The formulae of the fuels that I will be using are:
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Methanol CH3OH
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Ethanol C2H5OH
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Propanol C3H7OH
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Butanol C4H9OH
I will show the reaction that takes place, taking methanol as the example:
Structure of Methanol molecule
Reaction
CH3OH + 2O2 = CO2 + 2H2O
Methanol + Oxygen = Carbon Dioxide + water
I predict that the more bonds there are holding the carbon, oxygen and hydrogen atoms together, more energy will be required to break them apart and so they will evolve more energy per gram used. Incomplete combustion can affect my results. Too much, or too little fuel with the available combustion air may potentially result in unburned fuel and carbon monoxide generation. A very specific amount of O2 is needed for perfect combustion and additional Oxygen is required for good combustion. Too little Oxygen will result in more Carbon Monoxide and Carbon being produced. Carbon may become deposited on the bottom of the beaker – further reducing efficiency.
A longer molecule takes more energy to break its bonds, in this case Butanol, compared to a smaller molecule, Methanol which requires less energy to do so. I can come to predict that the longer the molecular structure in the fuel the more energy it will take to remove the bonds. So when I come to predicting results I can safely say that Butanol will evolve more energy than methanol simply because it has more bonds to break.
Preliminary Work
This experiment was done to see which mass of water would be best. The 25g mass was too large a rise as this caused too much heat to be lost to the environment, and 75g was too small. Therefore the 50g value was used, as this temperature was right for the calculations. Also I used a Bunsen to support the fuel while it was burning but I found out that this was unfair test as this caused the wick to be different distances from the beaker every time. Using a clamp stand allows the experiment to be fair as the distance between the wick and the beaker can be kept the same for every fuel.
Secondary Sources
I used the Science: Double Award Modular by Mary James Revision guide, bbc.co.uk/bitesize/revision and gcsewise.com websites.
Results
Test 1
Test 2
Averages
Conclusion
My results did agree with my prediction. Butanol was the most efficient fuel as it has longest molecules and, going back to my prediction, a longer molecule takes more energy to break its bonds compared to a smaller molecule. The longer the molecular structure in the fuel the more energy it will take to remove the bonds, so Butanol evolved more energy than other fuels simply because it has more bonds to break. Butanol was followed by other fuels in the order that I thought they would: Propanol, Ethanol and Methanol because that’s the order of how long their molecules are. This further assures me that my prediction was correct. Also the scale of blackness shows that both methanol and Ethanol fuels didn’t leave any copper deposited on the beaker whereas Propanol was 10 and Butanol was 5.5 on our scale. This could have affected my results as that means that incomplete combustion takes place, meaning that not all of the fuel is burned but my results agreed with my prediction which means that this factor didn’t affect my results by too much.
Complete combustion occurs if there are lots of oxygen atoms available when the fuel burns, then you get carbon dioxide (carbons atoms bond with two oxygen atoms). If there is a limited supply of oxygen then you get carbon monoxide (each carbon atom can only bond with one oxygen atom). This is when incomplete combustion has occurred. This is so because the carbon monoxide could react some more to make carbon dioxide. If the oxygen supply is very limited then you get some atoms of carbon released before they can bond with any oxygen atoms. This is what we call soot. Since heat is given out when bonds form, less energy is given out by incomplete combustion. So this is why it affects the outcome of the experiment.
Evaluation
The results indicate that I can draw a definite conclusion, as all fuels resulted in an exothermic reaction with similar results for each repetition. However, one of the Butanol trails resulted in an odd result which is circled in my results table. Over two minutes of heating in the first trial the temperature of Butanol rose by 16 Cº whereas in the second trial the temperature rose by 37 Cº but the temperature increase per gram stayed roughly the same. I think this is because we used different fuel burners and they had different size wicks that affected it. The temperature increase per gram was a bit different because some of the heat was lost to the surroundings into the air and it was more significant 2nd time when there was less fuel used and so less temperature rise. If I was to do it again I would repeat the experiment more times to get even more reliable results and burn fuels for a bit longer. Improving insulation techniques would be a valuable asset in obtaining the most reliable data I could. Another error is that of incomplete combustion. To overcome this problem, I would have to make sure a sufficient supply of oxygen was involved in the reaction.
I feel that this experiment could have been improved by comparing other hydrocarbons to the alcohol group such the alkane and alkene families. I could also work out the energy given out per mole using bond energies and compare this to my results.
