Preliminary Work:
Before I completed my experiment I completed some preliminary investigations. I completed an experiment to decide several potential variables within the final experiment. These include:
- The apparatus I will use in the final experiment (clamps, clam stands)
- The height the tin containing the water is away from the flame
- The amount of water
- The type of tin (percentage steel etc)
- Where the water comes from
I will burn three of the five alcohols: Ethanol, Propanol and Butanol. Although I have tried the experiment with 50cm3 and 150cm3 of water I felt that 100cm3 was the better amount. I also tried different periods of time but I chose five minutes because it was the one which did not take too long, but allowed the water to be heated sufficiently for the experiment. I also tried different heights that the tin should be from the flame but I decided that 15cm would be the best choice as it allowed the heat to reach the tin, but wasn’t too low. I will use 100cm3 of water in a normal tin picked at random which will be used for all of the experiments.
For this preliminary work I only burnt Ethanol, Propanol and Butanol to get an
idea, rather than spending too much time burning all of the alcohols as this would take too much time and may cause the final experiment to be rushed. Because it is only a preliminary investigation I only burnt each of the alcohols once, rather than burning the alcohols several times and getting an average. Although this may mean that my results are slightly inaccurate it will mean I have a general idea for the different alcohols.
These results are very useful. They show me that my hypothesis is pretty much correct. However I have to remember that heat from the alcohols may dissipate so these results may not be entirely accurate in terms of showing which alcohol releases the most energy. I also have to take into account that these results may be anomalies because I only completed the experiment once so I will only really know if my hypothesis is correct if my final results show a similar result trend. For the final experiment I have decided to weigh the alcohols both before and after they have been burnt. This will allow me to use the equations:
ENERGY = MASS (OF H2O) x SPECIFIC HEAT CAPACITY (OF H2O) x TEMPERATURE CHANGE
MOLES USED = MASS OF ALCOHOL BURNT / RELATIVE ATOMIC MASS
J/MOL = ENERGY / NO. MOLES
KJ/MOL = J/MOL / 1000
These equations will allow me to work out the actual KJ/mol that each of the alcohols released. This will mean that I can work out whether my hypothesis was exactly correct. I also have to be wary that the temperature change will not tell me the amount of energy released. This is because so many factors have to be taken into account as to where the energy goes. Although some of the energy will heat the water some of the heat will dissipate, and air currents in the room may promote this. That is why I will only be taking the energy released figure I calculate as a comparison to my hypothesis, and the temperature change will just show the efficiency of the alcohol to heat water.
Preliminary Conclusion:
After completing my preliminary investigation I have decided on all of my variables. I will use 100cm3 of water for the experiment, as this is not too little to prevent evaporation and it is not too much to mean that the water will be difficult to heat. I Have decided to have the tin 15cm away from the wick. This will mean that the heat can reach the tin, but it is not too close so that it becomes dangerous. I will use a tin that I have chosen at random from all of the tins that I will retain for every single one of my experiment repeats. I have decided to repeat the experiment a total of five times for each alcohol, and then use the data that I gather from these five attempts to work out an average which I will then use for all of my future calculations.
Method:
For my experiment to be 100% successful I must follow a strict method. Firstly, I will make sure that I have accurately measured 100ml of water in a measuring cylinder. I will use a measuring cylinder that has an accurate scale on the side so I can measure 100ml to within a single ml.
I will then secure a tin, picked at random, within a clamp. I will make sure that the positioning of the clamp on the side of the tin is exactly the same for all of the experiments that I perform. This will mean that the clamp has the same amount of heat to absorb or conduct away from the tin, so that the tin does not experience large variations in temperature between each experiment. I will also ensure that the tin is properly rinsed and cooled after each experiment so that it does not conduct heat from the previous experiment when water is placed in it.
After the tin is clamped in place and is above the alcohol itself, I will record the temperature of the water at the start of the experiment using a thermometer placed in the water. I will then remove the cover or lid that is covering the wick and ignite the alcohol. I will measure for five minutes the amount the temperature changes from the recorded starting temperature. After each one I will record the temperature change, and extinguish the flame using the lid. Before I begin the next experiment I will make sure that there is still enough wick showing above the top of the spirit burner so it can be efficiently burnt.
To make sure that my experiment is fair I will have to make sure that the amount of water is exactly 100ml every time I do the experiment. I will also repeat the experiment five times. This will mean that any anomalies in my results do not ruin my final results as I will be using the average from the five experiments. I will also only use one tin for all of my experiments because if I were to use a different one it may have different heat conducting capabilities. This could potentially cause the water to be heated more or less than it would be with a different tin.
To make sure that my experiment is safe I will be wearing safety goggles for the entire experiment. Because all of the alcohols are highly flammable I will have to be extremely careful when lighting them because if the spirit burners themselves get too hot the alcohols my combust. This is potentially extremely dangerous. I will also use a heat-proof mat for the duration of the experiment so that the spirit burner does not burn anything under or around it.
Diagram:
Results:
Below are the calculations I have made for each alcohol to work out the KJ/mol that each of the alcohols actually released. All of the calculations use the equations below:
ENERGY = MASS (OF H2O) x SPECIFIC HEAT CAPACITY (OF H2O) x TEMPERATURE CHANGE
MOLES USED = MASS OF ALCOHOL BURNT / RELATIVE ATOMIC MASS
J/MOL = ENERGY / NO. MOLES
KJ/MOL = J/MOL / 1000
Conclusion:
My results are partially conclusive. The temperature changes did not follow the pattern that I had predicted in my hypothesis. As the carbon chain length increased, the temperature change did not. However, after I preformed several calculations I worked out that in fact the alcohols energy release did match my hypothesis. Pentanol did release the most KJ/mol and Methanol did release the least KJ/mol.
There are several reasons why and how this may have happened. The most likely explanation is that the majority of the energy released by the alcohols dissipated. However, there are other reasons that this could have happened. For instance the flame height of all of the alcohols varied considerably. Methanol seemed to have a bigger flame than several of the other alcohols. This could have caused the alcohols to heat the water at different rate because of the height of the flame.
Also, the method of measuring the amount of heat energy released is not entirely accurate. This is because a lot of the energy will be lost to the surroundings. By just measuring the temperature change of the water we do not get a very accurate picture of the amount of energy that each of the alcohols released.
Overall I think that my results are not very good. They do not match my hypothesis, however the calculations that I made after I had gathered my results are conclusive as they do match my hypothesis. This is a reflection on the successful of the experiment itself.
Evaluation:
My results are not the best most conclusive set of results, and are far below my expectations of this experiment. There were many circumstances beyond our control that effected the experiment. Therefore, the evidence that we produce is not entirely accurate, however we did manage to get a full set of results so the experiment did go quite well. However, as I mentioned before there were a number of factors that we could not control that could have, and probably did, effect our results and the way our experiment went.
Firstly, the spirit burners had varying amounts of alcohol in them. This could have effected the amount of alcohol that was getting to the tip of the wick to be burnt. Also, the wicks were made of many different materials. Although the wick itself does not burn the different materials may have soaked up more of the alcohols allowing them to burn easier.
However, I do think that the method that we developed was the best way that we could have done the experiment. The overall method was very successful and allowed us to complete the experiment efficiently. However, I would quite like to repeat the experiment. I would definitely try to change the method so that the experiment is in a more controlled environment. This would prevent several factors, such as the wind, from effecting or results as they did in this experiment.
Overall the experiment was relatively successful and provided us with a fairly useless, but interesting, set of results.
