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Selective Precipitation

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State

Selective precipitation separates dissolved ions by raising a reagent's concentration gradually, so the least-soluble compound's Q exceeds its Ksp first, leaving other ions dissolved.

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Adding chloride slowly to a solution with both Ag+ and Pb2+ precipitates AgCl first, well before enough accumulates to precipitate PbCl2.

Watch for

This depends on a meaningful Ksp gap — near-identical Ksp values will not separate cleanly.