The purpose of the lab is to successfully calibrate a pipet and to use stoichiometry to launch a ‘rocket’ using the mixture of oxygen and acetylene. There will need to be an understanding of balancing chemical reactions and knowledge in what constitutes an ‘ideal mixture’ to successfully complete the explosion.
Set up and labeled two test tubes A and B in a test tube rack. Gathered test tube stoppers with plastic gas tube feeders. Gathered a plastic pipet and cut the tip of the pipet off, about 5 milliliters (mm) below the bulb (see figure 1) 1. Calibrated the plastic pipet bulb by filling the bulb completely with water and emptied the water into a graduated cylinder. Repeated the calibration of the bulb 3 times and averaged the results of the volumes. Gathered one graduated cylinder with about 80 milliliters of prepared yeast solution and one graduated cylinder with about 40 milliliters of Hydrogen Peroxide (H2O2). Gathered one graduated cylinder with approximately 100 milliliters of tap water. Gathered one weigh boat with 3 pea size quantities of Solid Calcium Carbide (CaC2). Filled pipet bulb completely with water and set aside until ready. Filled test tube A approximately halfway with the yeast solution and one quarter of the way with H2O2. Capped test tube A with the gas feed topper. Covered the spout of the topper and inverted test tube A to speed the reaction. Attach the pipet bulb to test tube A via the gas spout in the topper. As the bulb filled with oxygen gas (the product of the yeast and hydrogen peroxide reaction), the water inside the bulb will be displaced. Filled the bulb completely with O2 and capped the end to not allow gas to escape. Filled test tube B approximately three-quarters of the way with water and added one pea size amount of CaC2. Quickly topped test tube B and attached the bulb until test tube B stopped visibly oxidizing. Removed bulb, covering the tip to not allow the gases to escape. Moved to launch station while inverting tube to mix the gases. Lit a match and placed the bulb at the beginning of the launch ramp. Quickly put the match behind the opening of the bulb and waited until there was a reaction. Repeated the loading of the bulb with 50% C2H2 gas and 50% O2, 75% O2 and 25% C2H2, and 40% O2 and 60% C2H2. Measured the distance the bulb traveled and recorded the sound and visual differences between each launch.
Short Answer Questions:
By preforming this experiment, I was able to work on stoichiometry and balancing equations. We have been learning about limiting reactants in lecture and in the lab we had to use our knowledge on limiting and excess reactants to have the best mixture of O2 and C2H2 to create the best ‘explosion’. We also preformed combustion, which is chemical reaction that involves the combining of oxygen and another substance to form oxygen-containing compounds, often emitting heat in the process 2. With our knowledge on combustion, we knew that there would be a reaction from adding flames to the bulb full of gases.
Based on distance traveled, the best volume ratio that was tested was 2O2:3C2H2. With the 2:3 ratio, the rocket bulb traveled 420 cm, more than 200 cm farther than the 1:1 gas ration. Based on the balanced reaction, we would expect for a 9O2:11C2H2 ratio 3, which is very similar to a 2:3 ratio. Our observed best volume ratio is very similar to the best ratio and the difference can largely be contributed to our observed ratios being eyeballed and not accurate percentages.
When we were experimenting, my lab partner and I ran into a lot of problems. Initially we calibrated our pipet bulb with a longer stem than we ended up using at the end, so we had a higher volume recorded than the actual volume. Next, we were not fast enough in capping test tube B and we had several incomplete trials because we were not able to capture enough C2H2 to finish filling the bulb. Because we didn’t have enough Acetylene to fill the bulb, we had several trials when there was still water in the bulb and the reaction would not occur. When we were going to launch, we often didn’t rotate the bulb enough to completely mix the gases, which made it hard to ensure the reaction would be as it should be. Additionally, the launch site did not have the best setup and we did not have enough height to complete the launch with out hitting the ceiling. To have more accurate measurements in distance, we should have launched from the ground to give up a bit more height and to get rid of the sinks in the way. In response to not getting enough Acetylene gas, I would make sure that we moved quicker and had both partners working together in capping the test tube and connecting the rocket bulb. Our biggest error was that we discarded a lot of trials because we were not waiting long enough for the reaction to take place. We did not realize that the reaction could take some time to occur and had we just waited longer, we would have had more successful launches and better data to use. If we were to alter our method, I would wait for a longer length of time before discarding the bulb’s mixture.
If I were to redo this experiment, I would try launching the rocket using methane gas (CH4) and Oxygen gas(O2) or Benzaldehyde (C7H6O) and Oxygen gas. Any combination of a hydrocarbon and oxygen will create a combustion reaction, creating an explosion when ignited 4. I would mix several hydrocarbon gases to test which gas would launch the farthest. We could launch the rocket bulb the farthest by using the balanced chemical equation to find the ‘ideal’ mixture of gases to maximize the product, without running into problems with the limiting reactant. If we were able to use the ideal ratio of the gases, we could launch to the maximum distance without too much effort. Any compound with Hydrogen and Carbon in it should work for the combustion because you need to be able to make CO2 and H2O for the reaction to be considered a combustion reaction. Some chemicals that I would try are Ethane, C2H6, Butane, C4H10, and Propane, C3H8.
a. Based on your chemistry knowledge, offer a brief explanation why fluorine may be a better oxidizer to use than oxygen. (5 points)
b. Fluorine gas is poisonous and is very reactive, with the highest electronegativity. F2 is an unpredictable gas and could be dangerous if it were to react on accident.
In the lab, we learned that you can use stoichiometry or experiments to find the ideal mixture of the solutions. We were able to use prior chemistry knowledge to calibrate a pipet bulb and we deepened our understanding in stoichiometry. The lab was done to find to have a combustion reaction to launch a ‘rocket’ the farthest. We had errors in the calibration of the bulb because we changed the length of the stem half way through the experiment because our bulb was not emptying entirely of water. I would like to investigate farther what other chemicals could provide a farther launch distance.
1 C. C. Department, Experiment 4: Rocket Lab Handout, CSM Chemistry Department, 2018.
2 N. J. Tro, Chemistry: A Molecular Apporach Third Edition, Upper Sadle River: Pearson, 2012.
3 A. Rexwinkle, “Experiment 4: Rocket Pre Lab,” 2018.
4 P. Anne Marie Helmenstine, “Combustion Reactions in Chemistry,” ThoughtCo., 23 June 2018. Online. Available: https://www.thoughtco.com/combustion-reactions-604030. Accessed 24 September 2018.