Two students reacted bromooctane with chioride ion. Both students used the exact

Question

Two students reacted bromooctane with chioride ion. Both students used the exact same quantities and concentrations of chemicals and exact same reaction temperatures. However, the first student ran her reaction for one hour while the second student ran her reaction for two hours. Both students measured the refractive indexes of their product mixtures. Which student would obtain a higher refractive index? Explain. 5. Nucleophillic Substitution Reactions 1.5 148 1.40 1-45 1.44 1.43 1.42 10 20 30 40 so 6o 70 90 100 Percent Octyl Halide Product be mu

Explanation / Answer

For student 1, she ran the reaction for 1 hour. This means that reaction is not complete. Whole of the bromo is not replaced by chloro in bromooctane. So, more of bromooctane will be present as compared to chlorooctane. Suppose, at this point, 40 % chlorooctane is present and 60 % unreacted bromooctane is present in mixture.

Then from graph, refractive index of 40 % chlorooctane is 1.442 and of 60 % bromooctane is 1.472. Addition of both gives 2.914.

For student 2, she ran the reaction for 2 hours. This means that reaction is towards completion or might be complete. Most of the bromo is replaced by chloro in bromooctane. So, more of chlorooctane will be present as compared to bromooctane. Suppose, at this point, 40 % chlorooctane is present and 60 % unreacted bromooctane is present in mixture.

Then from graph, refractive index of 60 % chlorooctane is 1.438 and of 40 % bromooctane is 1.465. Addition of both gives 2.903.

This shows the higher refractive index for student 1 than for student 2.

In the graphs also, we can see that the slope for bromo is more than that for chloro. The slope for bromo is 0.00036 and for chloro, it is 0.00021. When the reaction is incomplete, then the refractive index will be higher due to more bromooctane.

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