Determining the Rate law when hydrogen peroxide is added to a solution of potass

Question

Determining the Rate law

when hydrogen peroxide is added to a solution of potassium iodide, the iodide ion is slowly oxidized to iodine according to the equation H2O2+2I-+2H+-->I2+H2O. The purpose of the experiment is to determine the rate law for the reaction. Rate = k[H20]a[I-]b

The rate with which we are concerned is one in which an equilibrium mixture will result if the concentration of the product, iodine, is allowed to build up. if our measurements are to be made on the actual rate of the forward reaction, rather than on the net difference between forward and reverse rates, it is essential that the reverse reaction be suppressed completely, e.g. by removing the iodine as quickly as it is formed which is done by adding sodium thiosulfate. I2+2S2O32--->2I-+S4O62-

solution

number

100.0

I have calculated the value of k for each of five cases from an experiment (where [H202] = 0.0005 M, and the time in seconds for each of the 5 solutions are: 1745, 998, 640, 287, and 145 respectively, using Rate = [H202]/t) and plugged these values into the 3 rate equations following for k:

1.Rate = k[H2O2][I-] so that k=Rate/([H2O2][I-])

2.Rate = k[H2O2]2[I-] so that k=Rate/([H2O2]2[I-])

3.Rate = k[H2O2][I-]2 so that k=Rate/([H2O2][I-]2)

Solution

Value of k from Equation 1

Value of k from Equation 2

Value of k from Equation 3

1

0.0127 M/s

2.583 M/s

2.863 M/s

2

0.0223 M/s

4.453 M/s

4.948 M/s

3

0.0347 M/s

6.944 M/s

7.716 M/s

4

0.0774 M/s

15.49 M/s

17.21 M/s

5

0.1533 M/s

30.65 M/s

34.06 M/s

I need to examine the values of k for constancy for each equation to determine the correct equation and i need to know the order of this reaction with respect to [H2O2] and with respect to [I-] and the average value of k.

solution

number

buffer (mL) 0.300M KI (mL) Starch (mL) 0.0200 M Na2S2O3 (mL) water 0.100 M H2O2 Total Volume 1 5.00 1.50 1.00 5.00 82.5 5.00

100.0

2 5.00 3.00 1.00 5.00 81.0 5.00 100.0 3 5.00 5.00 1.00 5.00 79.0 5.00 100.0 4 5.00 5.00 1.00 5.00 74.0 10.00 100.0 5 5.00 5.00 1.00 5.00 64.0 20.0 100.0

Explanation / Answer

The consistency of the calculate k value is good and the average are,

reaction 1 --> 0.06008 M/s

reaction 2 --> 12.024 M/s

reaction 3 --> 13.3594 M/s

order of reaction w.r.t,

[H2O2] --> 1

[I-] --> 2

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