Combustion of Alcohols Investigation

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Combustion of Alcohols Investigation

Aim

The aim of this investigation is to investigate which of a number of alcohols methanol, ethanol, propanol and pentanol is the most efficient fuel.

Possible Factors To Be Investigated

There are four main factors that could affect the heating done by a fuel. These four factors are:

  • Distance. The greater the distance of the heat source from the water, the more energy will be needed to heat the water. For example: It will require a lot less energy for the heat source to heat the water from 5cm than it would if the heat source was 10cm away. An increase in the amount of heat lost to the surroundings will mean the fuel will have to burn more and release more energy to achieve the same heating affect.

  • Temperature Rise. A lot more energy is required to raise the same amount of water by 100oC than to raise it by 10oC. This means that the fuel will have to burn longer to increase the temperature of the water by a larger amount.

  • Volume of Water.         A larger volume of water will require a larger amount of heat to raise its temperature to a certain level. For example: More heat energy will be required to raise 200cm3 of water from 20oC to 50oC than it will to raise a lesser amount of water by the same margin.

  • Size of Alcohol. Different types of alcohol are available to us at school and this is a key factor in choosing this for our investigation. They have a good variety of sizes and are definite in their sizes. Human errors could be made if any of the other factors are used such as when measuring distances or the temperature rise but the margin of error is greatly reduced when using this factor. It allows me to devise a clear hypothesis, which can be directly compared to my actual results to see how accurate and efficient the method of my experiment really is. As the size of the alcohol increases more energy is produced and released. This energy is released as heat. This is because as the alcohol gets larger it contains more bonds. When these bonds are broken energy is released. If more bonds are broken then more energy must also be released. I feel that this is a good factor to investigate for my experiment and will therefore be the key factor that I will investigate.

Apparatus Required

  • Methanol, Ethanol, Propanol and Pentanol (variety of alcohols)
  • Clamp stand
  • Beaker
  • Thermometer
  • 100cm3 of water
  • 4 heat-proof mats
  • Weighing Scales

                

Diagram of Apparatus

Method

The alcohol is weighed with the alcohol burner and it's lid and the weight is recorded. A beaker containing 100cm3 of water is suspended, using a clamp, above the alcohol burner. After originally doing the experiment and realising that placing the thermometer in the beaker could cause errors, it was decided that it should be suspended using a clamp, so as to only take a reading of the water temperature and not the container. The initial temperature of the water is measured. The temperature of the water is taken and then the fuel is lit. Heatproof mats surround the flame and beaker so as to let as little heat out as possible to the surroundings. The experiment is left until the temperature had risen by 20oC. The flame is then extinguished and the fuel is weighed again with the lid. This method was repeated for each of the four fuels and the results are recorded. This is repeated with each fuel twice to reduce the risk of anomalous results.

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Fair Test

  • Container size. The container size affects the volume of water inside it, I can't put 300cm3 of water inside a 200cm3 container. Also, if the volume of water I find most appropriate, only fills half the container, then the space not being used will be transferring more heat to air around, than if I used the same amount of water in a smaller, more appropriate sized container. It will be an unfair test if the size of the container differs in each repetition and will have to remain constant throughout.
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