- I multiplied the number of each bond that occurred for a particular molecule by the energy it used/released, to get how much energy was used/released in total through that bonding. I then added together the energy used to break every bond in the reaction to get a total energy used for the reaction. I also added together all the energy made from making bonds together for a total number of energy released.
E.g.:
Bonds Energies:
C-H → 413 C-O → 358 O-H → 464 O=O → 497 C-C → 346
3 x 413 = 1239
1 x 358 = 358
1 x 464 = 464
1.5 x 497 = 700.5 1239 + 358 + 464 + 700.5 = 2806.5
I entered the data into a spreadsheet and used Microsoft Excel to calculate the rest of the energy values.
- If I then subtract the energy lost from the energy made, then I get the total energy made from the reaction:
I furthermore predict that the results I get will show less energy than the theoretical energy. This would be because I cannot measure all the energy that is released, as some will be dispersed into the air, and also into the apparatus, such as the beaker, clamp, and thermometer.
I will also be using Propan-2-ol, which has a different isomer to the other results. I predict that the energy released from Propan-2-ol will be different to the other isomers, as some of the bonds that are broken will be different to the others.
Source: Microsoft Encarta Encyclopaedia 2003
To make sure that the investigation is fair, I will try and make sure that I keep all of the variables the same. I will change the type of alcohol so that I can compare them. I will try to keep the isomers of the alcohol as all the same type, i.e. all 1-ol; however this may prove difficult due to availability. I will also keep things such as time left to burn constant throughout each attempt.
I will also let the flame on the burner burn for 30 seconds before placing it beneath the beaker of water. This will allow it to stabilize, and the alcohol will be burning at a constant rate.
When I measure the mass of the spirit burner, I will measure it with the cap on. I will make sure that I measure the end mass with the cap on also, so that I do not get incorrect results.
I did some preliminary testing so that I could find out what mass of water I should use. A mass too low would heat up faster, and the temperature could get too hot. I gained the following results from my preliminary work:
I started with a mass of water of 20g, and burned Pentan-1ol. I used Pentan-1-ol, as I predicted that it would release the most energy. This would give me a ‘worst case scenario’, where the water would heat up the most. With 20g, the water became very hot, and this would be both dangerous, and could also affect the results, some of the water may have evaporated.
I increased this to 40g, but the water was still too hot. I then further increased the mass to 80g. This value seemed reasonable, as the temperature only increased to 45ºC. I then repeated the test using the same amount of water, but using Methanol, at the bottom of what I predicted would release the most energy, and Propan-2-ol, in the middle.
Apparatus and Diagram (diagram overleaf):
- Beaker
- Spirit Burner
- Clamp and Boss
- Retort Stand
- Heat Proof Mat
- Bunsen Burner
- Splint
- Thermometer
- Stopwatch
- Precise Balance (weight scales)
- Water
- Alcohols – Methanol, Ethanol, Propan-2-ol, Butan-1-ol, Pentan-1-ol
- Ruler
Method:
- I will set up the apparatus as shown above. The beaker will contain 80ml of water, measured out of a measuring cylinder. I will first use methanol in a spirit burner, and place this aside, not under the beaker of water, after measuring its mass. I will measure the temperature of the water, and record this.
- I will light the spirit burner using a splint, and leave it for 30 seconds to burn and let the flame stabilise. After 30 seconds, I will place the burner under the beaker, and start a stopwatch. After two minutes of letting the alcohol burn, I will extinguish the flame.
- I will wait a few seconds, and then take a measure from the thermometer for temperature. I will then measure the mass of the spirit burner (making sure to keep the cap on). I will record both these values.
- I will repeat the above steps, using the alcohol methanol, two more times to get repeated results. When I have finished repeating the methanol results, I will collect a different spirit burner with ethanol in it. I will then repeat all of the above steps once more, but this time using ethanol rather than methanol.
- I will repeat the experiment using ethanol two more times after the first, and then move onto the next alcohol, propan-2-ol. When I have repeated propan-2-ol two more times after the first, I will move onto butan-1-ol. After three butan-1-ol results, I will move onto the final alcohol, pentan-1-ol.
- Once I have all my results recorded, I will clear away the apparatus.
To keep the investigation safe, I will have to check a few things:
- The water does not get too hot.
- The Bunsen burner and spirit burner are kept away from places where they may easily be knocked.
- The wick of the spirit burner is on firmly. If it is not, then it may catch fire.
- I will wear safety goggles to protect my eyes.
- Any loose bodily articles are firmly secured, so they do not set alight.
Results
NOTE: Anomalous results highlighted in RED
After completing the investigation, I got the following results for temperature of the water and the mass of the spirit burner:
The mass was measured with a precise balance for accurate results, and the temperature with a thermometer. To get the values for change in mass and temperature rise, I will subtract the lower value from the higher value.
To get the numbers for the amount of energy liberated, in kilojoules, I used the following formula:
Water Mass x Specific Heat Capacity of Water x Temperature Rise
1000
I divide by 1000 to give me the answer in Kilojoules.
Water Mass = 80g
Specific Heat Capacity of Water = 4.2
Temperature Rise is shown in the above table.
If I substitute some numbers into the formula I get the following results:
Methanol 1 80 x 4.2 x 27 = 9.07 Kj
Ethanol 2 80 x 4.2 x 40 = 13.44 Kj
I used the Excel spreadsheet to work out the rest of the data.
