Hypothesis:
I predict that the greater amount of carbon chains the alcohol has the more energy it will give out. This will happen because the more chains there are the more bonds that need to be broken and therefore producing/releasing more energy.
Variables:
Explanation of variables:
I have chosen to control the mass of water that will be heated by the alcohol because if there is and inconstancy in the mass of water then the amount of heat energy given off by the alcohol being combusted and then be transferred to the water may not affect the overall temperature of the water there for making my experiment unreliable.
I must also keep the distance/height between the flame of the spirit burner and test tube the same. If I had one flame of the spirit burner at a distance of 20cm from the test tube and then in my next experiment the flame of the spirit burner was only 5cm away from the test tube then the rise in temperature would be greater than the one at 20cm as less would have been lost to its surroundings.
I have also chosen to keep the time allowed for the alcohol to burn the same. I have done this because if one alcohol is allowed to burn for one minute but a second alcohol was allowed to burn for five minutes then this would possible result in greater temperature change therefore my experiment unfair test and also making the joules/per mole untrue to the energy content they are potentially capable of.
Apparatus:
- Test Tube
- Clamp Stand
- Thermometer
- Range of alcohols (Spirit burner)
- Stop Watch
- Measuring Cylinder (smallest division of 1cm3)
- Heat proof mat
Diagram of apparatus:
Method:
Firstly I weighed the spirit burner (and recorded its weight in a table) with the alcohol already inside the spirit burner before I began my experiment. I then measure out 50cm3 of water with a measuring cylinder and them place the test tube in the clamp stand and tightened it gentle. Next I placed the test tube at a height of 3cm to the spirit burner. I lit the wick and started the stopwatch. I took the temperature every fifteen seconds for fives minutes after this I reweighed the spirit burner and recorded its new weight. I repeated this experiment three times for each alcohol and my results are shown in the table below.
NB** I will stir the water to make sure there is a fairer heat distribution and this will decrease the likely hood of hotspots and inaccurate results.
**To enable me to find out the energy given off by the alcohols per mole I will need to find their relative atomic mass of each**
**Energy off each alcohol is shown in below table. To find out the energy for each I used the formula:**
Q = Water Mass x Specific Heat Capacity x Temperature Change
Conclusion:
Having looked at my results I can see that Butan-2-ol is the most efficient fuel as it produces more heat/per mole. This proves my hypothesis to be correct as butanol has the most amount of carbon atoms and I state that the longer the chains of carbons the more atoms they have and therefore are able to realise a higher energy amount.
Evaluation:
The results I have obtained from my experiments are fairly accurate. However if I was to do this experiment again I could make it more accurate be changing and modifying certain things. For example instead of just using a test tube above the flame I could use a carilometer to place my test tube inside and therefore reducing heat lose from draughts and lose to the surroundings. I could also do this by making sure there was better insulation to the sides and top of the beaker. This could be done by using a metal (conductor of heat) as a beaker and also adding a lid.
This experiment has proved to have many sources of error to help irradiate these I could take a larger range of results. I could also investigate a larger range of alcohols and also the affects of burning them under different temperatures and pressures.
