Water and Ice- To determine the specific heat capacity of water (a) and the specific latent heat of fusion of water (b).

Procedure:

1. The aluminum calorimeter and the aluminum stirrer was taken out of the insulating jacket and measured with the triple-beam balance the total mass.
2. 100ml (100g) of water was added into the calorimeter. The reading of the balance was recorded to calculate the actual mass of water added.
3. Then the calorimeter was placed back into the insulating jacket, and next the heating coil and the thermometer were also inserted and finally the calorimeter covered properly.
4. As directed, the circuit was connected with the power supply pointed to 12V.
5. The initial temperature of water was recorded before the experiment began.
6. The power supply was switched on so that the current can be adjusted to 2A using a rheostat.
7. As soon as the proper adjustment was done, the stop watch was started immediately. The readings of the voltmeter and ammeter were recorded as well.
8. During the heating process, the water inside the calorimeter was stirred continuously. Meanwhile the temperature was recorded tabulated at each 30 seconds interval.
9. Step 8 was repeated until the thermometer had shown 10℃ increase.  Readings of the voltmeter and ammeter were taken again.
10. Power supply switched off.

Results:

2. By E=VIt, the total energy evolved during heating of heating coil is:

E=(2.6)(2)(2080)

E=10,816 J

3. Then by subsidizing the required data into (ii), we have:

10816=(100/1000)c(5.1)+(30.9/1000)(900)(5.1)

c=20,930 J kg-1 K-1

Discussion:

1. Compared to the standard value of specific heat capacity of water, 4200 J kg-1 K-1, the percentage error is (20930-4200)/4200x100%≈398%
2. Such enormous error cannot be accepted. Some unexplainable mistakes or faultiness must have occurred during procedures. Time, however, does not allow us to re-do the experiment. Thus, the experimental data remains valid.

Experiment (b): To determine the specific latent heat of fusion of water

Principle:                 An object absorbs latent heat of fusion while it melts. Specific latent heat   of fusion can be found by: E=mℓf, where energy E depends on the mass m of the object.

                In this experiment, some hot water heated ≥10℃ the room temperature in the calorimeter is to be cooled down by adding ice cubes into the until the temperature falls to 10℃ below the room temperature.

                The energy lost by water and calorimeter is E1=mwcw(T1-T2)+mccc(T1-T2)……(iii), while the energy gained by the ice during melting and heating to final temperature is E2=miceℓf+micecwΔT……(iv). Finally, by assuming all heat evolved is absorbed by the ice and thus the conservation of E1=E2, the specific latent heat of fusion of water can be found.

Procedure:

1. Using the same calorimeter as in experiment (a), the water inside and heating coil were removed while the rest were reserved. A hole on the cover of the calorimeter was allowed for putting water and ice into it.
2. The total mass of the whole assembly without containing water was measured with a triple-beam balance.
3. About 100g (100ml) of hot water was poured into the calorimeter and then the balance reading and the initial temperature were both recorded.
4. Ice cubes were added into the calorimeter one by one after each allowed to be melted totally with stirring. But before adding, the ice cubes were first dried with cloth.
5. Step 4 was repeated until the water temperature reached to 10℃ below room temperature. At the end, the final mass of the calorimeter and its content were measured.

Results:

2. By subsidizing the data into equations (iii) and (iv), we have

E1=(100/1000)(4200)(39.5-15)+(30.9/1000)(900)(39.5-15)

E1=10,971.345 J

E2=E1

                E1=(59/1000)ℓ+(59/1000)(4200)(0-15)

                ℓ f=248,955 J kg-1

Discussion: 

1. As the ice cubes were inserted into the hot water, its temperature falls gradually.
2. The magnitude of temperature fall of the hot water for each ice cube is proportional to the size of the ice cube to be added.
3. The resulting value of specific latent heat of fusion of water, when compared with its standard value of 334,000 J kg-1, is underestimated by:

(334000-248955)/334000 x 100%≈25.5%

Sources of error:

1. Heat is lost to the surroundings by convection, conduction and radiation.
2. Heat absorbed by the polystyrene foam in the jacket is not measured.
3. Thermometer is inaccurate in scale, thus errors may occur in measuring temperature with ordinary thermometer.
4. Personal errors may occur while taking thermometer readings and weighing objects as well.

Conclusion:                According to the comparison between the standard values and the experimental results, it is obvious that the methods used in their corresponding experiments cannot give accurate results. The main reason is believed to be due to the accounting of serious unmeasured heat loss and errors of system, personal, etc.