Indicators

When an acid is dissolved in water we get an acidic solution. When a base dissolves in water it is an alkali and makes an alkaline solution. If a solution is neither acidic nor alkaline it is neutral. Pure water is neutral, and so is paraffin.

Indicators are substances that change colour when they are added to acidic or alkaline solutions. Litmus, phenolphthalein, and methyl orange are all indicators that are commonly used in the laboratory.

Litmus

Litmus indicator solution turns red in acidic solutions and blue in alkaline solutions - and it turns purple in neutral solutions.

Litmus paper is usually more reliable, and comes as red litmus paper and blue litmus paper. The table shows the colour changes it can make.

The table above shows the colour changes it can make.