Question

What is the technique you would use to separate and collect hydrated copper (ll) sulfate, CuSO4⋅5H2O from its aqueous solution?

Answer 1

We will heat it ..........

Answer 2

Both copper sulphate and aluminium sulphate have almost equal, high solubilities in water though the potassium salt is comparatively less soluble. Hence, the copper salt cannot be separated from the mixture by fractional crystallization.

An easy chemical method is to treat the solution with excess of caustic soda (NaOH) when copper ions get precipitated as (insoluble) copper(II) hydroxide.

CuSO4 + 2NaOH = Cu(OH)2 + Na2SO4

Aluminium ions will initially form a white precipitate of aluminium hydroxide, but this amphoteric hydroxide will easily dissolve in excess alkali to form sodium aluminate.

Al2(SO4)3 + 6NaOH = 2Al(OH)3 + 3Na2(SO4)3

Al(OH)3 + NaOH = NaAlO2 + 2H2O

Potassium ions do not react with caustic soda (NaOH) and so they remain in solution.

The pale blue precipitate of cupric hydroxide is filtered off, washed with distilled water, and then dissolved in dilute sulphuric acid to get a blue solution of copper sulphate. This solution on evaporation will yield blue crystals of copper(II) sulphate pentahydrate, CuSO4.5H2O.

Hope,it helps you!