1. The Briggs-Rauscher Reaction An Oscillating Chemical Reaction

2. What is an Oscillating Chemical Reaction?
An oscillating chemical reaction is a rare process that
produces changes in color which repeatedly turn on and off
over many cycles.
These reactions are very complex and involve
several chemical reactions occurring at the same time.
Thomas Briggs and Warren Rauscher, two teachers at
Galileo High School in San Francisco discovered one of
the most dramatic examples of an oscillating chemical
reaction in 1973 and it now bears their name.

3. Reactants for Briggs-Rauscher Reaction
Potassium Iodate KIO3
Hydrogen Peroxide H2O2
Manganese Sulfate MnSO4
Malonic Acid HO2C-CH2-CO2H
Sulfuric Acid H2SO4
Starch Indicator + Water

5. How it works – Mechanism of Reaction
Research into the B-R reaction by other scientists in 1982, led to the discovery that some 11 steps are involved! The simple explanation is as follows:
The iodate ion is changed into iodine by hydrogen peroxide.
The color changes to amber:

6. How it works – Mechanism of Reaction
The free iodine reacts with malonic acid to produce
iodide ions.

7. How it works – Mechanism of Reaction
The free iodine combines with iodide very rapidly
to form the negative ion I3 , which reacts with starch
to form a dark blue complex:

8. The Blue Starch-Iodine/Iodide Complex

9. How it works – Mechanism of Reaction
4. After a period of time, the I3 ions are converted
back into iodine and iodide ions, so the dark blue color
disappears and the process repeats itself:

10. How it works – Mechanism of Reaction
5. Eventually the faster step 3 becomes dominant and
the change of I3 back to iodine/iodide stops after about
15 cycles, so the solution remains dark blue.
The overall chemical reaction is: