A colorless solution contains a mixture of chloride (Cl-) and nitrate (NO3-) ions. Which sequence of reagents will allow the chloride ion to be tested without interference from the nitrate ion?
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Correct answer
A. Add dilute nitric acid, then silver nitrate solution
Principle or equation
Chloride ions are confirmed by adding silver nitrate solution to produce a white precipitate of silver chloride, which is soluble in dilute ammonia. Nitrate ions do not interfere because silver nitrate is soluble; nitric acid is added to remove carbonate or sulfite impurities and to provide acidic medium.
Why this answer is correct
To test for Cl-, add dilute nitric acid (to acidify and remove any carbonate or sulfite that might also precipitate with Ag+) and then silver nitrate solution. A white precipitate of AgCl forms, confirming chloride. Nitrate ions do not react with silver nitrate to form a precipitate, so they do not interfere. Option B would introduce chloride ions, interfering. Option C tests for ammonium ions, not chloride. Option D tests for nitrate ions, not chloride.
Example
Cl-(aq) + Ag+(aq) -> AgCl(s) (white precipitate). The precipitate dissolves in dilute ammonia, confirming chloride.
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