Molecular Weight by Freezing Point Depression
David Mulkey
3/30/2011
Chemistry 118
Section M3
Group Members: Stephan Real and Justin Pollock
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Molecular Weight of the Unknown:
a.
The unknown used in the experiment was unknown number 709. In the
experiment the molecular weight for the unknown in the first trial was 136.766,
and the molecular weight for the unknown in the second trial was 135.366. The
standard deviation for the unknown was 136.066 + or  .9901.
The results from
the two trials showed that the molecular weight for the unknown was very precise
according to the standard deviation. The trials also showed that by using the class
average for trial one (183.817) and the class average for trial two (171.540) as the
accepted values the percent error for trial one in the experiment is 21.09%, and
the percent error for trial two in the experiment is 25.6%. For this reason, the
results were not as accurate according to the class averages.
2.
Determination of the K
f
of Water:
a.
In order to find the K
f
, the freezing point constant, of water the following equation
must be used:
K
f
= ∆T
f
/ i*m where ∆T
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