Which reagent would you use to test for sulfate ions by forming a white precipitate?

Which reagent would you use to test for sulfate ions by forming a white precipitate?

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

Answer: (B)

The test is about detecting sulfate ions by forming an insoluble sulfate salt. Sulfate ions react with barium ions to form barium sulfate, BaSO4, which is highly insoluble and appears as a white precipitate. The reaction is straightforward: Ba2+ + SO4 2- → BaSO4(s). Because BaSO4 has extremely low solubility, even a small amount of sulfate will produce a noticeable white solid, making this a reliable indicator for sulfate in solution. Other choices don’t give that clear, distinctive white solid specific to sulfate testing under normal conditions. For example, the test with sodium hydroxide targets metal ions to form hydroxides, not sulfate; copper sulfate already contains sulfate, so it wouldn’t indicate the presence of sulfate ions in a solution; while silver nitrate can form a precipitate with sulfate too, it’s not the standard, as Ba2+ is the classic, clearer test for sulfate due to the very low solubility of BaSO4.

The test is about detecting sulfate ions by forming an insoluble sulfate salt. Sulfate ions react with barium ions to form barium sulfate, BaSO4, which is highly insoluble and appears as a white precipitate. The reaction is straightforward: Ba2+ + SO4 2- → BaSO4(s). Because BaSO4 has extremely low solubility, even a small amount of sulfate will produce a noticeable white solid, making this a reliable indicator for sulfate in solution.

Other choices don’t give that clear, distinctive white solid specific to sulfate testing under normal conditions. For example, the test with sodium hydroxide targets metal ions to form hydroxides, not sulfate; copper sulfate already contains sulfate, so it wouldn’t indicate the presence of sulfate ions in a solution; while silver nitrate can form a precipitate with sulfate too, it’s not the standard, as Ba2+ is the classic, clearer test for sulfate due to the very low solubility of BaSO4.