HEAT OF CRYSTALLIZATION OF WAX
Do not write on this assignment.
Background
The process of crystallization (freezing) is the exact opposite of the process of fusion
(melting). When a substance undergoes a phase change from liquid to solid, heat is
released by the substance; therefore, crystallization is an exothermic process. This
would make fusion or the melting process endothermic.
Given that it is impossible to directly determine the heat energy content in a sample of
matter, we must measure this energy in a second hand fashion. A calorimeter is a device
that allows us to trace the flow of heat between two substances or bodies. The
properties of water make it well suited for use in a calorimeter. Water heats and cools
slowly allowing time to measure or track the heat flow by use of a thermometer. By
simple deduction we conclude that any temperature change in the water must
represent the energy lost or gain between the two substances. By use of a calorimetry
equation we can quantify this energy.
Purpose
Apply knowledge of heat transfer to determine the heat of crystallization of wax.
Equipment and Materials
o test tube
o 250/400-mL beaker
o hot plate or Bunsen burner
o 100-mL graduated cylinder
o thermometer
o ring stand with ring
o
o
o
o
o
o
wire gauze
Styrofoam cup
safety glasses
lab apron
wax
water
Safety
As usual, wear eye protection throughout the activity. Wax cannot be washed out of the
eye. Wear the lab apron to protect your clothing. Be mindful of long hair and sleeves
when lighting the Bunsen burner and heating the water. Inspect all glassware to cracks
or chips before heating.
Procedure
1. Place the ring stand and burner as far back on the bench top as possible.
2. Add about 250 mL of tap water using the beaker’s graduations as a guide. Place
the beaker and water on the wire gauze.
3. Position the ring such that the beaker rests about 3 or 4 inches above the
burner.
4. Make sure that the burner hose is securely attached to the burner and the bench
top gas outlet. Use the spark lighter to ignite the gas. Adjust the gas flow and air
flow to produce a hot flame about 3” tall with three visible regions. The tip of the
flame should be ‘kissing” the bottom of the wire gauze.
5. Heat until boiling. (The burner can be turned off once the water boils.)
HEAT OF CRYSTALLIZATION OF WAX
6. Get a sample of wax weighing approximately 7.000 g. Record its actual mass in
the data table. Add the wax to the test tube.
7. Place the test tube containing the wax into the boiling water. Gently swirl
occasionally until all the sample has melted.
8. Measure exactly 100.0 mL of tap water using the graduated cylinder. Pour the
water into the Styrofoam cup calorimeter. Place the Styrofoam cup with the
water into a beaker for stability.
9. Remove the melted wax sample from the water bath by holding the cool upper
part of the tube. Hold the sample up to the light and watch for the first sign of
cloudiness in the bottom of the tube.
10. At first sign, immediately place the tube into the Styrofoam cup calorimeter and
record the water’s initial temperature (T1) to the nearest tenth of a degree
Celsius.
11. Gently swirl the test tube until the wax completely solidifies. Record the highest
temperature of the water (T2) to the nearest tenth of a degree Celsius.
12. To clean up, return the test tube containing the solidified wax to the designated
container. Wash the glassware. Return all equipment to the lab drawers from
which they came.
13. Have a seat and start the calculations.
Hot Water Bath Set Up
No Thermometer in Wax Tube
Test Tube – Wax Sample
250 or 400 mL
Beaker
3 or 4
inches
SC6. Students will understand the effects motion of atoms and molecules in chemical and physical processes.
a. Compare and contrast atomic/molecular motion in solids, liquids, gases, and plasmas.
b. Collect data and calculate the amount of heat given off or taken in by chemical or physical processes.
c. Analyzing (both conceptually and quantitatively) flow of energy during change of state (phase).
 You exceeded the standards.
 You met the standards.
 You did not meet the standards.
HEAT OF CRYSTALLIZATION OF WAX
Name: __________________________________________
Date: ________________
Record data Answer these questions on the reverse. Respond in complete sentences.
Show all work when performing calculations. Round for significant digits.
Pre-lab Questions
1. Distinguish among thermal energy, heat, and temperature.
2. What is specific heat capacity?
3. Iron has a specific heat of 0.462 J/g.oC. What does this mean?
Data
volume of water in calorimeter (v1)
mass of wax sample (m2)
mL initial temperature (T1)
o
g final temperature (T2)
o
C
C
Calculations
1. Using the density of water, calculate the mass of the water (m1) in the calorimeter.
2. Calculate the change in the temperature (ΔT) of the water in the Styrofoam cup
calorimeter.
3. Calculate the heat gained by the water (Q) in the Styrofoam cup calorimeter.
Q  m1  T  C p
C p water  4.18 J
g  C
4. Calculate the heat of crystallization of wax. (observed value)
Q
heat of crystallization wax 
m2
5. Calculation your percent error. (theoretical value = 250 J/g)
Analysis and Conclusions
1. Compare and contrast the heats of fusion and crystallization for water.
2. Ice has a heat of fusion equal to 333.55 J/g. What would be its heat of crystallization?
SC6. Students will understand the effects motion of atoms and molecules in chemical and physical processes.
a. Compare and contrast atomic/molecular motion in solids, liquids, gases, and plasmas.
b. Collect data and calculate the amount of heat given off or taken in by chemical or physical processes.
c. Analyzing (both conceptually and quantitatively) flow of energy during change of state (phase).
 You exceeded the standards.
 You met the standards.
 You did not meet the standards.