AQA A Level Chemistry

Topic Questions

1.9 Oxidation, Reduction & Redox Equations

11 mark

Which row correctly describes oxidation and reduction in terms of electron transfer and changes in oxidation state?

 

Electron transfer 

Change in oxidation state

 

oxidation

reduction

oxidation

reduction

A

B

C

D

gain

loss

loss

gain

loss

gain

loss

gain

increase

increase

decrease

decrease

decrease

decrease

increase

increase

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21 mark

Which are the correct common oxidation states of fluorine, oxygen and hydrogen in compounds?

 

Fluorine

Oxygen

Hydrogen

A

- 1

- 2

+ 1

B

- 7

- 1

- 1

C

+ 1

+ 2

+ 1

D

+ 7

- 1

- 1

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31 mark

The heptahydrate mineral of magnesium sulfate is used in Epsom Salts for preparing therapeutic baths. Magnesium sulfate is also used in some medical applications.

What is the overall oxidation state of MgSO4?

  • -2

  • +2

  • +7

  • 0

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41 mark

Which compound shows nitrogen in the highest oxidation state?

  • NaNO2

  • N2O4

  • N2O

  • NO

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51 mark

Sulfur dioxide and oxygen difluoride react together. The oxidation state of fluorine in OF2 is -1.

SO2 + OF2 rightwards arrow SO3 + F2

Using oxidation states, which description about the elements is correct?

 

Sulfur

Fluorine

A

Oxidised

Reduced

B

Reduced

Oxidised

C

Oxidised

Oxidised

D

Reduced

Reduced

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61 mark

Which equation does not represent a redox reaction?

  • FeO + 2HCl rightwards arrow FeCl2 + H2O

  • Mg + CuSO4 rightwards arrow MgSO4 + Cu

  • Ca + 2HCl rightwards arrow CaCl2 + H2

  • C2H4 + 3O2 rightwards arrow 2CO2 + 2H2O

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71 mark

Which of these is a redox reaction?

  • KBr + H2SO4 ⟶ KHSO4 + HBr

  • Ca + S ⟶ CaS

  • Li2O + H2SO4 ⟶ Li2SO4 + H2O

  • MgO + SiO2 ⟶ MgSiO3

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81 mark

Which reaction shows hydrogen acting as an oxidising agent?

  • H2 + Br2 → 2HBr

  • H2 + C3H6O → C3H7OH

  • 2H2 + O2 → 2H2O

  • H2 + 2Li → 2LiH

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91 mark

Which of the following species contains the metal with the highest oxidation state?

  • MnO4-

  • TiO2

  • Cr2O72-

  • V2O5

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101 mark

Which of the following statements is correct for a reducing agent?

  • A reducing agent undergoes reduction

  • A reducing agent is an electron acceptor

  • A reducing agent is an electron donor

  • A reducing agent decreases in oxidation state

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11 mark

A solution containing both bromine and chlorine will produce bromate ions, BrO3.

The reactions leading to the production of BrO3 ions are:

1:     Br2  +  H2O  →  HBr  +  HBrO

2:     3HBrO  +  Cl2  →  2Cl   +  BrO3  +  Br2  +  3H+

Which statements about these reactions are correct?

 

Chlorine is reduced in reaction 2

Bromine is reduced in both reaction 1 and reaction 2

Bromine is oxidised in both reaction 1 and reaction 2

A

X

X

B

X

C

X

D

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21 mark

If a dilute acid is added to an aqueous solution containing nitrite ions, NO2, two different nitrogen compounds are released as gases.

2H+ (aq) + 2NO2 (aq) → H2O (l) + NO (g) + NO2 (g)

Which of the three statements below correctly describe the process?

 

 

The H+ (aq) ion is oxidised by NO2(aq).

Some nitrogen atoms are oxidised, and some nitrogen atoms are reduced.

The H+ (aq) ion acts as a catalyst.

A

X

B

X

X

C

X

D

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31 mark

What are the correct oxidation states for the elements in Fe3O4?

 

Fe

O

A

+3 and +4

-1

B

+2.67

-2

C

+2 and +3

-2

D

+4

-3

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41 mark

In terms of electron transfer, what does an oxidising agent do in a redox reaction?

  • Accept electrons

  • Donate electrons

  • Accept a pair of electrons

  • Donate a pair of electrons

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51 mark

Which species is the best oxidising agent?

  • F-

  • Cl -

  • F2

  • Cl2 

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61 mark

Potassium dichromate reacts with ethanedioic acid and sulfuric acid to form chromium (III) sulfate, potassium sulfate and two other products.

What is the reducing agent for this reaction?

  • H+

  • K+

  • C2O42-

  • Cr2O72-

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71 mark

Iron (II) sulfate reacts with potassium manganate (VII) in acidic conditions to produce iron (III) sulfate, manganese sulfate, potassium sulfate and water.

The unbalanced equation for this reaction is shown below.

