Planning - Variable input - Alcohol

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Nathaniel Caiden         Chemistry SC1

Investigating the factors that affect the amount of energy released when an alcohol burns

SKILL P~PLANNING

Input Variables

Alcohol        This is the variable I am going to investigate.  An increase in the length of carbon-carbon chains will result in an increase of energy given out.  This is due to the longer hydrocarbons having, a greater attraction to each other.  Therefore more energy is needed to break them down so more energy is given out since the reaction is exothermic.

Volume of Alcohol        A greater volume means more molecules of the alcohol.  More molecules will mean more atoms, hence more carbon-carbon chains.  As is described above more carbon-carbon chains in this experiment will mean more energy.  Therefore to keep this variable constant each alcohol will have the same number of molecules.

Isomers of Alcohol        Isomers may have different structures., and they may have different properties.  We know that branched chains have lower boiling points then straight ones.  Therefore to make sure that isomers do not effect the experiment only one isomer from each alcohol will be tested.

Volume of Water        To keep this variable constant the same volume of water for each experiment will be used.

Mass of Ceramic Wool        To keep this variable constant the same mass of ceramic wool will be used.

Container        To keep this variable constant only one container will be used for the whole experiment

Height of Container        To keep this variable constant the container will remain at the same height from the top of the crucible in each experiment

Output Variables

As a result of varying the alcohol (the input variable I am testing) I expect a change in energy, this will be shown by a change in the water temperature.  This will be measured by using the point at which no flame is visible.  The change in temperature will be measured by a thermometer, accurate to one degree centigrade.  Then the energy given out by the alcohol will be calculated by using the following formula, Energy = mass of water x change in temp x specific heat capacity, the result of this energy given by this equation will be plotted on a graph against the number of carbon’s in carbon-carbon chains.

Preliminary Work

The original apparatus for the experiment include: Bunsen burner, ceramic mat, 100ml beaker, measuring cylinder, boss and clamp, balance, pipette, centimetre ruler, crucible, ceramic wool stirring thermometer, splints, tongs, safety specs, tap water, methanol, ethanol, propanol, butanol, hexanol.

A Bunsen burner was set up to away from the other apparatus.  The mass of alcohol needed to achieve one mole, the decided temperature was calculated and noted for later reference.  This value was large and a large mass would be a long time for it to burn and would be quite dangerous.  Instead a hundredth of a mole was used.  A 100ml beaker was held above the desk by attaching it to a boss and clamp.  A ceramic matt was placed on the desk so that it was directly under the beaker.  A mass of 10 grams of ceramic wool, measured by the balance was paced into the crucible.  1.02 grams of hexan-2ol was placed into the crucible and the crucible was finally placed directly under the beaker, on the ceramic matt.  The beaker was filled with 25ml of water.  The preliminary experiment begun when with the aid of the Bunsen and splint the alcohol in the crucible was set alight.  The results were very close to boiling and a lot of soot was deposited on the beaker.  I tested with hexan-2-ol first since I predicted that this would give the greatest temperature change in the water.  If I had started with the ones with smaller carbon-carbon chains then the experiment would be void if the water boiled when any of the longer carbon-carbon chains were tested.  While varying the height of the container I realised that when if it was too close and on the crucible no oxygen could get to it and the alcohol wouldn’t burn for long.  To high and to much heat was lost in the atmosphere and not enough of this energy would be recorded by the apparatus.  The water was also varied.  When too little the water boiled rendering the experiment void.  To much and the rise in temperature difference between each alcohol was too little.  It was decided to add a total of 50ml of water in the beaker and have 6cm cm distance between the top of the crucible and the bottom of the beaker.  After repeating the above process altering the alcohol between methanol, the expected lowest temp change and hexan-1-ol the greatest it was concluded that a volume of 50ml was reasonable with a distance between of six centimetres between the top of the crucible and the bottom of the beaker.  The method chosen would allow enough measurable change in temperatures of the alcohols with smaller carbon-carbon chains while having a big change in temp but not too close to boiling, 100C.  However it was decided not to allow a temperature change of 70 or 60 in hexanol by altering the apparatus because these deposited soot and since one would have to wait a long time till the water temperature was low enough to continue the experiment on different alcohols.  Due to this the water in the beaker would remain constant since it would never be changed.  Also a large 250ml beaker was used and filled with cold water to quickly cool the smaller beaker so that the experiment could be conducted more rabidly.

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Relevant Background Knowledge

Alkanes are aliphatic hydrocarbons, a class of chemical compounds containing only hydrogen and carbon, with no carbon-to-carbon double or triple bonds. They therefore contain only saturated carbon atoms. Alkanes form a homologous series with the general formula CnH2n+2.  The simpler members of the alkane series are colourless gases. Methane (CH4) is a gas at normal temperatures, and has a boiling point of 164°C. Progressing up through the series, the alkanes are gases as far as pentane (C5H12), which has a boiling point of 35°C. Beyond C16H34, they are waxy solids. The carbon chain may be either ...

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