Presentation on theme: "The Briggs-Rauscher Reaction An Oscillating Chemical Reaction"— Presentation transcript:
1The Briggs-Rauscher Reaction An Oscillating Chemical Reaction
2What is an Oscillating Chemical Reaction? An oscillating chemical reaction is a rare process thatproduces changes in color which repeatedly turn on and offover many cycles.These reactions are very complex and involveseveral chemical reactions occurring at the same time.Thomas Briggs and Warren Rauscher, two teachers atGalileo High School in San Francisco discovered one ofthe most dramatic examples of an oscillating chemicalreaction in 1973 and it now bears their name.
3Reactants for Briggs-Rauscher Reaction Potassium Iodate KIO3Hydrogen Peroxide H2O2Manganese Sulfate MnSO4Malonic Acid HO2C-CH2-CO2HSulfuric Acid H2SO4Starch Indicator + Water
5How 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:
6How it works – Mechanism of Reaction The free iodine reacts with malonic acid to produceiodide ions.
7How it works – Mechanism of Reaction The free iodine combines with iodide very rapidlyto form the negative ion I3 , which reacts with starchto form a dark blue complex:
9How it works – Mechanism of Reaction 4. After a period of time, the I3 ions are convertedback into iodine and iodide ions, so the dark blue colordisappears and the process repeats itself:
10How it works – Mechanism of Reaction 5. Eventually the faster step 3 becomes dominant andthe change of I3 back to iodine/iodide stops after about15 cycles, so the solution remains dark blue.The overall chemical reaction is: