Q11 of 22 Page 1

A solution is prepared by dissolving 10 g of non-volatile solute in 200 g of water. It has a vapour pressure of 31.84 mm Hg at 308 K. Calculate the molar mass of the solute. (Vapour pressure of pure water at 308 K = 32 mm Hg)

Given,


Vapour pressure of pure water i.e. solvent, P° = 32 mm Hg


Vapour pressure of solution (i.e. after addition of solute into solvent), P = 31.84mmHg


W1, mass of solvent= 200g


W2, mass of solute = 10g


M1, molecular weight of solvent i.e. water = 18 gmol-1


M2, molecular weight of solute =?


According to relative lowering of vapour pressure,


=


=


M2 =


M2 = 180 gmol-1


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