A colorless solution contains a mixture of chloride (Cl-) and sulfate (SO4^2-) ions. Which sequence of reagents will allow the chloride ion to be tested without interference from the sulfate ion?
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Correct answer
A. First add barium nitrate solution, filter, then add silver nitrate solution to the filtrate.
Principle or equation
Sulfate ions are precipitated by barium ions, while chloride ions are precipitated by silver ions. To test chloride without sulfate interference, remove sulfate first by precipitation with barium nitrate, then test the filtrate for chloride with silver nitrate.
Why this answer is correct
Adding barium nitrate precipitates BaSO4 (white), which is removed by filtration. The filtrate now contains only chloride ions (and nitrate). Adding silver nitrate then gives a white precipitate of AgCl, confirming chloride. Silver sulfate is sparingly soluble, so sulfate must be removed first.
Example
To a sample, add Ba(NO3)2 solution; a white precipitate indicates sulfate. Filter. To the filtrate, add AgNO3 solution; a white precipitate indicates chloride.
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