KINETICS LAB
Editor's Note: Here is a glimpse of AP Chemistry, through Michaela D. ('15)'s lab report, completed during the oxidation unit.
Conclusion
The purpose of this lab was to determine the rate law of the oxidation of iodine by bromat in the presence of an acid. Ultimately my partners, Louis and Lisa, and I completed the purpose of this experiment as we were able to use our data, collected under different conditions, such as temperature change and the presence of a catalyst, in order to determine the differing and overall rate constants, reactant order(s) and rate(s) of the reaction. The average calculated reactant orders were: x=1.04 (I-), y=0.778 (BrO3-), z=1.43(H+). All these calculated reactant orders, when rounded, would’ve produced 1.00; in other words, the overall reaction was first order restricted. The average rate constant, k, was 0.8833 and the rates for each trial were accordingly: 1.61 x 10- 7, 4.62 x 10-7, 2.74 x 10-7, 3.65 x 10-7, 2.13 x 10-7, 5.04 x 10-7, 5.47 x 10-7. When we conducted the experiment under differing temperatures—approximately 0 degrees Celsius, twenty degrees Celsius, forty degrees Celsius—we noticed that as the temperature increased the rate of each experiment increased rate as well (i.e. the rate of each reaction increased as the temperature increased). Our results for the different temperature experiments were as followed: 4.81 x 108- (10 degrees Celsius), 1.61 x 107- (25.5 degrees Celsius) and 8.15 x 107- (50 degrees Celsius).
The rate constants for each of these reactions were as follows: 0.2484(10 degrees Celsius), 0.8315, (25.5 degrees Celsius), 4.209(50 degrees Celsius). Both our graphical representation of the experiment’s equilibrium—a generally linear representation-- and our calculated data reveal that the reaction was to be a limited first-order reaction.
There were a multitude of experimental and human errors within this lab that were not accounted for by significant figures. The experimental procedures included: method of creating the solutions and combining them together (the “snap” method), the different temperatures in which the chemical experiment was conducted under, and the use of wooden toothpicks to stir. The method of combing the solutions within each well was to manually add a certain number of drops as indicated within the lab. This posed a possible error because as the manual dropper was difficult to control, many of the wells had either too many or too few drops than as indicated within the lab and thus such wells may not have reacted properly. In the case that there were not appropriate amounts of chemical solutions within each well, the reaction would not have occured at the expected rate, and thus our calculations concerning the rate of the reactions would’ve been flawed. The snapping method was to fill each strip with an indicated amount of solutions, flip the second reaction strip upside down so that its wells coincide with those of the first, place the second reaction strip on top of the first and then shakes the reaction strips downward once vigorously. This posed a possible error for if one did not exert enough force in “snapping” the two reaction strips together, then the solutions from each opposite well of each reaction strip would not have been mixed in properly, delaying the onset of the reaction as indicated by the blue color. Ultimately this timing would’ve affected the rate for each of the reactants, as the change in time was used for each trial. In order to avoid these sources of error we could’ve used mechanical pipettes. As mechanical pipettes measure the exact amount (in form of drops) needed, we could’ve easily avoided the inevitable miscalculation of the drops of solutions for each well and thus could’ve received a more accurate representation of the different reaction rates for each trial. The second procedural error was that of changing the temperature of the reactions environment whilst keeping the temperature change constant throughout each trial in order to determine the effect temperature has on reaction rates. The instructions simply advised that in order to change the temperature from room temperature to forty degrees celcius, the reaction strip solely needed to be placed within a hot water bath approximately this temperature. In order to create a cooler environment, approximately twenty degrees celcius, the procedure indicated the addition of ice cubes to the warm water bath and the reaction strip to be added to it and the experiment done over again. This same procedure, the addition of the ice cubes, was to be repeated in order to get the environments temperature to zero degrees celcius. In order to avoid this possible source of error we could’ve simply changed the temperature of the entire lab, for as the heating and cooling systems are central and under our control, the different temperatures could’ve been more constant during each one of the trials of the experiment. The third procedural error was the use of wooden toothpicks to stir the differing solutions within the wells. Ultimately, due to woods tendency as a material to absorb liquid, less of the solutions would’ve been tested. This slight absorption could’ve lead to incorrect reaction rates as the chemical solutions of each well when combined would not have reacted properly. In order to avoid this possible source of error we could’ve used glass stirring rods instead because glass would not have absorbed the different solutions being combined, and thus would’ve probably given us more accurate or predictable results.
While there were a multitude of procedural errors within the lab, there were also many human errors committed by my partners, Lisa and Louis, and myself. The human errors within this lab included: miscalculation of drops of solution into wells and lack of stirring of solution within two of the experimental trials. As indicated in the procedure, different amounts in the form of drops of the solutions KI, distilled water, HCl, starch, and Na2S2O3 were to be added to different wells throughout the experiment. However, often times it was difficult to keep count or to produce the exact indicated amounts of drops for each trial because the process was indeed manual. Ultimately this led to the over addition or lack thereof of certain substances within each well of the reactant strips. This human error could’ve affected the time it took for the different solutions within each well to react and thus had changed the rates of these reactions. As suggested earlier in order to possibly avoid this source error in the future we could’ve used mechanical pipettes, which in measuring the exact amount of drops needed and used for each trial, would’ve given us better experimental data. The second error, the lack of stirring of the solution for experiments four and five, could’ve altered our results concerning the timing of the reactions—and thus the reaction rates—as if the chemicals were not properly introduced, the reactions would not occur either at all or as expected.
