Group Name Date Period
To measure the freezing point of stearic acid.
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.
Predict what you think will happen to the temperature when the stearic acid changes from a liquid state to solid state (freezes).
1. Obtain a test tube of liquid stearic acid from your teacher. 2. Record the temperature at t = 0 in the table below. 3.
keep stirring the stearic acid with the thermometer. 4. Start your stopwatch and gently place the test tube in the flask with tap water. 5.
KEEP STIRRING GENTLY
6. Record the temperature every 30 seconds (0.5 minutes) in the table below for 10 minutes. 5.
KEEP STIRRING GENTLY Data:
Time (min) Temperature ( C) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
On a separate sheet of graph paper, graph temperature (y-axis) versus time (x-axis)
1. What happens to the temperature when the freezing point is reached? How is this illustrated by the graph? 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? 5. Below is a graph of the temperature of H 2 O as heat is added to it. What is happening at the first flat part (plateau) of the graph? What is happening at the second plateau on the graph? Conclusion: Describe what happens to the temperature of a substance during a change of state.