Briggs-Rauscher Oscillating Color Change Reaction
Submitted By Honglan
Briggs-Rauscher Oscillating Color Change Reaction Introduction: The Briggs-Rauscher reaction, is one of the most common demonstrations of a chemical oscillator reaction. The reaction begins when three colorless solutions are mixed together. The color of the resulting mixture will oscillate between clear, amber, and deep blue for about 3-5 minutes. The solution ends up as a blue-black mixture. What we need: We need three different chemical solution. Solution A: Add 43 g potassium iodate (KIO3) to ~800 ml distilled water. Stir in 4.5 mL sulfuric acid (H2SO4). Continue stirring until the potassium iodate is dissolved. Dilute to 1 L. Solution B: Add 15.6 g malonic acid (HOOCCH2COOH) and 3.4 g manganese sulfate monohydrate (MnSO4 . H2O) to ~800 ml distilled water. Add 4 g of vitex starch. Stir until dissolved. Dilute to 1 L. Solution C: Dilute 400 mL of 30% hydrogen peroxide (H2O2) to 1 L. Then prepare all of each solution 300ml, 1L beaker, stirring plate, and magnetic stir bar. Procedure: First step, place the stirring bar into the large beaker.
Then, pour 300 mL each of solutions A and B into the beaker.
Third step, turn on the stirring plate. Adjust the speed to produce a large vortex.
Final, add 300 mL of solution C into the beaker. Be sure to add solution C after mixing solutions A + B or else the demonstration will not work.
Note: This demonstration evolves iodine. Wear safety goggles and gloves and perform the demonstration in a well-ventilated room, preferably under a ventilation hood. Use care when preparing the solutions, as the chemicals include strong irritants and oxidizing agents.
Now, here is the reaction formula
IO3- + 2 H2O2 + CH2(CO2H)2 + H+ --> ICH(CO2H)2+ 2 O2 + 3 H2O
The HOI product of the first component reaction is a reactant in the second component reaction:
HOI + CH2(CO2H)2 --> ICH(CO2H)2 + H2O
This reaction consists of two component reactions:
I- + HOI + H+ --> I2 + H2O
I2CH2(CO2H)2 --> ICH2(CO2H)2 + H+ + I-
The deep blue color is the result of the I- and I2 binding to the starch present in the solution.
Source: B. Z. Shakhashiri, 1985, Chemical Demonstrations: A Handbook for Teachers of Chemistry, vol. 2, pp. 248-256.