Acids and Alkalis
Many things around us are acids and many others are alkalis. Acids often taste sour, like lemon juice, vinegar and orange juice. Alkalis often feel soapy and slippery, like soap, toothpaste and baking soda. Some acids and alkalis can hurt our skin or make us sick, so we should never taste or touch them to find out what they are. Instead, scientists use a special paper called litmus paper to test them safely.
Using Litmus Paper
Litmus paper can be red or blue. It changes colour to show if a liquid is an acid or an alkali.
- An acid turns blue litmus paper red.
- An alkali turns red litmus paper blue.
Key idea / 要点
Acid turns blue litmus red. Alkali turns red litmus blue. Water does not change the colour.
Remember / 记住
- Never taste a liquid to test it.
- Lemon juice and vinegar are acids.
- Soap and toothpaste are alkalis.