The peroxydisulfate ion (S2O82-) reacts with the iodide ion in aqueous solution

Question

The peroxydisulfate ion (S2O82-) reacts with the iodide ion in aqueous solution via the reaction:S2O82- (aq) + 3I- 2SO4 (aq) + I3- (aq) An aqueous solution containing 0.050 M of S2O82- ion and 0.072 M of I- is prepared, and the progress of the reaction followed by measuring [I-]. The data obtained is given in the table below. The average rate of the reaction in the initial 400.0 s is __________ M/s. a. 6.00 b. 3.2 x 10-4 c. 1.25 x 10-5 d. 1.4 x 10-4 e. 2.7 x 104

Data: Time (s) 0.000 400.00 800.00 1200.00 1800.0

[I-] (M) 0.072 0.057 0.046 0.037 0.029

Explanation / Answer

Rate= 1/3 D[I-]/Dt = 1/3 (0.057-0.072)/(400-0) = -1.25x10-5M/s

The aswer is negative because it is the rate of consumption of the reagent, but the rate is expressed as a positive number, the correct option is c.

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