- Most oxides of metal, especially alkali and alkaline earth metals, are basic oxides.
- Basic oxides that dissolve in water are called alkalis.
- A basic oxide is an oxide that shows basic properties in opposition to acidic oxides and that either
- reacts with water to form an alkali; or
- reacts with an acid to form a salt.
- Sodium oxide, which reacts with water to produce sodium hydroxide
- Magnesium oxide, which reacts with hydrochloric acid to form magnesium chloride
- Copper(II) oxide, which reacts with nitric acid to form copper nitrate
- Most non-metal oxides dissolve in water to form acids, and are called acidic oxides.
- An acidic oxide is an oxide that either
- reacts with water to form an acid; or
- reacts with a base to form a salt.
- Carbon dioxide which reacts with water to produce carbonic acid.
- Sulfur dioxide, which does not form the non-existent sulfurous acid but does react with bases to form sulfites.
- Silicon dioxide, which does not react with water but will react with bases to form silicates
Not all oxide of non-metal are acidic oxide. For example, carbon monoxide (CO) is neutral.
- The metal oxides that can behave as both acids and bases and are said to be amphoteric oxides.
- Examples of amphoteric oxides are lead oxide, aluminium oxide and zinc oxide.