Making soluble salts (except sodium, potassium and ammonium salts)
2 marks · EasyA student tries to obtain hydrated magnesium sulfate crystals by evaporating the solution to dryness instead of crystallising it.
Explain, in two points, why this method does not produce hydrated crystals.
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Common mistakes: Not mentioning water of crystallisation; Describing loss of colour with no explanation
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Marking points
B1 · 1 mark · States that evaporating to dryness removes the water of crystallisation.
B2 · 1 mark · Explains that this produces anhydrous magnesium sulfate, not hydrated crystals.
Worked solution
1. Evaporating the solution to dryness drives off all the water, so no water of crystallisation remains in the salt.
2. This forms anhydrous magnesium sulfate (a white powder) instead of hydrated magnesium sulfate crystals.