#27Q2) Heat
Determination of specific latent heat of fusion of ice by the method of mixtures
Required Apparatus
A calorimeter, a stirrer, a thermometer, water, a sufficient quantity of ice, filter papers, a four beam balance, chemical balance, and a box of weights.
Scientific Theory
In the experiment above, let:
- : The mass of an empty calorimeter with a stirrer
- : Mass of the calorimeter with a quantity of water
- : The initial temperature of the water
- : Minimum temperature of the mixture when mixed with ice
- : Mass of the calorimeter with final contents
- : Specific heat capacity of water
- : Specific heat capacity of calorimeter metal
- : Specific latent heat of fusion of ice
Then since , assuming that no heat was absorbed from the surroundings during mixing:
Heat gained by ice = Heat lost by water and calorimeter (with stirrer)
Experimental Method
- Measure the mass of the calorimeter with the stirrer.
- Fill about two thirds of the calorimeter with water at room temperature and measure its mass again. Measure also the temperature of the water.
- Wipe out water from small pieces of ice using filter paper and put those one by one into the water in the calorimeter while stirring, taking care to insert one piece after the previous one has dissolved. Use a square-net stirrer to prevent the ice from floating in water.
- When the temperature of the water has fallen sufficiently (by about stop adding ice, stir the mixture well and record the lowest temperature of the mixture .
- Finally measure the mass of the calorimeter with its contents again .
- Substitute values of , , , and standard values for and in the expression given in the theory and calculate the value of .
Important Points
1
- Conclude the value obtained from the calculation as the specific latent heat of fusion of ice.
2
- Compare the value of specific latent heat of fusion of ice you obtained from the experiment with its standard value you would obtain from a data book and calculate its percentage error.
3
- It is advisable to determine the dew point approximately before mixing ice. Then by preventing the final temperature of the mixture going below the dew point, the error caused by the dew depositing on the calorimeter surface can be minimized.
4
- When the temperature of the calorimeter begins to fall below room temperature with the mixing of ice, it begins to gain heat from the surroundings. This can be minimized by lagging the calorimeter with heat absorbing materials.
5
- Or else the compensation method used in the method of mixtures can be used. Heat the calorimeter with water by about above room temperature. Considering this temperature as the initial temperature mix pieces of ice until the temperature of the water falls below the room temperature by the same number of degrees . Assuming that the heat lost by the system during the above room temperature compensated with the heat gained by the system during the below room temperature, the error due to heat gained from surroundings can be considered to have minimized.