Which test is used to identify sulfate ions in solution?

Which test is used to identify sulfate ions in solution?

• A. Add AgNO3 in acidic solution; white precipitate forms with halides.
• B. Add acid to release CO2; limewater turns cloudy.
• C. Warm with ammonia; damp red litmus blue.
• D. Add barium chloride solution; white precipitate BaSO4 forms (in acidic solution).

Answer: (D)

Identifying sulfate ions relies on forming an insoluble salt with a metal ion. When barium ions are present, sulfate ions give barium sulfate, BaSO4, which is white and settles out as a solid. Adding a solution of barium chloride provides Ba2+; if sulfate is in the sample, Ba2+ and SO4^2− combine to form BaSO4, producing a white precipitate that confirms sulfate. The note about acidic solution helps avoid interference from carbonate ions. In acidic conditions, carbonate ions are converted to CO2 and water, so they don’t form BaCO3, which would also precipitate and could lead to a false indication. Thus, the white BaSO4 precipitate under these conditions specifically signals sulfate ions. Other tests shown target different species (like carbonate or halides) and don’t identify sulfate in the same way.

Identifying sulfate ions relies on forming an insoluble salt with a metal ion. When barium ions are present, sulfate ions give barium sulfate, BaSO4, which is white and settles out as a solid. Adding a solution of barium chloride provides Ba2+; if sulfate is in the sample, Ba2+ and SO4^2− combine to form BaSO4, producing a white precipitate that confirms sulfate.

The note about acidic solution helps avoid interference from carbonate ions. In acidic conditions, carbonate ions are converted to CO2 and water, so they don’t form BaCO3, which would also precipitate and could lead to a false indication. Thus, the white BaSO4 precipitate under these conditions specifically signals sulfate ions. Other tests shown target different species (like carbonate or halides) and don’t identify sulfate in the same way.