Equation:
Hydrocarbon + water → carbon dioxide + Water (+ energy)
Apparatus:
- tin container x2 - weighing scales
- Alcohols (sprit lamp) - measuring cylinder
- Water - timer/stopwatch
- Thermometer
Diagram:
Method:
Making the Experiment Fair – In order to make sure that our results are reliable, we are going to repeat the experiment for each of the alcohols three times. I will also be using the same water container for each of the experiments in case one of them is thicker than the rest, therefore making it fair by making the heat conductivity fairer. Also, the container is going to be the same height above the sprit lamp each time so that the experiment leaves a smaller room for error. I will also be using the same amount of water (150ml) each time, measured as precisely as possible with a measuring cylinder. It is also important that when take the readings for the temperature of the water, that we take it from the water (once stirred) and not from the surface of the water container as the recordings may differ and affect the results. An accurate set of electronic scales are also going to be used as they can weigh the alcohol to two decimal points of a gram. Also, the weight of the alcohol must be taken as soon as possible after the time set is over, otherwise excess energy may be lost in the time in-between.
Making the Experiment Safe – Throughout the whole of the experiments I must ensure that I wear my safety goggles and an apron for in case the alcohol gets spilt. Also, the alcohol container and water container are extremely likely to be hot, so it is important that I use tongs to pick them up so that I do not burn my hands. It is also important to be precautions when lighting the alcohol, and to do this we will be using a splint and have our sleeves fully rolled up. When we are extinguishing the flame with the glass cap, I will again be using tongs so that the flame does not burn my hands or catch any of my clothing alight. Finally, it is extremely important that I am sensible through out the whole of the experiment and follow these safety measure correctly and fully so that an accident doesn’t occur.
Method – I plan to carry out the experiment by using all the safety and fairness issues stated above to give the most accurate and reliable results for each of the alcohols I use. I am going to record the mass of the alcohol and its sprit lamp before and after the after the experiment so I can compare alcohols. I will then set up the experiment as shown in the diagram. The tin container will hold 150ml of water, which will be recorded for its temperature soon before the experiment begins. I will then light the sprit lamp with a wooden splint and then check to see that the flame from the sprit lamp is in contact with the sprit lamp. Once the sprit lamp is lit, I will then start the timer. I will leave the experiment for three minutes. I will then remove the water container from above the sprit lamp, with the glass cap being placed on top of it immediately, and record the temperature of the water once it is stirred. I will then weigh the sprit lamp without the glass cap and record the change in its weight. This procedure will be repeated at least three times for each of my alcohols to ensure that I obtain reliable and accurate results. The results will be plotted into a table, where I will work out how much energy was used in the experiment with the results being plotted into a graph.
Formula:
This is the formula I will use when working out how energy was used for each of the alcohols:
Heat given out = mass of water x 4.2 x change in temperature
Units of Measurement:
The units I will be using for the formula are listed below:
- Energy given out: Joule (J)
- Mass of water: Grams (g) → 1cm³= 1
- Change in temperature: °C
Results:
Here are the results I obtained when I burned the following alcohols to find out how much heat energy is given off from them. The alcohols is used were Methanol, Ethanol, Propanol, Butanol, Pentanol, Hexanol + Heptanol:
I am now going plot my results into a graph and then comment on my results and my overall experiment procedure:
Conclusion:
Looking at my results into the combustion of my alcohols, I have noticed a number of patterns. I can simply look at my results and comment on what I have found from my six alcohols. In general I found that the more hydrocarbons in the chain molecules in each alcohol, the more heat energy it will produce. Although the Hexanol experiments did not work, but the results did still show that Heptanol alcohol produced the most amount of energy, due to it having more amounts of carbon molecules in the carbon chains of hydrocarbons cracking into simpler firms. These give out heat energy, and Heptanol gave us out the most amount of energy because there we more carbon molecules.
Evaluation:
Looking at my overall experiment plan and procedure used to obtain my results, I thought that it was a good enough way to investigate the combustion of different alcohols. The results I obtained were close to what I had predicted from the alcohols used. But, I wasn’t too happy with my Pentanol results, as they produced a higher amount of energy than was expected. The Pentanol did not follow the pattern I had predicted in my hypothesis about the number of carbon atoms in the hydrocarbon chain and how much energy it produced. This is as it produced more energy than Hexanol, although it has a smaller number of carbon atoms in its hydrocarbon chain. Based on what I had predicted, the Hexanol alcohol should have produced more heat energy than the Pentanol alcohol. There are many possible reasons as to why the Pentanol alcohol mite not have worked and have produced it anomalous results. It mite have been because the flame was not in contact with the water container, and therefore making the alcohol produce less heat to the water in the container. If the flame was too small, it would have given a low temperature reading to the 150ml of water.
The procedure of the experiment was enough for finding out the energy gained from the individual alcohols, but changes could have been made to make the reliability of the results more accurate. Using better and more affective equipment, like an electric thermometer could have done this. Electric thermometers can give readings to two decimal places.
I if I were to repeat the investigation, there would be a number of changes and improvements that I would make to the experiment. We could have extended the investigation slightly and used different flame sizes, this would have told us how much the alcohol uses its energy when the flame is increased in its length. I could have also changed the amount of water in the containers, or possibly even use different materials for the containers used, to vary the heat conduction present. Another thing that I could have done, would have been to change the time I was burning the alcohol for, and then check the temperature percentage increase of the water in the container at certain intervals of about a minute.
