base

In chemistry, a substance that accepts hydrogen ions, or protons. A base reacts with an acid, neutralizing it to form a salt: acid + base → salt + water. Metal oxides and metal hydroxides are bases; examples include copper oxide and sodium hydroxide. Bases can contain negative ions such as the hydroxide ion (OH⁻), which is the strongest base, or be molecules such as ammonia (NH₃). Ammonia is a weak base, as only some of its molecules accept protons.

OH⁻ + H⁺_(aq) → H₂O_(l)

NH₃ + H₂O → NH₄⁺ + OH⁻

Bases that dissolve in water are called alkalis.

Inorganic bases are usually oxides or hydroxides of metals, which react with dilute acids to form a salt and water. Many carbonates also react with dilute acids, additionally giving off carbon dioxide.