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Alcohol Combustion Investigation

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Introduction

Introduction In this investigation we are trying to find out which out four alcohols gives off the most energy when burnt. We are using Methanol, Ethanol, Propanol and Butanol. We will investigate this by burning the alcohol under a tin can of water after weighing it an when the water gets to a certain temperature we will put the alcohol out and weigh it again. Using this and the bond energy values for the equation of the burning of each individual alcohol we will be able to discover how much energy in Kj/mol each alcohol gives and therefore which one contains the most energy. 1. Safety * Burning alcohols, flammable - always wear goggles * Tin cans conduct heat - so they get hot * Thermometer filled with mercury - poisonous 2. Method a. Set up equipment as above. b. Weigh alcohol and record. c. Place underneath tin can, which will be filled with 200ml of water. d. Record temperature of water watching carefully until it reaches 40oC. e. Extinguish flame. f. Weigh alcohol and record. g. After each experiment I will empty out the water from the can and get a fresh amount from the tap so that the water always starts off cold. h. Also I will make sure that the alcohol is always the same distance from the can for every experiment. i. I will need to do this twice for each of the alcohols. Continue this method with other alcohols. 3. Prediction Because Butanol has the most bonds, I believe it must use the most energy. ...read more.

Middle

I decided to use 200ml of water because I though if I used any more than it would take up a lot more energy from the alcohol and time for the practical. * Same equipment set-up because if I didn't the tin could be closer to the flame or further away which would either give the water more or less energy. * Do not let the water boil/let off steam because if I let it boil/let off steam then the volume of water would change which in turn would make the results be different because the alcohol would be heating different volumes of water. * Stir the water so that it is heated evenly otherwise energy would only reach parts of the water and depending on where you placed your thermometer you could get different results. RESULTS Weight Before (g) Weight after (g) Weight loss (g) Average weight loss (g) Temp. Before (oC) Temp. After (oC) Change in temp. (oC) Methanol 155.89 183.64 2.25 2.21 22 40 18 Methanol 2 217.78 215.62 2.16 21 40 19 Ethanol 176.72 174.75 1.97 1.96 19 40 21 Ethanol 2 174.71 172.76 1.95 20 40 20 Propanol 200.19 199.18 1.01 1.21 25 40 18 Propanol 2 199.16 197.75 1.41 23 40 17 Butanol 170.53 169.14 1.39 1.28 20 40 20 Butanol 2 169.13 167.96 1.17 20 40 20 Now I am going to find the average if the energy released by using this formula: - Energy released = mass of water (ml) ? temp rise ? specific heat capacity of water (4.18Kj) Temp Rise (oC) ...read more.

Conclusion

An alternative method to the one I used would be to use a bomb calorimeter. Bomb calorimeters are more complex than your simple calorimeter. It consists of two main parts, the bomb and an outer shell filled with water and a thermometer. The bomb, or the inner compartment, is where the chemical reaction occurs. If the reaction is endothermic, the bomb will absorb heat from the water, causing the water's temperature to drop, which is detected by the thermometer. In an exothermic reaction, heat is absorbed by the water, causing its temperature to increase. This is what bomb calorimeter looks like. This is a much better method as the reaction takes place within a chamber so that no heat is lost. Because no heat is lost it means that the results will be much closer to the prediction. Also, it will be easier to keep the surroundings the same because it is in a chamber so there won't be any change in environment because a window is open or something like that. There is also another method that is not the best one but is better than the one I did. It is set up like this: The calorimeter is designed to make sure that as much as possible energy is transferred to the water. It is done in two stages: Stage 1 A measured quantity of fuel is burned and the rise in temperature recorded. Stage 2 The heater is switched on and kept on until the water reaches the same temperature as it did with the burning of the fuel and the time it takes is recorded. ?? ?? ?? ?? 1 Steven Cowling The burning of Alcohols ...read more.

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