Chemistry-Bases+Alkali

Bases

What a base is

Insoluble in water

A base is any metal oxide or hydroxide. Thus, it contains either oxide ions (O2-) or hydroxide ions (OH-).

A base is a substance that reacts with an acid to produce salt and water only.

base+acid --> salt+water

Basicity
1 hydrogen ion --> mono basic
2 hydrogen ion --> di basic
3 hydrogen ion --> tri basic

Alkalis (special class of bases)
An alkali is a base that is soluble in water.
Sodium oxide+water --> sodium hydroxide

Most bases are insoluble in water. (which is why alkalis are special)

Properties of alkali
1) Have a bitter taste and soapy feel
2) Turn red litmus paper blue
3) Produces hydroxide ions when dissolved in water
4) Can react with acids to form salt and water only. This reaction is called neutralisation.
In neutralisation reaction, hydrogen ions from the acid react with the hydroxide ions from the alkalis to form water.

5) When heated with ammonium salts, ammonium gas is produced:
alkali+ammonium salt --> ammonia+water+salt
ammonia can be recognised by its pungent smell. It also turns red litmus paper blue.

6) It can react with a solution of one metal salt to give metal hydroxide and another metal salt:
alkali+salt(of metal A) --> metal+salt(of metal B) hydroxide
The metal hydroxide will appear as precipitate if it is insoluble in water.

Uses of bases and alkali
Ammonia solutions: In window cleaning solution, in fertilisers
Calcium oxide: In neutralising acidic soil, to make iron, concrete and cement
Magnesium hydroxide: In toothpaste to neutralise acid on teeth, in antacids to relieve indigestion
Sodium hydroxide: In making soaps and detergents, in industrial cleaning detergent