Introductory Chemistry: A Foundation
9th Edition
ISBN:9781337399425
Author:Steven S. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Donald J. DeCoste
Chapter15: Solutions
Section: Chapter Questions
Problem 2QAP: ow do the properties of a nonhomogeneous (heterogeneous) mixture differ from those of a solution?...
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Question
I need help solving molality and determining molar mass
Transcribed Image Text:ft
Data
Solution
Observations
Pure Solvent
Time
Time
(minutes: Temp Observations
seconds) (°C)
(minutes:
seconds)
Temp
(°C)
0
40
76.1
0
0:15
0:30
80
76.9
0:15
0:30
73.6
72.1
0:45
70.6
0:45
10.7
0:60
10.0
0:60
68.4
1:15
69.7 solid
1:15
67.7 solid b
1:30
69.4
1:30
66.7
1:45 169.1
1:45
66.0
2:00 169.1
2:00
65.4
2:15
169.1
2:15
64.9
2:30
69.0
2:30
65.0
2:45
69.0
2:45
64.8
3:00
69.0
3:00
64.6
3:15
690
3:15
164.8
3:30
69.0
3:30
64.6
3:45
690
3:45 64.4
4:00
69.0
4:00
164.4
4:15
690
4:15
104.2
4:30
69.0
4:30
164.1
4:45
69.0
4:45
64.2
5:00
69.0
5:00
64.2
5:15 69.0
5:15
164.1
5:30
690
5:30
64.1
5:45 69.0
5:45
164.2
6:00
69.0
6:00 164.3
6:15
69.0
6:15
6:30
69.0
6:30
65.0
6:45
69.0
6:45
165.0
7:00
(૦૧ ૦
7:00
64.9
7:15
690
7:15
64.8
7:30
69.0
7:30
64.7
7:45
690
14.6
7:45
8:00
69-01
64.4
8:00
Continue recording data until it is so frozen it can no longer be stirred. You may need more than 8 minutes!
11) 68.5 cooled
Mass of test tube 13.84
Mass of test tube + stearic acid 19.94
Mass of unknown solute added for Trial #1
0.526
Mass of unknown solute added for Trial #2.909
Total mass of solute in Trial #2435
Trial #1
.كما
164.8
65.0
64.7
64.7
64.4
64.4
64.3
64.2
(04.0
64.0
64.0
63.8
(03.7
623.6
63.4
to Mana
Temp
(°C)
80
13.1
70.4
68.0
67.0
65.9
65.3
65.0
64.9
64.9
64.8
64. solid bo
64.7
64.9
63.2
63.0
300م)
Trial #2
Observations
Analysis
From your cooling curve data, what is the freezing point of pure stearic acid?
The dog
freezing
point for the
acid
was 69.7°C
steanc
Based on your best fit line analysis, what is the freezing point of each unknown solution? (Attach graph of
cooling curve data for both trials)
The cooling point for trial #1 was 67.7.
For trial #2
It was 64.8
Determine the molality of each unknown solution, using Kf = 4.50 °C/m for stearic acid.
Determine the molar mass of the unknown solute. (It is a non-electrolyte.) Show your work for both trials.
Compare your average molar mass to the accepted value for the molar mass of the solute (it is BHT, butylated
hydroxytoluene) and discuss the main sources of error.
Based on the molecular structures of stearic acid and BHT, does it make sense that BHT would dissolve in
stearic acid? Why is BHT a non-electrolyte?
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