8. record its mass and work out the change in mass
9. repeat steps 1-8 but this time using the other alcohols and record all the results
Diagram:
Safety: - wear safety goggles throughout the whole experiment
- don’t stand too close to the copper calumeter in case it falls
- make sure the copper calumeter is held tight
- make sure you light the spirit lamps safely
- make sure you put out the spirit lamp by placing the glass lid on top
Fair test:: In order to carry out my experiment fairly I will have to keep some things constant and others I will change. The things that I will change are the five alcohols. All the rest I will keep constant like the volume of water and the same copper calumeters. Also I will keep the temperature change the same and I will adjust the clamp (move it up or down) so that the distance between the copper calumeter and the spirit lamp is always the same. Otherwise some of the spirit lamps will transfer more or less heat energy to the water than others. I have to take into account that some of the heat energy will be lost to the surroundings, but I cannot do anything about that except to keep the spirit lamps close to the copper calumeters.
In my preliminary work I had some trouble in measuring the mass of the spirit lamp as the electric weigher kept changing slightly. However I can overcome this problem in my real experiment by choosing the reading which was in the middle even though it might still be quite inaccurate. I have to also make sure that the thermometers don’t touch the surface of the copper calumeters as it will be hotter than the actual water. So that my results are reliable I will have to repeat them twice from which I can then get the average and that will be a more reliable result as sometimes one of the results is wrong. However doing the experiment three times would give me more reliable results but I only have a limited amount of time in which to carry out all the experiments so that would not be possible.
Preliminary results:
Predictions: Looking back at the results and graph of my preliminary work, I can see that the line goes up as the heat produced by each of the alcohols becomes greater. Therefore, the more bonds there are in the alcohols, the more heat energy is produced per mole. My prediction is that pentanol will produce more heat energy than any of the others as there is more bond energy in that molecule than in the other of the other alcohols. This also means that the more carbon atoms there are, the more heat energy is released. I don’t think that my preliminary graph is correct because if the more carbon atoms there are, then the higher the heat energy will be: this is proven to be wrong as you would expect it to be a straight line (proportionality) whereas my graph shows that propanol is releasing the same amount of heat energy as ethanol but I would expect it to release about 600 kj/mol. Then there would be a straight line. The reason why I think pentanol will produce the most heat energy is because it has the most amount of carbon molecules which give out loads of heat energy due to the long chains of hydrocarbons cracking to form simpler forms and this gives out more heat energy because there are more of them. The alcohol that will produce the least heat energy is methanol.
Obtaining EVIDENCE –
Safety: During the practical, I had to consider safety procedures and these are listed at the top of page 2.
Results:
In my results I got some inaccurate results. If you look at the results for ethanol in the change in mass for 1st and 2nd time results, the difference between those two results was quite high and therefore one of those results must be wrong which would lead me to an inaccurate average for ethanol. However I did not have enough time to repeat that result and so I would just have to keep that result. When I do my graph, it will probably not be a straight line as one of my results is supposedly wrong.
There were also other factors that may have caused my results to be slightly wrong. These include energy lost to surroundings, radiation of heat out into the atmosphere, heat may be lost through gusts of wind, incomplete combustion, the amount of alcohol that the wick can burn, evaporation of water and different starting temperatures of the water. Although there are a lot of factors that made the experiment unfair, I did everything else fair (the factors which I could do something about) to make my results as accurate as possible.
ANALYSING AND CONSIDERING EVIDENCE –
From the results you can see that the more carbon molecules there are in the formula of the alcohols, the more heat energy is produced per mole. For clearer results see the next page with the graph.
The graph shows a line of a slight ‘S’ shape. At first the line starts off at 168 KJ/mol with methanol and more heat energy is produced form ethanol. Propanol however has the same amount of heat energy produced as ethanol but both butanol and pentanol produce a lot more heat energy according to the graph. Therefore the line is not straight and not a curve. All it is, is a slight ‘S’ shape. I think that this graph is incorrect because I expected a straight line because the more carbon atoms there are, the more heat energy should be produced but my graph did not show that. When I used my scientific knowledge, I predicted that the line will be straight meaning that an increase in carbon atoms would be proportional to the amount of heat energy produced.
Conclusion: I can see that in my results, I supposedly got the wrong results for ethanol because the my two results were very different yet in the graph, propanol seems to be the one that is incorrect because there should be a straight line and propanol is the one that seems to be too low. If it was higher then the results would be much more accurate. I cannot see any trend which matches my prediction or my scientific knowledge. All I can say is that I probably got the wrong results for propanol which led to an incorrect final result in the graph which was supposed to have a straight line and it didn’t. This might have been due to factors listed on the bottom of page 3. Overall, my results are not correct cannot reliable enough for me to write up a proper conclusion and they certainly don’t match my predictions although they are similar to my preliminary work. This must either mean that my results are correct and there isn’t supposed to be a pattern or all of my results are incorrect and I would need to carry out my experiment at least once more to get results which are more reliable and therefore have less mistakes.
EVALUATION –
My results were incorrect due to several factors that may have caused that to happen like the electrical weigher not working properly which would not have been my fault. I did not get a straight line due to an incorrect result for one or two of the experiments. I also would have repeated the experiments if possible but I didn’t have enough time and so the accuracy of my results were not up to standard meaning that I wasn’t able to carry out a proper conclusion or identify a trend from the graph.
If I was to improve the reliability of my results then I would use a wider range of alcohols like hexanol and heptanol which would help me see the trend even clearer and repeating the experiments more times would also give me much more reliable results as I would end up taking away the unusual ones and only taking the average of those that were close together. Therefore all the odd ones out would be discarded. Due to my unusual results, I don’t feel that I could justify a firm conclusion. I don’t think that the investigation was fair because a lot of the heat energy might have been lost to the surroundings or through gusts of wind, radiation in the atmosphere, the copper calumeter getting hot, heat getting lost faster to the air as there is a large heat difference leading to incorrect results at higher temperatures, the amount of alcohol the wick is able to burn (different sized wicks), evaporation of water, different starting temperatures of water and incorrect readings of the electric weigher and all these factors could have contributed to incorrect results.
