DETERMINATION OF MOLAR MASS BY FREEZING POINT DEPRESSION

The vapor pressure of a solvent is reduced when a solute is dissolved in it. As a result,
the boiling point, freezing point, and osmotic pressure are all changed. The number of solute
particles in a given amount of solvent determines the size of these changes. COLLIGATIVE
PROPERTIES are solvent properties that are dependent only on the amount of solute
dissolved and are unaffected by solute identity. The freezing point of the solution is lowered
and the boiling point is raised when a nonvolatile substance is used as the solute. Some common
uses of these colligative properties are the addition of antifreeze to automobile cooling water
to lower its freezing temperature, and the sprinkling of salt on icy sidewalks to melt the ice by
lowering its freezing temperature.
The addition of a solute to a solvent will decrease the freezing point (temperature) of
the solvent. The decrease in freezing point, ∆Tf, when a nonvolatile, nonionizing
(nondissociating) solute is dissolved in a solvent is proportional to the molal concentration, m,
of the solute present in the solution.

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#molar_mass_of_nonvolatile_solute
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