The Practical Experiment

Making tea with a calorimeter:

 So now you've learnt about how heat transfer works, specifically from a heating element to water in a kettle. We can apply this in a scientific way in this experiment to find the cp of a cup of tea

Aim:

To find the specific heat capacity (cp) of a cup of tea.

Equipment:

• • Glass beaker

  • Immersion heater connected to a DC circuit

  • Water

  • Teabag

  • Stirrer

  • Thermometer

Example set-up:

Method:

1. Place a beaker on a balance and press zero.

2. Fill the beaker with (cold) tea and record the mass of the tea.

3. Record the starting temperature of the water. 

4. Turn on the heating element at the same time you turn on the stopwatch. 

5. Mix constantly using the stirrer and every 30 seconds record the temperature against the time in a results table. 

Results:

1. Since Q = VIt = mcpΔT, you can plot a graph of temperature change against time. 

2. Draw a line of best fit and find its gradient (if its a straight line). 

3. Since this gradient M will be equal to P/(ρVcp), use cp= P/(ρV*M) to find the specific heat capacity.

Analysis of results

• Discuss the results shown on your graph - is best fit a line or a curve? Why?

• What value did you find for cp? Research the cp of water - are the values close? Is the result what you expected? If not, why not - what were the sources of uncertainty in the results?

• Calculate the uncertainty in your result using lines of best and worst fit 

Discuss sources of inaccuracy:

1. Energy loss to the surroundings - use an insulator with a lower thermal conductivity around the beaker, or use a bomb calorimeter instead of this slightly rudimentary set up.

2. Not all energy being transferred into the tea - ensure that immersion heater is fully submerged, or use a bomb calorimeter instead of this slightly rudimentary set up.

3. Incorrect reading of thermometer - Use an electronic temperature probe.

Conclusions:

• Summarize your findings from the experiment and whether they are what you expected