Heat of combustion of alkanols

Updated website at: http://sciencehsc.com.au 

 

Diagram:

alkanol prac

Method:

  1. Set up apparatus as shown.
  2. Light the first spirit burner.
  3. Adjust the height of the vessel so that the tip of the flame just touches the vessel.
  4. Weigh the burner (initial mass) with its liquid contents and record.
  5. Add 200 mL of cold water to the vessel using a measuring cylinder. Place the thermometer in the water and record its initial temperature.
  6. Light the wick and stir the water gently (to ensure uniform heating).
  7. When the temperature has risen 10C extinguish the flame by placing the cap.
  8. Again weigh the burner (final mass). Remove any soot from the bottom of the vessel and replace the water before testing the next alcohol.

Methods to reducing error when determining heat of combustion

  • Ensure the tip of the flame touches the vessel to minimise heat lost to the environment.
  • Use a copper can or perform experiment in a bomb calorimeter to contain as much heat as possible.

Remember there will always be heat loss to the environment thus the energy absorbed by the water is less than the amount of energy released by the fuel combusting. This loss of energy can be considerably large and thus will result in large inaccuracies.

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