A colorless solution contains a mixture of nitrate (NO₃⁻) and bromide (Br⁻) ions. Which sequence of reagents will allow the bromide 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
Bromide ions can be detected by adding silver nitrate in acidic conditions to form a cream precipitate of silver bromide. Nitrate ions do not interfere because they do not form a precipitate with silver ions.
Why this answer is correct
Adding dilute nitric acid removes carbonate or sulfite ions that might interfere. Then adding silver nitrate produces a cream precipitate of AgBr if bromide is present. Nitrate remains in solution and does not precipitate.
Example
To test for chloride, one adds dilute nitric acid then silver nitrate; a white precipitate indicates chloride. Similarly, bromide gives a cream precipitate.
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