Question

What do you mean by a precipitation reaction? Explain giving an example.

Answer 1

When two solutions containing soluble salts are combined, a double-displacement reaction occurs in which ions are exchanged between the compounds. When one such compound is in solid form (that is, insoluble in water), it settles to the bottom of the container. This solid is known as the precipitate, and the respective reaction is termed the precipitation reaction. A few examples of precipitation reactions are:

• \[\ce{CdSO4_{(aq)} + K2S_{(aq)} -> CdS_{(s)} + K2SO4_{(aq)}}\]
• \[\ce{2NaOH_{(aq)} + MgCl2_{(aq)} -> 2NaCl_{(aq)} + Mg(OH)2_{(s)}}\]

Answer 2

Any reaction in which an insoluble solid (called a precipitate) is formed that separates from the solution is called a precipitation reaction.

If barium chloride solution is added to copper sulphate solution, then a white precipitate of barium sulphate is produced along with copper chloride solution:

\[\ce{\underset{Barium chloride}{BaCl2_{(aq)}} + \underset{Copper sulphate}{CuSO4_{(aq)}} -> \underset{(White ppt{.})}{\underset{Barium sulphate}{BaSO4_{(s)}}} + \underset{Copper chloride}{CuCl2_{(aq)}}}\]