Chemistry with CBL 2 - 1

Experiment

2Freezing and Melting of WaterFreezing temperature, the temperature at which a substance turns from liquid to solid, and melting temperature, the temperature at which a substance turns from a solid to a liquid, are characteristic physical properties. In this experiment, the cooling and warming behavior of a familiar substance, water, will be investigated. By examining graphs of the data, the freezing and melting temperatures of water will be determined and compared.

Figure 1

MATERIALSCBL System 400-mL beakerTI Graphing Calculator waterVernier Temperature Probe 10-mL graduated cylinderVernier adapter cable icering stand saltutility clamp stirring rodtest tube

PROCEDURE

Part I: Freezing

1. Put about 100 mL of water and 5 to 6 ice cubes into a 400-mL beaker.

2. Put 5 mL of water into a test tube and use a utility clamp to fasten the test tube to a ring stand. The test tube should be situated above the water bath. Place a temperature probe into the water inside the test tube.

3. Plug the temperature probe into the adapter cable in Channel 1 of the CBL System. Use the link cable to connect the CBL System to the TI Graphing Calculator. Firmly press in the cable ends.

4. Turn on the CBL unit and the calculator. Start the CHEMBIO program and proceed to the MAIN MENU.

2 - 2 Chemistry with CBL

Experiment 2

5. Set up the calculator and CBL for one temperature probe and a temperature calibration.

¥ Select SET UP PROBES from the MAIN MENU.¥ Enter Ò1Ó as the number of probes.¥ Select TEMPERATURE from the SELECT PROBE menu.¥ Enter Ò1Ó as the channel number.¥ Select USE STORED from the CALIBRATION menu.

6. Set up the calculator and CBL for data collection.

¥ Select COLLECT DATA from the MAIN MENU.¥ Select TIME GRAPH from the DATA COLLECTION menu.¥ Enter Ò10Ó as the time between samples, in seconds.¥ Enter Ò90Ó as the number of samples (the CBL will collect data for a total of 15 minutes).¥ Press ENTER . Select USE TIME SETUP to continue. If you want to change the sample time or

sample number, select MODIFY SETUP.¥ Enter ÒÐ10Ó as the minimum temperature (Ymin). To enter ÒÐ10Ó, use (—) , not — .¥ Enter Ò30Ó as the maximum temperature (Ymax).¥ Enter Ò5Ó as the temperature increment (Yscl).

7. When everything is ready, press ENTER on the calculator to begin data collection. Then lower the test tube into the ice-water bath. Note: It will take 10 seconds for the graph to appear with the first data point plotted.

8. Soon after lowering the test tube, add 5 spoons of salt to the beaker and stir with a stirring rod. Continue to stir the ice-water bath during Part I.

9. Slightly, but continuously, move the probe during the first 10 minutes of Part I. Be careful to keep the probe in, and not above, the ice as it forms. When 10 minutes have gone by, stop moving the probe and allow it to freeze into the ice. Add more ice cubes to the beaker as the original ice cubes get smaller.

10. When data collection stops after 15 minutes, ÒSAMPLINGÓ will change to ÒDONEÓ on the CBL screen. Keep the test tube submerged in the ice-water bath until Step 12 below.

11. Press ENTER to display a graph of temperature vs. time on the calculator screen. On the displayed graph, analyze the flat part of the curve to determine the freezing temperature of water. As you move the cursor right or left, the time (X) and temperature (Y) values of each data point are displayed below the graph. Record the freezing temperature in your data table (round to the nearest 0.1¡C). Note: When you choose to do a second data collection in Step 12, the Part I temperature data will be stored in L4 so that Part I data can be printed along with the Part II data after the experiment is completed.

Part II: Melting

12. Press ENTER , then choose to repeat the data collection by selecting YES. Use the same Y-axis settings as in Part I.

13. Press ENTER on the calculator to begin data collection. Then raise the test tube and fasten it in a position above the ice-water bath. Do not move the temperature probe during Part II.

14. Dispose of the ice water as directed by your teacher. Obtain 250 mL of warm tap water in the beaker. When 12 minutes have passed, lower the test tube and its contents into this warm-water bath.

Chemistry with CBL 2 - 3

Freezing and Melting of Water

15. When data collection stops after 15 minutes, press ENTER to display a graph of temperature vs. time for Part II. On the displayed graph, analyze the flat part of the curve to determine the melting temperature of water. Record the melting temperature in your data table (round to the nearest 0.1¡C).

