Redox
6.4What the syllabus asks of you
- Use a Roman numeral to indicate the oxidation number of an element in a compound
- Define redox reactions as involving simultaneous reduction and oxidation
- Define oxidation in terms of: (a) gain of oxygen (b) loss of electrons (c) an increase in oxidation number
- Define reduction in terms of: (a) loss of oxygen (b) gain of electrons (c) a decrease in oxidation number
- Identify redox reactions as reactions involving gain and loss of oxygen, or gain and loss of electrons
- Identify redox reactions by changes in oxidation number using: (a) the oxidation number of elements in their uncombined state is zero (b) the oxidation number of a monatomic ion is the same as the charge on the ion (c) the sum of the oxidation numbers in a compound is zero (d) the sum of the oxidation numbers in an ion is equal to the charge on the ion
- Identify redox reactions by the colour changes involved when using acidified aqueous potassium manganate(VII) or aqueous potassium iodide
- Define an oxidising agent as a substance that oxidises another substance and is itself reduced
- Define a reducing agent as a substance that reduces another substance and is itself oxidised
- Identify oxidation, oxidising agents, reduction and reducing agents in redox reactions
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Chapter 6: Redox
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43 questions
1May / June 2026 · Paper 12 · Q16Show mark scheme →
Abrown | a reducing agent
Bbrown | an oxidising agent
Ccolourless | a reducing agent
Dcolourless | an oxidising agent
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2Oct / Nov 2025 · Paper 12 · Q18Show mark scheme →
Acolourless to purple; oxidised
Bcolourless to purple; reduced
Cpurple to colourless; oxidised
Dpurple to colourless; reduced
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3Oct / Nov 2024 · Paper 11 · Q18Show mark scheme →
Ahigher, reduced
Bhigher, oxidised
Clower, reduced
Dlower, oxidised
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4Oct / Nov 2024 · Paper 12 · Q20Show mark scheme →
Airon / oxidising agent
Biron / reducing agent
Csulfur / oxidising agent
Dsulfur / reducing agent
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5May / June 2024 · Paper 11 · Q21Also set in Oct / Nov 2018 Paper 11Show mark scheme →
AAcidified manganate(VII) ions change colour from colourless to purple when reduced.
BAll reactions that involve oxidation also involve reduction.
CDuring a reaction, oxidising agents lose electrons.
DReduction is the loss of hydrogen from a compound.
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6May / June 2024 · Paper 11 · Q22Show mark scheme →
ABromide ions are the oxidising agent.
BBromine is the reducing agent.
CChloride ions are the reducing agent.
DChlorine is the oxidising agent.
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7May / June 2024 · Paper 12 · Q20Show mark scheme →
ABromide ions are oxidised because they lose electrons.
BChlorine atoms are oxidised because they gain electrons.
CSodium ions are oxidised because they lose electrons.
DThis reaction does not involve oxidation or reduction.
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8Oct / Nov 2023 · Paper 11 · Q19Show mark scheme →
ANF3
BNH4+
CNO
DNO2+
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9Oct / Nov 2023 · Paper 12 · Q18Show mark scheme →
AChlorine is oxidised.
B$Cl^-$ ions are formed by loss of electrons.
C$Fe^{2+}$ ions have gained electrons.
D$Fe^{3+}$ ions are formed by oxidation.
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10May / June 2023 · Paper 11 · Q17Show mark scheme →
AOnly carbon is oxidised.
BOnly carbon is reduced.
COnly oxygen is oxidised.
DOnly oxygen is reduced.
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11May / June 2023 · Paper 11 · Q18Show mark scheme →
AMg + H₂SO₄ → MgSO₄ + H₂
BMgO + H₂SO₄ → MgSO₄ + H₂O
CMg(OH)₂ + H₂SO₄ → MgSO₄ + 2H₂O
DMgCO₃ + H₂SO₄ → MgSO₄ + H₂O + CO₂
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12May / June 2023 · Paper 12 · Q19Also set in Oct / Nov 2016 Paper 12Show mark scheme →
AChlorine is reduced by iron(II) ions.
BChlorine is the reducing agent.
CIron(II) ions are reduced by chlorine.