In correcting this lab for future use, I would make sure that the procedure in part three, “Determine the Activation Energy,” clearly indicated that the addition of ice to the otherwise warm water bath prepared for the forty degrees Celsius environment, was to be repeated (once for the twenty degree Celsius environment and the other, the repeat, for the zero degree Celsius environment). As well as this factor, I would also make sure that the procedure indicates a method by which to keep constant the different temperatures, as it was difficult throughout part three to maintain the same temperature for the three trials. For part three I would also make sure to change the format of the “Part 3 Data Table. Determine the Activation Energy” so that there are three columns for the “Times of Reaction” for the three trials and a fourth column for the average of the “Times of Reaction”. In general, I would make sure that a mechanical pipette, if possible, is used instead of the manual pipette for it would assure that a more precise measurement of each chemical solution was used in each trial. In general, I would also make sure that a glass stirring rod is used instead of the wooden toothpick for it would assure that less of the chemical solutions within each trial is absorbed.
The rate constants for each of these reactions were as follows: 0.2484(10 degrees Celsius), 0.8315, (25.5 degrees Celsius), 4.209(50 degrees Celsius). Both our graphical representation of the experiment’s equilibrium—a generally linear representation-- and our calculated data reveal that the reaction was to be a limited first-order reaction.
There were a multitude of experimental and human errors within this lab that were not accounted for by significant figures. The experimental procedures included: method of creating the solutions and combining them together (the “snap” method), the different temperatures in which the chemical experiment was conducted under, and the use of wooden toothpicks to stir. The method of combing the solutions within each well was to manually add a certain number of drops as indicated within the lab. This posed a possible error because as the manual dropper was difficult to control, many of the wells had either too many or too few drops than as indicated within the lab and thus such wells may not have reacted properly. In the case that there were not appropriate amounts of chemical solutions within each well, the reaction would not have occured at the expected rate, and thus our calculations concerning the rate of the reactions would’ve been flawed. The snapping method was to fill each strip with an indicated amount of solutions, flip the second reaction strip upside down so that its wells coincide with those of the first, place the second reaction strip on top of the first and then shakes the reaction strips downward once vigorously. This posed a possible error for if one did not exert enough force in “snapping” the two reaction strips together, then the solutions from each opposite well of each reaction strip would not have been mixed in properly, delaying the onset of the reaction as indicated by the blue color. Ultimately this timing would’ve affected the rate for each of the reactants, as the change in time was used for each trial. In order to avoid these sources of error we could’ve used mechanical pipettes. As mechanical pipettes measure the exact amount (in form of drops) needed, we could’ve easily avoided the inevitable miscalculation of the drops of solutions for each well and thus could’ve received a more accurate representation of the different reaction rates for each trial. The second procedural error was that of changing the temperature of the reactions environment whilst keeping the temperature change constant throughout each trial in order to determine the effect temperature has on reaction rates. The instructions simply advised that in order to change the temperature from room temperature to forty degrees celcius, the reaction strip solely needed to be placed within a hot water bath approximately this temperature. In order to create a cooler environment, approximately twenty degrees celcius, the procedure indicated the addition of ice cubes to the warm water bath and the reaction strip to be added to it and the experiment done over again. This same procedure, the addition of the ice cubes, was to be repeated in order to get the environments temperature to zero degrees celcius. In order to avoid this possible source of error we could’ve simply changed the temperature of the entire lab, for as the heating and cooling systems are central and under our control, the different temperatures could’ve been more constant during each one of the trials of the experiment. The third procedural error was the use of wooden toothpicks to stir the differing solutions within the wells. Ultimately, due to woods tendency as a material to absorb liquid, less of the solutions would’ve been tested. This slight absorption could’ve lead to incorrect reaction rates as the chemical solutions of each well when combined would not have reacted properly. In order to avoid this possible source of error we could’ve used glass stirring rods instead because glass would not have absorbed the different solutions being combined, and thus would’ve probably given us more accurate or predictable results.
While there were a multitude of procedural errors within the lab, there were also many human errors committed by my partners, Lisa and Louis, and myself. The human errors within this lab included: miscalculation of drops of solution into wells and lack of stirring of solution within two of the experimental trials. As indicated in the procedure, different amounts in the form of drops of the solutions KI, distilled water, HCl, starch, and Na2S2O3 were to be added to different wells throughout the experiment. However, often times it was difficult to keep count or to produce the exact indicated amounts of drops for each trial because the process was indeed manual. Ultimately this led to the over addition or lack thereof of certain substances within each well of the reactant strips. This human error could’ve affected the time it took for the different solutions within each well to react and thus had changed the rates of these reactions. As suggested earlier in order to possibly avoid this source error in the future we could’ve used mechanical pipettes, which in measuring the exact amount of drops needed and used for each trial, would’ve given us better experimental data. The second error, the lack of stirring of the solution for experiments four and five, could’ve altered our results concerning the timing of the reactions—and thus the reaction rates—as if the chemicals were not properly introduced, the reactions would not occur either at all or as expected.
In correcting this lab for future use, I would make sure that the procedure in part three, “Determine the Activation Energy,” clearly indicated that the addition of ice to the otherwise warm water bath prepared for the forty degrees Celsius environment, was to be repeated (once for the twenty degree Celsius environment and the other, the repeat, for the zero degree Celsius environment). As well as this factor, I would also make sure that the procedure indicates a method by which to keep constant the different temperatures, as it was difficult throughout part three to maintain the same temperature for the three trials. For part three I would also make sure to change the format of the “Part 3 Data Table. Determine the Activation Energy” so that there are three columns for the “Times of Reaction” for the three trials and a fourth column for the average of the “Times of Reaction”. In general, I would make sure that a mechanical pipette, if possible, is used instead of the manual pipette for it would assure that a more precise measurement of each chemical solution was used in each trial. In general, I would also make sure that a glass stirring rod is used instead of the wooden toothpick for it would assure that less of the chemical solutions within each trial is absorbed.
