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An investigation into the efficiency of alcohols as fuels.

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Introduction

Joe Taylor 11T Chemistry coursework An investigation into the efficiency of alcohols as fuels Planning The aim of the experiment is to investigate the use of five alcohols as fuels. The combustion of alcohols is exothermic, meaning that when burnt they give off more heat than they take in. This makes them useful as fuels, and many countries are adopting alcohol fuels, for example Brazil. Therefore it seems useful and topical that the efficiency of the alcohols should be investigated. The alcohols methanol, ethanol, propan-1-ol and propan-2-ol will be tested. In order to evaluate the efficiency of these alcohols as fuels, their enthalpies will be investigated. Alcohols are perfect for testing, as they are all liquids with the same weight. Therefore weight is not a variable, and it is only the heat given off that is to need be considered. From previous organic chemistry studies the structures and formation of alkanes, alkenes and alcohols were known, along with the energy values for the bonds within alcohols themselves. This allowed for the creation of the bond energy table below. Bond Bond Energy (kJmol-1) C-H 435 O=O 497 C=O 803 H-O 464 C-C 347 C-O 358 These are the alcohol's formulae: Methanol: CH3OH Ethanol: C2H5OH Propan-1-ol: C3H7OH Propan-2-ol: C3H7OH Pentanol: C5H11OH Each of these reacts with Oxygen (0=0) in combustion For a pictorial depiction of the alcohol's bonding see Appendix 1: Alcohol Structure So therefore, knowing the energy in each bond, ...read more.

Middle

The circle represents the alcohol burner, beneath the tin cup in order to heat it. The thermometer rests within, but not touching, the tin cup. Improvements Heat loss was a major factor in the inaccuracy of the preliminary results. Heat was not aimed solely at the tin can with the water. Much of the alcohol burnt therefore was used to heat the surrounding air, not the water in the can. Heat could escape in all directions; therefore this was a huge oversight in the planning of the preliminary test. Heat mats will be used as draught shield and to stop a large amount of heat escaping from our experiment. The tine cup had a dirty sooty bottom from previous uses. This can stop the full amount of heat given off by the alcohol burner heating the water within the tin can, thus rendering any results inaccurate. This will have to be cleaned in order to obtain accurate results. This preliminary investigation and experimentation allowed for a full experiment to be formulated with knowledge of how and why, but also how to keep the experiment relatively accurate. Therefore what follows is the final investigation and its crop of results. Obtaining evidence Method As in the preliminary experiment, the apparatus was set up as below As before 50cm3 of water was placed in the tin cup. ...read more.

Conclusion

Not only this, but an anomaly in ethanol, even with averages being taken. This leads one to consider improvements to this investigation. Improvements In an ideal situation, measures would be taken to reduce heat loss as far as possible. But as it is impossible to carry out this experiment in a vacuum, due to its need of oxygen gas in the surrounding atmosphere, the best thing to do would be to carry out the test in a sealed heatproof environment. This would increase the accuracy of the results greatly. More reading could have been taken. At a total of two reading per alcohol, anomalies were still present. To negate this and ascertain more accurate results, numerous repeats could have been done. A good balance between time and accuracy would have been 4 or 5 repeats. Reading of the thermometer was affected by the surface tension of the liquid inside, yet this is of negligible importance. No matter how much it was cleaned, there would always be dirt on the vessel for the water, affecting the results. To improve this an easier to clean vessel could be used. A set of scales with a greater sensitivity would increase accuracy also. Safety Goggles and lab coats were worn throughout the proceeding of the experiment, and apart from using a fume cupboard, this was as safe as things could be in a school environs. 1-Chemistry coursework-An investigation into the efficiency of alcohols as fuels ...read more.

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Response to the question

The student's response to the aim of the experiment was sound. They have shown a clear understanding of the topic - both in terms of understanding the experiment and in terms of linking the experiment to the chemistry behind it. ...

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Response to the question

The student's response to the aim of the experiment was sound. They have shown a clear understanding of the topic - both in terms of understanding the experiment and in terms of linking the experiment to the chemistry behind it. The answer is clearly and logically laid out with supportive material (i.e. diagrams) to demonstrate understanding. However, I would emphasise that the student could ensure that they scored full marks by always stating the obvious (in this case, the student obviously has a high understanding of the topic and fails to state the basics which would make it clear to the examiner that they have 'ticked the boxes' for the markscheme). Also, I would encourage the use of putting titles for diagrams or graphs and calling them 'figures' and referencing them when needed rather than using "the diagram above" or "the graph on the previous page". I think this makes it neater and clearer for the examiner.

Level of analysis

The student shows a high level of understanding for the topic. Their analytical skills are clearly shown in the content of this piece of work. However, they should make sure that they always support each point made - such as why heat loss would affect the experiment (they mentioned the use of heat proof mats to prevent the heat loss but did not explicitly say why this was necessary). Yet, this was only a small fault in the piece of work and would not greatly affect the mark. The examples used are clear and the diagrams help demonstrate the understanding of the student. One point I would suggest is that the student states the original equation rather than jumping straight in with the 'c' of 4200 in the equation to find the change in energy.

Quality of writing

There were a few spelling mistakes, which was shocking for such a high level piece of work. This would affect the mark slightly but not greatly - although this does show the examiner that the student has failed to check through their work thoroughly. The technical terms used perhaps should be define in a glossary to demonstrate further understanding of the chemistry however, this is not imperative. One thing I did pick up on was the use of 0=0 instead of O=O. Whilst it looks very similiar, it is best to avoid using 'zeros' instead of 'O's' here for oxgyens. The student exceeds the expectations of the level of the work required at this level as they have clearly got a very high level of understanding. It is detailed and clear and overall, would score a very high mark in my opinion, despite the small faults in it.


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