_FeSO4 + _KMnO4 + _H2SO4 → _Fe2(SO4)3 + _MnSO4 + _H2O + K2SO4

Which whole number stoichiometric coefficients are correct to balance the equation?

 

 

FeSO4

KMnO4

H2SO4

Fe2(SO4)3

MnSO4

H2O

A

10

2

8

5

2

8

B

10

2

4

5

2

8

C

5

2

8

5

1

4

D

5

1

4

5

1

4

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81 mark

Chromate (VII) and dichromate (VII) ions are both oxidising agents with chromium in the +6 oxidation state.

Which equation shows the correct ionic half equation for the chromate ion to form Cr3+?

  • CrO4- + 8H+ + 2e- → Cr3+ + 4H2O

  • Cr2O72- + 14H+ + 6e- → Cr3+ + 7H2O

  • CrO42- + 8H+ + 5e- → Cr3+ + 4H2O

  • CrO42- + 8H+ + 3e- → Cr3+ + 4H2O

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91 mark

Which one of the following is the electron arrangement of the strongest oxidising agent?

  • 1s2 2s2 2p4

  • 1s2 2s2 2p6 3s2 3p3

  • 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5

  • 1s2 2s2 2p6 3s2 3p6 

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101 mark

Potassium manganate (VII) reacts with hydrogen peroxide and sulfuric acid to form potassium sulfate, manganese sulfate, oxygen and water.

Which species is acting as the reducing agent in the reaction?

  • MnO4-

  • H2O2

  • H+

  • SO42-

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11 mark

Which statement about the redox chemistry of Group 7 is correct?

  • Bromine can oxidise chloride ions

  • In reactions with water, chlorine is oxidised and reduced

  • Iodide ions are the weakest reducing agent of the first four Group VII ions

  • Fluorine is a weaker oxidising agent than chlorine

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21 mark

Which reaction shows the species in bold acting as an oxidising agent?

  • 2MnO4- + 5SO32- + 6H+ → 2Mn2+ + 3H2O + 5SO42-

  • Fe2O3 + 3CO → 2Fe + 3CO2

  • Cl2 + 2Br- → 2Cl- + Br2

  • Mg + Fe2+ → Mg2+ + Fe

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31 mark

In which compound are there two different elements with the same oxidation state?

  • NH4Cl

  • Na2SO4

  • Mg(OH)2

  • HClO

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41 mark

Sulfuric acid and sodium bromide can react according to the following equation.

2NaBr (s) + 3H2SO4 (aq) rightwards arrow 2NaHSO4 (s) + SO2 (g) + Br2 (g) + 2H2O (l)

Which species has been oxidised in this reaction?

  • H+

  • Na+

  • Br

  • SO42−

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51 mark

The following reaction can be used to determine the mass of titanium dioxide in an ore.

3TiO2 + 4BrF3 rightwards arrow 3TiF4 + 2Br2 + 3O2

Which element decreases in oxidation state in this reaction?

  • fluorine

  • bromine

  • titanium

  • oxygen

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61 mark

In which reaction does hydrogen behave as an oxidising agent?

  • H2 + CuO → Cu + H2O

  • 2Na + H2 → 2NaH

  • H2 + Cl2 → 2HCl

  • C2H4 + H2 → C2H6

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71 mark

Chlorine gas forms different products when it reacts with hot and cold aqueous sodium hydroxide.

What are the correct oxidation numbers of chlorine in the products of these reactions?

 

Hot aqueous sodium hydroxide

Cold aqueous sodium hydroxide

A

B

C

D

+1, +6

+1, +6

-1, +5

-1, +5

-1, +1

-1, +2

-1, +1

-1, +2

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81 mark

Concentrated sulfuric acid can react with potassium halides according to the following equations.

Reaction 1:   8KI  +  5H2SO4  →  4K2SO4  +  H2S  +  4I 2  +  4H2O

Reaction 2:   2KBr  +  2H2SO4  →  K2SO4  +  SO2  +  Br2  +  2H2O

Reaction 3:   KCl  +  H2SO4  →  KHSO4  +  HCl

For each reaction, what is the largest change in the oxidation number of sulfur?

 

Reaction 1

Reaction 2

Reaction 3

A

8

4

1

B

8

2

0

C

4

2

0

D

4

1

1

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91 mark

Vanadium (V) oxide, V2O5, acts as a catalyst in the Contact Process, making sulfuric acid.

During one step of the Contact Process, the vanadium (V) oxide changes from the V5+ to the V4+ oxidation state which causes sulfur dioxide to be oxidised to sulfur trioxide.

Which is the correct formula of the V4+ intermediate species that is formed during the Contact Process?

  • VO43-

  • V2O4 

  • VO3-

  • VO2+

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101 mark

Titanium dioxide can be obtained from the ore ilmenite, Fe(II)TiO3.

                               FeTiO3 → TiO2

What is the change in the oxidation number of titanium in the reaction?

  • +3 to +4

  • +4 to +5

  • +6 to +4

  • No change in oxidation number occurs

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