Aim: My aim is to find out if there is a correlation between the length of the alcohol chain and the amount of energy given off when the alcohol is burnt. Hypothesis: I think that the longer the alcohol chain is, the more energy will be given off. This is because of the previous work we have done in class. We have learnt that the longer the alcohol chain is the more bonds are in the chain. More bonds means more stored energy, energy that will be released when the alcohol is burnt and its bonds broken.
Longer alcohol chains will have more bonds to break so when they do break there will be more energy given off. Apparatus: Crucible Alcohol Calorimeter Stand Boss Clamp Timer Rock wool Water Measuring tubes Thermometer Variables: Time allowed to burn Amount of alcohol burnt Type of Alcohol Amount of water used in the calorimeter Height of can above the flame o My input variable will be the type of alcohol I decide to burn. o My output variable will be the energy given off when the alcohol is burnt. Fait test: To make my test fair I will: Keep the amount of alcohol burnt each time the same (2 mls) Keep the amount of water in the calorimeter the same each time (90 mls (5 mols) ) Let each alcohol burn for the same amount of time (1 min 30 sec's) Keep the calorimeter at the same height above the crucible (9 cm) Method: I will put my 2 mls of alcohol into the crucible. I will then hold the can 9 cms directly above the crucible (using the stand, clamp and boss) with the 90 mls (5 mols) of water in it along with the thermometer. I will measure the starting temperature of the water so I can work out the temperature difference and then light the alcohol.
If the alcohol does not light I will use a bit of rock wool to get it going. Once the alcohol is lit I will start the timer. When the timer has reached 90 seconds I will take the crucible out from underneath the can and record the finishing temperature of the water in the can. By multiplying the temperature rise in degrees by 90 (because of the 90 mls of water in the can) and then by 4. 2 (waters specific heat capacity) you can work out how much energy was given off by the alcohol. Results: Alcohol Time Allowed to Burn Amount of Alcohol Starting temp' of water Finishing temp' of water Temp' difference Energy given off (KJ) Methanol 90 seconds 2 ml's /.
0625 mols 19 degrees Celsius 36 degrees Celsius 17 degrees Celsius 6426 Ethanol 90 seconds 2 ml's /. 04347826 mols 20 degrees Celsius 32 degrees Celsius 12 degrees Celsius 4536 Propanol 90 seconds 2 ml's /. 033333333 mols 20 degrees Celsius 27 degrees Celsius 7 degrees Celsius 2646 Butanol 90 seconds 2 ml's /. 027027027 mols 19 degrees Celsius 25 degrees Celsius 6 degrees Celsius 2268 Penta nol 90 seconds 2 ml's /. 022727272 mols 20 degrees Celsius 22 degrees Celsius 2 degrees Celsius 756 Hexanol 90 seconds 2 ml's /. 019230769 mols 19 degrees Celsius 20 degrees Celsius 1 degree Celsius 378 To work out how much energy was given off I multiplied the temperature difference of the water by 90 (because of the 90 mls of water in the can) and then multiplied that by 4.
2 (because 4. 2 is waters specific heat capacity). For each alcohol burn I tried to have the can at the same height (9 cm's) above the crucible. Analysis: On the previous page you can see a graph that completely undermines and destroys my prediction.
The graph shows a negative correlation which reads as follows; the shorter the alcohol chain is the more energy was given off when it was burnt. My prediction states that the longer the alcohol chain is the more energy should be given off. I have backed up my prediction with what I consider to be quite a reasonable argument that makes quite obvious sense So why then have the results gone the other way? I have three possible theories why the results were not as I expected. o Theory 1 is that I did not repeat my experiment enough times.
This means that rogue results went undetected and found there way into my graph giving it its negative correlation. o Theory 2 is that the can was too high above the crucible. I noticed that the longer the alcohol chain was the smaller it's flame was when it burnt. This meant that heat coming from the smaller flame had more chance to escape into the surrounding air rather than warming up the can. This could possibly explain the results.
o Theory 3 is that the results were completely right and that it was because I set a time limit on how long the alcohols were allowed to burn for meant that the longer alcohol chains were just not given enough time to release their energy. Maybe if I had not set a time limit the results would have created a positive correlation. I think it is probably a combination of all three of my theories that meant my results gave a negative correlation. Evaluation and Conclusion: On the whole I am quite happy with my method and my results. The results may not have been what I was expecting but as no results are wrong results I have had to try and work round them. The results were, in my opinion, as accurate as I could have made them.
I made sure that I did things as carefully and as accurately as possible and I think my results reflect this. I think that I have explained my results as fully as I can and that I have found out what caused them. I have presented my results in a clear and easy to read way. Having got no anomalous results I do not have any to explain. If I did this investigation again I would change a number of things. These things include: o Using a brand new can for water each time.
I would do this because when I burnt the alcohol it dirtied and blackened the bottom of the can. This may mean that unreliable results are given because having a black base on your can will absorb more heat than a can with a clean shiny base. o Repeating my experiment 3 times. I would do this to iron out any strange or rogue results. o Completing the entire practical in one day and in the same room. I would do this so that things like room temperature would affect my experiment less.
o Using the same mass of rock wool each time. I only needed rock wool for two of the alcohols but I think I should have used the same amount of rock wool each time to keep the experiment fair. o Finding and using an accurate way to place the crucible under my can of water. By doing this it will hopefully mean that the alcohol will heat the water a fully as possible with minimal loss of heat to the surrounding air. o Lowering the can of water. Looking back I think I should have probably done a preliminary experiment to find out the best height for the can.
By lowering the can it will hopefully mean less heat / energy is lost to the surrounding air. If I were to carry on this experiment in its present state I would probably go back and repeat the practical part again to hopefully give another set of results that I could compare my first with and hopefully get a better idea of what is going on.