Heat of Combustion Practical

Aim: To perform an experiment to determine and compare heats of combustion of least three liquid alkanols per gram and per mole.

Risk Assessment: Since alkanols are being burned there is exposure of a naked flame and a flammable hazard. Care must be taken to ensure that any spills are being cleaned up immediately and safety goggles are to be worn. A fire extinguisher should also be kept close by for emergencies.

Equipment: Electronic balance, aluminium can, thermometer, retort stand, clamp, boss head, spirit burners (ethanol, propanol and butanol), measuring cylinder.

Method:

  1. Weigh the aluminium can and record its mass.
  2. Measure 300mL of water and pour it carefully into the can.
  3. Insert a thermometer into the can and record its initial temperature in the water.
  4. Place the can in the clamp on the retort stand.
  5. Weigh the capped ethanol spirit burner and record the mass.
  6. Light the burner and heat the water until the temperature rises by 20oC
  7. Extinguish the flame and cap the burner. Stir the water gently and record the maximum temperature reached.
  8. Reweigh the spirit burner and determine the mass difference.
  9. Repeat the process for propanol and butanol

Discussion:

  • The main source of error on this experiment was the calorimeter as much of the heat was lost to the surroundings. This could have been improved by using a better insulated calorimeter or a wind break to minimise heat.
  • Incomplete combustion occurred as seen by the presence of black soot on the bottom of the can.
  • Failure the keep the thermometer in the middle of the can.
  • Heat absorption by the aluminium can, would not necessarily have been completely transferred to the water.

Conclusion: We successfully measured the heat of combustion of a series of alkanols.