The non metalic ions of the acid and the metal ions of the base form the salt. The salt ions normally stay in solution. The salt crystalizes out when the water is removed. Some salts are insoluble. They will precipitate out when the acid and base are added together.
Acidity is measured on a scale called pH .
The value of pH determines how acidic or basic a solution is. There are chemicals that change colour at different pH values. These are called indicators . One of the most famous is Litmus . Oxides Oxides are compounds containing Oxygen.