Preparation of Pure Sample of Potash Alum

Potash alum is a double salt of potassium sulphate and aluminium sulphate. It has the formula K2SO4.Al2(SO4)3.24H2O. It is prepared by dissolving an equimolar mixture of hydrated aluminium sulphate and potassium sulphate in minimum amount of water containing a little of sulphuric acid and subjecting the resulting solution to crystallization, when octahedral crystals of potash alum separate out.

This video explains how to prepare a pure sample of potash alum.