DIron(II) ions are the oxidising agent.
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13May / June 2023 · Paper 12 · Q20Show mark scheme →
Aacidified aqueous potassium manganate(VII); colourless to purple
Bacidified aqueous potassium manganate(VII); purple to colourless
Caqueous potassium iodide; colourless to purple
Daqueous potassium iodide; purple to colourless
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14Oct / Nov 2022 · Paper 11 · Q23Show mark scheme →
ACaCO3 + 2HCl → CaCl2 + H2O + CO2
BCu2+ + Zn → Cu + Zn2+
CFe2O3 + 3CO → 2Fe + 3CO2
DH2SO4 + Zn → ZnSO4 + H2
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15Oct / Nov 2022 · Paper 11 · Q25Show mark scheme →
Again, oxidised
Bgain, reduced
Close, oxidised
Dlose, reduced
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16Oct / Nov 2022 · Paper 12 · Q24Also set in Oct / Nov 2022 Paper 11Show mark scheme →
Acalcium carbonate to calcium oxide
Bcopper to brass
Cethene to poly(ethene)
Dsand to silicon
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17Oct / Nov 2022 · Paper 12 · Q25Show mark scheme →
AChlorine is the oxidising agent.
BIron gains electrons.
CIron is reduced.
DThis is not a redox reaction.
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18May / June 2022 · Paper 11 · Q23Show mark scheme →
AMn2+ and Cl –
BMn2+ and Cl 2
CMn6+ and Cl –
DMn6+ and Cl 2
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19May / June 2022 · Paper 11 · Q24Show mark scheme →
ACuO(s) + C(s) ⇌ CO(g) + Cu(s) | copper | copper oxide has given oxygen to carbon
BNa(s) + ½Cl₂(g) ⇌ NaCl(s) | sodium | sodium has lost an electron
CN₂(g) + 3H₂(g) ⇌ 2NH₃(g) | nitrogen | nitrogen has gained hydrogen
DZn(NO₃)₂(aq) + Mg(s) ⇌ Mg(NO₃)₂(aq) + Zn(s) | zinc | zinc has gained two electrons
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20May / June 2022 · Paper 12 · Q23Show mark scheme →
Ablue copper sulfate crystals turning to white powder when heated
Bcopper being deposited on the cathode during electrolysis
Cgreen gas being produced at the anode when sodium chloride is electrolysed
Dwhite precipitate forming when aqueous silver ions react with aqueous chloride ions
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21May / June 2022 · Paper 12 · Q24Show mark scheme →
Aoxidised, colourless
Boxidised, brown
Creduced, colourless
Dreduced, brown
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22Oct / Nov 2021 · Paper 11 · Q19Show mark scheme →
A1 and 2 only
B1 and 3 only
C2 and 3 only
D1, 2 and 3
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23Oct / Nov 2021 · Paper 11 · Q20Show mark scheme →
A1: NH4+ 2: NH4+
B1: NH4+ 2: NO2–
C1: NO2– 2: NH4+
D1: NO2– 2: NO2–
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24May / June 2021 · Paper 11 · Q20Show mark scheme →
A1 only
B2 only
C1 and 3
D2 and 3
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25May / June 2021 · Paper 12 · Q20Show mark scheme →
AX and Y are both reducing agents.
BX is an oxidising agent and Y is not a reducing agent.
CX is not a reducing agent and Y is an oxidising agent.
DX is not an oxidising agent and Y is a reducing agent.
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26Oct / Nov 2020 · Paper 12 · Q21Also set in Oct / Nov 2020 Paper 11Show mark scheme →
AThe change is reduction because there has been a gain of electrons.
BThe change is oxidation because there has been a loss of electrons.
CThe change is reduction because there has been a loss of electrons.
DThe change is oxidation because there has been a gain of electrons.
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27May / June 2020 · Paper 11 · Q18Show mark scheme →
ACu2+(aq) is oxidised to Cu(s) by gaining electrons.
BCu2+(aq) is reduced to Cu(s) by losing electrons.
CZn(s) is oxidised to Zn2+(aq) by losing electrons.
DZn(s) is reduced to Zn2+(aq) by gaining electrons.
