Making soluble salts (except sodium, potassium and ammonium salts)
4 marks · NormalState what would be produced if copper(II) sulfate solution was heated to dryness instead of being left to crystallise.
Explain why crystallisation is used to obtain hydrated copper(II) sulfate crystals rather than evaporating to dryness.
Describe a test to confirm if the product is a hydrated salt.
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.
Show answer
(a) Anhydrous copper(II) sulfate / white powder
(b) Water of crystallisation is lost during evaporation to dryness, producing the anhydrous salt; crystallisation allows water molecules to remain, forming blue hydrated crystals.
(c) Test: Heat the salt gently. Hydrated salt will lose water and turn from blue to white.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly identifies anhydrous copper(II) sulfate or describes as a white powder
E1 (b) · 1 mark · Mentions evaporation to dryness removes water of crystallisation
E2 (b) · 1 mark · States crystallisation forms hydrated/blue crystals (or allows water to remain)
B2 (c) · 1 mark · Describes a test for hydration (heat, colour change from blue to white, or water lost)
Worked solution
a) Heating copper(II) sulfate solution to dryness produces anhydrous copper(II) sulfate, which is a white powder.
b) Crystallisation allows water of crystallisation to remain in the crystals, making them hydrated and blue. If evaporated to dryness, the water is lost and the salt becomes anhydrous and white.
c) Test: Heat a sample. If it changes from blue to white and water is given off, it was hydrated.