Making insoluble salts

3 marks · Normal

Explain why mixing solutions of barium chloride and sodium sulfate produces a white precipitate, but mixing barium chloride and sodium chloride does not.

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

Barium sulfate is insoluble and forms a white precipitate when Ba2+ and SO4^2− ions meet in solution. In contrast, sodium chloride is soluble, so no precipitate forms when barium chloride and sodium chloride are mixed.

Also accept: A precipitate only forms if an insoluble salt is produced; NaCl remains dissolved, so no solid forms.

Common mistakes: Stating only that a precipitate forms without referring to solubility.; Confusing the identity of the ions involved.

Show mark scheme and worked solution

Marking points

M1 · 1 mark · States that barium sulfate is insoluble and forms a precipitate.

M2 · 1 mark · Links the precipitate to the reaction between Ba2+ and SO4^2− ions, not seen with Na+ and Cl−.

A1 · 1 mark · Correctly explains that sodium chloride remains soluble, so no precipitate forms in that case.

Worked solution

Mixing barium chloride and sodium sulfate brings Ba2+ and SO4^2− ions together, which react to form insoluble barium sulfate, a white precipitate. When barium chloride is mixed with sodium chloride, all resulting salts (barium chloride, sodium chloride) are soluble, so no precipitate forms.