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Comparing Energy Given When Different Alcohols Burn.

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Comparing Energy Given When Different Alcohols Burn Introduction In my experiment I am going to burn six alcohols in air, I will carry out a pilot and modify it, then I will carry out a final experiment twice and repeat any anomalous results, this will enable me to collect to sets of close results. I will evaluate what went wrong and say how these things could be put right. Theory The alcohols I plan to use are Methanol, Ethanol, Propanol, Butanol, Pentanol and Hexanol. These form the first part of an homologous series of alcohols, they are an homologous series because they have the same general formula of: CnH2n+1OH Name Formula Structural Formula Methanol CH3OH Ethanol C2H5OH Propanol C3H7OH Butanol C4H9OH Pentanol C5H11OH Hexanol C6H13OH When the alcohols burn in air they burn with a flame. Although the flame the alcohol burns with does get more orange, in colour and dirtier as you go down the series, also, the alcohols, such as Pentanol and Hexanol, do not burn as easily therefore you get incomplete combustion. Incomplete combustion is when not all the alcohol is burnt, even though there is nothing left, this is because the temperature of the alcohol gets so high that the liquid starts to evaporate. When this occurs you get a white smoke, this is the alcohol evaporating. Combustion is when a substance is burnt in air and the reaction is completed fully. ...read more.


* I will measure the length of the wick, which will be 3cm, 0.5cm taller than the mini beaker. * I will measure the height of the mini beaker, the one I a going to use is 2.5cm tall. My results show me that my method was not very accurate because the temperature rise for Butanol and Hexanol are only one degree away. I hope that my real results are more accurate than these, if they are not I will repeat the burning until it is a reliable result and class the other result as an anomalous result. Key Variables To make a fair test I must only change one variable at a time, the one I am investigating. I must keep all the other variables constant. Dependant - The dependant variable is the thing that you are measuring, in this experiment I am going to measure the temperature rise when different alcohols are burnt. Independent - The independent variable is the thing that you are going to investigate, in this experiment I am going to use different alcohol, which go down a series. Controlled - To make a fair test I must only change one variable at a time, the one I am investigating. I must keep all the other variables the same. * Same Apparatus - I must use the same apparatus for all my experiments because the apparatus may be a different shape or size. ...read more.


As I go down the homologous series the temperature will increase. This is because in a lower alcohol, such as Butanol or Hexanol there is a longer chain of carbon bond, which need a greater heat to be broken, carbon carbon bonds need more energy to break the bonds in the chain. The longer the chain the higher the temperature needed to break bonds. Methanol and Ethanol have a short carbon chain and therefore need less energy to break bonds. To break any bond a certain amount of energy is needed, the amount of energy needed to break bonds in the alcohols increases as you go down the alcohols. Diagrams Safety * Wear safety goggles when burning alcohol * Tie lose hair back * Take off all lose clothing * Keep the room you are carrying out the experiment in well ventilated Results In my results table I have marked all anomalous results with purple so that they stand out. I had an anomalous result in each different alcohol, when I found I had an anomalous I repeated the experiment so that all my results were with in 3oC of each other. I have not included any of my anomalous results in my average. See next page for results table. Analysis My results show me that as you go down the alcohol series the temperature the water increases to increases by around 6oC each time. I have drawn two graphs, I will number them 1 and 2, number 1 is for the average temperature, 2 is for the energy given out. Graph number 1 shows me that ...read more.

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