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Investigating the structure of a fuel and the amount of energy released during combustion

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Introduction

Investigating the structure of a fuel and the amount of energy released during combustion Aim We are trying to find out whether an increase in the number of carbon atoms and different structural formulae affect the amount of energy released during combustion. We have chosen to investigate 4 different alcohols: Ethanol, Propanol, Butanol and Octanol. Three of the alcohol's we are using have 2 different structures (these are called isomers): � Propanol = Propan-1-ol and Propan-2-ol � Butanol = Butan-1-ol and Butan-2-ol � Octanol = Octan-1-ol and Octan-2-ol We haven't chosen to use the different structures, because we only wish to investigate the number of carbon atoms in different alcohols, and see whether a different number of carbon atoms will affect the amount of energy released during combustion. Background Information Alcohol's I know that the alcohols I have chosen all produce an exothermic reaction during combustion and the products of the combustion of alcohols are water and carbon dioxide. The basic chemical formula for an alcohol is CnH(2n+1)OH. Ethanol = C2H5OH Propanol = C3H7OH Butanol = C4H9OH Octanol = C8H17OH Propanol, Butanol and Octanol have two different structures, 1-ol and 2-ol. They still have the same number of carbon bonds as each other, but their structures are slightly different: Ethanol = Propan-1-ol = Propan-2-ol = Butan-1-ol = Butan-2-ol = Octan-1-ol = Octan-2-ol = Measuring the energy output To measure the energy output it is not possible to measure the amount of heat directly, instead you have to use the standard method and look at the effect that energy has on the temperature of a known volume of water. ...read more.

Middle

5. Place the oil burner on a mat and then position the tin can so it is directly above the wick. 6. Surround the oil burner and tin can with tinfoil and light the wick. 7. Wait till the temperature rise is 20, then put out the lamp. 8. Weigh the ethanol, without the glass lid, and record weight. 9. Repeat this for propan-1-ol, butan-1-ol, and octan-1-ol. 10. Repeat the whole experiment 3 times; so as to get an average result - making it a fairer and more accurate result. From this experiment we needed to know the mass of the water, the temperature rise and the weight change of the alcohol. We needed to know the mass of the water and the temperature rise, so that we could find out the total energy released (Energy released = mass of water x temperature rise x 4.2J). The weight change of the alcohol could then help us to transfer this amount into moles, so we could compare our results to the theoretical answers and find out how accurate our results are. We surrounded the oil burner and copper can with a barrier of tinfoil, as it helps limit energy loss, raises accuracy and we will make sure there is a hole so the oxygen can get to the lamp stopping incomplete combustion, this will make less soot meaning less energy loss. Alcohol's are quite dangerous liquids to work with, as they are extremely flammable, so great care had to be taken that they weren't spilt and safety goggles were worn at all times. Results First results Weight before (g) ...read more.

Conclusion

Consequently there was a risk of different amounts of energy loss into the surroundings, also there would be a degree of incomplete combustion which would lead to energy loss. If I was to re-do this experiment I would use distilled water instead of the tap water we were using, as distilled water is pure and the tap water could have contained all sorts of things that could cause a change to our results. I would also use a buirette instead of the measuring tube we used, as the measuring tube is only accurate to half a millimetre. We measured the temperature of the water using a thermometer, which is also only accurate to half a degree, and if I did re-do this experiment I would measure the temperature using a data logger, as it is a lot more precise and accurate. The part of the experiment, which I thought, was the least accurate element was the insulating device, as even though it did reduce energy loss, it didn't work to a very high standard. If I was to improve this investigation I would devise some sort of sealed insulated unit, which stopped as much heat loss as possible and had a stirring device in it to continuously stir the water to make sure it was heated evenly. In my findings I worked out the accuracy of my results by comparing them to the theoretical equations of heat combustion, as well as the ones in the data book and then finding an average accuracy: If I was to further my investigation I would like to also investigate the alcohols between Butanol and Octanol, which have the structures: C5H11OH, C6H13OH and C7H15OH. This would enable me to prove my theory I explained in my conclusion. ...read more.

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