Practical activity

In this online experiment you will determine which food stores more chemical energy using a simple food calorimeter.

Task 1: You will perform a series of calorimetry experiments for different food: plantain chips, millet porridge, fufu, coconut peanuts and puff puff mix.

Task 2: Using the data of your calorimetry experiments, you will determine the number of calories per gram in different foods.

Task 1: Food calorimeter experiments

You will now carry out your calorimetry experiments. Remember that all your data should be recorded in your laboratory notebook.

The change in the temperature of water during the combustion of food is measured using a thermometer and it is a direct measure of the energy in food. Food samples should be weighed before and after the combustion to calculate the actual mass of food burned to heat one litre of water.

The food samples were prepared for analysis by drying them in an oven at around 50-60^oC overnight.

Detailed instructions are provided within the experiment. In preparation for the experiment read and reflect on the following summary of the steps you will need to take:

1. Choose a type of food from the list provided.
2. Weigh the crucible containing your selected food and record the initial mass.
3. Place the crucible with food on the moveable support of the calorimeter metallic base.
4. Move the empty glass water jacket with its integral combustion chamber and the attached copper spiral tube onto the calorimeter base. The manual stirrer used to homogenize the temperature of water is already placed inside the water jacket.
5. Add 1000 ml of fresh tap water into the glass water jacket. Once water has been transferred, the application will place the lid of the glass water jacket for you. The oxygen source and the water jet vacuum pump will be also connected to the in- and outlets of the food calorimeter.
6. Turn on the temperature display and the probe will be moved inside the glass water jacket.
7. Stir the water to ensure uniform temperature throughout the glass water jacket before taking a temperature reading.
8. Open the water tap to start the water jet vacuum pump. This will ensure suction of gases out of the combustion chamber.
9. It is now safe to open the regulator valve of the oxygen cylinder.
10. Bring the crucible and food closer to the igniter coil.
11. Turn on the low-voltage power supply. A video will start playing showing the combustion of your selected food. The application will turn off the power supply for you as soon as the food sample starts burning. The crucible will be moved to its original position. While the video is playing all the different parts of the calorimeter are locked down and you can’t change any settings.
12. Once the flame is extinguished, stir the water before recording the final temperature.
13. Close the regulator valve of the oxygen cylinder.
14. Close the water tap to stop the water-jet pump.
15. Remove temperature probe by switching off display and the application will start dissembling of food calorimeter for you.
16. Reweigh crucible with any remaining food residue and record the final mass.

Repeat these steps at least twice for each food. The water in the conical flask will be refreshed each time. Planning your experimental work will help your experiments to run smoothly in the virtual laboratory.

Table 3 shows a template you could use to record your observations.

Table 3 Calorimeter data for combustion of different foods.

Click on the icon to access the OpenSTEM Africa Virtual Laboratory Calorimetry homepage. Watch the introductory video before entering the experiment to carry out Task 1.

Task 2: Data analysis and discussion

Use your data from Task 1 to calculate your experimental energy of foods. Table 4 shows a template you could use to record your values.

Table 4 Experimental values of food energy

Now let’s discuss your experimental values of energy in different foods and compare your data with values of energy in food labelling.