Acids are a group of chemicals that taste sour, turn  litmus paper red and react with metals to form salts.

Acids release hydrogen ions, H⁺ in solution.

Bases are a group of chemicals that feel soapy to touch. They behave in an opposite manner to acids.

Alkalis are soluble bases.

Alkalis turn red litmus blue.

Alkalis release hydroxide ions, OH^-, in solution.

Neutral substances, such as water, are neither acidic or alkaline.

The strength of an acid is measured using a scale called the pH scale. The numbers go from 0 to 14.

An acidic solution has a pH number less than 7.

An alkaline solution has a pH number greater than 7.

A neutral solution has a pH number of exactly 7.

To find the pH number of any solution you use universal indicator. Universal indicator is a mixture of dyes that change colour depending on what they have been placed in.

A neutralisation reaction occurs when you add an acid to an alkali - they cancel one another out. A salt and water are the two products of neutralisation.