Determination of the Heat of Fusion of Ice
Purpose
We wanted to find how many calories are needed to melt 1 gram of ice.

Equipment
  • Hot plate
  • Watch glass
  • Vernier thermometer
  • 250 mL beaker
  • 100mL graduated cylinder (graduated in mL)
  • Electrical scale (graduated to 0.01g)
  • Tongs
  • Stopwatch (graduated to 0.1s)

Procedure
We decided to first calibrate the hot plates because we wanted to measure heat by establishing a rate and then measuring time but we needed to make sure that the rate was constant before we could do the main experiment (this was important because if they released different amounts of heat it would greatly affect the melting of the ice). We did this by setting three hot plates to the 4th temperature (after using a thermometer on each of the hot plates to ensure that they had heated up already). On top of each hot plate we put 100g of H2O (measured with a graduated cylinder) in a beaker and covered them with a watch glass. We used thermometers to find the temperature of the H2O as it heated (we tracked the temperature with Logger Pro). We watched as the temperature of the H2O steadily increased, after a while though, it started to level out (this was because heat was being released through evaporation as it was coming in through the hot plate) and we found that it lost 22 calories per second (we found this by dividing the calories by the change of mass). Since we would not have this problem with ice (because it was a problem with the H2O in the calibration, not with the hot plate), we continued with our original plan. The graphs for each of the hot plates from Logger Pro were very similar (so we knew that we could count on all of them).
For the main part of our experiment, we again measured 100mL of H2O with graduated cylinders and put the water into a beaker. We put the beaker (with the H2O) into the freezer over the weekend to freeze the water. We wanted to have as broad a piece of ice as possible so that the least amount of warmth from the hot plate would go into the air. We then took the ice out of the cold beaker (by running the beaker under warm water to melt the ice enough to slide it out) and put it into a room temperature beaker of the same size. We weighed the ice first, then placed this onto a hot plate (set to the 4th temperature), covered it with a watch glass and timed it; we took the beaker off when there was a noticeable amount of water that had melted from the ice (we did not want the water to take the heat away from the ice). We measured the ice before and after we put it on the hot plate, this helped us to determine how many calories/second were lost. We did this procedure twice (both of the experiments are represented below in the Data and Analysis).

Data and Analysis
Experiment #1
Trial
Initial Mass of Ice (g)
Final Mass of Ice (g)
D of Mass (g)
Time (s)
Cal/Gram
1
78.18
63.9
14.28
45.2
69.6
2
63.32
53.85
9.47
45.7
106
3
53.85
41.73
12.12
62.8
114
4
41.22
29.91
11.31
69.0
134
5
29.91
19.01
10.9
63.5
128
6
18.04
13.9
4.14
21.2
114

Experiment #2
Trial
Initial Mass of Ice (g)
Final Mass of Ice (g)
D of Mass (g)
Time
Cal/Gram
1
80.38
66.86
13.52
55.5
90.3
2
66.30
54.49
11.81
60.4
113
3
53.92
44.49
9.87
62.4
139
4
43.05
35.79
7.26
47.5
144
5
34.41
29.48
4.93
41.3
184
6
29.03
19.51
9.52
65.9
152

We took the data we got from the experiment and calculated the calories lost per gram of ice (we did this by dividing the change of mass by the time it took to melt the ice). The initial and final masses are shown in the second and third columns. Their difference (the fourth column) is how much ice melted during the time (fifth column) we heated the ice in the beaker. Since our calibration of the hot plate showed us that 22 calories went into the contents of beaker every second, we were able to figure out how many calories were responsible for melting that much ice (the sixth column). The results we got are shown in the graphs below.

Experiment #1
HoF_Experiment_1_Graph.jpg

Experiment #2
HoF_Experiment_2_Graph.jpg


Uncertainty Analysis
The data in the first experiment is tighter and has less variation. But the second experiment is more exact because there were other factors involved when we were doing the first one that make the results less reliable. Other factors included lack of the watch glass on some of the trials, starting the timer too late or too soon and loss of pieces of the ice during transition. By the second experiment, we were more learned about the process because we had more practice. We can definitely say that the amount of calories lost per one gram of ice is between 69.6 and 184, but our experiment was set up in such a way that we cannot be more exact. For each of the experiments the number of cal/gram was increasing, but each one dropped at the end. I believe that this could have been because the ice was smaller and therefore the heart from the hot plate was going into the air more than it did when the ice took up more space.

Conclusion
Our data supports the fact that the heat of fusion of water is 127 cal/g ± 45%.