Question

why crystallization considered better than simple evaporation to purify solids

Answer 1

Some substances decompose on heating during the evaporation process. For example sugar gets charred due to dryness. On filtering a mixture, some soluble impurities remain behind. On evaporation these contaminate the solid. Hence crystallization is way better than evaporation.

Answer 2

Why crystalization is better than evaporation?

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.