Acidic, neutral or alkaline?
Many liquids look the same: clear and watery. Scientists tell them apart with litmus paper, a strip that changes colour. There are two kinds, blue and red. An acidic solution, such as lemon juice or vinegar, turns blue litmus paper red. An alkaline solution, such as soapy water or baking soda in water, turns red litmus paper blue. A neutral solution, such as sugar water, salt water or pure water, changes neither strip. So the strip tells us the group, and the three groups are acidic, neutral and alkaline. Neutral does not mean safe to drink: we never taste a liquid to test it. Vinegar is only a weak acid, and we still handle it with care.
| Group | Blue litmus paper | Red litmus paper |
|---|---|---|
| acidic | turns red | stays red |
| neutral | stays blue | stays red |
| alkaline | stays blue | turns blue |
Predict and sort. With a grown-up, write the names of six kitchen liquids on cards: lemon juice, vinegar, soapy water, baking soda in water, sugar water and plain water. Before testing anything, put each card in a group you think is right: acidic, neutral or alkaline. Keep the cards for the next lesson to see how many you guessed. Do not taste or smell anything.