Which reagent is used to test for sulfate ions in solution?

• A. Barium nitrate
• B. Silver nitrate
• C. Sodium chloride
• D. Ammonium sulfate

Answer: (A)

Testing for sulfate ions relies on forming an insoluble salt with a specific metal ion. When barium ions meet sulfate ions, they produce barium sulfate, BaSO4, which is extremely insoluble and appears as a white precipitate that settles out. So adding a barium-containing reagent, like barium nitrate, to the solution will give a distinctive white precipitate if sulfate is present, confirming its presence. Sodium chloride wouldn’t reveal sulfate, because it introduces chloride ions instead. Ammonium sulfate is already a sulfate salt and wouldn’t indicate the presence of sulfate in the unknown solution. Silver nitrate could also precipitate silver sulfate in theory, but it’s not the preferred, reliable choice for detecting sulfate due to issues with selectivity and solubility.