Making soluble salts (except sodium, potassium and ammonium salts)
2 marks · HardDescribe two steps a student must carry out to obtain pure hydrated copper(II) sulfate crystals from a mixture of copper(II) oxide and dilute sulfuric acid, once the reaction has finished.
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Must show: filtration of excess solid, concentration and crystallisation step
Also accept: Filter off the excess copper(II) oxide, then heat and leave the solution to crystallise.
Common mistakes: Gives only one step.; Mentions evaporation to dryness instead of crystallisation.
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Marking points
B1 · 1 mark · Filters off excess copper(II) oxide or removes unreacted solid from the solution.
B2 · 1 mark · Warms/concentrates the filtrate and leaves it to crystallise (not evaporation to dryness).
Worked solution
The student should (1) filter the mixture to remove any unreacted copper(II) oxide, and (2) heat the filtrate to concentrate it, then leave it to cool and crystallise to obtain hydrated copper(II) sulfate.