Investigating the Energy Content of Foods | WJEC GCSE Biology Revision Notes 2018

Specified Practical: Investigating the Energy Content of Foods

We can investigate the energy content of food in a simple calorimetry experiment
This involved burning a sample of food under a known volume of water
The energy from the food is transferred into the heat of the flames, which in turn is transferred into the heat of the water
The change in temperature of the water sample reflects the quantity of energy in the sample and can be calculated mathematically

Apparatus

Boiling tube
Boiling tube holder
Bunsen burner
Mounted needle
Measuring cylinder
Balance/scales
Thermometer
Water
Food samples

Method

Use the measuring cylinder to measure out 25cm³ of water and pour it into the boiling tube
Record the starting temperature of the water using the thermometer
Weigh the initial mass of the food sample
Set fire to the sample of food using the Bunsen burner and hold the sample 2cm from the boiling tube until it has completely burned
Record the final temperature of the water
Repeat the process with different food samples
- e.g. popcorn, nuts, crisps

Investigating the energy content of food samples diagram

The energy content of food, downloadable AS & A Level Biology revision notes

Different food samples can be burned in a simple calorimetry experiment to compare the energy contents of the samples

Results

The larger the increase in water temperature, the more energy is stored in the sample
We can calculate the energy in each food sample using the following equation:

$energy transferred per gram of food (J) = \frac{mass of water (g) \times temperature increase ({}^{o}C) \times 4.2}{mass of food sample (g)}$

- 4.2 kJ is the specific heat capacity of water, meaning that it is the energy required to raise 1 kg of water by 1 °C
- 1 cm³ of water has a mass of 1 g

The energy content of food samples table

Food sample	Mass of water / g	Mass of food / g	Initial water temperature / °C	Final water temperature / °C	Change in water temperature / °C	Energy transferred per gram of food (J)
Popcorn	25	8.5	20.5	31.2	10.7	132.2
Walnut	25	8.1	20.4	34.1	13.7	177.6

Limitations

Incomplete burning of the food sample
- Solution: Relight the food sample until it no longer lights up
Heat energy is lost to the surroundings
- Solution: Whilst heat lost means that the energy calculation is not very accurate, so long as the procedure is carried out in exactly the same way each time (with the same distance between the food sample and boiling tube), we can still compare the results

Risk assessment

A hazard in an experiment is something that could potentially harm you
A risk is the harm that could occur as a result of the risk
A control measure is the action taken to reduce the chance of the hazard causing a problem

Risk assessment of calorimetry practical table

Hazard	Risk	Control measure
Burning food products can release allergens into the air	Risk of allergic reactions (skin rashes/breathing difficulties) or anaphylactic shock	Do not use nuts as the food source Keep all the doors and windows open for fresh air
Hot apparatus and water can burn	Hot apparatus can burn and hot water can scald if it gets on the skin Boiling water can spit onto skin over a distance	Leave the apparatus to cool before moving Make sure to point the boiling tube away from you during the experiment Wear safety goggles
Bunsen burner flame can burn	Flame can burn the skin when igniting the food sample	Keep hands a safe distance from the flame Use tongs or a mounted needle to hold the food
Burning food/dripping fat can burn	Burning food can burn the skin when heating water	Keep hands a safe distance from the flame Wear heat proof gloves

Examiner Tip

You may be asked to fill in a risk assessment in an exam for any of the specified practicals. Take a moment to memorise at least two of these and make sure you know the difference between a hazard, a risk and a control measure.

Investigating the Energy Content of Foods (WJEC GCSE Biology)

Revision Note