1. A student studies the kinetics of reaction 1 below using a clock reaction tec

Question

1. A student studies the kinetics of reaction 1 below using a clock reaction technique, reaction 2, and the procedures given in this experiment. For reaction mixture 1, he measures a time to color change of 121 seconds and for reaction mixture 2, he measures a time of 58 seconds. The temperatures of the reaction mixtures were the same for both experiments. (Reaction 1, slow) Reaction 2, fast) er (aq) + Brd," (aq) + 6H' (aq) 312 (aq) + Br (aq) + 3H20() 12 (aq) + 2 S,032-(aq) 21-(aq) + SO62-(aq) a. Determine the change in concentration of S2Os that occurred during the time period measured. This should be the same for both the reaction mixtures. First, use M,V1-M2V2 to determine the initial concentration of the S20s after mixing the contents of the two flasks but before the reation begins. Next, find the final concentration of S203 by remembering that all the S2o3 is consumed when the color change occurs. You can then find the change in the concentration of S203 [s203 o b. Use the stoichiometry of Reactions 1 and 2 to determine the change in concentration of BrOs during the same time period. ABrOs1

Explanation / Answer

a. The concentration of Na2S2O3 in flask I (M1) = 0.001 M

Th volume of Na2S2O3 (V1) = 10 mL

The total volume (V2) = 50 mL

Here, M1V1 = M2V2

i.e. 0.001 M * 10 mL = M2 * 50 mL

i.e. M2 = 0.001*10/50 = 0.0002 M

Therefore, the initital concentration of S2O3^2- = [S2O3^2-]0 = 2*10-4 M

Since, S2O3^2- is consumed completely, the final concentration of S2O3^2- = [S2O3^2-]t = 0

Therefore, the change in concentration of S2O3^2- = [S2O3^2-]t - [S2O3^2-]0 = 0 - 2*10-4 M = -2*10-4 M

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