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28May / June 2020 · Paper 11 · Q36Show mark scheme →
A1 only
B2 only
C1 and 2 only
D1, 2 and 3
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29May / June 2020 · Paper 12 · Q19Show mark scheme →
A1, 2 and 3
B1 and 2 only
C2 and 3 only
D3 only
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30Oct / Nov 2019 · Paper 11 · Q17Show mark scheme →
Athe oxidising agent is C(s); the reducing agent is H2O(g); the reaction is endothermic
Bthe oxidising agent is C(s); the reducing agent is H2O(g); the reaction is exothermic
Cthe oxidising agent is H2O(g); the reducing agent is C(s); the reaction is endothermic
Dthe oxidising agent is H2O(g); the reducing agent is C(s); the reaction is exothermic
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31Oct / Nov 2019 · Paper 12 · Q16Also set in Oct / Nov 2019 Paper 11Show mark scheme →
AC(s) + CO2(g) → 2CO(g)
BCl2(g) + 2I–(aq) → I2(aq) + 2Cl–(aq)
CMg(s) + CuO(s) → MgO(s) + Cu(s)
DZn(s) + 2H+(aq) → Zn2+(aq) + H2(g)
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32May / June 2019 · Paper 11 · Q20Show mark scheme →
Agas X: oxidising agent; gas Y: oxidising agent
Bgas X: oxidising agent; gas Y: reducing agent
Cgas X: reducing agent; gas Y: oxidising agent
Dgas X: reducing agent; gas Y: reducing agent
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33May / June 2019 · Paper 12 · Q20Show mark scheme →
Aoxygen gain, hydrogen loss, electrons loss
Boxygen gain, hydrogen loss, electrons gain
Coxygen loss, hydrogen loss, electrons loss
Doxygen loss, hydrogen gain, electrons gain
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34Oct / Nov 2018 · Paper 12 · Q19Show mark scheme →
AMg + 2HCl → MgCl2 + H2
BMgCO3 + 2HCl → MgCl2 + H2O + CO2
CMgO + 2HCl → MgCl2 + H2O
DMg(OH)2 + 2HCl → MgCl2 + 2H2O
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35May / June 2018 · Paper 11 · Q20Show mark scheme →
A1, 2 and 3
B1 and 2 only
C2 and 3 only
D3 only
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36May / June 2018 · Paper 12 · Q20Show mark scheme →
A1, 2 and 3
B1 and 2 only
C1 and 3 only
D2 and 3 only
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37May / June 2018 · Paper 12 · Q30Show mark scheme →
ACarbon is the oxidising agent.
BCarbon is the reducing agent.
CCopper(II) oxide is oxidised.
DCopper(II) oxide is the reducing agent.
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38Oct / Nov 2017 · Paper 11 · Q21Show mark scheme →
AIt becomes positively charged.
BIt combines with oxygen.
CIt gains an electron.
DIt gains a proton.
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39May / June 2017 · Paper 12 · Q18Show mark scheme →
AIt is a redox reaction.
BIt is exothermic.
CZinc is acting as a base.
DZinc is acting as a catalyst.
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40Oct / Nov 2016 · Paper 12 · Q27Also set in Oct / Nov 2016 Paper 11Show mark scheme →
ACaCO₃ → CaO + CO₂
B2C + O₂ → 2CO
CC + CO₂ → 2CO
DFe₂O₃ + 3CO → 2Fe + 3CO₂
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41May / June 2016 · Paper 11 · Q18Show mark scheme →
A2NH3 + H2SO4 → (NH4)2SO4
B2SO2 + O2 → 2SO3
C2KI + Cl2 → 2KCl + I2
DZn + H2SO4 → ZnSO4 + H2
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42May / June 2016 · Paper 11 · Q22Show mark scheme →
Abrown to colourless | no change
Bbrown to colourless | purple to colourless
Ccolourless to brown | no change
Dcolourless to brown | purple to colourless
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43May / June 2016 · Paper 12 · Q18Show mark scheme →
AElectrons are gained during the reaction.
BHydrogen is gained during the reaction.
CIt takes place at the negative electrode during electrolysis.
DOxygen is gained during the reaction.
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