Advanced Instruments 3300, User Manual

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measurement in other branches of chemistry, they are not used in
osmometry because the ratio of solute to solution is not linear.
Molality and osmolality are linear, independent of the effect of
temperature and volume displaced by solute. A calculated con-
version between units of molality and molarity is complex and
generally unnecessary when the terms are properly understood.
Freezing Point/Melting Point : The temperature at which the liquid
and solid phases of a substance will remain together in equilibrium.
Freezing-Point Depression : When a solute is added to a solvent, the
freezing point of the solvent is lowered. In aqueous solutions, one
mOsm of solute per kilogram of water depresses the freezing point by
1.858 millidegrees Celsius (m°C).
Supercooling : The tendency of a substance to remain in the liquid state
when cooled below its freezing point.
Crystallization Temperature : Aqueous solutions can be induced to
freeze (i.e., crystallize) most reliably when supercooled. When super-
cooled, agitating the solution (freeze pulse) induces crystal formation.
The crystallization temperature is the temperature at which crystalliza-
tion is induced. During crystallization, the heat of fusion raises the tem-
perature of the sample to an ice/water freezing-point plateau.
Heat of Fusion : The heat released when the mobile molecules of a liq-
uid are frozen into rigid ice crystals.
Freezing-Point Plateau : The constant temperature maintained during
the time that ice and liquid exist in isothermal equilibrium after crystal-
lization occurs.
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Foreword