A colorless solution contains a mixture of sulfate (SO4^2-) and nitrate (NO3-) ions. Which sequence of reagents will allow the sulfate ion to be tested without interference from the nitrate ion?
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Correct answer
A. Add barium chloride solution, then dilute hydrochloric acid.
Principle or equation
Sulfate ions form a white precipitate of barium sulfate when barium chloride is added. The precipitate is insoluble in dilute hydrochloric acid, confirming sulfate. Nitrate does not interfere because silver nitrate would test for halides, and other tests are for different ions.
Why this answer is correct
Barium chloride provides Ba2+ which precipitates BaSO4 (white). Adding dilute HCl ensures the precipitate is not carbonate or sulfite, which would dissolve. Nitrate ions do not react with Ba2+ or HCl, so no interference.
Example
If a solution contains sulfate, adding BaCl2 gives a white precipitate that does not dissolve in HCl. If the precipitate dissolves, sulfate is absent.
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