"Chemical pendulum" experiment

The Belousov-Zhabotinsky reaction

This stun­ning chem­i­cal ex­per­i­ment is a mod­i­fi­ca­tion of one of the most com­plex chem­i­cal re­ac­tions, the Be­lousov-Zhabotin­sky re­ac­tion.

Reagents and equip­ment:

  • con­cen­trat­ed sul­fu­ric acid;
  • so­lu­tion of ceri­um(IV) sul­fate (10.6 g in 1 liter);
  • so­lu­tion of mal­onic acid and potas­si­um bro­mide (32 g of mal­onic acid + 7 g of potas­si­um bro­mide in 1 liter);
  • so­lu­tion of potas­si­um bro­mate (38 g in 1 liter);
  • sat­u­rat­ed so­lu­tion of fer­roin;
  • beaker;
  • mag­net­ic mix­er.

Step-by-step in­struc­tions

Pour the so­lu­tion of potas­si­um bro­mate into the beaker, then the so­lu­tion of mal­onic acid and potas­si­um bro­mide, and then add the so­lu­tion of ceri­um(IV) sul­fate and con­cen­trat­ed sul­fu­ric acid. Then the sat­u­rat­ed so­lu­tion of fer­roin.

Pro­cess­es de­scrip­tion

The Be­lousov-Zhabotin­sky re­ac­tion is one of the most pop­u­lar re­ac­tions in sci­ence. It has been car­ried out by sci­en­tists in dif­fer­ent fields, such as chem­istry, physics, math­e­mat­ics and bi­ol­o­gy. Nu­mer­ous doc­tor­al dis­ser­ta­tions have been writ­ten about it, but the full mech­a­nism has yet to be ful­ly ex­plained. The most de­tailed mech­a­nism to­day is a set of 80 el­e­men­tary re­ac­tions.

The so­lu­tion changes col­or be­cause dif­fer­ent col­ors over­lap, for ex­am­ple the bromine re­leased has a red­dish-brown col­or, and the fer­roin so­lu­tion con­tain­ing bi­va­lent iron is red, and when it ox­i­dizes to a triva­lent state it turns blue. Ce⁺⁴ ions have a yel­low­ish-or­ange col­or, while Ce⁺³ ions are col­or­less. As all of these ox­i­da­tion-re­duc­tion re­ac­tions take place in the same ves­sel, this in­cred­i­ble change of col­or takes place.

Safe­ty pre­cau­tions

Wear pro­tec­tive gloves and glass­es. Ob­serve safe­ty rules when work­ing with con­cen­trat­ed acids.

Warn­ing! Only un­der pro­fes­sion­al su­per­vi­sion.