Chemistry coursework: Burning Fuels Investigation
Aim: To find out how much energy is released by each alcohol per gram (g).
Research: Alcohols are organic, and each one has its own formula. In this experiment we have used Ethanol, Propanol, Butanol, Pentanol Hexanol, Heptenol, and Octanol. Alcohols react with oxygen in the air to form water and carbon dioxide. The reaction that is involved in burning alcohols is exothermic because heat is given out. Form this reason the reactant energy is higher than that of the product.
When these alcohols are burnt they show a trend that the fewer the bonds the less energy is released, so the more bonds the more energy is released.
Alcohols are good to use in this experiment because they burn easily and all have simular chemical formulas.
The equation to work out the energy released per gram is:
Mass of water X 4.2 X change in temperature of water
Change in mass of fuel (in grams)
4.2 is the specific heat capacity of water.
This are the predicted results for burning fuels, calculated using bond energies from a book of data.
This is a preview of the whole essay
· Mass of the water 100ml
· Type of beaker
· Surrounding temperature of around 23ºC
· The height of the beaker from the wick
· Same set of scales
Pendiction: I predict that Octanol will release more energy because it has more bonds that the other alcohols, and than Ethanol will release the least due to its few bond properties. All of these bonds are called hydrocarbon bonds. As the list of alcohols go down it will have a steady increase in energy released. These bonds only ever realease there energy when they are burnt because they split. This tells us the more bonds the more energy in the alcohol, and more energy to be released.
Risk Assessment: Wear goggles at all times to protect eyes from alcohols. Make sure all long hair is tyed back so it doesn’t set alight or get alcohol on it. Be careful of the hot metal and only touch it when it has cooled down. Keep the cap on the spirit burner so that the flames from the alcohol cannot burn you.
Equipment: Bunsen burner, Heatproof mat, spirit burner and cap, alcohols, tripod, gauze, water, heatproof measuring beaker, clamp, scales thermometer.
- Weigh fuel burner with lid on
- Measure 100cm³ of water into a can beaker.
- Place the measuring beaker into the grasp of the clamp stand.
- Record the starting temperature of the water.
- Weigh the crucible, then weigh the alcohol to as near as possible 0.5 grams.
- Put the chosen alcohol under the beaker allowing the flame to just touch the beaker.
- Leave to heat up until the alcohol evaporates.
- Take the temperature when the alcohol has evaporated.
- Record the temperature of the water now.
- Weigh alcohol
- Record all results
Ethanol: 100 x 4.2 x 6.67 % 2.52 = 1111.67 kj
Propanol: 100 x 4.2 x 7 % 1.23 = 2390.25 kj
Butanol: 100 x 4.2 x 6.3 % 0.34 = 7782.35 kj
Pentanol: 100 x 4.2 x 5.5 % 1.23 = 1878.05 kj
Hexanol: 100 x 4.2 x 6.3 % 0.92 = 2876.09 kj
Heptanol: 100 x 4.2 x 5.3 % 6.52 = 341.41 kj
Octanol: 100 x 4.2 x 5 % 1.23 = 1707.32 kj
Conclusion: I found out that Butanol released the most energy which was very unexpected, and Heptanol realeased the least when it should have been the second highest. There are some results that do not exist in the table of results, which gives somethings not such a wide average. The results did not fit any pattern and did not come out as expected as in my prediction due to my research that I did. My graph goes up and down, which it should not do, its should go in a straight line up.
Evaluation: I believe that all of my results are very inaccurate. They all were not as they were meant to be, and results might have been incorrectly written down, or the experiment carried out incorrectly. To make the results slightly more accurate, I would use more accurate, maybe electronic ways of measuring temperature and volume, also measure the height of can above the flame. I would also have marked the beaker used, so that it could be used again, and had a more accurate timing system. As these errors were only small, they could not have made the massive differences between the predicted results, so there must have been other factors that caused the heat from the burner not to reach the water. These could have been energy wasted on heat and light.
Each of the alcohols were burnt by different groups, and each group could have done their experiment slightly different making the results different, which could have caused the results not to have come out as they were meant to.
The results for heptanol came out a surprise, as the mass of alcohol burnt was far greater for two of the experiments than any of the other results. Octanol did not burn as well as expected either.
The temperature variation in the water was simular for all of the results also this could be due to human error as the reading on the thermometer could have not been read in a straight line making mistakes in degrees centigrade. Even the electronic equipment could have made a difference like the time on the stopwatch, or the measuring cylinder for water, and even the temperature of the beaker. The mass balance results could have been different as the scales are very sensitive so almost anything could have changed the wieghts.