When barium chloride solution is combined with sodium sulphate solution, a chemical reaction takes place resulting in the formation of a precipitate of barium sulphate (BaSO₄) and sodium chloride (NaCl) solution:

BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)

In this reaction, the positively charged barium ions (Ba²⁺) from barium chloride combine with the negatively charged sulphate ions (SO₄²⁻) from sodium sulphate to form insoluble barium sulphate. This compound precipitates out of the solution due to its low solubility in water.

The remaining sodium and chloride ions remain in the solution as sodium chloride, which is soluble in water. The overall reaction results in the formation of a white, solid precipitate of barium sulphate and a clear solution of sodium chloride.