When a solution of sodium sulphate is added to a solution of barium chloride, a white precipitate of barium sulphate will be formed immediately. This precipitate is insoluble in dilute hydrochloric acid (dil.HCl) and also insoluble in water. This type of reaction is called precipitation reaction as the Baso4 precipitate thus formed is of white colour.
The equation of the above mentioned reaction is given as follows:
Na2SO4 (aq) + BaCl2(aq) -------> BaSO4(s) + 2NaCl(aq)
Since, barium sulphate is insoluble in water, so it will precipitate as a solid, where as the sodium chloride will remain in solution.