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Leaving Cert Chemistry: Oxidation and reduction

How often Oxidation and reduction comes up on the Chemistry papers, every year it was asked, and questions to try.

HL Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker

OL Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

June 2027 is the first exam on the new Chemistry course. These come from the 2016–2026 papers, so read them as a guide.

Oxidation and reduction, Higher Level(9 marks)

Quick ones on Oxidation and reduction.

(a)Oxidation number of oxygen in hydrogen peroxide, H2O2?
  1. -2
  2. -1
  3. 0
(b)Colour change when acidified potassium manganate(VII) acts as an oxidising agent?
  1. Colourless to purple
  2. Orange to green
  3. Purple to colourless
(c)Oxidation number of manganese in the MnO4- ion?
  1. +7
  2. +4
  3. +2
Show the answers

(a) -1

(b) Purple to colourless

(c) +7

Your turn: Higher Level questions on Oxidation and reduction.

Higher Level

Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q11(b)
2025Q1, Q4(k)
2024Q10(a)
2023Q1, Q4(j)
2022Q11(a)
2021Q1, Q3
2019Q4(d)
2018Q4(f), Q4(g)
2017Q1, Q4(d), Q4(i)
2016Q10(b)

Links open the State Examinations Commission’s paper for that year.

More Oxidation and reduction questions

Oxidation and reduction, 2 marks

Oxidation number of manganese in manganese dioxide, MnO2?

  1. +2
  2. +7
  3. +4
Show the answer

+4

Two oxygens give 2 x (-2) = -4. The compound is neutral, so Mn = +4.

Oxidation and reduction, 2 marks

Oxidation number of carbon in carbon dioxide, CO2?

  1. +2
  2. +4
  3. -4
Show the answer

+4

Two oxygens at -2 each total -4, so carbon must be +4 for a neutral molecule.

Oxidation and reduction, 2 marks

In 2Mg + O2 -> 2MgO, which substance is the reducing agent?

  1. Magnesium
  2. Oxygen
  3. Magnesium oxide
Show the answer

Magnesium

Magnesium loses electrons (0 to +2) and gives them to oxygen. The substance that gives electrons is the reducing agent.

Ordinary Level

Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q10(a)
2025Q9
2024Q4(j)
2023Q10(b)
2022Q9
2021Q10(b)
2019Q4(d)
2018Q9
2017Q4(c)
2016Q7

Links open the State Examinations Commission’s paper for that year.

More Oxidation and reduction questions

Oxidation and reduction, 2 marks

Reduction in terms of electrons?

  1. Loss of electrons
  2. Gain of protons
  3. Gain of electrons
Show the answer

Gain of electrons

Remember OIL RIG: Oxidation Is Loss, Reduction Is Gain of electrons.

Oxidation and reduction, 2 marks

What is a reducing agent?

  1. A substance that is unchanged by a reaction
  2. A substance that gives away electrons and is itself oxidised
  3. A substance that accepts electrons and is itself reduced
Show the answer

A substance that gives away electrons and is itself oxidised

A reducing agent causes reduction in something else by giving it electrons. Zinc and magnesium are examples.

Oxidation and reduction, 2 marks

Oxidation in terms of oxygen?

  1. Gain of oxygen
  2. Loss of oxygen
  3. Gain of hydrogen
Show the answer

Gain of oxygen

When magnesium burns it gains oxygen to form magnesium oxide, so the magnesium is oxidised.

Other Chemistry topics

All of Leaving Cert Chemistry