CAIE IGCSE Chemistry 6.4 Redox Question Bank

Practise recognising redox from equations, oxidation numbers and electron transfer in metal, oxide and displacement reactions.

Exam points

distinguish oxidation and reduction in ionic equations using electron transfer
identify oxidising and reducing agents from changes in oxidation number

Covered syllabus points

6.4.1—Roman numeral to indicate the 6.4.2—Redox reactions as involving 6.4.3—Oxidation as gain of oxygen and 6.4.4—Redox reactions as reactions involving 6.4.5—Oxidation and reduction in redox 6.4.6—Oxidation in terms of: (a) loss of 6.4.7—Reduction in terms of: (a) gain of 6.4.8—Redox reactions as reactions involving 6.4.9—Redox using oxidation numbers: (a)6.4.10—Redox reactions by the colour changes 6.4.11—An oxidising agent as a substance that 6.4.12—Reducing agent as a substance that 6.4.13—Oxidising agents and reducing agents

[Maximum number: 3]

Sulfur is a Group VI element.

(a)

$\mathrm{Na}_{2} \mathrm{SO}_{3}$ is oxidised by acidified aqueous potassium manganate(VII).

[ 3 ]

(i)

State what VII refers to in the name potassium manganate(VII).

[ 1 ]

(ii)

State the colour change when this reaction happens.
from to

[ 2 ]

[Maximum number: 4]

(a)

When magnesium is added to aqueous copper(II) sulfate a reaction occurs. The ionic equation for the reaction is shown.

\mathrm{Mg}+\mathrm{Cu}^{2+} \rightarrow \mathrm{Mg}^{2+}+\mathrm{Cu}

[ 4 ]

(i)

Give one change you would observe during this reaction.

[ 1 ]

(ii)

Explain why this is a redox reaction.

[ 1 ]

(iii)

Identify the oxidising agent in this reaction. Give a reason for your answer.

[ 2 ]

$\mathrm{Cu}^{2+}$ OR copper(II) ions OR copper ions

gains electrons

[Maximum number: 1]

This question is about nitrogen and some of its compounds.

Some of the ammonia made by the Haber process is converted into nitric acid.

The first stage of this process is the oxidation of ammonia to make nitrogen monoxide.

4 \mathrm{NH}_{3}(\mathrm{~g})+5 \mathrm{O}_{2}(\mathrm{~g}) \rightleftharpoons 4 \mathrm{NO}(\mathrm{~g})+6 \mathrm{H}_{2} \mathrm{O}(\mathrm{~g})

The process is carried out at $900^{\circ} \mathrm{C}$ and a pressure of 5 atmospheres using an alloy of platinum and rhodium as a catalyst.

The forward reaction is exothermic.

State the meaning of the term oxidation.

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Covered syllabus points

6.4 Redox question 1

Question (a)

Question (i)

Question (ii)

6.4 Redox question 2

Question (a)

Question (i)

Question (ii)

Question (iii)

6.4 Redox question 3