Salts a wide range of chemical compounds including common salt. The scientific definition of a salt is a compound formed when the hydrogen of an acid has been replaced by a metal; a rule is that when an acid reacts with an alkali the product is a salt plus water. For example, the formula of hydrochloric acid is HCl—one atom of hydrogen and one of chlorine. The acid reacts with sodium, Na, to make common salt or sodium chloride, NaCl. The hydrogen has been replaced by sodium. In this case the hydrogen is released as a gas. For an example of a reaction between an acid and a base, one may again take hydrochloric acid, this time reacting with caustic soda or sodium hydroxide, NaOH—one atom each of sodium, oxygen, and hydrogen. The reaction is:
