PRECIPITATION REACTION

 A chemical reaction in which a precipitate is produced is known as precipitation reaction.

Precipitate is a thick substance which is in soluble in water (shown is picture below).

Example for precipitation reaction 

When sodium sulphate is added to test tube containing barium chloride, a white substance which is insoluble in water (precipitate)is produced in that test tube. That white precipitate is barium sulphate. Chemical equation of about reaction is 

Sodium sulphate + barium chloride —> barium sulphate + sodium chloride

Na₂SO₄ +BaCl₂ −−>BaSO₄ +  2NaCl