The type of reaction where an insoluble substance called a precipitate is formed when there is exchange of ions between the reactants is called a precipitation reaction.

Example 1: On mixing sodium carbonate solution with calcium chloride solution, a white precipitate of calcium carbonate is formed.

\(Na_2CO_{3(aq)}+CaCl_{2(aq)} \rightarrow CaCO_{3(s)} \downarrow + 2NaCl_{(aq)}\)

Example 2: On mixing sodium sulphate solution with barium chloride solution, a white precipitate of barium sulphate is formed.

\(Na_2SO_{4(aq)}+BaCl_{2(aq)} \rightarrow BaSO_{4(s)} \downarrow +2NaCl_{(aq)}\)