National 5BiologySQARevision NotesUnit 1: Cell BiologyRespirationPractical: Energy Content of Food

Practical: Energy Content of Food (SQA National 5 Biology): Revision Note

Exam code: X807 75

Cara Head

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Cara Head

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Investigating the energy content of food

  • 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

Examiner Tips and Tricks

Note that this practical is a 'suggested practical' in the specification, rather than content that all students are expected to learn. Some schools may choose to complete alternative practicals, or may miss out practical work that is not realistic, e.g. due to equipment or time constraints.

Apparatus

  • Boiling tube

  • Boiling tube holder

  • Bunsen burner

  • Mounted needle

  • Measuring cylinder

  • Balance/scales

  • Thermometer

  • Water

  • Food samples

Method

  1. Use the measuring cylinder to measure out 25cm3 of water and pour it into the boiling tube

  2. Record the starting temperature of the water using the thermometer

  3. Weigh the initial mass of the food sample

  4. 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

  5. Record the final temperature of the water

  6. Repeat the process with different food samples

    • e.g. popcorn, nuts, crisps

Experiment setup with a test tube of water held by a stand, a thermometer, and burning food on a mounted needle below.
Different food samples can be burned in a simple calorimetry experiment to compare the energy contents of the samples

Expected 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:

E n e r g y space t r a n s f e r r e d space p e r space g r a m space o f space f o o d space open parentheses J close parentheses space equals space fraction numerator m a s s space o f space w a t e r space open parentheses g close parentheses space x space t e m p e r a t u r e space i n c r e a s e space open parentheses ring operator C close parentheses space x space 4.2 over denominator m a s s space o f space f o o d space s a m p l e space open parentheses g close parentheses end fraction

  • 4.2 kJ is the specific heat capacity of water

    • 1 cm3 of water has a mass of 1 g

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 the same way each time (with the same distance between the food sample and boiling tube), we can still compare the results

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    Cara Head

    Author: Cara Head

    Expertise: Biology & Psychology Content Creator

    Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding