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 dilute hydrochloric acid, then barium chloride solution.
Principle or equation
Sulfate ions can be identified by adding a barium salt in acidic conditions to form a white precipitate of barium sulfate. Nitrate ions do not interfere because barium nitrate is soluble.
Why this answer is correct
Adding dilute hydrochloric acid removes any carbonate or sulfite interference and provides an acidic medium. Then adding barium chloride solution produces a white precipitate of BaSO4 if sulfate is present. Nitrate ions do not form a precipitate with barium.
Example
Ba^2+(aq) + SO4^2-(aq) → BaSO4(s) (white precipitate).
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