Moderate

The determination of correct molecular weight from Raoults law is applicable to_________________?

Correct answer: D. non volatile solute in a dilute solution

  • A. a volatile solute in dilute solution
  • B. a non-electrolyte & non volatile solute in concentrated solution
  • C. a non-electrolyte & non volatile solute in concentrated solute
  • D. non volatile solute in a dilute solution

Explanation

Raoult's law gives the relative lowering of vapour pressure for a dilute solution containing a non-volatile solute, and this relation is used to calculate the solute's molecular mass. Students may choose a volatile solute because vapour pressure is involved, but the standard molecular-mass method requires a non-volatile solute so only the solvent contributes appreciably to vapour pressure.

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About Evaporation, Boiling Point and Vapour Pressure

Evaporation is the escape of higher-energy molecules from a liquid surface, while vapour pressure is the pressure exerted by vapour in equilibrium with that liquid. The topic distinguishes evaporation from boiling and relates both to temperature, intermolecular forces, surface area, atmospheric pressure and the boiling point.

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