CAIE IGCSE Chemistry 6.4 Redox Topic Practice

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Covered syllabus points

6.4.1—Roman numeral to indicate the6.4.2—Redox reactions as involving6.4.3—Oxidation as gain of oxygen and6.4.4—Redox reactions as reactions involving6.4.5—Oxidation and reduction in redox6.4.6—Oxidation in terms of: (a) loss of6.4.7—Reduction in terms of: (a) gain of6.4.8—Redox reactions as reactions involving6.4.9—Redox using oxidation numbers: (a)6.4.10—Redox reactions by the colour changes6.4.11—An oxidising agent as a substance that6.4.12—Reducing agent as a substance that6.4.13—Oxidising agents and reducing agents

Question 1

[Maximum number: 1]

Chromium forms the compound chromium(III) sulfate.
What does the (III) represent?

A

the charge on a sulfate ion

B

the number of chromium ions combined with one sulfate ion

C

the number of sulfate ions combined with one chromium ion

D

the oxidation state of chromium

Question 2

[Maximum number: 1]

Ethanol can be turned into ethanoic acid by passing it over hot copper(II) oxide.

CH3CH2OH+2CuO→CH3COOH+H2O+2Cu\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}+2 \mathrm{CuO} \rightarrow \mathrm{CH}_{3} \mathrm{COOH}+\mathrm{H}_{2} \mathrm{O}+2 \mathrm{Cu}

What is this type of reaction?

A

precipitation

B

redox

C

thermal decomposition

D

neutralisation

Question 3

[Maximum number: 1]

When heated strongly, silicon(IV) oxide reacts with carbon.

SiO2+2C→Si+2CO\mathrm{SiO}_{2}+2 \mathrm{C} \rightarrow \mathrm{Si}+2 \mathrm{CO}

Which term describes what happens to silicon(IV) oxide?

A

thermal decomposition

B

neutralisation

C

oxidation

D

reduction

Question 4

[Maximum number: 1]

Which equation represents a redox reaction?

A

AgNO3+NaCl→AgCl+NaNO3\mathrm{AgNO}_{3}+\mathrm{NaCl} \rightarrow \mathrm{AgCl}+\mathrm{NaNO}_{3}

B

PCl5+4H2O→H3PO4+5HCl\mathrm{PCl}_{5}+4 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{H}_{3} \mathrm{PO}_{4}+5 \mathrm{HCl}

C

3Fe+4H2O→Fe3O4+4H23 \mathrm{Fe}+4 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Fe}_{3} \mathrm{O}_{4}+4 \mathrm{H}_{2}

D

MgCO3+2HCl→MgCl2+CO2+H2O\mathrm{MgCO}_{3}+2 \mathrm{HCl} \rightarrow \mathrm{MgCl}_{2}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}

Question 5

[Maximum number: 1]

The equation for the reaction of magnesium with carbon dioxide is shown.

2Mg+CO2→2MgO+C2 \mathrm{Mg}+\mathrm{CO}_{2} \rightarrow 2 \mathrm{MgO}+\mathrm{C}

Which statement about this reaction is correct?

A

Magnesium is oxidised and carbon dioxide is reduced.

B

Magnesium is reduced and carbon dioxide is oxidised.

C

Magnesium and carbon dioxide are both oxidised.

D

Magnesium and carbon dioxide are neither oxidised nor reduced.

Question 6

[Maximum number: 1]

The electrical energy, or voltage, of two simple cells is measured.

cell 1

cell 1

cell 2

cell 2

statement 1 The voltage of cell 1 is greater than cell 2.
statement 2 Zinc is more reactive than copper.
statement 3 Magnesium is oxidised in both cells.
statement 4 Magnesium atoms lose electrons to form magnesium ions.
Which option is correct?

A

All the statements are correct.

B

Only statements 1 and 3 are correct.

C

Statement 2 is correct and explains statement 1.

D

Statement 4 is correct and explains statement 3.

Question 7

[Maximum number: 1]

Which of these reactions shows only reduction?

