I will repeat this experiment for all of the fuels at least twice, taking the weight and the temperature before and after for each to give a more accurate and reliable set of results at the end of the experiment.
Safety;
To make it safe to do the experiment I have to wear safety goggles because some of the fuels are corrosive, with means if it touches your skin it will itch and sting. My personal processions .e.g. my bag and coat have to be out my way because if any fuel spills on them it will smell and stain it badly. If my skin does come into contact with the chemicals then I will have rinse and wash it off immediately. The room will have too be well ventilated to allow the heat and smell escape but not to well ventilated because that can affect the investigation, the stools will have to be put neatly under the table or out the way so I have enough room to not spill or fall over.
Predictions;
I predict the more chemical bonds there are between the carbons and the hydrogen atoms, the more the heat will be produced because the chemical bonds are where the energy for the reaction is stored.
Alcohol burns where the air has oxygen in it. The amount of heat produced and fuel burnt depends on how much oxygen there is in the air present. Full combustion will produce a blue flame. It should only generate two things;
Water Vapour,
Carbon Dioxide,
I think the pentanol will be the most efficient and raise the temperature of the water the most, because it has got the more amount of intramolecular bonds( between the carbons and the hydrogen atoms) which is where the heat energy for the reaction stored. Methanol will raise the temperature of the water the least, because it's got the least amount of intramolecular bonds, there fore it is weaker and allows the heat to break the bonds up more quickly and easily. Then because of that, less energy is used.
So I predict that pentane will release the most heat energy and raise the water temp the most.
Variables;
The variables I must keep the same constantly through out the experiment are;
- The mass of water (30 cubic centimetres)
- The type of boiling tube I use (glass)
- The height of the boiling tube from the crucible
- The same set of measuring scales.
- The same amount of fuel (30 drops)
- The same amount of mineral wool.
The variable that must be used is the…
Preliminary Investigation;
In the preliminary investigation we filled the boiling tube up with 30cc’s of water, and then we put 10 drops of ethanol in the crucible and weighed it. I recorded the weight of it at 11.72 grams. We then took the temperature of the water at 24 C in the boiling tube. Then we set the fuel alight by using the taper to catch the flame from the Bunsen burner. We then waited for the fuel to burn out, when it did eventually burn out we recorded the temperature straight away at 30 C. That’s a 6 C raise. Then we weighed the crucible again, this time weighing 11.56 after we burnt the fuel in it.
So to work out the heat combustion of the five fuels I have to do the calculations below;
11.72
11.56 –
00.16 = mass of Ethanol.
Mass of water x heat capacity x temperature rise
30 grams 4.2 6 C
= 756 joules = in how much heat was transferred.
For 1 gram;
4725j is the answer for how much energy 1 gram gives off.
0.16 756
In the real experiment I hope to have a time limit to how long I want the fuel to burn for and I am going to put 30 drops of the fuel in to hopefully get clearer results
Results;
The results I have achieved will now be placed in a table.
My first set of results is;
My second sets of results are;
My average results are;
Next, I will work out the heat transferred for each alcohol.
The equation for this is:
Heat transfer=mass(g) x Temp change(c) x specific heat capacity(j)
I will only do this for the average results. As basically, that is all that is needed.
Also, the specific heat capacity of water is known to be 4.2j.
Calculations;
Methanol;
Heat transfer=mass(g) x Temp change(c) x specific heat capacity(j)
30 8 4.2
= 1008 joules of heat transferred.
For I gram of methanol;
12.545
11.98 -
00.565=weight of fuel burnt.
1784j = energy given for I gram
0.565 1008
Ethanol;
Heat transfer=mass(g) x Temp change(c) x specific heat capacity(j)
30 8 ½ 4.2
= 1071 joules of heat transferred
For I gram of Ethanol;
12.685
12.175-
00.510= weight of fuel burnt
2100 = energy given for I gram
0.510 1071
Propanol;
Heat transfer=mass(g) x Temp change(c) x specific heat capacity(j)
30 15 ½ 4.2
= 1953 joules of heat transferred
For I gram of Propanol;
12.60
12.08-
00.52= weight of fuel burnt
3755= energy given for I gram
0.52 1953
Butanol;
Heat transfer=mass(g) x Temp change(c) x specific heat capacity(j)
30 20 ¼ 4.2
= 2614.5 joules of heat transferred
For I gram of Butanol
12.415
12.01-
00.405= weight of fuel burnt
6455.5= energy given for I gram
0.405 2614.5
Pentanol;
Heat transfer=mass(g) x Temp change(c) x specific heat capacity(j)
30 26 ½ 4.2
= 3339 joules of heat transferred
For I gram of Pentanol
13.81
13.035-
00.775
7308= energy given for I gram
0.775 3339
Energy transferred for 1 gram;
Conclusion;
I have found out that my prediction was correct. In my prediction I said that the amount of heat produced per gram would increase as the number of chemical bonds and carbons in each of the fuels increase. This statement turned out to be true. As you can see from my graph, Pentanol had the highest amount of heat produced, and this also had the highest number of chemical bonds. This is just as I had said in my prediction. Also, Methanol had the lowest amount of heat energy produced, just as I had predicted. So, I conclude that the Pentanol gave out the most heat energy out of the alcohols. I had investigated was Pentane, and the least efficient was Methanol. The reason why the pentanol was the fuel to give out the most heat energy was because, it had the most amount of chemical bonds so it took more energy to break the bonds up, therefore, giving out the heat energy.
Below is a table of how many carbons are in each fuel;
Evaluation;
This experiment has gone quite well. My prediction was correct. However, I could have done certain things to make my results more accurate.
Firstly I would have made my experiment more accurate if I had a simple draft screen to block any unnecessary wind or breezes from cooling down the boiling tube while the experiment is going on.
I did not get a clear anomalous result because there wasn't a very strong wind but just a mild one. Also because of the other students moving and using their Bunsen burners, that could have either cooled down my experiment or heated it up more. I was lucky not to get a big anomalous result, but instead I got little anomaly.
A problem I kept on having during my experiment was that the crucible got to hot to pick up, I dropped it 2 or 3 times. That could have caused fuel to spill out. I overcame the problem by picking the crucible up with several paper towels.