Cryoscopic Determination of Molar Mass
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Transcript of Cryoscopic Determination of Molar Mass
Introduction
What is Cryoscopy?
study or practice of determining the freezing point of liquids.
Freezing point
Freezing point depression+ solute
Introduction
=molar mass of the unknown solute, = , = ; = and is the mass of the solute and
solvent, respectively
Introduction
In the experiment, the molar mass of the unknown solid was determined by the freezing point of the benzene and the freezing point depression of the solution when the unknown was added,
Data and Results
Time
(s)
Benzene°C
Unknown°C
0 10.041 12.12520 8.054 10.30640 6.384 8.19560 5.125 6.72380 5.315 4.793
100 5.322 3.876120 5.323 5.285140 5.33 5.284
Time(s)
Benzene°C
Unknown°C
160 5.33 5.284180 5.33 5.274200 5.33 5.264220 5.33 5.145240 - 4.98260 - 4.7280 - 4.559
Table 1 temperature reading for benzene and the solution at an interval of 20 sec
Data and Results
0 100 200 3000
2
4
6
8
10
12
timr,t
tem
pera
ture
, °
C
0 100 200 3000
2
4
6
8
10
12
14
time, t
Tem
pera
ture
, °C
Figure 2 cooling curve (a) pure solvent To= 5.330 °C (b) solution Tf= 5.256 °C
Data and Results
Trial To T ΔTf M Mave
1 5.330
5.256
-0.074
191.3
195.32 5.36
05.28
4-
0.071199.4
Table 2 Freezing point depression and molar mass of unknown solid for each trial
Discussion
When a known mass of solute is added in a solvent, the freezing point of the solvent decreases to an extent equal to the number of solute added.
T1
T1
T2 Molar mass
T2 Molar mass
Conclusion
color-= dark yellow
Trial To T ΔTf M Mave
1 5.330
5.256
-0.074
191.3
195.32 5.36
05.28
4-
0.071199.4