Which observations would correctly distinguish sulfuric acid from aqueous sodium sulfate when using a carbonate test, a metal test, and litmus?

• A. Carbonate test: CO2 is produced only with sulfuric acid; metal test: hydrogen is produced only with sulfuric acid; litmus turns red only with sulfuric acid.
• B. The carbonate test produces CO2 for both salts; the metal test produces hydrogen for both; litmus turns red for both.
• C. The carbonate test produces CO2 only with sodium sulfate; the metal test produces hydrogen with sodium sulfate; litmus turns red with sodium sulfate.
• D. The carbonate test produces no gas; the metal test produces oxygen; litmus remains blue.

Answer: (A)

The main idea is using simple qualitative tests to tell an acid apart from a neutral salt solution.

Carbonate test: CO2 gas is evolved when carbonate reacts with an acid. Sulfuric acid provides the protons to drive this reaction, producing CO2, water, and a sulfate salt. Aqueous sodium sulfate has no extra acid to react with the carbonate, so no CO2 is released.

Metal test: Metals react with acids to produce hydrogen gas and a salt. With sulfuric acid, you’d see hydrogen gas evolve. In a solution of sodium sulfate, there’s no acid present to drive that reaction, so no hydrogen is formed.

Litmus test: Acids turn blue litmus red. Sulfuric acid will change litmus to red. Sodium sulfate solutions are essentially neutral, so they don’t turn litmus red.

So the combination of CO2 from the carbonate test, hydrogen gas from the metal test, and red litmus with the acid all point to sulfuric acid rather than the neutral salt sodium sulfate.