Freezing Point Depression and Boiling Point Elevation Lab
Purpose: In this experiment you will investigate the effect that adding a solute has on the boiling and freezing
points of a solvent.
Background: Usually the Introduction is one paragraph that explains the objectives or purpose of the lab. In
one sentence, state the hypothesis. Sometimes an introduction may contain background information, briefly
summarize how the experiment was performed, state the findings of the experiment, and list the conclusions of
the investigation. Even if you don't write a whole introduction, you need to state the purpose of the experiment,
or why you did it. This would be where you state your hypothesis.
Materials:
100ml Graduated Cylinder
150ml Beaker
250ml Beaker
Crushed Ice
Salt (Sodium Chloride)
Thermometer
Stirring Rod
Wire Gauze
Distilled Water
Calcium Chloride
Ring Stand and Ring
Clamp
Bunsen Burner
Sugar (Sucrose)
Slotted Rubber Stopper
Procedure:
1. Freezing Point Depression
 Because of the difficulties that would be involved in trying to weigh a sample of ice accurately, we
will be making only a “semi-quantitative” study of freezing point lowering.

 Weigh out separately the following samples for use in the freezing point study: 0.1mol of sucrose,
0.1mol of sodium chloride, and 0.1mol of calcium chloride.

 Fill the 150mL beaker with ~100ml crushed ice, packing the ice as tightly as possible in the beaker.
Add 25.0mL of distilled water to each beaker. By adding the liquid water, we are constructing the
solid-liquid equilibrium system, whose temperature should be exactly 0˚C as long as any ice is
present in the system. Although we do not know the exact mass of water (both ice and liquid) in the
beaker, we can assume that the total amount in beaker is very nearly 100ml.

 Determine the temperature of the ice/water mixture. Make certain that the thermometer is held in the
middle of the ice/water mixture and does not touch the walls or bottom of the beaker. Note if the
temperature as read on your thermometer differs from 0˚C. Keep this error in mind when reading the
temperatures of the experimental solutions during the rest of this experiment.

 Add the weighed sample of sucrose to the 150mL beaker containing the ice/water mixture. Stir the
sugar with a stirring rod until it dissolves as much as possible. Then determine the temperature of the
ice/water/sugar mixture. Record the value after making any adjustments based on error noted when
measuring the temperature of the ice/water mixture prior to adding the solute.

 Repeat the process using fresh ice/water with the sodium chloride and then again with the calcium
chloride sample in place of the sucrose. Record the freezing point temperature of the mixture after
making any adjustments based on error noted when measuring the temperature of the ice/water
mixture prior to adding the solute.
2. Boiling Point Elevation

Set up an apparatus for boiling (ring stand, ring, wire gauze, clamp, slotted rubber stopper, and
thermometer). Set up the thermometer so that the temperatures above 100 ˚ C can be easily read.
Make sure the thermometer can be supported in the middle of the liquid being heated, and that it
is not resting on the bottom of the beaker in contact with the burner flame.

Weigh out separately the following samples for use in the boiling point study: 0.1mol of sucrose,
0.1mol of sodium chloride, and 0.1mol of calcium chloride.

With your graduated cylinder, measure out exactly 100mL of distilled water and transfer to the
250 beaker. Begin heating the water and bring it to a gentle boil.

When the water is gently boiling, determine its temperature. The boiling point of water varies
with atmospheric pressure, but should be very near 100 ˚ C. Note if the temperature as read on
your thermometer differs from 100˚C. Keep this error in mind when reading the temperatures of
the experimental solutions during the rest of this experiment.

Turn off the flame and then very slowly and carefully add the weighed sodium chloride sample
you prepared to the hot water. Restart the flame and stir the solution with a stirring rod to
dissolve the sodium chloride while bringing the solution to a gentle boil. Determine the
temperature of the boiling salt water mixture. Record the value after making any adjustments
based on error noted when measuring the temperature of the boiling water prior to adding the
solute.

Repeat the boiling point determination for sucrose and calcium chloride, using fresh 100mL
portions of water for each sample. There is no need to boil the water prior to adding the solute
since you already know the thermometer’s error. As a matter of fact, it is much safer to add the
solute to the room temperature distilled water and then heat the solution to boiling.

Determine the temperature of the boiling solutions. Record the values after making any
adjustments based on error noted when measuring the temperature of the boiling water prior to
adding the sodium chloride in the previous step.
Data Table: Aqueous Solutions
Freezing Points Particles (n) Mass Solute Measured Calculated
Compound
(grams)
Temp. ˚C Temp. ˚C
Sucrose
C12H22O11
Sodium Chloride
NaCl
Calcium Chloride
CaCl2
Boiling Points
Sucrose
C12H22O11
Sodium Chloride
NaCl
Calcium Chloride
CaCl2
Error
Calculations: Molality = m = moles of solute particles / kg of solvent
∆Tf = Kf m
Kf = -1.86˚C/molal
FP = 0˚C + ∆Tf
∆Tb = Kb m
Kb= 0.52˚C/molal
BP = 100˚C + ∆Tb
1. Convert the mass of each solute into moles.
2. Calculate the number of moles of particles (ions) for each solute using particles/compound in the above
table.
3. Calculate the molality for each of the three solutions assuming that each solute was dissolved in 100ml
of water. (Density of H2O = 1.0g/ml.)
4. Calculate the ∆T for the FP of each solution and add it to the FP of H2O. Record this value in the data
table.
5. Calculate the ∆T for the BP of each solution and add it to the BP of H2O. Record this value in the data
table.
6. Calculate the difference between the measured value from the lab and the calculated value from the
formula. Record this error in the data table.
Use the questions below to help guide you when you write your conclusion and analysis for the lab report.
Conclusion:
1. Which solute produced the largest depression in the FP? Which solute produced the largest elevation in
the BP?
2. Which solute produced the smallest depression in the FP? Which solute produced the smallest elevation
in the BP?
3. Are the measured temperatures for the solutions consistent with the trend you would expect based on
the number of particles produced when each of the respective solutes dissolve? EXPLAIN.
4. Explain the differences between the measured temperatures and the calculated temperatures (i.e. list
three possible sources of error).
5. Describe, on a microscopic basis, how a liquid boils and how the addition of the solute changes this
process.
6. A solution is made consisting of 2.05g aluminum chloride (AlCl3) dissolved in 9.87g of water (H2O).
Calculate the FP and the BP of this solution.
Background
When a solute is dissolved in a solvent, the properties of the solvent are changed by the presence of the solute.
The magnitude of the change generally is proportional to the number of moles of solute added per kilogram of
solvent (molality). Colligative properties of a solution are those properties of a solvent that are changed only by
the number of solute particles present, without regard to the particular nature of the solute. These properties
include changes in vapor pressure, the boiling point, and the freezing point. When a solute is added to a solvent,
the amount of solvent that can escape from the surface of the solution at a given temperature is lowered, relative
to the amount of particles that can escape from the pure solvent. Therefore, the vapor pressure above such a
solution will be lower than the vapor pressure above of the pure solvent under the same conditions. Molecules
of the solute physically block the surface of the solvent, thereby preventing as many solvent molecules from
evaporating at a given temperature. The presence of a solute lowers the temperature at which the solution
freezes and raises the temperature at which the solution boils relative to the pure solvent.