Belousov-Zhabotinsky reaction

Сolours suddenly changes on and off in a very peculiar manner

Scientific name: Nonlinear chemical oscillator with malonic acid and potassium bromate

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Safety

Wear goggles and disposable gloves

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Reaction formula

3CH2(COOH)2 + 4BrO3- → 4Br- + 9CO2↑ + 6H2O

Step-by-step instruction

  1. First we need to prepare all the components. 9 g of propane-1,3-dioic (malonic) acid, 8 g of potassium bromate(V) and 1.8 g of manganese(II) sulfate-1-water are required.
  2. Place the flask with dilute sulfuric acid (10 wt%) on a magnetic stirrer and stir it to form a vortex.
  3. Add malonic acid and potassium bromate to the sulfuric acid solution and wait for all the components to dissolve.
  4. Add manganese sulfate.
  5. The solution will immediately become red. After one minute it will turn colorless. The color of the solution will change in an “oscillation mode” with a period of about 20 seconds. The period of the oscillations will increase as the reaction passes.

Scientific background

BZ reaction is a class of oscillating chemical reactions. It is a good example of nonequillibrium thermodynamical processes. In BZ reaction the catalytic oxidation of different reductions by bromnovatic acid (HBrO3) take place. The reaction proceeds in an acidified water solution. Metals of variable valence are used as catalysts, for example Mn and Ce. Ethylaceton and malonic acid are typical reducting agents in BZ reaction. During the reaction the oscillations of concentrations of oxidized and reduced forms of the catalyst and some intermediate products are observed. The detailed mechanism of this oscillation reaction is very complex and still is not fully understood. In general it could be simplified to three processes:

1)Branched chain reaction between oxidant and autocatalyst HBrO2. This results in the self-accelerating oxidation of metal ions:

HBrO3+HBrO2 ↔ 2BrO2∙ + H2O

BrO2∙ + Mn + H+ ↔ Mn+1 + HBrO2

2)Inhibition of the oxidation process as a result of a rapid reaction, which terminates the oxidation chain:

H+ + Br- + HBrO2 ↔ 2HOBr

3)Brominating of the reducing agent:

HOBr + CH2(COOH)2↔ CHBr(COOH)2+H2O

Since this reaction is far from equilibrium it could be considered as an interesting model of nonequilibrium phenomena in other fields of science. For example it could be used to describe population waves in biology.

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Published on 25 December 2014

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst