Acids, Bases and Salts

An acid produces hydrogen ions in water. A base produces hydroxide ions in water. This is why dry HCl gas does not change dry litmus, but hydrochloric acid solution does.

Indicators show whether a solution is acidic or basic. Litmus, methyl orange and phenolphthalein are common indicators. pH tells how acidic or basic a solution is: lower pH means stronger acidity and higher pH means stronger basic nature.

When an acid reacts with a base, salt and water are formed. This is neutralisation. For example, hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water.

Common salt is sodium chloride. It is a starting material for many useful substances, including sodium hydroxide, bleaching powder, washing soda and baking soda. Each has its own preparation, properties and uses.