Heating and Cooling Curve of Water

Purpose: To observe the temperature of water over a period of time.

To determine the shape of a heating/cooling curve.

To learn more about heat transfer during changes of state.

Materials:

Ice, water, stirring rod, temperature probe, beaker, hot plate

Method:

1.  Collect the necessary materials and fill the beaker with an ice-water mixture (about half of the mixture should be ice, and half water). The beaker should be about 2/3 of the way full.

2.  Place the beaker on the hot plate. Before turning on the hot plate, determine the initial temperature of the mixture using the temperature probe.

3.  Put thermometer into the mixture.

4.  Begin stirring the mixture with the stirring rod and turn on the hot plate. Do not stop stirring until the experiment is finished.

5.  Record any qualitative observations you may have, for example, about the state of the mixture (solid, liquid, gas, or a mixture of these). You may choose to use the back of this sheet, a separate page, or a Word document on the computer to record these.

6.  Record All Quantitative data meaning every 30 seconds record the Temp from the Thermometer.

7.  When the water boils, continue to take measurements for another 5 minutes. Then, turn off the hot plate and begin to clean up.

Observations:

Time / Temp

Analysis:

1.  Why is the graph called both a HEATING curve and a COOLING curve? Sketch a more appropriate way to draw a cooling curve (i.e., if you did the experiment by cooling water vapour to water and then to ice)?

2.  What happened to the temperature when the ice was melting? What happened to the temperature after all the ice had melted? What happened to the temperature when the water was boiling?

3.  Explain why the temperature did what it did in question #3.

4.  The melting point of ethanol is –115ºC and the boiling point of ethanol is 78ºC. Sketch what you think the heating/cooling curve would look like for ethanol.

Conclusion:

Write an appropriate conclusion statement for this lab. Your conclusion should answer the purpose of the lab. Also mention any sources of experimental error that might have thrown your results off (this does not include the incompetence of the experimenters!!)