Hydrocarbon + Oxygen carbon dioxide + Water + (energy)
Hypothesis:
My prediction for this experiment on investigating the energy produced by different alcohols is that, the longer the hydrocarbons in the chain of the alcohols, the more heat it will produce. After the alcohols have been lit by the splint it will give out oxygen and water as well as heat energy to heat the water, which will crack the hydrocarbons into simpler molecules and then will combust later, making this experiment an exothermic reaction. Therefore the long chains of hydrocarbons produce more energy than smaller chain molecules as the long chain breaks in to smaller hydrocarbons meaning theirs more, making the boiling point decrease, which makes them more flammable and more volatile. Therefore I would expect that when the alcohol is being burned and producing heat energy, carbon dioxide, and water will be produced meaning the alcohol would lose some mass which would evaporate into the air. I therefore predict that when there is a shorter chain of hydrocarbons than another alcohol, it would produce more heat than the other alcohol meaning it would have a greater difference in mass compared to a longer chain of hydrocarbons, which could mean that the smaller hydrocarbons combust quicker then longer hydrocarbons as they are less volatile.
Using the table below I am able to predict the energy given out by each of the alcohols:
Methanol (CH3OH) would burn with a very clean flame; produce the least amount of energy as they have the least amount of hydrocarbons. This is because they only have 1 carbon atom, which combust in the shortest amount of time, out of the 4 other alcohols.
This is the complete combustion balanced equation showing methanol heated with carbon dioxide and water.
CH3OH + 1.5O2(g) CO2(g) + 2H20(g)
Left Hand Side (LHS) = 2872.5 Right Hand Side (RHS) = 3462
2872.5 – 3462 = -589.5
Ethanol (C2H5OH) will burn with a very clean flame; produce the second least amount of heat energy as they have the second least amount of hydrocarbons. This is because they have only 2 carbon atoms in the 5-hydrocarbon chain, which will combust and be used in forms of heat energy really fast compared to Pentanol.
This is the complete combustion balanced equation showing Ethanol heated with carbon dioxide and water.
C2H5OH + 3O2(g) 2CO2(g) + 3H2O(g)
LHS = 4835 RHS = 5996
4835 – 5996 = -1161
Propanol (C3H7OH) would burn with again a very clean flame producing heat energy between the Ethanol and Butanol alcohols. This is because the ethanol alcohol has 2 carbon atom and Butanol has 4 carbon atoms, where as Propanol has 3 carbon atoms producing more heat energy then Propanol.
This is the complete combustion balanced equation showing Propanol heated with carbon dioxide and water.
C3H7OH + 4.5O2(g) 3CO2(g) + 4H2O(g)
LHS= 6797.5 RHS= 8530
6797.5 – 8530 = -1732.5
Butanol (C4H9OH) would produce more heat energy then Propanol and will combust longer than Propanol as it has more hydrocarbon chains as it started off volatile before heating it, which then gets heated to crack the hydrocarbon chains to make them produce more heat energy.
This is the complete combustion balanced equation showing Butanol heated with carbon dioxide and water.
C4H9OH + 6O2(g) 4CO2(g) + 5H2O(g)
LHS= 8760 RHS= 11064
8760 - 11064= -2304
Pentanol (C5H11OH) would produce the most amount of heat energy as it has the most amounts of hydrocarbon chains with the most carbon atoms, which crack into simpler forms to become more volatile, less viscous, and more flammable and produce loads of energy in forms of heat.
This is the complete combustion balanced equation showing Pentanol heated with carbon dioxide and water.
C5H11OH + 7.5O2(g) 5CO2(g) + 6H2O(g)
LHS= 10722.5 RHS= 13598
10722.5 – 13598 = -2875.5
Table of Predicted Energy Values
I will then draw a graph comparing these predicted results with results I get from my experiment. I predict that there will be a difference between the experimental results and the predicted results, as the results of my experiment are very likely to be hindered by other factors which are not able to be controlled efficiently by me.
