Which ion yields a white precipitate when treated with acidified aqueous barium nitrate?

• A. Sulfate
• B. Nitrate
• C. Chloride
• D. Carbonate

Answer: (A)

Sulfate ions form an insoluble compound with barium ions. In acidified aqueous barium nitrate, the sulfate combines with Ba2+ to produce barium sulfate, BaSO4, which appears as a white precipitate. This reaction is why the test specifically signals sulfate: BaSO4 is largely insoluble and shows up as a solid.

Nitrates and chlorides stay as soluble salts with barium, so no solid precipitate forms. Carbonate would normally precipitate as BaCO3, but the acid in the solution reacts with carbonate to form CO2, preventing a carbonate precipitate from forming.