Bases are chemical substances that have a bitter taste, are soapy to touch, and turn red litmus blue. A base is a substance that dissolves in water to produce hydroxide ions (OH–) in the solution.
NaOH(s) → Na+(aq) + OH–(aq)
Classification of Bases:
Bases are of two types:
A base that completely ionizes in water and thus produces a large amount of hydroxide ions is called a strong base.
Examples: Sodium hydroxide and potassium hydroxide.
A base that is partially ionized in water and thus produces a small amount of hydroxide ions is called a weak base.
Examples: Ammonium hydroxide and calcium hydroxide.
Properties of Bases (Physical Properties):
- Bases have a bitter taste.
- Bases feel soapy to touch.
- Bases turn red litmus to blue.
- Bases conduct electricity in solution due to the presence of ions in water.
1. Reaction with metals
Bases react with some metals to form hydrogen gas. The gas evolved burns with a pop sound showing that it is hydrogen gas.
Base + Metal → Salt + Hydrogen gas
2NaOH(aq) + Zn(s) → Na2ZnO2(aq) + H2(g)
2. Reaction of a Non-metallic Oxide with Base:
Bases react with non-metallic oxides to produce salt and water.
Example: Carbon dioxide, which is a non-metallic oxide reacts with Calcium hydroxide, which is a base, to produce salt and water.
Since this is similar to the reaction between a base and an acid, we can say that nonmetallic oxides are acidic in nature.
Base + Non-metallic oxide → Salt + Water
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)