The negative sign before each overall heat change shows that the energy was released, exothermic.
From these results, I can see that Pentanol gives out the most energy when it is burnt, and Methanol releases the least. Using these, I can make a prediction. If Pentanol releases the most energy, then compared to the others, it should take the least amount of mass of alcohol to heat it. Likewise, Methanol releases the least amount of energy, so it will use more mass to heat the same amount of water.
To make sure that my experiment is as fair as possible, I will use the same amount of water; the same temperature rise and I will keep the test tube the same distance from the alcohol. Some of the energy released will be lost to the air, so I will create a skirt to go around the bottom of the test tube in a bell shape. I will make this out of aluminium foil because the shiny side will reflect the heat well.
I weighed each alcohol before igniting it, and recorded the weight. I then placed the alcohol under the skirt and only removed the lid just before it was lit, to reduce the amount escaping into the atmosphere. I carefully watched the thermometer until it had risen to 80ºC. As soon as it had reached 80ºC, I put out the flame. I then weighed the alcohol again and noted that down. I was then able to work out how much alcohol was used.
I did each alcohol three times so that I could make my results as accurate as possible. The results I obtained are below.
The graph on the next page shows the mass changes that I obtained from each attempt on each alcohol.
With my three different results for each alcohol, I then found the average by adding them all up and dividing the total by three. The results, for average mass changes, I got from this were:
These results show me how many grams were needed to heat the water from 25oC to 80oC. To find out how much of a mole each amount is, I need to divide the amount of grams by the total atomic mass of the alcohol.
To get the total atomic mass, I have to add the atomic masses of each element together
Carbon has an atomic mass of 12.
Oxygen has an atomic mass of 16.
Hydrogen has an atomic mass of 1.
Methanol: Has the chemical structure:
(1x12) + (1x16) + (4x1) = 12 + 16 + 4 = 32. Then I must divide my result by this:
0.8/32 = 0.025
Ethanol: Has the chemical structure:
(2x12) + (1x16) + (6x1) = 24 + 16 + 6 = 46. Then I must divide my result by this:
1.0/46 =0.022
Propanol: Has the chemical structure:
(3x12) + (1x16) + (8x1) = 36 + 16 + 8 = 60. The I must divide my result by this:
1.2/60 = 0.02
Butanol: Has the chemical structure:
(4x12) + (1x16) + (10x1) = 48 + 16 + 10 = 74. Then I must divide my result by this:
1.2/74 = 0.0162
Pentanol: Has the chemical structure:
(5x12) + (1x16) + (12x1) = 60 + 16 + 12 = 88. Then I must divide my result by this:
0.7/88 = 0.007954
My results are shown on the next page.
This graph shows that my prediction was correct. Pentanol used the least amount of moles to heat the water, and methanol used the most. I can therefore conclude that the longer the hydrocarbon molecule, the more energy is released when making bonds.
I think my experiments went pretty good. There were a few discrepancies that could have occurred for many reasons. Poor quality equipment or simply human error could have caused this. I think there is one main anomaly that I can identify. This is on the 3rd attempt of the experiment, using methanol. Somehow, after burning the alcohol, it gained 0.7g of mass??!! Apart from this, I think the rest of the experiment went okay. The results came out pretty good.
I think the quality of my results is poor. However, I think that they could be improved by repeating the experiments with more time and less haste. Also, I think it would be beneficial to use more alcohols, such as hexanol, heptanol and octanol. This would give me a wider range of results and I would be able to draw a better conclusion that was more precise.