Acids and alkalies.

There are very many different chemicals - so many that it’s impossible to study them all. To make things simpler, scientists Put chemicals which behave the same way into groups or sets. You Have already met the set of metals. Acids and alkalis are two More of these chemical sets.

You can find out if a substance is an acid, or an alkali, by dissolving it and adding universal indicator. The diagram shows you how to do this.

The indicator's colour changes if acid or alkali is added to it. And so, by matching the indicator colour to a colour chart. you can find out what kind of substance has been added.

When acids and alkalis are mixed, they cancel each other out, You can use indicator to show this also.

The experiment on the right shows what happens when acid is added to alkali with indicator in it. At the beginning, before any acid has been added, the indicator is violet. Each time acid is added, it cancels out some of the alkali, this makes the indicator colour gradually change. Eventually the indicator goes green. Then the solution is neutral (neither acid nor alkali). Exactly the right amount of acid has been added to cancel out or neutralize all the alkali.