The amount of energy required to convert a solid to a liquid, at constant pressure
and temperature, is called the heat of fusion of the substance. In this
experiment, the heat of fusion of ice will be determined.
The ice will be melted by placing it in a known volume of hot water contained
in a plastic cup. The system will be left undisturbed until all the ice has
melted. The amount of heat lost by the hot water in this process can be calculated
according to the following equation.
The heat lost by the water will be absorbed by the melting ice. The volume of ice that melts can be determined by measuring the volume of the water in the cup before the ice is added and after the ice has melted.
The mass of melted ice can be calculated from its volume and density.
If the mass of the ice melted and the heat absorbed by the ice are known, the heat of fusion of ice can be calculated.
MATERIALS NEEDED:
Safety goggles
400-ml beaker
wire gauze
plastic foam cup
gas burner
thermometer
100-ml graduated cylinder
ring stand
beaker tongs
250-ml beaker
ring support
spatula
PROCEDURE:
1. Add approximately 100 ml of water to a 250-ml beaker, and heat the water to 60 deg. C, using a gas burner and standard ring stand assembly. While the water is heating, fill a plastic foam cup halfway with ice cubes. Place the cup in a 400-ml beaker for support.
2. When the temperature of the water has reached 60 deg. C, use two 20 ml portions of this hot water to preheat a 100-ml graduated cylinder. Rinse the cylinder with each of the hot water portions and discard the rinses.
3. Pour 30.0 ml of the hot water into the graduated cylinder. Record the volume on the DATA TABLE. Measure and record the temperature of the water to the nearest 0.5 deg. C, and record on the DATA TABLE.
4. Quickly drain any excess water from the ice cubes in the cup. Add the measured hot water to the ice in the cup. Stir the ice water rapidly, but with care, until its temperature falls to 2 deg. C. At this point, some unmelted ice should remain in the cup. If, in fact, all the ice has melted, add a bit more so that some ice remains unmelted when the temperature is 2 deg. C or below. Record on the DATA TABLE the lowest temperature of the mixture of ice and water to the nearest 0.5 deg. C.
5. Using a spatula, quickly remove any unmelted ice from the cup. As you remove the ice, drain as much water as possible back into the cup.
6. Carefully pour the cold water from the cup into the graduated cylinder and record the final volume to the nearest 0.1 ml on the DATA TABLE.
| DATA TABLE: |
| Initial volume of hot water. _______ ml |
| Initial temperature of hot water. _______ deg. C |
| Final temperature of water and melted ice. _______ deg. C |
| Final volume of water and melted ice. _______ ml |
CALCULATIONS:
7. Calculate the change in temperature of the hot water. This is simply the initial temperature of hot water - final temperature of water and melted ice.
8. Calculate the mass of the hot water. Don't forget that 1 ml of water has a mass of 1 g. This is because the density of water is 1 g/ml. So the volume in ml is the mass in grams.
9. Calculate the heat lost by the hot water. (See equation 1 in the introduction.)
The specific heat of water is
4.18 joule/g x deg. C . Your answer will have
Joule as the unit.
10. Calculate the volume of ice melted. (See equation 2 in the introduction.)
11. Calculate the mass of ice melted. (See equation 3 in the introduction.) As in step 8, 1 ml of water has a mass of 1 g. So its just the volume changed to grams.
12. Calculate the heat of fusion of ice in joules/g. (See equation 4 in the introduction.) The heat absorbed by the ice is the same as the heat lost by the hot water, so it's the answer from step 9. The mass is from step 11.
The accepted value for the heat of fusion of water (ice) is 334
joules/g. How did your results compare to this accepted
value?