Vapour pressure of water at 293 K is 17.535 mm Hg. Calculate the vapour pressure of water at 293 K when 25 g of glucose is dissolved in 450 g of water.

Given- Vapour pressure of water, = 17.535 mm Hg


= 25 g of glucose


= 450g of water


Molar mass of water, H2O = 1 + 1 + 16 = 18 g mol-1


Molar mass of glucose, C6H12O6 = (12×6) + (1×12) + (16×6) = 180 g mol-1


Using Raoult’s law for solution of non-volatile solute,


Equation 1


where is the mole fraction of the solute




Substituting the value of in equation 1, we get,









Thus, the vapour pressure of water at 293 K at the given conditions is 17.437 mm Hg


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