Acids & Alkalis
Science: KS3, topic 2.2.3
Acids and Alkalis
Many chemicals can be classed as either acids or alkalis.
Acids
- Acids are a group of chemicals.
- Everyday acids often taste sharp or will sting if you get them in a cut.
- Laboratory acids have the hazard symbol ‘irritant’ or ‘corrosive’ on them.
Alkalis
- Alkalis are also a group of chemicals.
- Many soaps are alkalis and laboratory alkalis are also ‘irritant’ and ‘corrosive’.
- Alkalis can be thought of as the opposite of acids.
Universal indicators
- Indicators are a special type of chemical that will turn a different colour in acid or alkali conditions.
- Universal indicator can either be as paper or a solution.
- If you put universal indicator into an unknown solution, it can turn any colour of the rainbow to show you whether you have an acid or an alkali.
- Universal indicator will also show you how strong your acid or alkali is based on the colour.
Litmus paper
- Litmus paper is either blue or red in colour and will change colour to tell you whether you have an acid or alkali.
- If you have an acid, the paper will be red.
- If you have an alkali, the paper will be blue.
- Litmus paper cannot tell you how strong the acid or alkali is.
- Red litmus paper will not change colour in acid or neutral.
- Blue litmus paper will not change colour in alkali or neutral.
Test yourself on Acids & Alkalis
What colour does litmus paper turn in acid?
What colour does litmus paper turn in alkali?
Which of these are true of acids and alkalis?
A solution does not change the colour of red litmus paper or blue litmus paper. What type of solution is it?
A solution turns blue litmus paper red but does not change the colour of red litmus paper. What type of solution is it?