The method of the experiment: firstly, I will need to setup the calorimeter; by placing 600ml of water inside it; then let it equilibrate; while it is equilibrating I will attach the water pump, one end on the calorimeter and the other on a tap. I will then need to get my first alcohol burner and weigh it, once weighed it can be raised up to the calorimeter via the wooden blocks. I will record the weights in a table. The next step would be to carefully place the mercury thermometer inside the calorimeter, and stirring the water with the stirrer inside the calorimeter, while equilibrating. The final things before starting the experiment; turn on the tap and get a match. Finally, I can light a match and start the experiment, I will need to take the temperature before I light the burner and every 30 seconds for 3 minutes.
Once the 3 minutes are over I can weigh up the burner again and record the data. I will need to repeat these steps 12 times. As I am using four different alcohols, it will be a good idea to redo each one 3 times. This will increase the accuracy of the experiment. Also, to improve the precision, I am using a mercury thermometer which I may be able to use to record the temperatures to 2 decimal places, i.e. 22.55ºc.
After my preliminary testing, I found that the burner could easily be affected by heat loss via the calorimeter; if the gap between the burner and the calorimeter is too much then too much heat will be lost. If it’s too close, the burner will not produce the full potential of heat. This is why I am using wooden blocks to firmly hold it in the correct place. Another way of preventing heat loss is a simple water pump, this quite simply attaches to the top if the calorimeter and sucks up the hot air through the calorimeter. Finally, the calorimeter could produce hotspots in the water, so a stirrer will be necessary.
I am not expecting perfect results every time, but if an anomalous result occurs I will still include it but show the anomaly either in my results tables or on my graph.
These are my results tables; I have separated them in way that shows each experiment I carried out. I have three tables as I tested each alcohol three times.
From these results I have calculated the ΔH=mcΔt. Firstly I calculated the mass of water (g) multiply by 4.2, and as the mass of water was always the same, 600, it will always be 2,520. I then need to multiply 2,520 by the change in temperature.
For Methanol the changes in temperatures were 3.2, 1.7 and 3.1, so I will add these up and divide them by 3 for the average. Which gives me 2.67.
For Ethanol the changes in temperatures were 4.0, 1.4 and 1.8, so I will add these up and divide them by 3 for the average. Which gives me 2.4.
For Butanol the changes in temperatures were 2.0, 0.9 and 1.2, so I will add these up and divide them by 3 for the average. Which gives me 1.37.
For Propanol the changes in temperatures were 2.7, 1.4 and 1.7, so I will add these up and divide them by 3 for the average. Which gives me 1.93.
I will then need to multiply 2,520 by the average number for each alcohol, which will give me the energy,
From here I will need to work out the number of moles which is of alcohol burnt divided by the relative mass.
The relative mass:
Methanol is 32
Ethanol is 46
Butanol is 60
Propanol is 74
Following this, I need to divide the energy by mol; this will give me my result in J mol–1, the final stage will be to divide this number by 1,000 to get my final result in KJ mol–1.
The correlation between the Mr and energy of combustion is as one gets higher, so does the other. Although you need more energy per Mr to break the bonds, the higher the Mr the higher the energy you get back out of it.
I believe that my evidence is fairly reliable, but obviously not perfect. My results to follow a trend but enthalpies of combustion are not even half way close. Techniques should be improved to receive better results, for example; the way we equilibrate the calorimeter and check the temperature. The calorimeter should be properly equilibrated before we even touch it, but also every time we touch the calorimeter the temperature of the water could be affected, it may only be 1º or so but the results will be effected. Also the temperature needs to be checked throughout the calorimeter as hotspots are produced.
The results – energy of combustion – we received compared to the actual results are quite different, e.g. Methanol; my result is 221.21 KJ mol–1 whereas the actual results are 726 KJ mol–1.
