PHASE CHANGES IN WATER

Purpose:

The purpose of this experiment is to observe the phase changes in water over a temperature range of approximately -10° C to 100° C and to describe the behavior of the molecules in the water at any temperature point in terms of their kinetic energy and/or potential energy.

Introduction:

When a cube of ice is heated with a constant amount of heat being added with time there are periods of time when the temperature of the water is increasing and periods of time when there is no change in the temperature Knowing that temperature is a measure of average kinetic energy, we will attempt to describe a graph of temperature vs. time in terms of the kinetic energy (energy of motion) and the potential energy (stored energy) of the molecules.

Equipment required:

CBL unit

temperature probe that has been previously frozen in ice

TI82/83 with linking cable

Ring stand with iron ring

Bunsen burner

100 ml beaker

wire gauze

TI Graph link to connect to PC (optional)

Equipment Setup Procedure:

Connect the CBL unit to the TI82/83 calculator with the linking cable using the I/O ports at the bottom edge of each unit. Press the cable ends in firmly. Connect the temperature probe to Channel 1 (CH 1 ) on the top of the CBL unit. Turn on the CBL unit and the calculator.

Experimental Procedure:

  1. Place the beaker containing the temperature probe frozen in ice on your ring stand. Light the burner but do not put it under the beaker.
  2. Start the program CHEMBIO on the TI82/83 by pressing PRGM and select CHEMBIO. Press ENTER, then press ENTER again to go to the MAIN MENU.
  3. Set up the calculator and CBL for a temperature probe.
  4. Select SET UP PROBES from the CHEM MAIN MENU.
  5. Enter "1" as the number of probes.
  6. Select TEMPERATURE from the SELECT PROBE menu.
  7. Enter "1" as the channel number.
  8. Set up the calculator and CBL for data collection.
  9. Select COLLECT DATA from the CHEM MAIN MENU.
  10. Select TIME GRAPH from the DATA COLLECTION menu.
  11. Enter "8" seconds as the time between samples.
  12. Enter "90" as the number of samples
  13. Enter, Enter to USE TIME SETUP
  14. Enter "-5" as Ymin, "110" as Ymax, "115/10" as Yscl
  15. Enter to begin
  16. Place the burner under the beaker and stir the water slowly and carefully with the temperature probe as the ice melts. Continue stirring throughout the data collection period.
  17. When the CBL indicates "done", press ENTER on the calculator to display a graph of your data.

Analysis and Conclusions:

Q1. When the phase changes occurred in the sample, what can you say about the temperature?

Q2. Describe the changes that you see in the graph in terms of the kinetic energy and/or the potential energy of the water molecules. You should find 4 distinct areas on the graph that should be explained.

Clean Up

  1. On the calculator, select Enter, "NO" to repeat and "QUIT"
  2. Dry the probe and return the other materials to their proper place.