16. A good way to compare the two curves is to view both sets of data on one graph:¥ Press ENTER , then select NO to return to the MAIN MENU. Select QUIT to exit the program.TI-82 or TI-83 Calculators: ¥ To set up the graph for melting of ice (Part II), press 2nd [STATÊPLOT], then select

Plot1. Use the arrow keys to position the cursor on each of the following settings. Press ENTER to select any of the settings you change: Plot1 = On, Type = , Xlist = L1, Ylist = L 2, and Mark = ¥

¥ To set up the curve for freezing of water (Part I) on the same graph, press 2nd [STATÊPLOT], then select Plot2. Use these settings: Plot2 = On, Type = , Xlist = L1, Ylist = L4, and Mark = ¥

¥ To set the scaling and increments for each axis, press WINDOW . Scale time (X) from 0 to 900 seconds with increments of 100 seconds. In the same manner, scale temperature (Y) from Ð10 to 30¡C with increments of 5 ¡C. Press GRAPH to view the graph. Two curves should be displayed, one for freezing water and one for melting ice.

TI-85 Calculators: ¥ To set up the graph for melting ice (Part II), press STAT , then select < EDIT>. Select < L1>

(time) as the xlist Name and press ENTER . Select < L 2 > (temperature) as the ylist Name and press ENTER .

¥ To rescale the x and y axes, press GRAPH , then select < RANGE >. Rescale the time by entering a value of 0 for xMin, 900 for xMax, and 100 for xScl. Rescale the temperature by entering a value of Ð10 for yMin, 30 for yMax, and 5¡C for yScl.

¥ Plot a graph of temperature vs. time (Part II) by first pressing STAT < DRAW >. Then press <CLDRW> to clear the graph screen. Press < xyLINE > to display a plot of temperature vs. time, then press CLEAR .

¥ To set up the graph for freezing water (Part I) on the same graph, press STAT , then select <ÊEDIT>. Select < L1> (time) as the xlist Name and press ENTER . Select <L4 > (temperature) as the ylist Name and press ENTER .

¥ Press STAT < DRAW >, then press < xyLINE > to display a plot of temperature vs. time. Press CLEAR . Two curves should be displayed, one for freezing water and one for melting ice.

TI-86 Calculators: ¥ To set up the graph for melting ice (Part II), press 2nd [STAT], and select <ÊPLOT>.

Select <PLOT1>. Press to move to a new setting, and press ENTER or the menu keys to change a setting. Use the following settings: Plot1 = On, Type = (select <xyLine>), Xlist Name = L1, Ylist Name = L 2, and Mark = ¥

¥ To set up the graph for freezing of water (Part I) on the same graph, select <PLOT2>. Use these settings: Plot1 = On, Type = , Xlist Name = L1, Ylist Name = L 4, and Mark = ¥

¥ To rescale the x and y axes, press GRAPH , then select < WIND >. Scale time (X) from 0 to 900 seconds with increments of 100 seconds. In the same manner, scale temperature (Y) from Ð10 to 30¡C with increments of 5 ¡C.

¥ Press <GRAPH> to view the graph of temperature vs. time. Two curves should be displayed, one for freezing water and one for melting ice.

2 - 4 Chemistry with CBL

Experiment 2

TI-92 Calculators: ¥ To set up the graph for melting of ice (Part II), first view the data matrixÑpress APPS ,

select Data/Matrix Editor, then Current. Press F2 to select the Plot Setup menu. Highlight Plot 1 and press F1 to select it. Choose xyline for the Plot Type, then Dot for the Mark. Press C 1 to enter the x-axis (time) and C 2 to enter the y axis (temperature). Press ENTER twice.

¥ To set up the graph for freezing of water (Part I) on the same graph, first press ESC to return to the Data/Matrix Editor. Press F2 to select the Plot Setup menu. Highlight Plot 2 and press F1 to select it. Choose xyline for the Plot Type, then Dot for the Mark. Press C 1 to enter the x axis (time) and C 4 to enter the y axis (temperature). Press ENTER twice.

¥ Press [WINDOW]. Scale the time from 0 to 900 with increments of 100. Scale the temperature from Ð10 to 30¡C with increments of 5¡C. Press ENTER .

¥ Press [GRAPH] to view the graph of temperature vs. time, with both curves displayed.

17. Use the TI-Graph Link cable and program to transfer the graph of temperature vs. time to a Macintosh or IBM-compatible computer. Print a copy of the graph. Label each curve as freezing of water or melting of ice. Then proceed directly to Step 1 of Processing the Data.

DATA TABLE

Freezing temperature of water ________¡C

Melting temperature of water ________¡C

PROCESSING THE DATA1. What happened to the water temperature during freezing? During melting?

2. According to your data and graph, what is the freezing temperature of water? The melting temperature? Express your answers to the nearest 0.1¡C.

3. How does the freezing temperature of water compare to its melting temperature?

4. Tell if the kinetic energy of the water in the test tube increases, decreases, or remains the same in each of these time segments during the experiment.

a) when the temperature is changing at the beginning and end of Part Ib) when the temperature remains constant in Part Ic) when the temperature is changing at the beginning and end of Part IId) when the temperature remains constant in Part II

5. In those parts of Question 4 in which there was no kinetic energy change, tell if potential energy increased or decreased.