Required practical

Measuring the specific heat capacity of water

There are different ways to determine the specific heat capacity of water. In this required practical activity it is important to:

  • measure and observe the change in temperature accurately
  • use the appropriate apparatus and methods to measure the specific heat capacity of water

Aim of the experiment

To measure the specific heat capacity of water.

Method

  • Place one litre (1 kg) of water in the calorimeter.
  • Place the immersion heater into the central hole at the top of the calorimeter.
  • Clamp the thermometer into the smaller hole with the stirrer next to it.
  • Fully insulate the calorimeter by wrapping it loosely with cotton wool.
  • Record the temperature of the water.
  • Connect the heater to the power supply and a joulemeter and turn it on for ten minutes. Stir the water regularly.
  • After ten minutes the temperature will still rise even though the heater has been turned off and then it will begin to cool. Record the highest temperature that it reaches and calculate the temperature rise during the experiment.

Results

Record results in a suitable table. The example below shows some suitable results.

Energy supplied (J)Initial temperature (°C)Final temperature (°C)
100,0001538

Analysis

The water has a mass of 1 kg and the heater supplied 100,000 J, whilst the temperature rose 23°C.

Using the example results:

c = \frac{\Delta Q}{m\Delta \theta }

c = \frac{100,000}{1 \times 23} = 4,300~J/kg {\textdegree}C

The actual value for the specific heat capacity of water is 4,200 J/kg°C. The calculated value does not match exactly but it is in the correct order of magnitude.

Evaluation

  • All experiments are subject to some amount of experimental error due to inaccurate measurement or variables that cannot be controlled. In this case, not all of the heat from the immersion heater will be heating up the water, some will be lost to the surroundings.
  • More energy has been transferred than is needed for the block alone as some is transferred to the surroundings. This causes the calculated specific heat capacity to be higher than for one kilogram (kg) of water alone.
  • The lid on the calorimeter has reduced much thermal energy loss, and the use of cotton wool insulation has also helped to insulate the calorimeter. Thicker insulation would improve the accuracy of the results even more.

Hazards and control measures

HazardConsequenceControl measures
Hot immersion heater and sample materialBurn skinDo not touch when switched on. Position away from the edge of the desk. Allow time to cool before packing away equipment. Run any burn under cold running water for at least 10 minutes.