The pH Scale
The pH scale is a scale from 0 to 14, which shows how
acidic or basic a substance is. Acidic substances have a pH less than 7, basic substances have a pH over 7, and neutral substances
have a pH of 7. To measure the pH of a solution you can use either a pH indicator or pH paper.
Indicators
Not all indicators determine the pH of a substance,
but they can determine whether a substance is acidic, basic or neutral. Acid-base indicators indicate when an acid or base
is present by changing their colour. Some indicators occur naturally in dyes in plants, while others are synthetic. Litmus
for example is a natural indicator. It comes from lichens. In an acidic solution, litmus turns red and in a basic solution
it turns blue. Phenol red is a synthetic indicator. In acidic solutions it turns yellowy-orange and in a basic solution it
turns red.
Most indicators have only two colours. Universal indicators
are a mixture of several different indicators. It can determine the pH of a solution by the variety of colours it can turn.
For example if a substance with a pH of 7 was tested with a universal indicator it would turn green, and if the substance
had a pH of 4 the universal indicator would turn orange.
pH paper can also be used to test the pH of a substance.
The pH paper is simply dipped into the solution and the colour of the paper is matched the pH chart.
