What is neutralisation?
Neutralisation is the chemical reaction between an acid and an alkali that produces salt and water. During the reaction the acidic and alkaline properties cancel each other out, and the mixture moves towards a pH of 7 (neutral).
Key idea
The word equation for neutralisation is:
acid + alkali → salt + water
For example: hydrochloric acid + sodium hydroxide → sodium chloride + water.
What happens to the pH?
If you slowly add an alkali to an acid, the pH rises from below 7 towards 7. When exactly enough alkali is added, the solution becomes neutral. Adding too much alkali would make the solution alkaline (pH above 7). An indicator can be used to show when neutralisation is complete.
Neutralisation in daily life
Neutralisation is very useful in everyday situations:
- Indigestion — antacid tablets contain a mild alkali to neutralise excess stomach acid.
- Bee stings — a bee sting is acidic, so baking soda (an alkali) helps.
- Wasp stings — a wasp sting is alkaline, so vinegar (an acid) helps.
- Farming — farmers add lime (an alkali) to neutralise acidic soil.
Example
When you have a sore stomach from too much acid, an antacid tablet neutralises the extra acid and eases the pain.