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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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An experiment to investigate the factors that determine the amount of energy released when alcohols are burned Planning Background Knowledge All hydrocarbons contain carbon atoms in a chain that have formed bonds with other hydrogen atoms to become stable large molecules. Methane consists of only one carbon atom: Methane (CH4) Hydrocarbons with more than one carbon atom form a carbon chain within the molecule. Here, the carbon atoms form a bond with each other to form a chain, and each atom forms bonds with other hydrogen atoms to become stable. Ethane contains 2 carbon atoms in a chain whereas as propane contains 3 and butane contains 4: Ethane (C2H6) Propane (C3H8) Butane (C4H10) The number of carbons in a chain in a hydrocarbon may be very large and also has more hydrogen atoms bonding with the carbon atoms to make the molecule stable. We can find a relation between the number of carbons in the hydrocarbon and the number of hydrogens. From the structural formulas of methane, ethane and propane above, we can see that for each carbon atom, two hydrogen atoms are included to form bonds with it plus an extra hydrogen atom for each of the carbon atoms on each end of the carbon chain. This gives the formula: CnH2n + 2 where n is equal to the number of carbon atoms in a chain. This rule applies to all hydrocarbons provided that all the carbons in the chain form single bonds. Such hydrocarbons are called alkanes. Alkane molecules are able to occur with one of the hydrogen atoms replaced with another atom or molecule. Alcohols are formed in this way where a hydroxide (OH) molecule replaces one of the hydrogen atoms that has formed a bond with atom and the hydroxide molecule forms a bond with the carbon atom. Again, different types of alcohols can be formed due to the different number of carbon atoms in a chain. ...read more.


This is by measuring how much it heats up a certain amount of water. To do this, we must suspend the water in a container above the burning alcohol and measure the temperature of the water before and after burning the alcohol. Then we can calculate the temperature rise: After calculating the temperature rise, we can calculate the amount of energy produced by multiplying the amount of energy required, in joules, to raise 1cm3 of water by 1oC (4.2 joules), by the volume of water, in cm3, and by the temperature rise of the water, in oC. Hence, we get the formula: After working out the energy produced, I divide it by the number of moles burned in order to calculate the amount of energy released by the alcohol per mole. This gives us: = energy produced per mole (Joule mole-1 or J m-1) Using this method of measuring energy has also produced us with many factors of the experiment that we must keep constant to ensure a fair test. These include keeping the volume of water in the container constant and keeping the distance between the burning alcohol and the container of water constant. We must also try to keep the burning alcohol directly underneath the container of water for every reading. Preliminary work Before actually doing the experiment, I was allowed one session to perform rough pilot experiments in the laboratory in order to obtain an idea of what techniques and equipment shall be best to use. Safety While performing these experiments, I discovered that it was necessary to protect myself. The reaction of burning the alcohols is exothermic and gives out a lot of heat that may be quite dangerous since it might lead to a spark or an unexpected reaction. I therefore found it necessary to wear safety spectacles, to prevent any hot substances from coming into contact with my eyes. ...read more.


Again the mass of the alcohol would be measured according to the mass given in the table. Before the next alcohol is lit, the bottom of the conical flask would first be wiped of soot using the tissue. This would ensure a fair test in that the soot from previous alcohols will not be able to affect the heating of the water from following alcohols. Also, the temperature of the water in the flask would be measured again before it is heated and after it is heated. The temperature rise shall also be calculated. This shall be done for all the alcohols, using a new piece of 50g ceramic wool for each alcohol and using the mass of a hundredth of the molecular mass of each alcohol as shown in the table. The bottom of the conical flask shall also be wiped before the burning of each alcohol for a fair test. After each alcohol has been tested, they shall all be tested for a second time in the same way, each with its own 50g of ceramic wool and under exactly the same conditions, and a second temperature rise reading shall be made for each alcohol. Another replicate of results should have therefore been recorded. The results will then be analysed and if two results of temperature rise for an alcohol are not similar, the experiment will be repeated again for that particular alcohol. The third result will then be compared with the other two. If it is similar to one of them, it will replace the other. This will help to get rid of any unreliable results and replace them with more reliable accurate results. After this has been carried out, the average temperature rise over the two replicates shall be calculated. Then, these readings shall be used to calculate the amount of energy released per molecular mass for each alcohol. This shall be done by using the following equation: These final results will be the most accurate and will be used to draw graphs and conclusions from. ...read more.

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