Question

Briefly describe how to separate,
(i) Sulphur from a mixture of sulphur and sand.
(ii) Black $CuO$ from a mixture of $CuO$ and $ZnO$.

Answer 1

i) Dissolve the mixture of sulphur and sand in carbondisulphide. Carbondisulphide will dissolve sulphur but not sand. Filter the solution. Sand is separated as the residue. The filtrate is contains sulphur in carbondisulphide. Evaporate the filtrate to vaporize carbondisulphide. Crystals of sulphur are left behind.

ii) Copper oxide is basic in nature whereas zinc oxide is amphoteric in nature. Therefore, on treating the mixture with NaOH (strong base), zinc oxide reacts to form sodium zincate which dissolves in water, whereas copper oxide will remain undissolved. And hence can be separated through filtration.