Question

A)In the experiment, you will be measuring the time it takes for the solution to turn blue. If you have initial concentrations of I^- = 0.022 M, BrO₃^- = 0.013 M, H⁺ = 1.8 x 10^-5 M, and S₂O₃^2- = 0.007 M, what is the concentration of S₂O₃^2- when the solution turns blue?

B)In the experiment, you will be measuring the time it takes for the solution to turn blue. If you have initial concentrations of I^- = 0.023 M, BrO₃^- = 0.023 M, H⁺ = 1.8 x 10^-5 M, and S₂O₃^2- = 0.006 M, what is the concentration of I^- when the solution turns blue?

C)An experiment is run and found to obey the rate law rate = kX²Y. Additionally, it is found that it has an activation energy of 170,821 J/mol. If the rate constant for the reaction is 2.5 x 10^-2 M^-2s^-1at 267 ^oC, what is the rate constant at 235 ^oC?

Answer 1

Part A) At first, the I2 produced by reaction [2] is gobbled up by the thiosulfate as fast as it is made, The products of this reaction are colorless – you can’t see them. However, once the thiosulfate is used up, the concentration of I2 is free to react with starch, forming a starch complex you can see (it’s deep blue). So concetration of S2O32-=0M when solution turns blue.

6 I-(aq) + BrO3 -(aq) + 6 H+(aq)----> 3 I2(aq) + Br-(aq) + 3 H2O [1]

I2(aq) + 2 S2O3 2-(aq)-----> 2 I-(aq) + S4O6 2-(aq) [2]