Question

Name the technique used to separate alum from impure sample why is this technique is better than simple evaporation

Answer 1

Potash alum is highly water soluble. To prepare pure crystals of potash alum, dissolve the sample in distilled water and remove the insoluble impurities by filtration. This solution is concentrated to the crystallisation point and cooled. Colourless transparant crystals of potash alum separate.

Answer 2

Crystallization technique is used to separate alum because,

1. It occurs on the entire surface.
2. we get solid in the pure crystallized form.
3. The soluble impurities get removed in this process.
4. It doesn't require very high temperature conditions.