PURPOSE: This lab is used to introduce the concept of boiling

EQUIPMENT: The following equipment is needed


Equipment setup: make a setup like the following diagram.

Computer Setup: Perform the following steps in setting up the ULI and computer






Discuss the following questions with your lab partner. Look at your graphs to support your answers.

Teacher notes:

Rationale: This experiment is used as an introduction to the process of boiling. It gives students a visual representation of the concept of boiling as a cooling process. It also emphasizes the importance of atmospheric pressure in considering the boiling process.

Data/Graphs: The following graphs are representative of expected graphs

Part 1

Part 2

If the students believe that the water temperature is decreasing for other reasons than the boiling process (which it is to a small extent) have them reheat their water to boiling then insert a temperature probe. Then have them remove the heat source and follow the temperature over approximately the same time period without cooling the flask with ice. A graph of that cooling process would look like this:

Superimposing these graphs (which can be done within the MacTemp program if you have moved Data A to Data B) makes it easy to see that the temperature drops much more rapidly when ice is applied.

Safety notes: This experiment can be used with upper level responsible students. If you do let the students do the complete experiment, please be aware of the following:

The danger of the flask breaking (even though I have never had it occur) is definitely present. Make sure the flask is Pyrex, thick walled and free of scratches. Still Extreme care is needed.

If a Bunsen burner is used as a heat source, you will need to support the flask with a ring and wire gauze. After removing the Bunsen burner, the ring and wire gauze must be lowered. This ring will be hot and should be handled only with gloves or a wet rag.

The main danger is of the liquid superheating (which I have had occur) Allowing the water to boil several minutes should eliminate this problem but some students forget to keep the water boiling. They then reheat it as fast as possible. Giving the flask a swirl before stoppering it should also help. If the water is super heated, it will blow off the stopper/temperature probe and force hot boiling water all over you and or your students. To avoid this problem I always do this step myself.

Possible additional methods: If doing this experiment as a demonstration, Part two may be set up with two probes connected to the computer with two setups. After boiling, treat both setups exactly the same except one setup has ice applied while the other does not. The graphs of both are then collected and displayed simultaneously.

Written by Elliott Amstutz, July 1997