A colorless solution contains a mixture of sulfate (SO4^2-) and chloride (Cl-) ions. Which sequence of reagents will allow the sulfate ion to be tested without interference from the chloride ion?
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Correct answer
A. Add barium nitrate solution, then dilute nitric acid.
Principle or equation
Barium sulfate is insoluble in dilute nitric acid, while silver chloride is insoluble in dilute nitric acid but silver sulfate is slightly soluble. To test sulfate in presence of chloride, add barium nitrate (which gives a white precipitate of BaSO4) and confirm it does not dissolve in dilute nitric acid.
Why this answer is correct
Barium nitrate provides Ba^2+ which precipitates BaSO4. The precipitate is insoluble in dilute nitric acid, confirming sulfate. Chloride does not interfere because Ag+ is not added. Option B tests chloride, not sulfate. Option C adds HCl which introduces chloride and may precipitate AgCl if Ag+ were present, but here it's for sulfate? Actually adding HCl then BaCl2 would still precipitate BaSO4, but the HCl does not interfere, but the question asks for testing sulfate without interference from chloride, and adding HCl introduces more chloride but does not interfere with BaSO4 precipitation. However, the best sequence is to add barium nitrate first, as it directly tests sulfate without adding chloride. Option D tests chloride.
Example
To a sample, add a few drops of barium nitrate solution. A white precipitate forms. Then add dilute nitric acid; the precipitate remains, indicating sulfate.
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