Practical: Energy Content of a Food Sample (Edexcel IGCSE Biology)

Spec point — 2.33B · practical: investigate the energy content in a food sample

Practical: Energy Content of a Food Sample

We can investigate the energy content of food in a simple calorimetry experiment

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 25 cm³ of water and pour it into the boiling tube

• Record the starting temperature of the water using the thermometer

• Record the mass of the food sample

• Set fire to the sample of food using the bunsen burner and hold the sample 2 cm 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

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:

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

• 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

Limitations

• Incomplete burning of the food sample

  • Some food may not burn completely, so not all of the energy of the food is released
  • Solution: relight the food sample until it no longer lights up

• Heat energy loss to the surroundings

  • Some of the energy from the burning food escapes into the air instead of heating the water
  • This can make the calculated energy values lower than the true values

• Ways to reduce heat loss:

  • Simple improvements:

    • Keep the boiling tube close to the burning food (but safely)
    • Use a piece of aluminium foil around the tube to reduce heat loss

  • An alternative is to use a calorimeter:

    • A calorimeter is a piece of equipment that captures almost all of the heat released when food burns
    • Instead of burning food in open air to heat water in a boiling tube, the food is burned inside the calorimeter
    • This reduces heat lost to the surroundings and transfers more of the food’s energy to the water. As a result, the calculated energy content (from measuring the temperature change in the water) is more accurate and closer to the true energy stored in the food