Lesson 3, Topic 3
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6.4.2 Defining Reduction (Demo)

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Remember that reduction and oxidation occur in a redox reaction.

The word redox is “created” from the words reduction and oxidation. Redox shows that oxidation and reduction always take place together.

Take a look at the reaction between copper(II) oxide and hydrogen:

copper(II)oxide plus hydrogen produces copper plus water

You will notice that H2 gains oxygen to become H2O. Of course, the process is oxidation.

Now observe the CuO and Cu part of the equation;

Copper(II) oxide, CuO loses oxygen to form copper, Cu.


When a substance loses oxygen, we say the substance has been reduced.
Reduction is the loss of oxygen.

cooper(II) oxide plus hydrogen gives copper plus water


Info: As you define oxidation as the gain of oxygen, it can also be defined as the loss of hydrogen. In the same way, you define reduction as the loss of oxygen, you can also see it as the gain of hydrogen.

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