Explain the following in terms of gain or loss of oxygen with two examples each. (a) Oxidation (b) Reduction

Oxidation reactions involve a substance gaining oxygen. A common way to identify these reactions is in their chemical equations.
In an oxidation reaction, oxygen is added to an element or compound, changing its chemical structure.
Let's look at two examples to understand this better.
In the reaction \(\text{2Mg} + \text{O}_2 \rightarrow \text{2MgO}\), magnesium \(\text{Mg}\) gains oxygen to form magnesium oxide \(\text{MgO}\). This is an example of oxidation because oxygen is added.
Another example is the formation of carbon dioxide. When carbon \(\text{C}\) reacts with oxygen \(\text{O}_2\), it forms carbon dioxide \(\text{CO}_2\). The chemical reaction is written as \(\text{C} + \text{O}_2 \rightarrow \text{CO}_2\). Here, carbon is oxidized as it gains oxygen.

Reduction reactions involve a substance losing oxygen. These reactions remove oxygen from an element or compound.
Reduction can be observed in various chemical reactions where the final product has less oxygen.
Consider the reaction \(\text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O}\). Here, copper(II) oxide \(\text{CuO}\) loses oxygen to form copper \(\text{Cu}\). This is a reduction reaction because oxygen is removed from the copper compound.
Another example is the reduction of iron(III) oxide. When iron(III) oxide \(\text{Fe}_2\text{O}_3\) reacts with carbon monoxide \(\text{CO}\), it forms iron \(\text{Fe}\) and carbon dioxide \(\text{CO}_2\). The reaction is written as \(\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2\). Here, iron(III) oxide loses oxygen and is reduced to iron.

Understanding the gain or loss of oxygen helps us identify oxidation and reduction reactions. When a substance gains oxygen, it undergoes oxidation.

• For example, turning magnesium \(\text{Mg}\) into magnesium oxide \(\text{MgO}\) by gaining oxygen is oxidation.
• Another example is forming carbon dioxide \(\text{CO}_2\) from carbon \(\text{C}\) and oxygen \(\text{O}_2\).

In contrast, a substance undergoes reduction when it loses oxygen.

For instance, converting copper(II) oxide \(\text{CuO}\) to copper \(\text{Cu}\) by losing oxygen is a form of reduction.

Similarly, reducing iron(III) oxide \(\text{Fe}_2\text{O}_3\) to iron \(\text{Fe}\) involves losing oxygen.

Oxidation and reduction always happen together: when one substance gains oxygen, another loses it. This dual process is called a redox reaction.