Why some metals tarnish
We have seen that articles made of iron — nails, barbed wire, cutting tools — tarnish quickly. Yet we have also seen that ornaments made of gold do not tarnish however long they are kept.
The question
Have you ever asked why? Both are metals and both are exposed to the air — so why does one tarnish and the other not?
The answer is the reactivity of the metal. Some metals react very readily; others hardly react at all.
Four things to investigate
Studying the reactions metals give with air, water and dilute acids will give you an answer. To those we add the reactions metals give with the salt solutions of other metals.
- Metals with air
- Metals with water
- Metals with dilute acids
- Metals with the salt solutions of other metals
All of it leads to one place
Put these four sets of observations together, arrange the metals in order of their reactivity, and what you have is the activity series — one of the most useful tools in chemistry.
In this section we look at the reactions with air and water; in the next, at acids and salt solutions.