Advanced Instruments 3300, User Manual

Page: 13 / 77

Foreword
Principles of Freezing-Point Osmometry
When a solute is dissolved in a pure solvent, the following
changes in the solution's properties occur:
• the freezing point is depressed,
• boiling point is raised,
• osmotic pressure is increased, and
• vapor pressure is lowered.
These are the so-called "colligative" or concentrative proper-
ties of the solution which, within reasonable limits, change in
direct proportion to the solute concentration; in other words,
the number of particles in solution.
Of the colligative properties, measurement of the freezing
point allows the concentration of an aqueous solution to be
easily determined with great precision.
The freezing point of pure H
2
O is pre0.010°C. One
mole of a non-dissociating solute such as glucose (where the
solute does not dissociate into ionic species, but remains
intact), when dissolved in 1 kilogram (kg) of water will
depress the freezing point by 1.858°C. This change is known
as the freezing point depression constant for water. The
freezing point depression also depends upon the degree of dis-
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