Preliminary Work:
We did the preliminary work as a trial to see what factors should be changed and we were trying to find the factors that would give us accurate results. The preliminary work also gave us the chance to try our equations to figures out energy per mole. Our results were complete so we were able to do this.
After testing one of the alcohols to burn for 6 minutes with the water 8cm above the surface. We had decided to do some changes to the factors. We decided to change the height from 8cm above the table surface to 7cm above the tables surface. We then decided that 6 minutes was too long so we shortened it on 4 minutes.
We had decided that these factors would be used in the experiment. We also decided that we should test each alcohol 2 times so that we can obtain an accurate average result.
Obtaining results:
To get the results I will use 3 equations stated below:
Firstly to figure out the total amount of energy released:
Energy=mass/volume of water x Specific heat capacity of water x Temperature rise
Secondly to figure out how many moles:
Moles=Alcohol burnt (g) ÷ Relative Formula Mass
Then to find out how much energy produced by each mole:
Energy per Mole=Energy ÷ Moles
I will take all the measurements required before and after the experiment to be able to use the equations to figure out whether the amount of carbon in alcohols has an affect on the amount of heat that is released when heated by combustion.
Setting up:
Apparatus:
- Alcohols
- Clamp
- Clamp stand
- Stopwatch
- Top-pan Balance
- Water
- Copper can
- Measuring cylinder
- Thermometer
Diagram:
Method:
First of all get all the apparatus and set them up as shown in the diagram above. Take the alcohol and weigh it, take down the mass and then fill your measuring cylinder with water until the level that you want it (200ml) and put it into the copper can, then take the temperature of the water and record that. When both those are done check that the clamp is set at the right distance from the surface. When all these are done we an start the experiment.
- Take the cap off the alcohol and light it under the copper tin.
- Start the stop watch.
- Wait till the set time has finished.
- Recap the alcohol
- Take temperature of water.
- Weigh the alcohol
- Figure out temperature rise and alcohol burnt
- Use the equations to figure out the energy per mol.
- Repeat with other alcohols
You should test each alcohol twice so that you can figure out an accurate average. Plot your results on a graph and see if you get a positive or negative correlation.
Safety precautions:
To be safe whilst doing this experiment you must wear safety goggles. You must also set up your apparatus in a safe place. Regarding the experiment, if there is a lack of oxygen to the flame of the alcohol, then carbon monoxide is formed, there is a toxic gas.
Fair test:
We must keep some factors of the experiment the same so that it will be a fair test such as the amount of water and the room temperature and the time in which we leave the alcohol to burn. To also make it fair, we will be doing the experiment twice. This will help us know if we got anomalous result. It will also give us accuracy when we figure out an average.
Results: Averages of two tests for each experiment
Above is the result average of the 2 sets of results that I got. The results show that more carbon atoms present in the alcohol then the more energy was needed to break the bond. I used the 3 equations to find out the energy per mole. Below is a graph showing a positive correlation of “more carbon=more energy per mole.
Conclusion
From the results that I obtained and by analyzing the graph, I can see that the more carbon in an alcohol means that is requires more energy. The reason that it takes more energy is because there are more carbon bonds. This means to break the bond more energy is required.
We can see that energy is being given out because it is an exothermic reaction. We know this because it is giving out heat and also because bond making is taking place.
The alcohols with more carbon have stronger intermolecular forces, therefore, more energy is required to break these strong forces.
My results, in fact, agree with my prediction. I predicted simply that more carbons means more energy. I predicted this because I knew the reaction would be bond making, therefore, it is exothermic which means energy is given out.
Evaluation
The procedure was complete. We obtained all the results that we wanted and they were fairly accurate which indicated that there were no problems in the procedure.
There were no anomalous results. They were fairly accurate and you an clearly see the positive correlation in the graph. The quality of the evidence is fairly accurate. K There is not definite straight line in the positive correlation but it is fairly close with no results being too far away from the line of best fit. We could have done the experiment more times to get more accurate results, therefore, reducing the amount of time we burnt the alcohols would give us more time to re-test the alcohols. Also if I was to do the experiment again, I would use a great number of alcohols making it easier to make a line of best fit. The evidence is fairly reliable because we kept it a fair test by keeping certain factors consistent, therefore, we know that the results are reliable enough to be correct. It can support my conclusion.
Other experiments we could do could be to see whether the amount of carbon in an alcohol would affect the rate of speed at which it burns.