The BriggsRauscher Reaction An Oscillating Chemical Reaction What

The Briggs-Rauscher Reaction An Oscillating Chemical Reaction

What is an Oscillating Chemical Reaction? u An oscillating chemical reaction is a rare process that produces changes in color which repeatedly turn on and off over many cycles. u These reactions are very complex and involve several chemical reactions occurring at the same time. u 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. Briggs-Rauscher Reaction - 2

Reactants for Briggs-Rauscher Reaction Potassium Iodate - KIO 3 Hydrogen Peroxide - H 2 O 2 Manganese Sulfate - Mn. SO 4 Malonic Acid - HO 2 C-CH 2 -CO 2 H Sulfuric Acid - H 2 SO 4 Starch Indicator + Water Briggs-Rauscher Reaction - 3

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: 1. The iodate ion is changed into iodine by hydrogen peroxide. The color changes to amber: Briggs-Rauscher Reaction - 5

How it works – Mechanism of Reaction 2. The free iodine reacts with malonic acid to produce iodide ions. Briggs-Rauscher Reaction - 6

How it works – Mechanism of Reaction 3. The free iodine combines with iodide very rapidly to form the negative ion I 3 - , which reacts with starch to form a dark blue complex: Briggs-Rauscher Reaction - 7

The Blue Starch-Iodine/Iodide Complex Briggs-Rauscher Reaction - 8

How it works – Mechanism of Reaction 4. After a period of time, the I 3 ions are converted back into iodine and iodide ions, so the dark blue color disappears and the process repeats itself: Briggs-Rauscher Reaction - 9

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