Q11 of 26 Page 1

A solution is prepared by dissolved 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).


According to Raoult’s law,

Where PO→ Vapour pressure of pure water


P → Vapour pressure of solution


w → Weight of solute


m → Molecular weight of solute


W → Weight of solvent


M → Molecular weight of solvent


Thus,


Or, 0.005 m = 0.9 or, m = 180


Thus molar mass of the solute 180 gm./mol


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(i) Which one of the following is a polysaccharide :

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