Question

Consider the reaction of peroxydisulfate ion (S2O2−8) with iodide ion (I−) in aqueous solution:
S2O2−8(aq)+3I−(aq)→2SO2−4(aq)+I−3(aq).
At a particular temperature the rate of disappearance of S2O2−8 varies with reactant concentrations in the following manner:

Experiment	S2O2−8(M)	I−(M)	Initial Rate (M/s)
1	0.018	0.036	2.6×10−6
2	0.027	0.036	3.9×10−6
3	0.036	0.054	7.8×10−6
4	0.050	0.072	1.4×10−5

Part A

Determine the rate law for the reaction.

A) rate=k[S2O2−8]2[I−]

B) rate=k[S2O2−8][I−]2

C) rate=k[S2O2−8][I−]

D) rate=k[S2O2−8]2[I−]2

Part B

What is the average value of the rate constant for the disappearance of S2O2−8 based on the four sets of data?

Part C

How is the rate of disappearance of S2O2−8 related to the rate of disappearance of I−?

A) the rate of disappearance of I− is one-third the rate of disappearance of S2O2−8

B) the rate of disappearance of S2O2−8 is one-third the rate of disappearance of I−

C) the rate of disappearance of S2O2−8 is equal to the rate of disappearance of I−

Part D

What is the rate of disappearance of I− when [S2O2−8]= 3.5×10^−2 M and [I−]= 5.0×10^−2 M ?

Express your answer using two significant figures.