Summary
Many substances we use every day are acids or bases. Acids, like lemon juice or vinegar, taste sour. Bases, like soap or baking soda, feel slippery and taste bitter. To tell how acidic or basic a substance is, we use the pH scale, which runs from 0 to 14.
On the pH scale, 7 is neutral (pure water). Below 7 the substance is acidic, and the lower it is, the stronger; above 7 it is basic. To measure pH we use indicators, which change colour, like litmus paper. When an acid is mixed with a base in the right amount, they neutralise: the result is water and a salt, and it stops being corrosive.
Key points
- Acids taste sour (lemon, vinegar); bases taste bitter and feel slippery (soap).
- The pH scale measures acidity, from 0 to 14.
- pH 7 = neutral (water); below 7 = acid; above 7 = base.
- The further from 7, the stronger the acid or base.
- Indicators (litmus paper) change colour depending on the pH.
- An acid and a base neutralise and form water and a salt.
- Strong acids and bases are corrosive: handle them with care.