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What are alcohols?

Extracts from this document...

Introduction

What are alcohols? Alcohols are a specific group of substances that are hydroxyl derivatives of hydrocarbons but more explicitly they are types of fuel. A fuel is a substance (e.g. methane) that readily undergoes combustion (the combustion of a substance involves its reaction with oxygen and the release of energy) and gives out large amounts of energy. The combustion of fuels is usually an exothermic reaction. The distinction between alcohols and other fuels, such as methane, is that alcohols are a homologous series of compounds that contain the -OH group of atoms as the functional group. The functional group in a molecule is the group of atoms within the structure that determines the characteristic reactions of that substance. All the earlier, smaller alcohols have a neutral pH, and are colourless liquids that do not conduct electricity. The general chemical structure of an alcohol is as follows: CnH(2n+1)OH By far the most well known alcohol is ethanol, which often goes by the common name of alcohol itself. Its chemical formula is C2H5OH. It is produced in industry by reacting ethene and steam together. They are first compressed to 60 atmospheres and passed over a catalyst (immobilised phosphoric(v) acid) at 300�C. 300�C, 60 atmospheres ethene + steam -------� ethanol phosphoric acid fuel + oxygen --� carbon dioxide + water and replacing the fuel with the alcohol gives: alcohol(CnH2n+1OH) + oxygen(O2) --� carbon dioxide(CO2) + water(H2O) What am I going to investigate? The aim of the investigation is to work with the combustion of specific alcohols. However, just mindlessly burning fuels is not going to achieve anything extensive. I need to have something to study. Firstly I have to narrow down the investigation by stating which alcohols I am going to work with. Below are the alcohols I will use: * Methanol (CH3OH) 1 carbon atom least carbon Atoms * Ethanol (C2H5OH) 2 carbon atoms * Propan-1-ol (C3H7OH) ...read more.

Middle

* The alcohols being used cause a lot of irritation if they come into contact with the skin it may be therefore a good idea to use rubber gloves when handling the alcohols. * When using the thermometer it must be place on a level surface so that it may not drop off as the mercury inside the thermometer is extremely hard to clean up and is poisonous. * When using the Bunsen burners it must be made sure that the gas taps are not left on without being connected to the burners, once the gas taps have been turned on they should be lit as soon as possible. FAIR TESTING * To allow fair testing all of the alcohols mass must be measured with the lid on and rounded off to two decimal places. * Every time the Aluminium calorimeter is going to be used, the build up of carbon soot must be removed to allow a fair conduction of the heat from the alcohol being used. Analysis From the results of the main experiment there seems to be a varied selection of values. For each alcohol the quantities are within a small range, which is good and hopefully not drawing out any anomalous results. I cannot be sure as to whether they are "correct" or not because they are merely showing the mass of fuel burnt needed to release the same amount of energy and as I explained before in my hypothesis, the alcohols have to be compared by how many moles of each were burnt. Now I need to convert the results so that they show the number of moles of each alcohol burnt rather than the mass of each burnt. Regarding my hypothesis, the point I made was that the bigger the alcohol molecule, the more energy is released. My results seem to be in accordance with this statement as the graph shows. ...read more.

Conclusion

the enthalpy change of combustion of ethanol is 0.53% Propan-1-ol The uncertainty in reading a thermometer that measures to 0.1 oc is 0.05 Therefore the percentage uncertainty in reading the thermometer is the uncertainty divided by average temperature change of water being heated by the combustion of propan-1-ol 0.05 x100 = 0.5% 10 The uncertainty in reading the 100cm-3 measuring cylinder that measures to 1cm-3 is 0.005 The average value of water recorded was 100.00cm3 0.005 x 100 = 5.00x 10-3% 100 The uncertainty in reading a balance that meat measure to 2 decimal places it 0.005 the average mass recorded is the average (start mass + average end mass)/2 204.87+204.53 =204.7 2 0.005 x 100=2.44 x 10-3% 204.7 The percentage my result is out is 741 x 100=36.7% 2021 It is unsettling to see that my result is just over 1/3 of the actual result 36.7-100= -63.3% from the actual enthalpy change of combustion of propan-1-ol My total percentage uncertainty is 0.51% Butan-1-ol The uncertainty in reading a thermometer that measures to 0.1 oc is 0.05 Therefore the percentage uncertainty in reading the thermometer is the uncertainty divided by average temperature change of water being heated by the combustion of butan-1-ol 0.05 x100 = 0.5% 10 The uncertainty in reading the 100cm-3 measuring cylinder that measures to 1cm-3 is 0.005 The average value of water recorded was 100.00cm3 0.005 x 100 = 5.00x 10-3% 100 The uncertainty in reading a balance that meat measure to 2 decimal places it 0.005 the average mass recorded is the average (start mass + average end mass)/2 192.17+191.93 =192.05 2 0.005 x 100=2.60 x 10-3% 1920.05 The percentage my result is out is 1300 x 100=48.6% 2676 48.6-100= -51.4% from the actual enthalpy change of combustion of butan-1-ol My total percentage uncertainty is 0.51/% As I have established that the percentage uncertainty hasn't had a considerable effect on my experiment the only way I can think of improving my procedure is eradicate some of the procedural errors. ...read more.

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