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Reduction

Reduction is a change in which a substance loses oxygen, gains hydrogen, or gains electrons.

In one line: Reduction: remove oxygen, add hydrogen, gain electrons.

Understand it

Reduction is the opposite side of oxidation. In school chemistry, it is seen when oxygen is removed from a compound or electrons are gained by a substance. Reduction and oxidation usually appear together in the same reaction.

Example

When copper(II) oxide turns into copper in the presence of hydrogen, copper(II) oxide is reduced.

Rule to remember

Reduction = removal of oxygen, addition of hydrogen, or gain of electrons.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1CuO + H₂ → Cu + H₂O.
2Copper(II) oxide loses oxygen, so it is reduced.

Method you can reuse

1Look for oxygen removal or hydrogen addition.
2Check electron gain if given.
3Name the substance as reduced.

Sketch it in your answer

Show the substance before and after reaction with oxygen removed or electrons gained.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

If a substance gains electrons in a reaction, what is this change called?

Think first, then show answer

This change is called reduction because gaining electrons is one of the main signs of reduction.

Common wrong answer

Calling it oxidation because the overall reaction has two substances reacting. The correct clue is oxygen loss or electron gain.

Don't mix this up

Students sometimes confuse reduction with loss of mass or with decomposition; those are different ideas.

Exam tip

If oxygen is removed from a compound, write reduction confidently and then support it with the reason.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

A question may ask which substance is reduced, or whether oxygen is removed or electrons are gained.

1
Enough for 1 mark
Reduction is a change in which a substance loses oxygen, gains hydrogen, or gains electrons.
2
Add for 2 marks
Example: When copper(II) oxide turns into copper in the presence of hydrogen, copper(II) oxide is reduced.
3
Add for 3 marks
Reduction is the opposite side of oxidation.

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