Bases:
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:
Strong Bases:
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.
Weak Bases:
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.
Chemical Properties:
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)