The equipment should be set up as the following diagram:
Now weigh the mass of the lamp again and record it. All the results that have been recorded should be put into a table like the following:
The mass of alcohol burned = 2.33g
(Mass of lamp and lid before - mass of lamp and lid after experiment)
We only did this experiment once because it was a pilot experiment, if it was a proper experiment then we would have to repeat the experiment at least three times and then take an average of them to ensure results were as reliable as possible. Also if we were doing the definitive experiment the method would have to be more accurate and we would use distilled water instead of ordinary, as distilled water is pure and would give us a more accurate result as normal water has other chemical in it. Also to measure the amount of water we would use a burette, which would give us the accurate amount of water we wanted which was 50cm3. Also whilst doing the experiment you could put a lid on top of the beaker to prevent excess heat loss. The lid couldn't be airtight as some oxygen would have to get to the experiment or oxidation wouldn't take place.
Prediction:
I predict that the alcohol which will burnt the most energy will be Butanol, then Propanol, then Ethanol and finally Methanol. This means that if you plotted a graph to show which alcohol gave out the most heat per mole it would look like this:
Heat given out
Per mole (kJ/mol)
Alcohols (in order of
smallest structure
to biggest.)
As the alcohols atomic structure gets increased then so does the amount of heat given out. We know this due to the chemical reactions of bond breaking and bond making. The chemical reaction of bond breaking is an endothermic reaction, which is when heat is gained. The chemical reaction of bond making is an exothermic reaction, which is when heat its lost or given out.
Below are the structures and the equations of the alcohols:
Methanol (CH3OH)= H
H C O H
H
Propanol (C3H7OH)= H H
H C C O H
H H
Ethanol (C2H5OH)= H H H
H C C C O H
H H H
Butanol (C4H9OH)= H H H H
H C C C C O H
H H H H
This also helps with the prediction by showing that there are more atoms in Butanol than there are in Methanol which means that more heat would be given out, as there are more atoms to react with.
From the structures we can see that Butanol has the most amount of bonds and should therefore give off more heat energy than the other alcohol's as there are more bonds to break thus giving off more energy.
Results Tables:
Here are the results for each of the experiments that were done using the four alcohols; Methanol, Ethanol, Propanol and Butanol. We repeated the results three times each to make sure that the results were accurate as possible and so we could take an average at the end of the results to give us a more accurate reading of how much heat energy was produced for each alcohol.
The table above shows the mass differences and the temperature rises between the alcohol's before and after the experiment.
Below shows the heat gained by water for each of the alcohol's, this is worked out by; m c T
(m= mass of water-50cm3, c= 4.2J/g/oC, T= temperature rise)
For example methanol on the first experiment gained 6300J/g/oC (50 x 4.2 x 30)
Heat per gram alcohol burnt is worked out by the answer to the last question i.e.
mc T divided by the mass difference. All results are to one decimal place. E.g. methanol's 1st experiment -6300/3.13= 1993.7 (1dp) the other results are as follows:
The RMM for each alcohol is as follows:
Methanol (CH3OH)= (1x12)+(4x1)+(1x16)= 32
Ethanol (C2H5OH)= (2x12)+(6x1)+(1x16)= 46
Propanol (C3H7OH)= (3x12)+(8x1)+(1x16)= 60
Butanol (C4H9OH)= (4x12)+(10x1)+(1x16)= 74
Now that we have found the RMM we can find the Heat given out per mole. WE find this by; heat per gram (to 1d.p.) x RMM/1000. Here are the results:
(* This means that the result wasn't used to find the average, as it was too different to the other numbers.)
Analysis:
We can see from the graph plotted of the average heat given out per mole, that it has the same positive correlation to the graph of the actual results. Although the data are very different from one another, the graph still shows us which alcohol gives out the most and least energy, being Methanol giving out the least and Butanol giving out the most.
The graph also proves the theory of as the structure of alcohol increases then so does the amount of energy given out. This also goes back to when
How reliable was the experiment?
We can see from the graph that the results weren't accurate this can be due to many different factors such as:
- Heat loss, when some of the heat created from the experiment is lost into the air, this can also be from the heat shield which might reflect some of the heat away from the experiment as well as back towards it.
- The room temperature, which may have been different causing the water temperature to be different to start.
- The thermometers, which might not have been very accurate.
- Not stirring the water the same speed, causing each reading to be different.
- Incomplete combustion, when carbon was left on the bottom of the beaker as soot, which meant not enough oxygen could get to the experiment so all the carbon dioxide wasn't completely made.
- The flame height might have been different each time causing different amounts of heat to be produced from the flame for each experiment.
- There may have been a draught in the room, which would also affect the temperature of the room and the experiment.
- When the beaker was washed after the experiment there may still have been some carbon on the bottom of the beaker and some water still inside the beaker as well.
Evaluation:
For this result we could re do it and try to make the results more accurate. If we did the experiments again then we should maybe use a whole new method. The method we could use which is proven to be more accurate is by using the Heat of Combustion Apparatus. Below is a diagram to show how this apparatus works: