Answer:
Certain
compounds when dissolved insuitable solvents either dissociate or associate.
For
example ethanoic acid dimerises in benzene due to hydrogen bonding while in
water, it dissociates and forms ions. As a result the number of chemical
species in solution increases or decreases as compared to the number of
chemical species of solute added to form the solution, Since the magnitude of
colligative property depends on the number of solute particles, it is expected
that the molar mass determined on the basis of coelegative properties will be
either higher or lower than the expected value or the normal value and is
called abnormal molar mass.
In
order to account for the extent of dissociation or association of molecules
insolution, Van't Hoff introduced a factor i, known as the Van't Hoff factor.
It can be denned as follows : 1
1
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