A

Cu2++2e−→Cu\mathrm{Cu}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Cu}

B

Fe2O3+3CO→2Fe+3CO2\mathrm{Fe}_{2} \mathrm{O}_{3}+3 \mathrm{CO} \rightarrow 2 \mathrm{Fe}+3 \mathrm{CO}_{2}

C

HCl+NaOH→NaCl+H2O\mathrm{HCl}+\mathrm{NaOH} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}

D

Mg+ZnSO4→Zn+MgSO4\mathrm{Mg}+\mathrm{ZnSO}_{4} \rightarrow \mathrm{Zn}+\mathrm{MgSO}_{4}

Question 8

[Maximum number: 1]

Chlorine displaces bromine from aqueous potassium bromide.
The ionic equation for the reaction is shown.

Cl2+2Br−→2Cl−+Br2\mathrm{Cl}_{2}+2 \mathrm{Br}^{-} \rightarrow 2 \mathrm{Cl}^{-}+\mathrm{Br}_{2}

Which statement about this reaction is correct?

A

Bromide ions act as an oxidising agent.

B

Bromide ions are oxidised as electrons are lost.

C

Chlorine acts as a reducing agent.

D

Chlorine is reduced as electrons are lost.

Question 9

[Maximum number: 2]

Hydrogen iodide thermally decomposes into iodine and hydrogen. The reaction is reversible.

2HI( g) colourless gas →⇌I2( g) purple gas +H2( g) colourless gas \underset{\text { colourless gas }}{2 \mathrm{HI}(\mathrm{~g})} \rightarrow \underset{\substack{\mathrm{I}_{2}(\mathrm{~g}) \\ \text { purple gas }}}{\rightleftharpoons}+\underset{\substack{\mathrm{H}_{2}(\mathrm{~g}) \\ \text { colourless gas }}}{ }

Fig. 4.1 shows a gas syringe containing a mixture of hydrogen iodide, iodine and hydrogen gases. The gas syringe is sealed and the mixture is heated to 300∘C300^{\circ} \mathrm{C}. The mixture of gases reaches equilibrium and is purple.

Fig. 4.1

Fig. 4.1

Deduce the oxidation number of iodine, I, in:

HI
I2\mathrm{I}_{2}.

Question 10

[Maximum number: 1]

Hydrogen iodide is dissolved in water.

HI→H++I−\mathrm{HI} \rightarrow \mathrm{H}^{+}+\mathrm{I}^{-}

Which row describes the final colours seen when the solution is tested with damp red litmus paper and with acidified aqueous potassium manganate(VII)?

damp red
litmus paper

acidified aqueous potassium
manganate(VII)

blue

brown

blue

colourless

red

brown

red

colourless

Question 11

[Maximum number: 1]

Substance J takes part in a redox reaction.
In the reaction, J gains electrons.
Which statement is correct?

A

J is the oxidising agent and it is oxidised in the reaction.

B

J is the oxidising agent and it is reduced in the reaction.

C

J is the reducing agent and it is oxidised in the reaction.

D

J is the reducing agent and it is reduced in the reaction.

Question 12

[Maximum number: 1]

Ethanol is manufactured by two methods:
method 1 fermentation of aqueous glucose
method 2 catalytic addition of steam to an alkene.

Ethanol can be converted to ethanoic acid by reacting it with an acidified oxidising agent.

State, in terms of redox, what type of reagent ethanol is in this reaction.

Question 13

[Maximum number: 1]

The equation for the reaction of sulfur dioxide with acidified potassium dichromate(VI) is shown.

3SO2+Cr2O72−+2H+→3SO42−+2Cr3++H2O3 \mathrm{SO}_{2}+\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+2 \mathrm{H}^{+} \rightarrow 3 \mathrm{SO}_{4}^{2-}+2 \mathrm{Cr}^{3+}+\mathrm{H}_{2} \mathrm{O}

What is oxidised and what is the oxidising agent?

oxidised

oxidising agent

SO2\mathrm{SO}_{2}

Cr2O72−\mathrm{Cr}_{2} \mathrm{O}_{7}{ }^{2-}

SO2\mathrm{SO}_{2}

H+\mathrm{H}^{+}

Cr2O72−\mathrm{Cr}_{2} \mathrm{O}_{7}{ }^{2-}

H+\mathrm{H}^{+}

Cr2O72−\mathrm{Cr}_{2} \mathrm{O}_{7}{ }^{2-}

Cr2O72−\mathrm{Cr}_{2} \mathrm{O}_{7}{ }^{2-}

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