Question

I already answered the first three questions and put the answer down I just don't know how to answer the last question which asks to calculate K in the rate law?

A clock reaction is run at 20 ºC with several different mixtures of iodide, sodium bromate and acid, to form iodine. Thiosulfate is used to react with the iodine formed initially. Starch indicator is added to form a blue color when all the thiosulfate has been used up and the iodine concentration begins to rise. The following sets of mixtures are used.

Initial concentrations in reaction mixtures
Run number [I^-]      [BrO₃^-]      [H⁺]
1 0.002          0.008       0.02
2 0.002       0.016            0.02
3 0.004         0.008         0.02
4 0.002        0.008             0.04   
[S₂O₃^2- ] is equal to 0.0001M in each reaction mixture.
The rate law is :
  
Rate = k [ I^-]^a   [ BrO₃^-]^b   [H⁺]^c


Reaction time in run number 1 30
Reaction time in run number 2 30
Reaction time in run number 3 15
Reaction time in run number 4 30

Calculate the following
a in the rate law

a=1

A clock reaction is run at 20 ºC with several different mixtures of iodide, sodium bromate and acid, to form iodine. Thiosulfate is used to react with the iodine formed initially. Starch indicator is added to form a blue color when all the thiosulfate has been used up and the iodine concentration begins to rise. The following sets of mixtures are used.

Initial concentrations in reaction mixtures
Run number [I^-]      [BrO₃^-]      [H⁺]
1 0.002          0.008       0.02
2 0.002       0.016            0.02
3 0.004         0.008         0.02
4 0.002        0.008             0.04   
[S₂O₃^2- ] is equal to 0.0001M in each reaction mixture.
The rate law is :
  
Rate = k [ I^-]^a   [ BrO₃^-]^b   [H⁺]^c


Reaction time in run number 1 30
Reaction time in run number 2 30
Reaction time in run number 3 15
Reaction time in run number 4 30

Calculate the following
b in the rate law

b=0

A clock reaction is run at 20 ºC with several different mixtures of iodide, sodium bromate and acid, to form iodine. Thiosulfate is used to react with the iodine formed initially. Starch indicator is added to form a blue color when all the thiosulfate has been used up and the iodine concentration begins to rise. The following sets of mixtures are used.

Initial concentrations in reaction mixtures
Run number [I^-]      [BrO₃^-]      [H⁺]
1 0.002          0.008       0.02
2 0.002       0.016            0.02
3 0.004         0.008         0.02
4 0.002        0.008             0.04   
[S₂O₃^2- ] is equal to 0.0001M in each reaction mixture.
The rate law is :
  
Rate = k [ I^-]^a   [ BrO₃^-]^b   [H⁺]^c


Reaction time in run number 1 30
Reaction time in run number 2 30
Reaction time in run number 3 15
Reaction time in run number 4 30

Calculate the following
c in the rate law

C=0

If the rate law for the clock reaction is:

   
Rate = k [ I^-] [ BrO₃^-] [H⁺]

A clock reaction is run with the following initial concentrations:

[I^-]               [BrO₃^-]            [H⁺]                         [S₂O₃^2-]
0.002                   0.008                   0.02                          0.0001  

The reaction time is 28 seconds

Calculate k in the rate law:?

Answer 1

Rate = k [ I-]a   [ BrO3-]b   [H+]c

calculation of "a"

using the values that you have calculated for b and c and dviding rate expression obatined in trial 2 by that in 3.

we get (1/2)a = 1/2; which shows a = 1.

putting these values of a= 1, b=0, and c= 0 in rate law

rate = k[I-]

reaction is first order w.r.t [I-]

Now,

using initial concentrations:

[I-]               [BrO3-]            [H+]                         [S2O32-]
0.002                   0.008                   0.02                          0.0001  

The reaction time is 28 seconds to alculate k.

(0.0001/28) Ms-1 = k (0.002) M

k = 1.78 x 10-3 s-1