The Freezing Point Lab
Purpose: To measure the freezing point of stearic acid.
Background Information: To cool a substance we must remove energy from it. As energy leaves a
substance the molecules move slower and the temperature decreases. However, when the substance changes
state something different happens. In this lab we will observe stearic acid cooling to its freezing point to try
and find out what happens.
Hypothesis: Predict what you think will happen to the temperature when the stearic acid changes from a
liquid state to solid state (freezes). Write your Hypothesis in a complete sentence.
Materials:
beaker
test tube
test tube holder
stearic acid
graph paper
Thermometer
stopwatch or clock
Procedure:
1. Create TWO tables of Time in minutes versus Temperature in Celsius. The time should be in half
minute intervals from 0 minutes to 10 minutes. See below for an example.
2. Obtain a test tube of liquid stearic acid from your teacher out of the hot water bath. Use your test tube
holder to grab and hold it!
3. Record the temperature at t = 0 s in the table immediately after removing it from the hot bath.
4. Start your stopwatch and as soon as the test tube leaves the hot bath.
5. Gently place the test tube in the beaker and gently keep stirring the stearic acid with the thermometer.
6. KEEP STIRRING GENTLY with the Thermometer and record the temperature every 30 seconds (0.5
minutes) in the table below for 10 minutes.
7. Repeat steps #2-6.
Data: You need two!
Time (min)
0
Temp. (C)
0.5
1
1.5
2
….
….
9
9.5
10
Graph: On a separate sheet of graph paper, make a complete graph of temperature (y-axis) versus time
(x-axis). Use two different point protectors or colors for your two different trials.
Questions: in complete sentences
1. What happens to the temperature when the freezing point is reached? How is this illustrated by the graph
you made?
2. What is the freezing point of stearic acid?
3. If you were to heat up the frozen stearic acid, at what temperature would it melt at? What would happen
to the temperature as it melted?
4. If you continued to heat the stearic acid until it started to boil, what would happen to the temperature as it
is boiling?
Conclusion:
Describe what happens to the temperature of a substance during a change of state in complete sentences.
Make sure to discuss what a continual addition of heat would do to substance.