Question

PART 1
>>Trial 1
Reactant Solution A

10 ml I^-, 5.0 ml S2O3^2-

Reactant Solution B

10 ml S2O8^2-, 1 ml starch

time to react = 10 seconds


>>Trial 2
Reactant Solution A

10 ml I^-, 5.0 ml S2O3^2-

Reactant Solution B

5 ml S2O8^2-, 1 ml starch

time to react = 20 seconds

>>Trial 3
Reactant Solution A

5 ml I^-, 5.0 ml S2O3^2-

Reactant Solution B

10 ml S2O8^2-, 1 ml starch

time to react = 20 seconds

How do trial 2 and 3 in the above table differ? More than one response is possible.
A) Trial 2 has twice as much I– as Trial 3
B) Trial 3 has twice as much S2O82– as Trial 2
C) Trial 3 has half as much S2O32– as Trial 2
D) Trial 2 has half as much starch as Trial 3

I chose A and B for this question

PART 2

Which of the four proposed mechanisms below would be supported by these results? Note: there may be more than one answer.

Mechanism 1:
I^- + I^- > I2^2- (slow)
I2^2- + S2O8^2– > I^2 + SO4^2- (fast)

Mechanism 2:
I2^2- + S2O8^2– > [S2O8xI]^3- (slow)
[S2O8xI]^3- +I^- > I2 + 2SO4^2- (fast)

Mechanism 3:
I^- + S2O8^2– <> [S2O8xI]^3- (fast)
[S2O8xI]^3- + I^- > I2 + 2SO4^2- (slow)

Mechanism 4:
2I^- + S2O8^2– > I2 + 2SO4^2-

I'm really not sure how to answer this part, if anyone can help that would be greatly appreciated!!

Answer 1

I looked part 2 for a bit and by looking at the slow step and using that to figure out the rate law I think it might be mechanism 2, would this be right?