Iodine Clock Reaction - lab write-up PDF

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1 Iodine Clock Reaction SCH 4U Wednesday, May 16, 2018 Purpose The purpose of this lab is to analyse the data obtained from an iodine clock reaction with different concentrations to determine the order of reaction with respect to [A]. Observations Relative [A]

Time (s)

Rate 1 x time (s)

Analysis

103

100%

14.55

68.73

90%

15.46

64.68

80%

17.12

58.41

70%

23.16

43.18

60%

25.63

39.02

50%

28.99

34.49

40%

34.01

29.40

30%

48.01

20.83

20%

73.98

13.52

10%

154.03

6.49

2

The observations were graphed into two forms: rate vs. concentration and rate vs. concentration2. In each graph, the line of best fit was forced to be linear so that when comparing the correlation coefficients, it would be easier to tell which graph fits best for the data. Based on the fitting, the order of reaction with respect to [A] can be found. By just looking at the graphs above, it is clear that the first graph (first order) fits the data much better as the line of best fit hits more data points than on the second graph (second order). Furthermore, the correlation coefficients of each line can be seen on the respective graph. The closer the value is to 1, the better the line fits the data. Again, it is clear that the first graph fits better as the coefficient is

3 0.99 while the second graph is 0.929. This means that the rate of the reaction is directly proportional to the concentration of [A]. According to the analysis of the graphs, the experiment is a first order with respect to [A]. Another way to find the order of reaction is to directly work with the values. By comparing different values of concentration with their rates, the order can be found: Concentrations Concentration 1 Concentration 2

=[

Rate 1 x ] Rate 2

100% vs. 50%

80% vs. 40%

60% vs. 30%

40% vs. 20%

2 = [ 68.73 ]x 34.49 2 = 1.99x x≐1

2 = [ 58.41 ]x 29.40 2 = 1.99x x≐1

2 = [ 39.02 ]x 20.83 2 = 1.87x x≐1

2 = [ 29.40 ]x 13.52 2 = 2.17x x≐1

As seen in the calculations above, the exponent value of the concentration [A] consistently turned out be closer to 1 than any other number. Hence, the experiment is a first order with respect to [A]. This means that if the concentration doubles, so does the rate of the reaction. This exact relationship is clearly seen in both the graph and the calculations. Results Through analysing the data with graphs and calculations, it was determined that the order of reaction is a first order with respect to [A]. Discussion In this activity, the order of reaction with respect to [A] was successfully determined using two methods: graphing and calculations. Both ways, the experiment showed a linear relationship, meaning that the rate of the experiment was directly proportional to the concentration [A]. Hence, this iodine clock reaction was a first order reaction with respect to [A]. Overall, the reaction behaved in an expected way according to the rate law. As the concentration of [A] decreased, the reaction took longer meaning that the rate decreased as well. Despite the success of the lab, there were some oversights with the process and equipment of the activity. For example, after preparing all of the different concentrations of [A] for the experiment, the tubes were generally left alone for lengthy periods while other tubes were tested on. This can cause the reactant in [A] and the added water to separate a bit. This can change the time reading drastically as the concentration that rises to the top reacts easily with [B] compared to the rest of the solution. Thus, the first show of colour happens much earlier than it was supposed to, creating a lag between the first show and the actual reaction. Due to this

4 oversight, a few of our tests had to be redone to get more accurate readings. Due to the concentration buildup at the top of the tube, colour showed up around four times faster than it was supposed to according to the different time readings for the redone tests. Some other factors that could affect the results is that the transfer pipette was not cleaned when switching between [A] and [B]. This could have affected the experiment to some degree such as starting the reaction a bit earlier due to the presence of both reactants. Furthermore, when timing the iodine clock reaction, the results are prone to human error as it depends on pure reflex. This can cause some discrepancy between the recorded time and actual time of the reaction, thus affecting the final calculations. These different limitations in equipment and lab procedure could have affected the final observations, altering the process to identifying the order of the reaction. For future improvements, some extra steps can be taken for more accurate results. For example, before adding [B] to the solution, the tube containing [A] should be mixed to ensure that no concentration has risen to the top. By doing this, there will not be a show of colour way before the rest of the tube turns and the time reading can be done correctly. Hence, the test will not need to be done again, saving materials and time. Furthermore, the transfer pipette should be cleaned with distilled water before switching from [A] to [B]. This ensures that there is no mixing of reactants before the testing period starts, resulting in more accurate results. Another step that can be taken to ensure the best answers is to have multiple people in the group timing the iodine clock reaction. This way, the two values can be compared to test for accuracy and the best timing recorded. Another method is to test which group member has the best reflexes and to assign the role of timing to that member. Hence, the group can have the most accurate timings, making the results that much more accurate. For future studies, we could find the order of the reaction with respect to [B] instead of [A]. This way we can see how different reactants affect the reaction. Another test could be to find the effect of temperature on the rate of a reaction. The reactants would remain the same, with only the temperature varying to get results. Another study could be to see how adding a third reactant, such as sulfite, affects the iodine clock reaction. Sulfite is supposed to slow down or reverse the reaction when present. Increasing the concentration of sulfite should lengthen the time, decreasing the rate of the reaction (Harrington & Mosher, 2015). This relationship can be studied to see how it works or what exactly is

5 happening. These are some improvements concerning the activities equipment and procedure as well as some questions that can be explored in future studies. Conclusion In conclusion, the order of the reaction with respect to [A] was successfully found by analysing data from different concentrations in the iodine clock reaction. According to both the graph and calculations, the order of the reaction was found to be a first order with respect to [A]. Knowing the effect reactants can have on the rate of a reaction is extremely important in many applications. For example, if a medicine is developed for a specific disease, it is important to optimize its rate of effect in our body. However, if the medicine releases heat while reacting, the rate must be decreased to ensure that the patient does not experience a high fever due to the medication. To control the rate of reaction of the medicine, we must understand how the components and concentrations affect how fast it works. Another example is in the chemical industry. When making products, the rate of the reaction indicates the rate of production. In order to meet demands, safety standards, and make profit, the rate of the reaction must be optimized (Socratic, 2015). Hence, it is very important to study and understand the correlation between concentration of reactants and the rate of the reaction for different reactions. Only then can we control these variables for our own needs such as in these applications.

References

6 Harrington, R., & Mosher, D. (2015). Make a clear liquid turn black in midair with this bizarre science experiment. Retrieved from http://www.businessinsider.com/how-iodine-clock-experiment-works-ingredients-2015-1 2 Socratic. (2015). How do rates of reaction apply to daily life? Retrieved from https://socratic.org/questions/how-do-rates-of-reaction-apply-to-daily-life...