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An Investigation to see how the energy released by burning Alcohols depends on the number of Carbon atoms they contain.

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Introduction

An Investigation to see how the energy released by burning Alcohols depends on the number of Carbon atoms they contain I intend to burn 5 different alcohols (methanol, ethanol, propanol, butanol and pentanol) to see if the number of carbon atoms in each one affects the energy they release. Methanol has one carbon atom; ethanol has two, and so on until pentanol which has five. To do this I am going to do a simple experiment. Each alcohol will be in a spirit burner, and a tin of pre-measured water will be held above. I will weigh the spirit burner before I light it. Once lit, I will wait for it to heat the water to a pre-arranged temperature. Then I will weigh the spirit burner again and record the loss in mass. When I have collected weights for each alcohol, I can then begin calculating the energy lost during burning. It is important that the volume of water and temperature are kept the same for each experiment, otherwise the results cannot be compared. ...read more.

Middle

Control of variables is important to this experiment, as they can seriously affect trends in results. Temperature of each experiment is not a problem; they will all be done in a controlled environment. Positioning of the flame of the burner is crucial, as the temperature of a flame varies, so the same part of flame must be concentrated on the same part of the tin each time. The water must be constantly mixed to stand the best chance of having a constant temperature. Care must be taken not to read temperatures if the thermometer is on the can's base, as this will be hotter than the water and therefore inaccurate. Water volume makes a lot of difference, as more energy is required to heat a larger volume of water. The temperature increase of the water is also important, because if I don't measure a trend displaying increase my results will be poor. Safety goggles must be worn as the experiment involves naked flames. Care must also be taken to not inhale the gases from each alcohol. ...read more.

Conclusion

Methanol had the largest average mass loss. This is because it contained only 1 carbon atom, which when burnt in air gave out less energy than ethanol, for example. My results point towards a rough trend of average mass loss decreasing as carbon atom content increases. However, due to inaccuracies in the experiment, the trend is very weak and has irregular spacings between alcohol groups. These inaccuracies could have been: Height of the flame: Even with the two blocks in place, the height of the flame will vary, due to the height of the wick, and the amount of alcohol in the wick. Heat loss: Heat from the flame can easily be lost in the air, and there was no system in place to control it. Concentration of heat: Stirring the water to keep its temperature constant was not a very accurate method. Evaporation of alcohol: The stronger alcohols evaporated quickly if the tops of the spirit burners were left off. Ideally, if I was to repeat the experiment, I would insulate it to prevent excessive heat loss. I'd cap the spirit burners as quickly as possible, and try to heat the water evenly. Joe Wightman 11JPB ...read more.

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