Ch. 8 Lab – What’s a Cooling Curve?

Goal: How is temperature affected by changing the state of matter from a liquid to a solid?

Hypothesis: Base your reasoning on prior knowledge of melting ice, freezing water, and the temperatures associated with each process. Discuss your ideas with a classmate before writing them down.

How do you think a graph might look? / Explain your reasoning.

Procedure Steps:

  • Obtain a test tube with melted stearic acid in it. Stearic acid is a waxy substance similar to candles.
  • Record the temperatureas soon as you remove it from the hot water, and continue recording the temperature every minute until all is solidified. CAUTION!! DO NOT STIR WITH THERMOMETERS, THEY WILL BREAK.
  • You may keep the test tube at your desk until the temperature has come down the room temperature, which is approximately 23 degrees Celsius.
  • Place the test tube with the thermometer into the beaker of hot water. Once the stearic acid has melted, the thermometers can be removed and cleaned.

Data and Observations:

Table I: Temperature change over time

Time (min)
Temp. (◦C)

Graph Cooling Curve for Stearic Acid

Analysis and Conclusions

  1. Label the regions on the graph where stearic acid is liquid, solid, & melting.
  2. What is the freezing point temperature of stearic acid? ______
  3. What do you predict the melting point temperature to be? ______
  4. What would an ideal graph (cooling curve) look like? Explain why you think those characteristics would be ideal. Why is yours not quite ideal (most likely)?
  1. Did your data-based graph match your prediction? ______
  2. Your data should show that liquids can cool, and solids can cool, but something prevents substances from cooling while they are in the process of changing. What could be happening to the heat while the temperature remains the same? ______
  3. The temperature at which a liquid becomes a solid is the same temperature at which that same solid will become a liquid. In other words, the freezing point and melting point is the same.
  4. What is the freezing point and melting point of water? ______
  5. What is the freezing point and melting point of stearic acid? ______
  6. Predict what the graph would look like if you had been given solid stearic acid and measured the temperature each minute as it changed into a liquid (opposite of your lab). Sketch the predicted graph.
  1. Scientists sometimes have to determine the melting and freezing point of an unknown substance in order to identify it. Describe the steps they would follow to do this. ______