Acid Base & Salt - Class 10th Science
What is a Base?
A base gives bitter taste. A base feels soapy when touched. A base turns red litmus paper blue.
Example: Caustic soda (sodium hydroxide), washing soda (sodium carbonate), potassium hydroxide, slaked line (calcium hydroxide), etc.
All metal oxides, metal hydroxides, metal carbonates are base.
Chemical properties of base are just opposite to that of acids. When a base is added to acid, both neutralize each other, in such reactions respective salts are formed along with water.
Oxides, hydroxides, and carbonates of all metals are base.
Example:
Calcium is an alkaline earth metal, thus its oxide, calcium oxide (quick lime), its hydroxide, which is known as calcium hydroxide (slaked lime) and its carbonate calcium carbonate (lime stone) are base.
Sodium is an alkali metal, thus sodium oxide, and sodium hydroxide and sodium carbonate are base.
Potassium is an alkali metal thus potassium oxide, potassium hydroxide and potassium carbonate are base.
Types of base:
On the basis of solubility in water, bases are divided into following two types:
(a) Water soluble base - Alkalis.
(b) Water insoluble base - base.
Most of the bases are insoluble in water. Bases which are soluble in water called alkalis.
Alkalis
Water soluble base is known as alkalis.
Alkali is a basic ionic salt of alkaline metals. Lithium, sodium, potassium, etc. are called alkali metals. Beryllium, magnesium, calcium etc. are called alkaline earth metals. Therefore hydroxides of alkali and alkaline earth metals are called alkalis.
Example: sodium hydroxide, calcium hydroxide, potassium hydroxide, lithium hydroxide, etc.
Ammonium hydroxide is another important base, although it is the hydroxide of non-metal.
Ammonia is a hydride (salt) of non – metal, but it is a base.
Most of the reactions takes place in aqueous state, thus water soluble base are more useful.
Properties of Base:
- Bitter in taste
- Solution of base feels soapy in touch
- Turn back red litmus paper blue which turned red by an acid.
- Neutralises an acid
- Dilution of base is exothermic
- Base neutralizes acid
- A base forms salt and water when reacts with acid