Fair Testing:
To make the results reliable for each different alcohol I will be repeating the experiment to get an average from both results and to reduce the impact of anomalies, I will also be keeping the same copper calorimeter for each experiment as some might be thicker then others, which can cause a change in conductivity and results. I have also kept the same height of the copper calorimeter the same so the tip of the flame would touch the bottom of the calorimeter for each experiment knowing it will be a fair test. I will also have the same thermometer and the same amount of water in the calorimeter. The thermometer would be fixed in the middle of the calorimeter to give the reading of just the temperature of the water and not the conductivity of the copper calorimeter.
Apparatus:
· Copper calorimeter,
· Water,
· Thermometer,
· Timer,
· Measuring cylinder,
· Alcohols, (sprit lamp)
· Bunsen burner,
· Retort stand,
· Clamp,
· Weighing balance
Diagram
Safety procedures
· Make sure goggles and lab coat are worn through out the whole experiment,
· Be ware of the hot water in the calorimeter,
· Make sure copper calorimeter is tied tightly to the metal rod,
· Make sure alcohol is lit safely with your selves rolled up out of the way,
· Make sure the sprit lamp is put out by putting on the glass top after use.
Method:
I plan to carry out this experiment by using all the safety issues and fair testing procedures to give me the most reliable and most accurate set of results on each alcohol. I plan to record the mass of the alcohol sprit lamp before the experiment and after, which would tell me how much alcohol was used in each experiment, which I can compare to other alcohols. I will place 100cm3 of tap water into the copper calorimeter and clamp it to the retort stand; I will then hold the thermometer in the centre of the water in the calorimeter recording just the water temperature. This will give the most accurate set of results as the thermometer will not touch the copper calorimeter at all therefore only recording water temperature and not the calorimeters. I will then light the sprit lamp with a wooden splint wearing my safety glasses, and making sure the tip of the flame reaches the calorimeter flask at the same time will be starting the stop clock. Then I will then let the alcohol burn until the temperature has risen by 20oC for each alcohol, then it will immediately be put out and weighed. I will then record the finishing temperature of the water as the water will still be heated by the conduction of the copper calorimeter. I will then do the same thing for each alcohol and repeat, giving me the most reliable and accurate results, also ruling out any potential anomalies.
I found that by placing a hardboard draught excluder around the experiment, and a cardboard lid with a hole for the thermometer on top of the can, the heat lost was significantly reduced to make this experiment more accurate. Stirring the water means that there is uniform temperature in the can, and monitoring the temperature rise to ensure uniform heating. The can is copper as copper is a good conductor of heat, so more is transferred to the water. The height of the can above the flame is also a factor, so this needs too be kept constant just touching the can.
When I record the readings of the temperature I will be plotting down the readings for each alcohol on a graph. I will then repeat the experiment for each alcohol twice more, which will give an average of the three; I can then draw a graph of all alcohols showing the temperature against time, so that I can compare them to each other helping me to explain the results. I will also work out how much heat went into the copper calorimeter tin from the alcohol burning by using the following formula:
Heat given out(J) = mass of water(g) x 4.2(specific heat capacity of water) x change in temperature(oC)
Then after working out the number of moles for each alcohol and then will use this and the calculation for heat energy given out to determine the energy given out per mole.
Results:
I tested each alcohol twice. Butanol was not tested as it was unavailable to us.
Heat given out(J) = mass of water(g) x 4.2(specific heat capacity of water) x change in temperature(oC)
Mass Change ÷ Relative Molecular Mass = Number of Moles
I have converted the Joules into Kilojoules to make it a smaller number and so I can therefore compare the results with my predicted results.
Energy ÷ Moles = Energy per mole
Next I calculated the average for each of the two results for each alcohol and compare it with predicted results:
I can compare these results much easier on a graph therefore I have plotted the results above against the number of Carbon Atoms in each of the alcohols:
From this graph it is clear that the experimental results are much lower than those of the predicted results. Nevertheless it still shows a strong positive correlation, and the most likely reason for the difference is the loss through heat convection. This graph shows my predictions to be correct as the experimental results show a strong positive correlation which matches the strong correlation of predicted results.
From my graph I can now give an estimation of the Energy per Mole of Butanol by marking a point at 4 carbon atoms as that is how many carbon atoms are in Butanol and then where the y point meets this x point on the best fit line, I have my value. My predicted value of Butanol is the value of 2304(KJ/Mol), where as using my experimental results I would find the value to be about 1258(KJ/Mol).
