ]

(ii)

State why the half-equation represents an oxidation reaction.

[ 1 ]

All question bank results loaded

Covered syllabus points

(i) Electrolysis question 1

Question (a)

Question (i)

Question (ii)

Question (iii)

(i) Electrolysis question 2

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (b)

Question (i)

Question (ii)