To Investigate the Combustion of Fuels
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To Investigate the Combustion of Fuels Plan A fuel is a substance from which energy can be obtained, usually by combustion. I have chosen to use four different alcohols as fuel - methanol, ethanol, propanol and butanol. We can measure how much energy is released by putting the burning fuel under a beaker of water, and recording how much the temperature goes up by. Then the equation E = MC?T is used, where: E = Energy Released M = Mass of material heated C = Specific heat capacity of the material. For water this is 4.2 ?T = Temperature change Method For this investigation I will need: Clamp Stand Metal dish Conical flask Bunsen burner Thermometer Measuring cylinder Wooden splints Scales Water Four spirit burners containing ethanol, methanol, propanol and butanol I will set up this equipment as shown below. First I will light the Bunsen burner, and make sure it is at least a metre away from the rest of my apparatus. Then I will measure out 100ml of water (which equals 100g) using the measuring cylinder, and pour it into the conical flask. Next I will record the temperature of the water using the thermometer, and record the total mass of the spirit burner with its lid on using the scales. I will take the lid off the spirit burner, and set the distance between the top of the wick and the bottom of the beaker to 10cm.
Although I would expect my actual results to follow the same pattern as my predicted results, I would only expect my actual results to be a small fraction of them. This is because not all of the energy will get to the water for reasons such as: - Some energy is used to heat the container. - Energy heats up the surroundings due to radiation and convection currents. - Draughts disperse energy. Preliminary Experiment I carried out a preliminary experiment to help me decide how to conduct my actual experiment. In it I used the same basic method found in my actual experiment. Fuel Height of flask above wick (cm) Mass of Water (g) Mass of spirit Burner(g) Temperature (oC) Time (s) Before After Before After Methanol 5 50 248.42 247.76 22 32 44.93 Methanol 5 100 247.76 246.81 19 29 67.22 Butanol 5 100 271.94 271.54 22 32 31.27 Butanol 10 100 271.54 270.84 22 32 62.49 Things I found out: -50g of water is not enough to cover the whole thermometer bulb. 100g are sufficient. -The height should be measured from the top of the wick to the bottom of the flask. 10cm should be used here, as if the distance is less, when using butanol a black layer of carbon is left on the bottom of the flask. -The temperature will be allowed to rise by 10oC before the flame is put out, as this takes an appropriate amount of time to do.
Although my results agreed partly with my predictions, by the alcohols that had more carbon and hydrogen molecules releasing more energy than the alcohols with less, it disagreed in that in my prediction, as the number of carbon atoms increased, I predicted the amount by which the energy released goes up would decrease, but my results showed that as the number of carbon atoms increased, the amount by which the energy released goes up also increased. This, combined with the large amount of anomalies and the amount that my results were spread out, gives an unreliable conclusion. In the experiment with methanol, where I only had one anomaly, the highest amount of energy that I recorded to be released was 3111.11 J g-1, which was roughly 30% bigger than the smallest. I had to include both results, though, as the third result was right in the middle of the two, so I could not say which one was anomalous and which was correct. If I had taken another reading, I might have been enough to decide, and it would make my evidence more reliable. If I had more time to study the combustion of fuels, I would look at alcohols further along in the chain, such as pentanol. I would also look at how quickly energy is released by different fuels. For this I would set up the experiment in virtually the same way, but I would put out the flame after a minute and measure how much 100g of water rises in temperature in that time.
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