Investigating which alcohol is most efficient at heating water

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GCSE CHEMISTRY COURSEWORK: Planning

Investigating which alcohol is most efficient at heating water

Independent Variable:

  • Type of alcohol e.g. methanol, ethanol etc.

Dependent Variable:

  • Mass of alcohol burnt for a temperature rise of about 10°c.  This is a sensible rise of water temperature because it is large enough to measure changes in the mass of alcohol burnt but small enough that it won’t take too long to do each one.

I will investigate how the type of alcohol affects the mass needed to create a temperature rise of about 10°c in water.  

Hypothesis

I predict that as you go up the series of alcohols e.g. from methanol to ethanol etc. less alcohol will have to be burnt for the temperature rise of about 10°c in the water.  I believe this because of the results of my preliminary work (below) which shows that the amount of energy given off any alcohol is directly proportional to the size of the molecule.  Here is a sketch graph of what I expect to happen:

   

        

Safety

  • Safety goggles should be worn at all times
  • Keep clothing away from the flame
  • Keep Bunsen flame on the safety flame when not using it

Apparatus

  • Tin can
  • 300ml measuring cylinder
  • Clamp stand and boss
  • 8x spirit burners (one for each alcohol)

Diagram of apparatus

        can containing water

                     x   x         x

        x      x=clamps

        Heat (from spirit burner)

Controlled variables-fair test

To make the investigation fair I will ensure that as many variables as I can remain the same:

  • Liquid used
  • Amount of liquid (400ml)
  • Can used
  • Length of wick penetrating the top of the spirit burner
  • Distance of can above flame
  • Starting temperature of water
  • Ensure there are no drafts from open windows to blow the flame

However, there are also uncontrollable variables such as: room temperature and soot on the bottom of the can etc.

Preliminary Work 1

I carried out preliminary trial runs to test the suitability of my plan.  I used three alcohols:  The smallest in the range of alcohols I have been given (methanol), the middle of the range (propanol), and the largest in my range (octanol).  

These are my results:

Methanol: Weight difference: 1.20g

               Temperature difference: 10.50 degrees Celsius

Propanol: Weight difference: 1.20g

               Temperature difference:  13.50 degrees Celsius

Octanol:  Weight difference:  0.79g

               Temperature difference:  10.50 degrees Celsius

I found no problems with the experiment so am not change anything for the real thing.

Final method

For each experiment, 400ml of water will be measured with a measuring cylinder and put into a can.  Measurements will be taken at the level of the top of the water to reduce parallax error.  I will weight for the water to become room temperature.  The mass of the spirit burner before heating will be weighed.  I will leave the cap on (explained later).  The can will be suspended on in the middle of the flame to ensure that as much of the available heats goes into the water that is possible.  The alcohol will be lit quickly to ensure that heat from the Bunsen flame does not transfer to the water and affect the readings.  I will stir the water with a thermometer all the time to ensure and even temperature (no spots of high temperature).  I will wait for the temperature to rise by about 10°c and extinguish the flame quickly with the cap.  The cap will remain on the spirit burner to stop smoke from being lost (reason for leaving cap on in first weighing).  The mass of the spirit burner after heating will be recorded.  This will be carried out three times for each alcohol and an average will be calculated.  Anomalous results will be repeated.  This will increase accuracy.  

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Preliminary Work 2

I was able to work out the amount of energy that should be released by each alcohol by firstly working out the energy required for bond breaking.  This was done by counting the number of different bonds broken i.e. C-H and using a data table to find out the amount of energy required.  Secondly, I worked out the energy released by bonds being made again by counting the bonds and using a data table.  I subtracted the second number from the first to work out the energy released ...

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