Objective & Introduction
(1 mark)
Maternal & Methods (1 mark)
Results (2 marks)
Discussion (2 mark)
Conclusion (2 mark)
Q-A & Ref (2 marks)
Total
CHM271
PHYSICAL CHEMISTRY
LABORATORY REPORT
TITLE
: FREEZING POINT DEPRESSION
EXP. NO
GROUP’ S
MEMBERS
:5
GROUP
: AS1202C
DATE
: 12 MAY 2020
LECTURER
: SHARIFAH NADZIRAH BINTI WAN HAMID
: 1. MUHAMMAD AIMAN BIN HAMZAH
(2019250358)
MOHAMMAD FATTAH BIN
2. MOHAMMAD
KHAIRULLAH (2019288244)
AHMAD ADLI BIN SAHREN
3. (2019276462)
SYARIFAH FATMATUZAHRAA BINTI
4. WAN
ABDILLAH EDRUCE (2019236874)
VALEIRIA ENA ANAK PALI
5. (2019271626)
INTRODUCTION
Several important properties of solution depend on the concentration of the dissolved solute
and the nature of the solvent. These properties are called colligative properties because they
all depend on the number of solute particles present, whether these particles are atoms,
molecules or ions. The colligative properties are vapour pressure lowering, boiling point
elevation, freezing point depression and osmostic pressure.
OBJECTIVES
1. To determine the freezing point of a pure solvent and a solution of an unknown.
2. To determine the molar mass of the unknown solid using freezing point depression
method.
APPARATUS
 Boiling tube
 Thermometer
 Water bath
 Ice
 Glass rod
 Stopwatch
CHEMICALS
 Cyclohexane, C6H12
 An unknown solid
PROCEDURES
Part I : Freezing Point of the Solvent
1. 30 ml of cyclohexane is poured into a boiling tube.
2. The tube is placed in a 250 ml beaker full of ice and put a thermometer inside the tube.
3. The temperature is stampled for every 30 seconds when the temperature has dropped to
10ᵒC until the crystals is appeared and the temperature reading became constant. This
temperature is recorded as the freezing point of pure cyclohexane.
Table 5.1 Temperature of cyclohexane
Time (s)
0
30
60
90
120
150
180
210
240
Temp (ᵒC)
10
8
7
7
6
6
5
5
5
Part II: Sample Preparation and Freezing Point of the Mixture (solution)
1. 0.5 g of unknown is weighed as a solute into a small dry test tube.
2. The tube is placed with the solvent and thermometer (from procedure 1) back into a beaker
of boiling water (water bath).
3. The thermometer is removed after the solvent melts and the solute sample is added. The
solution is stirred (after the solvent and solute melts gently with thermometer.
4. The solution is removed from heat and cooled at room temperature for about five minutes.
5. The tube is placed in an ice-filled beaker.
6. The temperature is stampled for every 30 seconds when the temperature has dropped to
10ᵒC until the crystals is appeared and the temperature reading became constant. This
temperature is recorded as the freezing point of pure cyclohexane.
Table 5.2 Temperature of mixture
Time (s)
0
30
60
90
120
150
180
210
240
Temp (ᵒC)
10
6
5
4
3
3
3
3
3
DISCUSSIONS
1. What causes freezing point depression?
Freezing point depression is the temperature changes (lowering) of the freezing point of a
solvent caused by adding a ionic solute.
2. Is freezing point depression negatives?
The change in the freezing point is proportional to the amount of solute added. The change in
the freezing point is negative because the temperature of the solution is lower than the pure
solvent.
3. What is the difference between freezing point and freezing point depression?
The freezing point is the temperature at which the liquid changes to a solid. The freezing
point depression is the difference in the freezing points of the solution from the pure solvent.
QUESTIONS
1. What is the freezing point depression, ∆T, for the solution?
∆T = Kf x m
∆T = 20 x (84)
∆T = 1680 ᵒC/m
2. The freezing point depression constant, Kf, for the cyclohexane is 20.0 ᵒC/m and the
density of cyclohexane is 0.799g/ml. Calculate the molarity of solution.
0.799/20.0 = 0.04 mole
3. How many kilograms of solvent were used?
30 ml = 0.03 kg
4. What is the number of moles of solute?
0.03/(12x6 + 1x12) = 3.57 x10^-4 mol
5. What is the molar mass of the solute?
12x6 + 1x12 = 84 g/mol
6. Why is the curve for freezing of a solution different in slope from freezing of the solvent?
The freezing point depression change because of adding an unknown solid into cyclohexane
solution which turns it to a solvent.
7. What are the natural random uncertainties in reading your thermometer and balance?
+0.1 and – 0.1.
CONCLUSION
The purpose of this experiment was to determine the molar mass of an unknown, non-volatile
solute. The cooling curves for the solutions were generally accurate, and resulted in a realistic
molar mass, which means this lab was a success. This lab could have been improved by
adding ice in between each addition of solution 1 so each trial was done the same, and
making sure that the solution in the test tube is fully submerged in the ice bath.
REFERENCE
1. https://www.coursehero.com/file/p6dbd49k/Conclusion-The-purpose-of-thisexperiment-was-to-determine-the-molar-mass-of-an/
.