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Chemistry LibreTexts

Oscillating Clock

The Briggs-Rauscher reaction is an oscillating reaction like the Belousov-Zhabotinsk reaction.

Introduction

Reactions

The essential features of the system depend on two key processes, each involving many reactions working together:

  • A ("non-radical process"): The slow consumption of free iodine by the malonic acid substrate in the presence of iodate. This process involves the intermediate production of iodide ion.
  • B ("radical process"): A fast process involving manganese and free radical intermediates, which converts hydrogen peroxide and iodate to free iodine and oxygen. This process also can consume iodide up to a limiting rate.

IO3- + 2 H2O2 + CH2(CO2H)2 + H+ -> ICH(CO2H)2 + 2 O2 + 3 H2O

The striking visual demonstration occurs by the addition of a starch indicator.

Safety

Do not drink this.