To confirm the presence of sulfate ions, which sequence is correct?

• A. Acidify with hydrochloric acid, then add barium chloride; white precipitate forms.
• B. Add sodium hydroxide; the solution turns yellow.
• C. Add silver nitrate; no precipitate forms.
• D. Add ammonia; color changes.

Answer: (A)

Testing for sulfate ions relies on forming a white, insoluble precipitate with barium ions. Acidifying the solution first removes carbonate interference, so carbonates don’t react with the barium solution and mimic a sulfate result. Then adding barium chloride supplies Ba2+; if sulfate is present, BaSO4 forms as a white solid, giving a clear positive indication. This sequence is preferred because it’s specific and reliable for sulfate in mixtures. Other options don’t provide the same definitive, selective result: sodium hydroxide doesn’t give a characteristic sulfate test, ammonia isn’t a dependable indicator, and silver nitrate would not be as selective in the presence of other ions.