Testing
I’m going to do a quick test, because I want to know what is the happening about the experiment. First, I put 100ml (not accurately) of water in a measuring cylinder, and then I put the measuring cylinder on the retort stand to hold it. After that I put the alcohol underside the measuring cylinder, finally, start combust. In this test, I found out that, I need to control the temperature accurately. It is because I want to make this experiment be a fair test. So that, every time, I raise 30 ℃ then gets the alcohols out.
Prediction
In this experiment, I will predict that as the weight of the alcohols is given more, then the temperature of the water goes up quicker, so therefore I would predict that the water need more heat energy by the alcohols. I will repeat this experiment three times, so I can make it more accurate.
During the experiment, there has something that are difficult to control, such as:
- The temperature
Because during heating the water, there may have some water evaporate to the air, so therefore the volume of the water wouldn’t be accurate.
- The heat of energy given from the alcohols
The reason of this happen which is because the condition in the lab may change, as the condition changed, the heat energy from the flame wouldn’t all goes to the water, and therefore it will change the temperature of the water.
I predict that the more bonds there are holding the carbon, oxygen and hydrogen atoms together, more energy will be required to break them apart. For example Ethanol has the formula C H OH. In this formula you have five C-H bonds, one C-C bond, one C-O bond and one O-H bond. To separate these types of bonds you require a certain amount of energy which I will show in a table.
Method
· Measure 100cm of water in to a glass beaker
· Place the beaker into the grasp of the clamp stand.
· Record the starting temperature of the water
· Weigh the spirit burner with the lid on.
· Put the chosen alcohol burner under the beaker allowing the flame to just touch the beaker.
· Leave to heat up until the temperature of the water is exactly 30ºC more than the original temperature.
· Weigh the spirit burner
· Record all results
The variables that must remain constant throughout the experiment are…
· Mass of the water 100cm
· Type of beaker, glass
· Temperature rise of 30ºC.
· Surrounding temperature of around 23ºC
· The height of the beaker from the wick
· Same set of scales
· Weigh the spirit burner with the lid on.
Diagram of the Experiment
Obtaining
Summary table
Here is the table of the results of the reaction on the comparing the heat energy produced by combustion of various alcohols
Average table
Here is the table of the average result on the comparing the heat energy produced by combustion of various alcohols
Here is the structure of the alcohols.
As you can see a longer molecule takes more energy to break its bonds, in this case Pentanol. Compared to a smaller molecule, methanol that requires less energy to do so. I can come to predict that the longer the molecular structure in the alcohol the more energy it will take to remove the bonds. So when I come to predicting results I can safely say that pentanol will evolve more energy than methanol simply because it has more bonds to break.
Analysis
As you can see in the obtaining section I have recorded all the information from the results that I need to complete the calculations…
· Energy evolved
· Energy per gram
· Energy per mole
First of all I will calculate the amount of heat energy. I will achieve this by using this simple formula…
Amount if heat energy = Mass of solution x Temperature change x SHC
Amount of heat energy = 100ml x 30ºC x 4.2
As you can see all of the alcohols will have the same amount mass of solution because all the numbers that are filled in the formula remain constant for each alcohol and the same numbers are applied for each individual alcohol.
To find out how much energy is produced per mole we use the formula?
Energy per mole = Amount of heat energy / number of moles
EVALUATION
I believe my results were very inaccurate. Below is a list of reasons why it was an inaccurate experiment.
1. Energy given off through sound and light.
2. Heat conducted and convected away through the air.
3. Radiation of heat out into the atmosphere.
4. The fact that the beaker gets hot.
5. The rubber clamp transferred heat way.
6. Heat may be taking away through guts of wind.
7. The fact that at higher temperatures, heat is lost faster to the air and out of the beaker, due to the bigger heat difference, making the higher temperatures more inaccurate, and making a shallower gradient on the graph.
8. By incomplete combustion
9. The amount of energy you give the alcohol originally.
10. The availability of alcohol for the wick to burn, if not enough then the wick would burn not the alcohol, which would give an inaccurate result.
11. Evaporation of water so there will be less water to heat, making the water hotter.
12. The size of the wick.
13. Not all of the water was the same temperature.
14. The flame size changed due to the type of alcohol; hence it was a different distance away from the beaker each time.
Conclusion
The equipment that I used in this experiment was very inaccurate because heat is a bad way of transferring energy without any loss of it. Any molecule will conduct heat, radiation happens and can be reduced but not completely halts. I feel that the most limiting factor of the experiment is the convection of air and to a lesser extent, of water. Also during the experiment, some of the water will have evaporated, thus the water mass/temp reading will be altered.
I feel that this experiment could have been improved by using a wider range of alcohols such as hexanol and heptanol. This would give a better graph reading and a wider range of results to support a firm conclusion. On the other hand, if I had started below room temperature, so that the amount of energy gained, from room temperature might equal the energy lost at temperatures higher than room temperature. Next time reducing heat lost would be my main priority. Improving insulation techniques would be a valuable asset in obtaining the most reliable data I could.
Another error is that of incomplete combustion. Complete combustion occurs if there are lots of oxygen atoms available when the fuel burns, then you get carbon dioxide (carbons atoms bond with two oxygen atoms).
If there is a limited supply of oxygen then you get carbon monoxide (each carbon atom can only bond with one oxygen atom). This is when incomplete combustion has occurred. This is so because the carbon monoxide could react some more to make carbon dioxide. If the oxygen supply is very limited then you get some atoms of carbon released before they can bond with any oxygen atoms. This is what we call soot. Since heat is given out when bonds form, less energy is given out by incomplete combustion. So this is why it affects the outcome of the experiment. To overcome this problem, I would have to make sure a sufficient supply of oxygen was involved in the reaction.
