propanol – C3H7OH
butanol – C4H9OH
pentanol – C5H11OH
hexanol – C6H13OH
- Matches
- Water
- Measuring cylinder
- Thermometer
- Safety glasses
- Electronic balance
This is the method I will be using:
- Measure 100cm3 of water and pour into a colorimeter
- Place the colorimeter in the grasp of the clamp stand
- Record the starting temperature of the water
- Chose the alcohol you wish to use first. For this experiment, I will be using methanol, propanol, butanol, pentanol and hexanol.
- Weigh the spirit burner (to 2 decimal places) with the lid on
- Put the chosen alcohol burner under the colorimeter allowing the flame to just touch it.
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Leave to heat up until the temperature of the water is your chosen amount above the original water temperature, in my case 30°C more.
- Weight the spirit burner.
- Record all results. You can now work out the amount of energy transferred and thus the heat combustion of the alcohol by using these two formulas:
- Energy transferred(KJ) = Mass (water) x Temperature rise x SHC
(SHC = Specific heat capacity)
- Heat of combustion = energy transferred x formula mass
Diagram:
Results:
We repeated the experiment for propanol again as we realised that we must have made a mistake somewhere along the line. The second sets of results were much more what we expected to get.
Energy Transferred - 0.1 x 30 x 4.2 = 12.6KJ
Energy per gram of fuel:
ethanol - 12.60/0.90 = 14KJ/g
propanol - 12.60/0.86 = 14.65KJ/g
butanol - 12.60/0.84 = 15KJ/g
pentanol - 12.60/0.76 = 16.58KJ/g
Heat of combustion
ethanol – 14 x 46 = 644KJ/mol
propanol – 14.65 x 60 = 879KJ/mol
butanol – 15 x 74 = 1110KJ/mol
pentanol – 16.58 x 88 = 1459KJ/mol
hexanol – 21 x 102 = 2142KJ/mol
Graph to show the relationship between the molecular mass and the heat of combustion
Analysis:
In this experiment I proved that my hypothesis was correct and that as the molecular structure increases, so does the heat of combustion, the energy required to break the molecule. This is due to the larger molecule having more bonds than the smaller one and thus meaning that the larger the molecular structure, the more energy needed to break them apart. My graph also concludes the fact that my prediction was correct as we can see a strong curve with a positive correlation, showing a relationship between the two factors and meaning that they depend on one another.
Evaluation:
This experiment was a success and we received the best result we could have possibly received in the environment we were in.
Although I believe this experiment went very well, we did see a yellow flame coming from the spirit burner and also sot was found on the bottom of the colorimeter. This suggests that not enough oxygen was present which means incomplete combustion occurred and thus meaning the results we received for the heat of combustion are not accurate.
We tried to make the experiment as accurate as we could, by doing such thing as using a shield to stop the wind from reaching the flame, however the first set of results did produce some anomalies. In these results we received the answer 13.42g for the mass of alcohol used for the alcohol propanol. Looking at the other results we had collected we realised that this was not correct and something must have not been accurate, maybe we did not weigh it correctly. To ensure this experiment was as reliable as possible we then decided to repeat the experiment for the alcohol propanol. Repeating this alcohol, the result produced was much more like what we had expected the first time and so the first result was disregarded for the rest of the experiment.
If I were to repeat the experiment again I would perhaps use different temperatures, raising the original temperature of the water by a different amount. With these other results I would be able to compare them with the first set of results and record any change. Also, to perhaps make it a fairer test and therefore more accurate, I would use the same amount of alcohol each time and see if this would cause a change in my original results.
Based on my prediction I believe this was a suitable procedure to use to get the appropriate results I wanted. It was simple to understand and easy to undertake and my results were accurate as possible for our environment, which proves the suitability of the experiment.
Overall, I enjoyed this experiment and believe it went well.
