Making sodium, potassium and ammonium salts
2 marks · NormalExplain why titration is needed instead of the excess solid method when preparing potassium salts from acid and alkali solutions.
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Also accept: No insoluble excess for filtration, so titration is needed to find the neutralisation point; Since potassium compounds are all soluble, excess cannot be filtered so titration is used
Common mistakes: Because you cannot evaporate the solution afterward; Because you need large crystals (incomplete: does not address need for titration)
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Marking points
B1 · 1 mark · States potassium (or sodium, ammonium) salts are all soluble so excess solid cannot be separated by filtration.
B2 · 1 mark · States that titration is needed to accurately find the volumes that neutralise each other (or to prepare a pure salt without indicator).
Worked solution
Potassium salts are all soluble, so any excess solid would dissolve and cannot be filtered off. The titration method is therefore used to find the exact volume of acid and alkali needed to neutralise each other.