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Using Freezing-Point Depression to Find Molecular Weight
At = Fpt of lauric acid - Fipt of lauric acid + benzoic acid
THE DATA
. Determine the difference in freezing temp
temperatures, At, between the pure lauric acid (t) and
the mixture of lauric acid and benzoic acid (tz). Use the formula, At = t1 - tz.
my = At
KF
=
of
= mot / kg .
2. Calculate molality (m), in mol/kg, using the formula, At = Kr. m (K, = 3.9.C-kg/mol for
lauric acid).
C. kg/ mol
3. Calculate moles of benzoic acid solute, using the answer in Step 2 (in mol/kg) and the mass
Moles of benzoic acid = my * Mass of solvent in ky
shauric aid
(in kg) of lauric acid solvent.
4. Calculate the experimental molecular weight of benzoic acid, in g/mol. Use the original mass
of benzoic acid from the Data and Calculations table, and the moles of benzoic acid you
found in the previous step
motes / 16 * 0. 00406 by
. Determine the accepted molecular weight for benzoic acid from its formula, C&amp;HSCOOH.
motes .
6. Calculate the percent error.
Mole. wt of benzoic acid (experimental) -
Mass in 9
DATA AND CALCULATIONS
motes
Mass of lauric acid
4.06
9
Mass of benzoic acid
Accepted ((6 15 (OOH ) ( 7 * 12. 01 ) + ( 6 * 1-01 ) + ( 2* 16 )
0 . 5 3 4
Freezing temperature of pure lauric acid
44- 1
9 / mo
Freezing point of the benzoic acid-lauric acid
. C
mixture
35-5
1. error =/ Theoretical - Experimental
Freezing temperature depression, At
Theoretical
* 100 %.
. C
Molality, m
mol/kg
Moles of benzoic acid
mol
Molecular weight of benzoic acid (experimental)
g/mol
Molecular weight of benzoic acid (accepted)
Percent error
g/mol
%
v with Vernier
Chemistry with Vernie

t=freezing point of pure solvent(lauric acid)-freezing point of (lauric acid+benzoic... View the full answer

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