1. Iodine Clock Reaction
We will begin by describing a proposed reaction mechanism for the iodine clock reaction. There are several variations to this reaction, the one in focus being the “iodate variation”.
The reagents used are:
Bottle A: Potassium iodate (KIO3)
Bottle B: Sodium bisulfite(NaHSO3)
Sulfuric acid (H2SO4) – This is a catalyst
Starch indicator

2. The overall process that takes place can be described by the following reaction mecanism(Arthur Moss, 1978):
Steps 1 and 2, commonly referred to as the Landolt and Duchman reactions respectively, are dominant so long as HSO3- is in excess.
Once it’s consumed, step 3 can no longer occur and an appreciable concentration of I2 becomes present.

3. The starch indicator then rapidly combines with the iodine (triiodide, I3- , is actually present as well, in equilibrium with I2  and I-) to form the signature, deep blue, iodine-iodide-amylose complex  (John A. Church and Sanford A. Dreskin, 1968).
Iodine Clock Reaction

4. Rate Law Expression
The rate law for this reaction will be in the form:
Rate = k [IO3 ] x [HSO3 ] y
where k is the rate constant for this reaction at a particular temperature, and x and y are the reaction orders for the iodate and bisulfite ions respectively.
Since we are only looking at the effect of changing the concentration of the iodate solution (bottle A), the x-value is what you will determine in this experiment.

5. Drops of A before mixing
Data
If you don’t have “good numbers” work with the following:
Time (s)
Drops of A before mixing
10.0 10
12.3 9
15.6 8
20.4 7
27.8 6
40.0 5
62.5 4
111.1 3
250.0 2
1000.0 1

6. Graphing Your Data
When plotting reaction rate vs initial conc of A, compare your plot to the following to determine the order of the reaction.