Making soluble salts (except sodium, potassium and ammonium salts)
3 marks · EasyA student is making hydrated iron(II) sulfate crystals using dilute sulfuric acid and iron(II) oxide.
State why the student adds excess iron(II) oxide to the acid.
Describe how the student removes the unreacted iron(II) oxide from the mixture.
Explain what the student should do next to obtain hydrated iron(II) sulfate crystals.
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(a) To ensure all the acid reacts (is neutralised)
(b) Filter the mixture to remove the unreacted iron(II) oxide
(c) Evaporate the solution to concentrate it and then allow it to crystallise
Common mistakes: Not mentioning the purpose of excess base; Not specifying filtration; Suggesting evaporation to dryness instead of crystallisation
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States that excess is added to ensure all the acid is neutralised.
B2 (b) · 1 mark · Describes filtration to remove unreacted base.
B3 (c) · 1 mark · Describes concentrating the solution and crystallisation (not evaporation to dryness).
Worked solution
(a) The student adds excess iron(II) oxide to make sure all the sulfuric acid has reacted, so no acid remains.
(b) The mixture should be filtered to separate the unreacted solid iron(II) oxide from the solution.
(c) Next, the filtrate should be heated to concentrate the solution and then left to crystallise, forming hydrated iron(II) sulfate crystals.