The pH scale: acids and bases
What is pH?
Scales are used in measurement. The pH scale is used to measure the strength of an acid or a base.
Strong acid: pH is between 0 and 3.
- A pH of less than 7 indicates that the substance is an acid.
- A pH of more than 7 indicates that the substance is a base.
- If the pH is 7, the substance is said to be neutralóneither an acid nor a base.
Weak acid: pH is between 3 and 7.
Strong base: pH is between 11 and 14.
Weak base: pH is between 7 and 11.
- The lower the pH, the more acidic a substance is.
- The higher the pH, the more basic a substance is.
Safe handling of acids and bases
Strong acids and bases can be dangerous if they are not handled correctly. Clean up spills of acids or bases immediately.
When using acids or bases, be careful not to spill any on yourself or your clothes! If you do, wash thoroughly under running water immediately. Continue rinsing for at least five minutes.
Testing for acids and bases
Acids and bases can be detected by using a group of chemicals called indicators. There are many naturally occurring indicators, such as red cabbage, blueberries and cherries. Litmus is made from lichen, but many indicators used today are synthetic.
A simple indicator to use is litmus paper, which can be red or blue.
- In an acid, red or blue litmus paper is red.
- In a base, red or blue litmus paper is blue.
Universal indicator can be used in paper or liquid form. The colour of the indicator should be compared with a colour chart to determine the pH of a substance.