ALUM
 
 DEFINITION
 
  Alum is a series of double sulphate salts of monovalent cations and trivalent cations containing
24 molecules of water of crystallization.
 
GENERAL FORMULA
 
Family of alum can be represented by a simple formula:
M2SO4.T2(SO4)3. 24H2O
  Where
        M = monovalent cation (Na+, K+,NH4+)
        T = trivalent cation (Al+3,Fe+3,Cr+3)
NOMENCLATURE
OF ALUM
 
If alum contains aluminium then it is named with monovalent cation.
  For example:
  K2SO4.Al2(SO4)3.24H2O                    (potash alum)

If alum does not contain aluminium then it is named with trivalent cation.
  For example:
  K2SO4.Cr2(SO4)3.24H2O                   (chrome alum)
 
EXAMPLES
 
  K2SO4.Al2(SO4)3.24H2O                    (potash alum)
(NH4)2SO4.Al2(SO4)3.24H2O              (ammono alum)
(NH4)2SO4.Fe2(SO4)3.24H2O             (ferric alum)
K2SO4.Cr2(SO4)3.24H2O                   (chrome alum)
 
 PREPARATION OF POTASH ALUM
 
  Potash alum is commonly known as "PHITKARI"
Potash alum is prepared by mixing equi-molecular masses of potassium sulphate and aluminum sulphate in water followed by evaporation
 
K2SO4 + Al2(SO4)3 + 24H2O K2SO4.Al2(SO4)3.24H2O
 
PROPERTIES AND USES
 
  It is white crystalline solid.
It is soluble in water.
It is used for the purification of water.
It is also used in leather industry and in paper industry.
It is used in fire extinguisher.
Melting point is 92oC
 
PHUL PHITKARI
 
  When potash alum is heated at 200oC it loses all molecules of water of crystallization and become a porous mass known as phul phitkari or burned alum.
 
....ATTENTION....
 
  Alum has a large molecular size and it has a property of blood clotting. Therefore, it must be used carefully in the purification of water otherwise you may suffer a great deal.
 
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