Making insoluble salts
2 marks · HardDescribe how you could make an insoluble salt of calcium sulfate using solutions of soluble salts.
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Mix a solution of calcium nitrate with a solution of sodium sulfate (or potassium sulfate); a white precipitate of calcium sulfate will form.
Must show: Name a suitable calcium salt solution, Name a suitable sulfate salt solution, Description of mixing to form precipitate
Also accept: Mix calcium chloride and sodium sulfate solutions; Use potassium sulfate instead of sodium sulfate
Common mistakes: Suggesting insoluble calcium salts as starting materials; Not mentioning that a precipitate forms
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Marking points
M1 · 1 mark · Names one suitable soluble calcium salt and one suitable soluble sulfate salt.
E1 · 1 mark · Describes mixing solutions to form a precipitate of calcium sulfate.
Worked solution
To make insoluble calcium sulfate, mix solutions of calcium nitrate and sodium sulfate. The reaction will produce a white precipitate of calcium sulfate.