What is oxidation, in terms of electrons?

loss of electrons. OIL: Oxidation Is Loss.

2Mg + O₂ → 2MgO. What happens to the magnesium?

It is oxidised. It gains oxygen (and loses electrons).

What happens to a reducing agent during a reaction?

It is oxidised. It gives away electrons, so it is itself oxidised.

Fe₂O₃ + 3CO → 2Fe + 3CO₂. Which substance is reduced?

iron(III) oxide. It loses its oxygen.

What does the (II) show in copper(II) oxide?

The copper has an oxidation number of +2. The copper is present as Cu²⁺.

2Na + Cl₂ → 2NaCl. What happens to the chlorine?

It is reduced. Each chlorine atom gains an electron to become Cl⁻.

Oxidation and reduction · Cambridge IGCSE Combined Science

In plain words

Oxidation first meant gaining oxygen, as when iron rusts, and reduction meant losing it. Chemists then spotted what is really going on underneath: electrons moving. A substance that loses electrons is oxidised; one that gains electrons is reduced. One can't happen without the other, so the pair is called redox.

Three things to know

Oxidation is gain of oxygen, or loss of electrons. Reduction is loss of oxygen, or gain of electrons.
An oxidising agent oxidises something else and is itself reduced. A reducing agent reduces something else and is itself oxidised.
A Roman numeral in a name gives the oxidation number of the metal: iron(III) oxide contains Fe³⁺.

Worked example

Zn + Cu²⁺ → Zn²⁺ + Cu. Which substance is oxidised?

Zinc starts as an atom, Zn, and ends as an ion, Zn²⁺.
To become 2+ it must have lost two electrons.
Losing electrons is oxidation, so zinc is oxidised (and the copper ions are reduced).

Tips and tricks

OIL RIG: Oxidation Is Loss, Reduction Is Gain. It's about electrons.
The agent is the opposite of what happens to it: the thing that gets oxidised is the reducing agent.

6 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Oxidation and reduction: 6 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

What is oxidation, in terms of electrons?
- gain of electrons
- loss of electrons (the answer)
- sharing of electrons
- no change in electrons
OIL: Oxidation Is Loss.
2Mg + O₂ → 2MgO. What happens to the magnesium?
- It is oxidised. (the answer)
- It is reduced.
- It is neutralised.
- It is decomposed.
It gains oxygen (and loses electrons).
What happens to a reducing agent during a reaction?
- It is reduced.
- It is oxidised. (the answer)
- It is unchanged.
- It is a catalyst.
It gives away electrons, so it is itself oxidised.
Fe₂O₃ + 3CO → 2Fe + 3CO₂. Which substance is reduced?
- iron(III) oxide (the answer)
- carbon monoxide
- iron
- carbon dioxide
It loses its oxygen.
What does the (II) show in copper(II) oxide?
- There are two copper atoms.
- There are two oxygen atoms.
- The copper has an oxidation number of +2. (the answer)
- It is the second oxide discovered.
The copper is present as Cu²⁺.
2Na + Cl₂ → 2NaCl. What happens to the chlorine?
- It is oxidised.
- It is reduced. (the answer)
- It loses electrons.
- Nothing.
Each chlorine atom gains an electron to become Cl⁻.

6 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

4 questions, 8 marks. Write your answers on paper, then check them.

Oxidation and reduction

Cambridge IGCSE Combined Science 0653 · 8 marks · papermunch.org

Name ______________________________ Date ______________

CuO + H₂ → Cu + H₂O. State which substance is oxidised and which is reduced.[2]
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Hydrogen is oxidised (it gains oxygen). Copper(II) oxide is reduced (it loses oxygen).
I got this one
Define oxidation and reduction in terms of electrons.[2]
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Oxidation is the loss of electrons. Reduction is the gain of electrons.
I got this one
Mg + Cu²⁺ → Mg²⁺ + Cu. State which substance is oxidised, and explain why.[2]
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Magnesium: it loses two electrons to become Mg²⁺.
I got this one
In the reaction above, identify the oxidising agent and explain your choice.[2]
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Cu²⁺ (copper ions): it takes electrons from the magnesium and is itself reduced.
I got this one

Answers: Oxidation and reduction

1. Hydrogen is oxidised (it gains oxygen). Copper(II) oxide is reduced (it loses oxygen).
2. Oxidation is the loss of electrons. Reduction is the gain of electrons.
3. Magnesium: it loses two electrons to become Mg²⁺.
4. Cu²⁺ (copper ions): it takes electrons from the magnesium and is itself reduced.