BRIGGS-RAUSCHER REACTION
NEEDED

     -  Potassium iodate : KIO3
     -  Sulfuric acid : H2SO4
     -  MnSO4 . H2O
     -  Malonic acid
     -  Starch
     -  12% hydrogen peroxide : H2O2
     -  Sodium thiosulfate : Na2S2O3

PROCEDURE

          Prepare the three solutions as follows:

          Solution A: Dissolve KIO3 (21.5 g) in water
     (500 ml) and add H2SO4 (2.25 ml).
          Solution B: Add malonic acid  (7.8 g) and
     MnSO4.H2O (1.7 g) to water (300 ml). Dissolve
     starch (2 g) in boiling water (200 ml) and after
     cooling it down to room temperature mix it to
     the acidic manganese solution.
          Solution C: 12% hydrogen peroxide (500 ml).

          Pour all three solutions into a 2 litre beaker
     under strong stirring.

COMMENTS

         One of the most spectacular chemical
     reactions there is. The oscillation proceeds for
     five to ten minutes.
          Chemicals here are quite oxidising and
     irritant, so take care in the preparation of the
     solutions. Iodine produced in the course of the
     reaction is volatile, so the room should be well
     ventilated (a fumehood is better but not really
     necessary for this reaction.
          The resulting iodine is reduced to iodide by
     the final addition of sodium thiosulfate
     (exothermic reaction).
          The mechanism is faaaaar too complicated
     to have any use in class.

LITERATURE

          An Oscillating Iodine Clock
          T. S. Briggs, W. C. Rauscher, J. Chem. Educ.,
     1973, 50, 496.
          DOI: 10.1021/ed050p496

          The oscillatory Briggs–Rauscher reaction. A
     skeleton mechanism for oscillations
          R. M. Noyes and S. D. Furrow, J. Am. Chem.
     Soc., 1982, 104, 45.
          DOI: 10.1021/ja00365a011
Caption
FOTO