Using this graph I can work out the gradient of the two best fit lines. They are:
For the Experimental Result Best Fit Line: y = 314.53x + 0
For the Predicted Results Best Fit Line: y = 576.09x + 0
I can then use this information to work out the percentage of energy lost between the two results is by working out the difference between the two gradients and the dividing it by the predicted results gradient, then multiplying this value by a hundred. This comes out to be 45.4% energy lost.
Conclusion
Looking at my results on investigating into the combustion of a range of alcohols, I noticed a number of patterns. Looking at the results I can simply say what has been found out of the 4 different alcohols. I found out that the more hydrocarbons in the chain molecules in each alcohol, the more heat energy it will produce. This explains that the Pentanol alcohol produced the most amount of energy as it had the most amounts of carbon molecules in the hydrocarbon chain out of the alcohols. These gives out lots of energy due to the big long chains of hydrocarbons cracking into simpler forms, which gives out more heat energy as there are more of them.
With this in mind I can conclude that alcohols follow the same pattern as their alkanes, and being a homologous they are a series of compounds which have the same general formula, the same functional group and similar chemical properties. I have noticed that for the predicted results the energy value goes up in even steps of 571.5(KJ/Mol). Alcohols are a series of hydrocarbon derivatives with at least one hydrogen atom replaced by an -OH group. These alcohols are good solvents for some organic soils, notably rosin, but as this experiment shows are flammable and can form explosive mixtures with air.
Looking at the graph I noticed that there were many patterns; I noticed that the methanol alcohol with the least amount of carbon atoms in the hydrocarbon chain produced the least amount of energy excluding the odd result of the Propanol alcohol. I noticed that the more carbon atoms in the alcohol the more heat it produces within the five minutes of readings. Looking at the sequence of the number of carbons in the alcohol, from the least, Methanol, to Ethanol, to Propanol and to Pentanol, is in order of the amount of heat energy produced, from the least to the most producing heat energy. The temperature rise is very similar for all the alcohols ranging from 21.5 to 24.5oC. Also looking at my scientific explanation I was correct for all the alcohols apart from Propanol, as I got an anomalous result for the alcohol that could have been for a number of reason, which are mentioned in my evaluation.
Evaluation
Looking at the overall experiment and procedure used to find the results obtained, I thought that it was a good enough way to make me investigate the combustion of different alcohols. The results I got were near enough of what I would have expected from the alcohols used, which I have mentioned in my conclusion. The only set of results I was unhappy with was the enthalpy of the first Propanol reading. This first Propanol reading looks to be an anomalous result. Propanol didn't follow the pattern in the sequence of the carbon atoms in the hydrocarbon chain as its mass change did not seem to decrease, which was wrong, as methanol should have produced the least amount of heat energy as it had the least amount of carbon atoms.
The Propanol alcohol should have produce a heat energy between the alcohols Ethanol and Pentanol as Pentanol has 5 carbon atoms and ethanol has 2, where as Propanol has 3 making the results in between the two. The odd result of the Propanol alcohol could have been an anomalous result for a number of reasons. It could have been because the tip of the flame might have not been touching the bottom of the copper calorimeter, making the alcohol produce less heat to the water in the calorimeter. It could have also been because of the flame as it might have been too small, which might have also gave a low temperature reading to heat the 100cm3 of water.
The procedure of the experiment was good enough of finding out the energy gained from the individual alcohols, but changes could have been made to make the reliability of the results more accurate. This could have been done by using a better and more accurate thermometer, such as an electric thermometer, which have gave me a much more pin point set of results.
If I were to do this experiment again I would make a number of improvements or changes, I could use a Bomb Calorimeter which submerges the reaction inside an insulated container of water. An electrical heating device starts the reaction inside a sealed reaction vessel and the temperature rise of the water which surrounds it is measured. Bomb calorimeters are often used to find the calorific value of foods.
Looking at the experiment I did I thought we could have extended the results we achieved by using different flame lengths, this would have told us how much the alcohol uses its energy when the flame is increased. I could have also changed the amount of water in the copper calorimeter, or even change the concentration of alcohol to see the effect.