The Freezing and Melting of Water

Problem: What are the freezing and melting points of water and what is the relationship between the 2 points?

Hypothesis: When we put the test tube in the ice water with salt, the freezing point of the water will be 3ºC. The water will turn completely to ice in 10 minutes. The melting point of the will be 25ºC and it will melt quickly and be gone in 15 minutes.

Materials:
computer
Vernier computer interface
Logger Pro
Temperature Probe
test tube
600 mL beaker
water 15 mL graduated cylinder
ice salt stirring rod

Procedure: Prepare the computer to collect data. Put ice and water into the beaker. Put 5 spoonfuls of salt into a graduated cylinder. Pour 5 mL of tap water into the graduated cylinder and then into the test tube. Place the temperature probe into the test tube and start collecting data. Put the test tube inside of the beaker. Add in the salt and stir with the stirring rod until the salt is dissolved. Add more ice to the beaker as the original ice cubes melt. Stir the temperature probe slowly but consistantly in the test tube for the first 10 minutes. The program will automatically stop collecting data after 15 minutes. Highlight the flat part of the curve and then press the "Statistics" button. The mean temperature is the freezing point. To hide the curve of this run, click the Temperature vertical-axis label of the graph, click More,  and uncheck the Run 1 Temperature box. Click okay. Start collecting data again. Hold the test tube with the temperature probe above the ice water for 12 minutes. Pour out the ice water and fill the beaker with 250 mL of warm tap water. The put the test tube and temperature probe into the beaker for the remainder of the time. The program will automatically stop collecting data after 15 minutes. Highlight the flat part of the curve and then press the "Statistics" button. The mean temperature is the melting point. To display both of the runs, click More and check the Run 1 Temperature and Latest Temperature  boxes. Click ok. Label both of the curves by clicking Text Annotation from the Insert button in the tool bar. Type Freezing Curve or Melting Curve in the edit box. Then drag each box to be near its curve. Drag the arrow to the curve of the right line. 

Data:

This is the ice, salt, and water mixture with the test tube and temperature probe in it. The beaker is foggy and has condensation on the outside. This is at about 11 minutes. 

This is the ice barely melting during the 12 minutes that it was held above the ice bath. There is a little bit of salt around the test tube. The ice is still frozen, but there is a little bit of water around the temperature probe and at the top of the ice. 

This is right after we put the test tube into the beaker with warm water. The water wasn't even that warm and the ice immediately started to melt. You can see the ice shrinking away from the sides of the test tube.

This is at about 13 minutes into the second run and the ice is completely gone. 

This is my sketch of the first run before the salt was stirred in and before the water was frozen. 

This is the graph showing the 2 temperature runs. The blue run shows the melting curve and the red line shows the freezing curve. The water froze at -0.2812ºC and melted at 3.034ºC. The water froze at about 5 and a half minute and the ice melted at about 13 minutes. The temperature continued to increase even after the ice melted which is why there is a big increase in temperature towards the end of the experiment.

Conclusion:
The water's freezing point was -0.2812ºC and its melting point was 3.034ºC. My hypothesis was pretty far off. I thought the freezing point was going to be 3ºC. The water never even froze all of the way through, but that might be because we moved the temperature probe around quite a bit. I thought the melting point would be 25ºC which was off by about 22ºC. In my hypothesis's defense, the temperature did raise to 29.1ºC after the 15 minutes; however, the ice melted at 13 minutes instead of 15 minutes.  There may have been more accuracy if we had been able to use a ring stand and utility clamp instead of holding the test tube. It would also be interesting to see how the test would work without the salt or with more water in the test tube. The freezing and melting points were closer together that I though they would be and they were different from what I thought they would be, but the experiment was overall successful.