Which reagent is used to confirm the presence of sulfate ions by forming a white precipitate?

• A. Barium nitrate
• B. Calcium chloride
• C. Sodium sulfate
• D. Potassium chloride

Answer: (A)

Sulfate ions are detected by forming an insoluble precipitate with barium ions. Adding a reagent that supplies Ba2+ ions, such as barium nitrate, leads to the formation of barium sulfate (BaSO4), which is a white precipitate because BaSO4 has very low solubility in water. This distinct white solid confirms the presence of sulfate.

The other options don’t provide Ba2+ ions. Calcium chloride would introduce Ca2+, and calcium sulfate is only sparingly soluble, so it’s less reliable for a clear precipitate. Sodium sulfate already contains sulfate, so it won’t test for its presence. Potassium chloride provides chloride ions, not sulfate, so no precipitate forms.