AIM: To prepare crystals of Potash alum.
Potash alum, a double salt, commonly known as ‘fitkari’ has the formula K2SO4.Al2(SO4)3.24H2O. It can be prepared by making an equimolar solution of potassium sulphate and aluminium sulphate in the minimum amount of water. A few ml of diluted H2SO4 is added to prevent the hydrolysis of Al2(SO4)3.18H2O. Cooling of the hot saturated solution yields colourless crystals of Potash alum.
K2SO4 + Al2(SO4)3.18H2O + 6H2O → K2SO4.Al2(SO4)3.24H2O
Colour of the crystals: Colourless
Shape of the crystals: Octahedral.