The Swedish chemist, Arrhenius proposed the following definition of an acid.
An acid is a substance which ionises or dissociates in water to produce hydrogen ions,
.
Hydrochloric acid
Aqueous hydrochloric acid,
As the gas dissolves in water, the hydrogen chloride molecule reacts with water and ionises to produce hydrogen ion,
The hydrogen ion then attaches itself to a water molecule to form the hydroxonium ion,
Hence, the overall equation for the ionisation of hydrogen chloride is as follows.
For convenience, we will be referring hydroxonium ion as hydrogen ion.
The ionisation of hydrochloric acid in water can be represented as follows.
Other acids ionise similarly in water.
Nitric acid
The product is hydrogen ion and nitrate ion.
Sulphuric acid
The product is hydrogen ion and sulphate ion.
Phosphoric acid
The product is hydrogen ion and phosphate ion.