Preparing Potash Alum Crystal (Volumetric Analysis)

AIM: To prepare crystals of Potash alum.

THEORY:

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

RESULT–

Colour of the crystals: Colourless

Shape of the crystals: Octahedral.

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