AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Oxidation is the loss of electrons and reduction is the gain of electrons.
Full specification wording
Oxidation and reduction in terms of electrons (HT only): Oxidation is the loss of electrons and reduction is the gain of electrons.
At the higher tier, the definitions of oxidation and reduction expand beyond oxygen transfer to involve the movement of electrons.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 1 of 2
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
At the higher tier, the definitions of oxidation and reduction expand beyond oxygen transfer to involve the movement of electrons. This is often remembered using the acronym OILRIG: Oxidation Is Loss, Reduction Is Gain of electrons. In displacement reactions or electrolysis, metals and non-metals change their oxidation state by transferring electrons. For example, when magnesium reacts with copper(II) sulfate, the neutral magnesium atoms lose two electrons to form Mg²⁺ ions, meaning magnesium is oxidised. Simultaneously, the Cu²⁺ ions gain two electrons to form neutral copper atoms, meaning the copper ions are reduced. Understanding these half-equations is crucial for explaining the underlying ionic chemistry.
What earns the marks
- Define oxidation as the loss of electrons.
- Define reduction as the gain of electrons.
- Identify the species losing electrons in a given reaction as being oxidised.
- Identify the species gaining electrons in a given reaction as being reduced.
- Write balanced half-equations to demonstrate the transfer of electrons.
Common mistakes and how to put them right
Reversing the definitions of oxidation and reduction.
Put it right: Use the OILRIG mnemonic to remember Oxidation Is Loss, Reduction Is Gain of electrons.
Stating that the whole compound is reduced.
Put it right: Specify the exact ion that gains electrons, such as the copper(II) ion rather than copper sulfate.
Putting electrons on the wrong side of a half-equation.
Put it right: Electrons should be on the right side for oxidation and on the left side for reduction.
Exam tips
- Always write the charges on ions clearly, such as Fe²⁺ or Cl⁻, to help track electron movement.
- Split full ionic equations into two half-equations to easily identify which species is oxidised and which is reduced.
- Remember that spectator ions do not participate in electron transfer and can be ignored when identifying oxidation and reduction.
Try the lesson
The start of the Oxidation and reduction in terms of electrons (HT only): Oxidation is the loss of electrons and reduction is the gain of electrons. lesson, made from checked teaching notes for this specification point.
Have a go first
In terms of electrons, what happens to a substance when it is oxidised?
Listen
At the higher tier, the definitions of oxidation and reduction expand beyond oxygen transfer to involve the movement of electrons. This is often remembered using the acronym OILRIG: Oxidation Is Loss, Reduction Is Gain of electrons. In displacement reactions or electrolysis, metals and non-metals change their oxidation state by transferring electrons. For example, when magnesium reacts with copper(II) sulfate, the neutral magnesium atoms lose two electrons to form Mg²⁺ ions, meaning magnesium is oxidised. Simultaneously, the Cu²⁺ ions gain two electrons to form neutral copper atoms, meaning the copper ions are reduced. Understanding these half-equations is crucial for explaining the underlying ionic chemistry. A strong answer earns marks for these points. Define oxidation as the loss of electrons. Define reduction as the gain of electrons. Identify the species losing electrons in a given reaction as being oxidised. Identify the species gaining electrons in a given reaction as being reduced. A common slip: Reversing the definitions of oxidation and reduction. Instead, Use the OILRIG mnemonic to remember Oxidation Is Loss, Reduction Is Gain of electrons. Exam tip: Always write the charges on ions clearly, such as Fe²⁺ or Cl⁻, to help track electron movement.
See it
Key words
Say what each word means before you turn the card.
Oxidation
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Reduction
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Half-equations
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See every definition
- Oxidation
- The loss of electrons, remembered using the acronym OILRIG.
- Reduction
- The gain of electrons, remembered using the acronym OILRIG.
- Half-equations
- Balanced equations that demonstrate the transfer of electrons, with electrons on the right side for oxidation and on the left side for reduction.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
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