A base is any substance that increases the concentration of the OH - ion when it dissolves in water. These definitions tie the theory of acids and bases to a simple laboratory test for acids and bases. Compounds that contain hydrogen bound to a nonmetal are called nonmetal hydrides . Metal hydrides , on the other hand, contain hydrogen bound to a metal. A similar pattern can be found in the chemistry of the oxides formed by metals and nonmetals.
Nonmetal oxides dissolve in water to form acids.
CO 2 dissolves in water to give carbonic acid, SO 3 gives sulfuric acid, and P 4 O 10 reacts with water to give phosphoric acid. Metal oxides , on the other hand, are bases. Metal oxides therefore fit the operational definition of a base. We see the same pattern in the chemistry of compounds that contain the OH, or hydroxide, group. The table below summarizes the trends observed in these three categories of compounds.