Which observation confirms the presence of sulfate ions when using the acidified barium nitrate test?

• A. White precipitate forms
• B. Blue precipitate forms
• C. Red precipitate forms
• D. No precipitate

Answer: (A)

Sulfate ions are detected because they react with barium ions to form barium sulfate, which is extremely insoluble and appears as a white solid. The solution is acidified to prevent carbonate ions from also forming a precipitate, which could mask the result. So seeing a white precipitate confirms sulfate ions are present. A colored precipitate or no precipitate wouldn’t point to sulfate in this test.