Separation of mixtures
4 marks · NormalDescribe the steps needed to obtain pure crystals of copper sulfate from a mixture of copper sulfate and sand.
Explain why filtration is a necessary step in this process.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) — · must show dissolve in water, filter to remove sand, crystallise copper sulfate
(b) — · must show sand does not dissolve, copper sulfate solution passes through
Common mistakes: claiming both are soluble; reversing filtration and crystallisation
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · States or describes dissolving the mixture in water
M2 (a) · 1 mark · States filtration and crystallisation in correct order (or equivalent process)
E1 (b) · 1 mark · Explains sand is insoluble / copper sulfate is soluble
E2 (b) · 1 mark · Explains that filtration removes sand and leaves copper sulfate solution
Worked solution
a) Add water to the mixture of copper sulfate and sand. Stir to dissolve the copper sulfate. Filter the mixture to remove the sand (residue), leaving copper sulfate solution as filtrate. Heat the filtrate to concentrate it, then allow it to cool and crystallise. Collect the copper sulfate crystals.
b) Filtration is necessary because sand does not dissolve in water, but copper sulfate does. The filter paper traps the sand (as residue), while the copper sulfate passes through as solution.