When certain metals react with oxygen in the presence of moisture they corrode. When a spanner, consisting mainly of iron is left outside in the rain, a thin layer of a reddish-brown powder starts to form on its surface within a few weeks.

Here are the answers to Question 6:

6.1 The process is rusting.

6.2 The common name for the reddish-brown powder is rust.

6.3 Three ways to prevent the process are:

• Painting the iron surface.
• Oiling or greasing the iron surface.
• Galvanizing (coating with zinc).

6.4 The balanced chemical equation for the reaction is:

$$4\text{Fe(s)} + 3\text{O}_2\text{(g)} + 6\text{H}_2\text{O(l)} \rightarrow 2\text{Fe}_2\text{O}_3 \cdot 3\text{H}_2\text{O(s)}$$