What we know about pH indicators

1. Only a small amount of indicator is needed for testing

2. Indicators weak acids or bases

2.1. Some fruits are acidic

2.2. Some fruits are alkali

3. Indicators change colour when in contact with acid or alkali

3.1. Indicators that change to a single colour in acidic/alkali solution

3.2. Universal indicators which change into many colours in solutions with different pH

4. Indicators change colours immediately in contact with acids or bases