Base: definition in chemistry
Base: A substance that accepts hydrogen ions (H⁺) or produces hydroxide ions (OH⁻) in water, giving a pH above 7. Bases that dissolve in water are called alkalis.
Bases neutralize acids, forming a salt and usually water. Strong bases such as sodium hydroxide dissociate completely in water, while weak bases such as ammonia react with water only partly. Basic solutions turn red litmus blue and feel slippery, and concentrated ones can burn skin as badly as strong acids.
Examples
- Sodium hydroxide (NaOH) — used in drain cleaners
- Ammonia (NH₃) — in household glass cleaners
- Magnesium hydroxide (Mg(OH)₂) — milk of magnesia, an antacid
- Sodium bicarbonate (NaHCO₃) — baking soda, a mild base
On the periodic table
Oxides and hydroxides of metals on the left of the table, especially in groups 1 and 2, are basic, and the alkali metals are named for the strong alkalis they form.