Chem 17 Full Report
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Transcript of Chem 17 Full Report
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Marie Antoinette Torres Nov. 27, 2012
A 20L Dec. 4, 2012
Group 3
Colligative Properties
I. Introduction
A phase change is the change from one physical state to another, accompanied by a change in
energy of the system. From an ordered state, energy must be supplied to overcome the intermolecular
forces of attraction to transform the substance into a less ordered state. The phase changes involved in
this exercise were melting, freezing, and boiling.
Melting is the conversion of a substance from solid to liquid. An increase in temperature and
kinetic energy disrupts the arrangement of the solid until the intermolecular forces of attraction are
overcome, resulting in the fluid motion of the particles. Freezing is the conversion of a substance from
liquid to solid. Due to the decrease in temperature and kinetic energy of the liquid, a structure is formed
and the liquid substance becomes solid. Boiling is the change from liquid to gas. It occurs when the
vapor pressure of the liquid becomes equal to the atmospheric pressure.
Colligative properties are the properties of solutions that are dependent not on the nature of
the solute, but on the amount present. The properties involved in this exercise were boiling point
elevation and freezing point depression. In boiling point elevation, the boiling point of the solution
increases as the concentration increases. In freezing point depression, the presence of a solute
decreases the freezing point of the solution.
The objectives of this exercise were:
1. to describe colligative properties of solutions;
2. to determine the effect of solute concentration on boiling point and freezing point of
the solution; and
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3. to compute for the molar mass of an unknown solute using freezing point depression
data.
II. Materials
A. Reagents
Naphthalene
B. Apparatus
Test tubes Iron stand
Iron clamp Iron Ring
Thermometer Bunsen burner
4 250-mL beakers
III. Procedure
Two grams of naphthalene were obtained and put in a test tube. Then, the tube was put in a
250 mL beaker. Distilled water was poured to the beaker until the water level is above the sample in the
test tube. The beaker was then heated until the sample has melted and the temperature reached 90:C.
After the sample has reached 90:C, the beaker was put off the flame. Its temperature was then
recorded at 15 second intervals until the temperature reached 70:C.
0.20 g of an unknown substance and 2.0 g of naphthalene were mixed in a test tube. The tube
was then put in a 250 mL beaker with a water level just above the sample. The beaker was then heated
until the sample has melted and the temperature reached 90:C. After reaching that temperature, the
beaker was put off the flame. The temperature of the sample was recorded every fifteen seconds until it
dropped to 70:C.
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100 mL of distilled water was obtained and put into a 250 mL beaker. The distilled water was
then heated and its temperature recorded at 15 second intervals until it has reached its boiling point.
100 mL of distilled water was obtained and transferred into a 250 mL beaker. 1.5 g of an
unknown sample was obtained and dissolved into the water. The solution was then heated. Itstemperature was recorded every fifteen seconds until the solution has reached its boiling point.
IV. Data and Observations
Table 1.1. Determination of the Freezing Point of Naphthalene
Time (s) Temperature (:C) Phase Time Temperature (:C) Phase
0 90 Liquid 315 78 Liquid
15 90 Liquid 330 77 Liquid-Solid
30 88 Liquid 345 77 Liquid-Solid
45 88 Liquid 360 77 Liquid-Solid
60 88 Liquid 375 76 Liquid-Solid
75 87 Liquid 390 76 Solid
90 86 Liquid 405 76 Solid
105 86 Liquid 420 76 Solid
120 84 Liquid 435 76 Solid
135 84 Liquid 450 76 Solid
150 83 Liquid 465 74 Solid
165 82 Liquid 480 74 Solid
180 82 Liquid 495 74 Solid
195 81 Liquid 510 74 Solid
210 80 Liquid 525 74 Solid
225 80 Liquid 540 74 Solid
240 79 Liquid 555 72 Solid
255 79 Liquid 570 72 Solid
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270 78 Liquid 585 72 Solid
285 78 Liquid 600 72 Solid
300 78 Liquid 615 70 Solid
Figure 1. Cooling Curve of Naphthalene
Table 1.2. Determination of the Freezing Point Depression of Naphthalene
Time (s) Temperature (:C) Phase Time Temperature (:C) Phase
0 90 Liquid 390 74 Solid
15 89 Liquid 405 74 Solid
30 88 Liquid 420 74 Solid
45 87 Liquid 435 74 Solid
60 86 Liquid 450 73 Solid
75 85 Liquid 465 72 Solid
90 84 Liquid 480 72 Solid
105 84 Liquid 495 71 Solid
0
10
20
30
40
50
60
70
80
90
100
030
60
90
120
150
180
210
240
270
300
330
360
390
420
450
480
510
540
570
600
Naphthalene
Naphthalene
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120 83 Liquid 510 71 Solid
