The pH scales measures the acidity or alkalinity of a solution. Acids and bases have a wide variety of uses and can react together in neutralisation reactions.
Neutralisation is the reaction of an acid with a base that results in the pH moving towards seven. It is a useful process that occurs in everyday life such as in the treatment of acid indigestion and the treating of acidic soil by adding lime.
When an acid is neutralised, its pH increases towards seven. When an alkali is neutralised, its pH decreases towards seven.
Several different bases can neutralise acids, and water is always produced as a result of these reactions.
\[Acid + alkali \to salt + water\]
\[Acid + metal\,oxide \to salt + water\]
Metal oxides and alkalis are two types of base. Basic substances neutralise acids, resulting in the pH of the acid increasing towards 7, and water being produced. A soluble base dissolves in water to form an alkali.
To name the salt, the metal ion from the alkali (or base) replaces the hydrogen ion from the acid - (alkali to front, acid to back). For example:
\[\begin{array}{l} \text{Hydrochloric acid} + \text{sodium hydroxide} \to \\ \text{sodium chloride} + \text{water} \end{array}\]
| Acid name | Salt name ending |
|---|---|
| Hydrochloric acid | ...chloride |
| Sulfuric acid | ...sulfate |
| Nitric acid | ...nitrate |
During every neutralisation reaction, water is formed.