Next, to get Kilojoules per Mole, I used the following formula:
RAM / Change in Mass x Energy Liberated
This small table shows the RAM of the different alcohols:
Methanol – 32
Ethanol – 46
Propan-2-ol – 60
Butan-1-ol – 74
Pentan-1-ol – 88
If I put the figures into the formula I get:
Methanol 1 32 / 1.4 x 9.07 = 207.36 Kj/Mole
Ethanol 2 46 / 1.56 x 13.44 = 396.31 Kj/Mole
I then averaged these results to give me my final results for energy released when the alcohols were burnt.
To average the results, I added the three results together, and then divided this sum by three. For example:
Methanol 207.36 + 205.89 + 208.62 = 621.87
621.87 / 3 = 207.29
I will finally create a table to compare the results to the energy that theoretically should have been released.
Anomalous Results:
There are several results that do not follow the pattern of the other results of that type for the alcohol; however they did not make the final result that I had wrong. There was one value which I thought was anomalous, which I highlighted in red. This was too far away from the other results, and would have made the final results inaccurate.
On the next page, I have displayed all the information in a single table so that it can be easily read.
I have plotted both the theoretical results and the results I got on this graph so that I can compare them easily.
Using these results, I conclude that different alcohols release different amounts of energy. Methanol releases the least, and pentan-1-ol releases the most. As you increase the number of atoms in the alcohol, you increase the amount of energy released. This is because there are more bonds made, and the energy is released when bonds are made. I can also see a pattern in the results. The amounts of energy release all fit closely to the line of best fit. The results I have increase by about 200 Kj/Mole each time.
These results concur with my prediction. I predicted that the energy released would increase as you increased the number of atoms in the alcohol. I also predicted that the energy I got out would be less than the theoretical energy, and this was true. Not all the energy went into the water, and therefore I could not account for all of it in my results. However I can compare my results to my theoretical results. If I work out what percentage of the theoretical results the results I have from the experiment are then I may see a pattern.
To work out what percentage the results are, I should take the result I have from my experiment, and divide it by the theoretical results. If I then multiply it by one hundred I will get the percentage.
E.g.
Methanol 207.9 / 539.5 x 100 = 38.42%
If I did this for al the results, I get this:
These results show that the results I had were all about 40% of the theoretical results. The result for propan-2-ol is not as accurate as the other values. This is possibly because it is a different isomer to the other alcohols.
This also backs up the prediction I made that the propan-2-ol would be slightly different to the other results. This is because the molecule has a different structure, and therefore the bonds are broken differently. This means that more/less energy is used to break them.
The results show that it releases less energy than the others do, compared to the theoretical energy. This tells me that it uses up more energy to break the bonds.
Evaluation
During the investigation there were some difficulties. Some of the variables proved difficult to control, such as length of the wick on the spirit burner, and the distance between the beaker and the spirit burner. The distance between the spirit burner and beaker was done using a ruler. We measured 12cm; however it was not entirely accurate, as it was difficult to get the clamp to sit in the correct position.
The length of the wick was also very difficult. We judged it by eye; however this was not very accurate.
The results that I gained were very accurate. They all lied very close to the line of best fit on the graph. They also were all almost 40% of the theoretical results. The slight exception was propan-2-ol, which appeared slightly anomalous compared to the others. This was most likely because it was a different isomer to the other alcohols.
I think that my results are very accurate, and are by far reliable enough to support a firm conclusion, stated in the analysis.
Sources of error that could have affected my results are listed here:
- Energy in other objects, not just water. Objects such as the glass beaker also would have some of the energy in them. If I wanted to get more accurate results, I would have to calculate the energy in the apparatus and add this in also.
- Variations in wick length and distance between beaker and burner may have made a difference in the results. More/less energy may have been transferred into the water on different attempts.
- Mistakes when reading thermometer temperature or water amount in measuring cylinder may have meant that the temperature values are not correct, and may be slightly out.
To improve this experiment, I could correct all the mistakes that were made in this investigation. I would make sure that all variables were controlled and measured accurately, so that the results were affected as little as possible.
I would use the same isomer of alcohol each time, so that I would get consistent results. I would also measure the energy in other items such as the beaker, so that I could get much more accurate results, and this would allow me to form an even firmer conclusion.
If I were to further extend this investigation, I could investigate the other variables.
The main variable is isomers of the alcohols.
The method for investigating isomers would be almost identical to this investigation. I would simply replace the 1-ol isomers with 2-ol. I would predict that the 2-ol isomers would release less energy than the 1-ol isomers. The results from this investigation suggest this, as more bonds must be broken, therefore using more energy.
I would also compare the 2-ol results with the results from this investigation, and I would also work out new theoretical results so that I could form a conclusion, and see how the different isomers vary from each other.
Another variable I could investigate is the time left for the alcohol to burn. To investigate this, I would use an identical set up to my current investigation. I would, however, repeat the investigation several times leaving the alcohol to burn for more or less time. I would have a range of results which I could compare to come to a conclusion. I would predict that as you increase the time left for the alcohol to burn, the energy released would increase. If you increase the burning time, then you are increasing the amount of time there is for reactions to take place, and more bonds will make and break. As you increase the number of bonds that are made, you also increase the energy that is released, as making bonds releases energy.
