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The pH scale measures a solution’s acidity or alkalinity. The range for the pH scale is 0 (strong acid) to 14 (strong alkali).

• pH 0 – 2: strong acid, for example hydrochloric acid or sulfuric acid.
• pH 3 – 6: weak acid, for example ethanoic acid.
• pH 7: neutral
• pH 8 – 11: weak alkali, for example ammonia.
• pH 12 – 14: strong alkali, for example sodium hydroxide or potassium hydroxide.

Universal indicator solution or paper turns a range of colours, depending on the strength of the acid or alkali.

pH can be accurately measured using a pH meter or pH probe.

It gives a direct reading of the pH usually to one or two decimal places.