The pH Scale
Science: KS3, topic 2.2.6
The pH scale
Acids and alkalis all have a pH, which is a number that tells you how strong the acid or alkali is. It starts at zero and goes up to 14.
The pH scale
- Anything below 7 is an acid.
- The lower the number, the stronger the acid.
- Anything above 7 is an alkali.
- The higher the number, the stronger the alkali. pH 7 is neutral – these chemicals are neither acid nor alkali.
- Pure water has a pH of 7.
- Each pH number is also given a colour.
- The colours on the pH scale are what colour the chemical will go if ‘universal indicator’ is added.
Common acids
- Lemon juice.
- Hydrochloric acid.
- Sulfuric acid.
- Nitric acid.
- Vinegar.
Common alkalis
- Soap.
- Toothpaste.
- Ammonia.
- Sodium hydroxide.
- Lithium hydroxide.
- Calcium oxide.
Test yourself on The pH Scale
Which of these is an acid?
Which of these is an alkali?
Name the three types of substance on the pH scale, grouped by their pH number.
Substance A has a pH of 1. Substance B has a pH of 4. Which statement is correct?