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An experiment to investigate the factors that determine the amount of energy released when alcohols are burned.

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Chemistry SC1 An experiment to investigate the factors that determine the amount of energy released when alcohols are burned By Khalid Attia Planning Statement of Problem In this investigation, I will be investigating all of the factors that determine the amount of energy released when any given alcohol is burnt. Input Variables In this investigation, there are many different variables that will affect the amount of energy produced when alcohols are burnt. These variables are called the Input Variables and they are the following: 1) Number of Carbon atoms present (type of alcohol) 2) Concentration of alcohol (purity) 3) Amount of alcohol (volume or mass) 4) Oxygen supply (for combustion) Each of these variables will affect the amount of energy produced when an alcohol is burnt in similar ways but some variables have a larger affect than others, therefore choosing the right one is essential. If the number of carbon atoms in the alcohol is increased, its molecular structure will be larger. This can be seen from this general equation - CnH2n+1OH. When combustion is complete, carbon dioxide and water are formed, therefore if there are more carbon atoms, there will be more carbon dioxide and water produced, this will require a large amount of energy to make the bonds in these compounds. Therefore if more carbon atoms are present in the alcohol, more energy will be released. I can predict that the two will be directly proportional. The purity of alcohol is a variable that will have the same effect on the energy produced as the number of carbon atoms present in the alcohol. A pure alcohol will have many more alcohol molecules in it than a less pure one. Having more alcohol molecules means having more carbon atoms, and as I've explained previously, having more carbon atoms in an alcohol will produce more energy. I can again predict that purity of alcohol and the energy produced by the alcohol will be directly proportional. ...read more.


7. Splints 8. 100ml beaker 9. 30cm3 of Water 10. Bunsen burner 11. Thermometer 12. Electronic balance 13. Safety Specs 14. Apron 15. Pipette 16. 10ml Measuring Cylinder 17. 25ml measuring cylinder 18. Ruler This is how the apparatus was set up: I carried out the following procedure for each different type of alcohol and compiled some raw data. First, I fitted a boss and clamp to a retort stand to hold my beaker; then, I measured out 30ml of water in my 25ml measuring cylinder and poured it into the beaker and inserted a thermometer to start measuring a start temperature. Then I weighed 0.28 grams of ceramic wool and inserted it at the bottom of my crucible, which was placed on a heat resistant mat. I then measured out 1cm3 of an alcohol (e.g. Methanol), and poured it onto the ceramic wool in the crucible. Now that all of the apparatus was in place, I placed the top of the crucible two centimetres away from the base of the beaker and then I checked the start temperature and recorded it. The next stage was to light a splint by inserting it into a Bunsen burner, and then, set the alcohol in the crucible alight! After the alcohol had finished burning completely, I stirred the water and took an end temperature. Now that I had a start temperature and an end temperature, I could deduce the temperature rise and use it in the formula to work out the energy produced by the alcohol in Joules. The following are the results that I obtained from my preliminary work experiments. Type of Alcohol Start Temperature (oC) End Temperature (oC) Temperature Rise (oC) Methanol 24 89 65 Ethanol 23 91 68 Propan-1-ol 24 92 68 Butan-1-ol 24 95 71 Hexan-1-ol 24 Boiled - As we can see from these results, the temperature rise is very high, there was not much of a range between the end temperatures, and so therefore I would need to change some of the set-up to make my investigation more reliable and fairer. ...read more.


Some of my results were slightly anomalous, especially the energy given off from the Hexan-1-ol. All of the anomalous results were highlighted in my results tables and clearly labelled on my graph. The only explanations I can give for the anomalies are incomplete combustion, heat loss, or human error (i.e. incorrect measurements of water, alcohol, distance between tip of crucible and base of beaker or temperature). The test was as fair as possible, and even if there were errors such as heat loss, they affected each and every experiment and therefore made hardly any effect on my results. The procedure I used was also reliable as the oxygen supply and heat loss were factors that again, affected each experiment and therefore didn't have much of an effect on my results. There are, however, improvements that could be made to this experiment, such as using a conical flask instead of a beaker as it has a large base and would therefore intercept all of the heat of the flame produced from the burning alcohol and will therefore make the results more reliable. In addition, covering the top of the conical flask with foil and making a small hole for the thermometer would ensure that no heat could escape from the top of the conical flask. As a conical flask would be used instead of a beaker, there would be space for improvement, literally, as I could make the space between the base of the conical flask and the tip of the crucible larger so as to give the burning alcohol a larger oxygen supply. This would therefore allow every alcohol to undergo complete combustion and therefore make all of the results more reliable and the Hexan-1-ol in particular, would then fit into the trend. I can finally come to a firm conclusion that, in theory, the number of carbon atoms in an alcohol and the energy that it releases when burned are directly proportional. The only extra work that can be carried out to provide additional information is by using that set-up and apparatus I mentioned above under how to improve the experiment. ...read more.

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