Unit 5

Unit 5

Molar Mass Determination by Depression of the
Freezing Point

February 7, 2012

Adrienne Oxley

Lab Partner: Everett Spell

Title page includes the name of the
experiment, the date, your name and
your lab partner’s name.

This experiment focused on colligative properties, properties
that are based on the concentration of solute particles present and not
In text references are
shown as superscripts
which correspond to a
numbered reference
found at the end of the
report (in the reference

the chemical identity of the solute. Freezing point depression was used
to study the molar mass of a substance.1 This colligative property is
based on the idea that a solution freezes at a lower temperature than
the pure solvent.1,2 By adding unknown impurities to a solution of
water and studying the effects this solute “impurity” has on the freezing
point, valuable information about the identity of the substance can be
obtained. The following equation describes the idea of freezing point
ΔTf = iKfm
The ΔTf term indicates the change in temperature observed for the

Introduction includes
explanation of concepts
found in key equations.
All variables used are
clearly defined (see
highlighted portion)

solution relative to that of the pure substance (the freezing point
depression), kf is a term specific to the identity of the solvent being used
(in this case water is used and kf is 1.86 ⁰C/m), and m is the molality of
particles in the solution (a measure of moles of solute per kg of solvent).
By measuring a change in temperature,
the molality of an aqueous solution can
be calculated and this information can
Use figures whenever
possible to illustrate
points (Note: if you use a
figure, you need to
reference it and refer to
it in the text – there
should be explanation of
the figure).

subsequently be used to determine
molar mass (provide the initial mass of
sample was recorded).
Figure 1...

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