135 82 Liquid 525 70 Solid
150 82 Liquid
165 81 Liquid
180 81 Liquid
195 80 Liquid
210 80 Liquid
225 79 Liquid
240 78 Liquid
255 77 Liquid
270 77 Liquid
285 76 Liquid
300 76 Liquid-Solid
315 75 Liquid-Solid
330 75 Liquid-Solid
345 75 Liquid-Solid
360 75 Liquid-Solid
375 74 Solid
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Figure 2. Freezing Point Depression of Naphthalene
Table 1.3. Determination of the Boiling Point of Distilled Water
Time (s) Temperature (:C) Phase Time Temperature (:C) Phase
0 34 Liquid 165 77 Liquid
15 34 Liquid 180 81 Liquid
30 40 Liquid 195 85 Liquid
45 43 Liquid 210 89 Liquid
60 47 Liquid 225 93 Liquid-Gas
75 52 Liquid 240 96 Liquid-Gas
90 58 Liquid 255 98 Gas
105 60 Liquid 270 98 Gas
120 64 Liquid 285 98 Gas
135 68 Liquid
150 72 Liquid
0
10
20
30
40
50
60
70
80
90
100
030
60
90
120
150
180
210
240
270
300
330
360
390
420
450
480
510
Napthalene + Unknown
Napthalene + Unknown
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Figure 3. Heating Curve of Distilled Water
Table 1.4. Determination of the Boiling Point of Distilled Water + Unknown solute
Time Temperature Phase Time Temperature Phase
0 32 Liquid 180 81 Liquid
15 34 Liquid 195 85 Liquid-Gas
30 38 Liquid 210 88 Liquid-Gas
45 40 Liquid 225 93 Liquid-Gas
60 46 Liquid 240 98 Liquid-Gas
75 52 Liquid 255 99 Liquid-Gas
90 56 Liquid 270 99 Gas
105 60 Liquid 285 99 Gas
120 65 Liquid 300 99 Gas
135 69 Liquid 315 99 Gas
150 74 Liquid 330 99 Gas
165 78 Liquid
0
20
40
60
80
100
120
015
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
Distilled water
Distilled water
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Figure 4. Heating Curve of Distilled Water + Unknown Solute
Table 1.5. The Boiling Point of distilled water and dH2O + unknown solute at different concentrations
Group Amount of Solute (g) Boiling Point of dH2O Boiling Point of dH2O +
unknown solute
1 0.5 99 100
2 1.0 98 98
3 1.5 98 99
4 2.0 98 99
5 2.5 96 97
0
20
40
60
80
100
120
0 30 60 90 120 150 180 210 240 270 300 330
distilled water + unknown solute
distilled water + unknown
solute
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V. Discussion
In the experiment, the freezing point of pure naphthalene was 76:C. The experimental value
was far from the actual freezing point of naphthalene. A possible source of error might be an incorrect
amount of sample used in the experiment.
The freezing point of the naphthalene solution acquired is 74:C. There was a 2:C difference
between the pure naphthalene and the naphthalene solution. The presence of a solute decreased the
freezing point of the solution. The presence of more solute makes it easier for the solution to crystallize
as it cools.
The molality of the solution is 0.29 m. This could be computed dividing the freezing point
depression by the molal freezing point depression constant.
The moles of solute used in the solution could then be computed.
The molar mass of the solute is 344.82 g/mol.
The boiling point of distilled water in the experiment is 98:C while the boiling point of the
solution is 99:C. The increase in the boiling point was caused by the presence of solute. The more
concentrated the solution becomes, the more crystalline is its structure. Because of the structure
becoming more ordered, it would take more energy to break the bonds of this structure. More energy
would result to an increase in boiling point.
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VI. Conclusion
The freezing point of a solution decreases as the amount of solute increases. More solute mixed
into a solution would create more bonds with the solvent molecules. As more bonds are formed, the
structure becomes more crystalline. If the structure is becoming more crystalline, then it would be
easier for the solution to take shape and freeze.
Boiling point is directly proportional to the amount of solute present in the solution. The
presence of solute increases the boiling point of the solution. As a solution becomes more concentrated,
more bonds are formed. An increased amount of energy is required to break these bonds. A higher
temperature is needed to produce an increased amount of energy.
VII. References
Guch, I. (2009). Fun With Colligative Properties. Available:
http://misterguch.brinkster.net/colligativepropertiestutorial.html
Helmenstine, A.M. Freezing Point Depression, What Freezing Point Depression Is And How It
Works. Available:
http://chemistry.about.com/od/solutionsmixtures/a/freezingpointde.-Nxc.htm
Laboratory Instruction Manual for Chem 16.1 General Chemistry I Laboratory. Los Banos,
Laguna: Institute of Chemistry, University of the Philippines Los Banos.
http://chemistry.about.com/od/solutionsmixtures/a/freezingpointde.-Nxc.htmhttp://chemistry.about.com/od/solutionsmixtures/a/freezingpointde.-Nxc.htmhttp://chemistry.about.com/od/solutionsmixtures/a/freezingpointde.-Nxc.htm