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Why is the vapous pressure of an aqueous...

Why is the vapous pressure of an aqueous solution of gulucose lower than that of water ?

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In pure liquid, the entire surface of liquid is occupied by the molecule of water. When a non-volatile solute, e.g., glucose is dissolved in water, the fraction on surface covered by the solvent molecules gets reduced because some positions are occupied by glucose molecules. So, number of solvent molecules escaping from the surface is reduced. That is why vapour pressure of aqueous solution of glucose is reduced.
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VMC MODULES ENGLISH-THEORY OF SOLUTIONS-JEE Advanced (Archive)
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