Salt preparations
3 marks · NormalCopper(II) sulfate can be made by adding excess copper(II) oxide to dilute sulfuric acid.
Explain why an excess of copper(II) oxide is added during the preparation.
Describe what the student should do after all the acid has reacted, to obtain dry copper(II) sulfate crystals.
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) To ensure all sulfuric acid reacts and no acid remains in the solution. · must show all acid neutralised, no acid left
(b) Filter the mixture to remove unreacted copper(II) oxide, then evaporate the filtrate to partially concentrate the solution and allow copper(II) sulfate crystals to form as it cools. · must show filter, evaporate solution, form crystals
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Marking points
E1 (a) · 1 mark · Explains that the excess is to ensure all the acid reacts, so no acid is left in solution.
M1 (b) · 1 mark · States filter to remove unreacted copper(II) oxide.
M2 (b) · 1 mark · Describes evaporating the solution and allowing it to crystallise.
Worked solution
a) An excess of copper(II) oxide ensures that all the sulfuric acid reacts and none remains in the solution.
b) After the reaction, unreacted copper(II) oxide is removed by filtration. The solution is then gently heated to evaporate some water, and copper(II) sulfate crystals form on cooling.