AS Level Chemistry chapter 6: Electrochemistry MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

22 exam-style questions on Electrochemistry, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

22 questions · 1 topics · 10 per test

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What chapter 6 covers

Ten Electrochemistry questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. Calcium hydride reacts with water: CaH2(s) + 2H2O(l) → Ca(OH)2(aq) + 2H2(g). Which statement is correct?

  1. A
    it is not a redox reaction because no element changes its oxidation number
  2. B
    hydrogen in CaH2 is reduced from +1 to 0 and hydrogen in water is oxidised from −1 to 0
  3. C
    calcium is oxidised from 0 to +2 and hydrogen in water is reduced
  4. D
    hydrogen in CaH2 is oxidised from −1 to 0 and hydrogen in water is reduced from +1 to 0
Show answer

Answer: D. In a metal hydride hydrogen is −1 (Ca is +2 throughout). The H− loses electrons to form H2 while H(+1) in water gains them, so hydrogen is both oxidised and reduced.

2. What is the systematic name of NaClO?

  1. A
    sodium chlorate(V)
  2. B
    sodium chloride(I)
  3. C
    sodium chlorite
  4. D
    sodium chlorate(I)
Show answer

Answer: D. In ClO− oxygen is −2, so chlorine is +1: chlorate(I). NaClO3 is sodium chlorate(V). The Roman numeral gives the oxidation number of chlorine.

3. Chlorine reacts with hot concentrated aqueous sodium hydroxide: 3Cl2 + 6NaOH → 5NaCl + NaClO3 + 3H2O. Chlorine changes from oxidation number 0 to

  1. A
    −1 and +5
  2. B
    +1 and +5
  3. C
    −1 and +7
  4. D
    −1 and +1
Show answer

Answer: A. Cl is −1 in NaCl and +5 in NaClO3, a disproportionation. Electrons balance: five Cl atoms each gain one electron, one Cl atom loses five. −1 and +1 is the cold, dilute reaction.

4. What is the name of K2MnO4?

  1. A
    potassium manganate(IV)
  2. B
    potassium manganate(V)
  3. C
    potassium manganate(VI)
  4. D
    potassium manganate(VII)
Show answer

Answer: C. 2(+1) + Mn + 4(−2) = 0, so Mn = +6: potassium manganate(VI). Potassium manganate(VII) is KMnO4, where the single K makes Mn +7.

5. Which species can act only as a reducing agent, and never as an oxidising agent?

  1. A
    I−
  2. B
    H2O2
  3. C
    Fe2+
  4. D
    SO2
Show answer

Answer: A. Iodine is already at its lowest oxidation number (−1) in I−, so it can only lose electrons. Fe2+ (+2), O in H2O2 (−1) and S in SO2 (+4) are in intermediate states and can be oxidised or reduced.

6. In which species does nitrogen have an oxidation number of +3?

  1. A
    N2O
  2. B
    NH4+
  3. C
    NO3−
  4. D
    NO2−
Show answer

Answer: D. In NO2−: N + 2(−2) = −1, so N = +3. Nitrogen is −3 in NH4+, +1 in N2O and +5 in NO3−.

7. In the reaction 2Fe3+ + 2I− → 2Fe2+ + I2, which species is the oxidising agent?

  1. A
    I−
  2. B
    Fe2+
  3. C
    Fe3+
  4. D
    I2
Show answer

Answer: C. The oxidising agent gains electrons and is itself reduced. Fe3+ gains an electron to become Fe2+, so Fe3+ is the oxidising agent; iodide loses electrons and is the reducing agent.

8. What is the oxidation number of sulfur in the thiosulfate ion, S2O32−?

  1. A
    +4
  2. B
    +6
  3. C
    +2
  4. D
    −2
Show answer

Answer: C. Three oxygens contribute −6. The overall charge is −2, so 2S + (−6) = −2, 2S = +4, S = +2. Sulfur is +4 in SO32− and +6 in SO42−; thiosulfate is neither.

9. Which reaction is NOT a redox reaction?

  1. A
    Cl2 + 2Br− → 2Cl− + Br2
  2. B
    2Mg + CO2 → 2MgO + C
  3. C
    2CrO42− + 2H+ → Cr2O72− + H2O
  4. D
    Cr2O72− + 14H+ + 6Fe2+ → 2Cr3+ + 6Fe3+ + 7H2O
Show answer

Answer: C. Chromium is +6 in both CrO42− and Cr2O72−, and no other element changes oxidation number, so this is an acid–base change, not redox.

10. What is the formula of sodium nitrate(III)?

  1. A
    NaNO3
  2. B
    Na3N
  3. C
    NaNO
  4. D
    NaNO2
Show answer

Answer: D. Nitrogen +3 with oxygen −2 and an overall −1 charge gives NO2−, so NaNO2. NaNO3 is sodium nitrate(V).

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Ways to practise this chapter

Electrochemistry: questions students ask

How many Electrochemistry MCQs are there?

22, each with the answer and a short explanation, across 1 topics: Redox processes: electron transfer and changes in oxidation number (oxidation state). Every chapter test draws ten of them, so you can take it many times.

Is the AS Level Chemistry chapter 6 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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