“Chemical waves” experiment

How to make solution change color itself

If you like to watch waves break­ing on the seashore, this im­pres­sive ex­per­i­ment is for you!

Safe­ty pre­cau­tions

Pro­tec­tive gloves must be worn for this ex­per­i­ment.

Warn­ing! Only un­der pro­fes­sion­al su­per­vi­sion.

Reagents and equip­ment:

  • so­lu­tion of bro­mo­ma­lonic acid (10 g/l);
  • so­lu­tion of potas­si­um bro­mate (10 g/l);
  • fer­roin (1% sol.);
  • cu­vette;
  • pipette;
  • wa­ter.

Step-by-step in­struc­tions

Pour the so­lu­tion of bro­mo­ma­lonic acid (C₃H₃O₄Br) into the cu­vette, then the so­lu­tion of potas­si­um bro­mate (KBrO₃) and the fer­roin (re­dox in­di­ca­tor), The col­or of the so­lu­tion starts to os­cil­late in waves from red to blue. The ef­fect of col­ored “waves” is cre­at­ed.

Pro­cess­es de­scrip­tion

The col­or of the so­lu­tion changes from red to blue and back be­cause of the ox­i­da­tion-re­duc­tion re­ac­tions tak­ing place in the so­lu­tion. The iron in the fer­roin re­acts with potas­si­um bro­mate and changes from ox­i­da­tion state +2 (red col­or – fer­roin) to ox­i­da­tion state +3 (blue col­or – fer­ri­in).

6[Fe(phen)₃]²⁺ + 6H₃O⁺ + КBrO₃ = 6[Fe(phen)₃]³⁺ + 9H₂O + КBr

Then the com­plex of iron +3 (blue col­or) ox­i­dizes the bro­mo­ma­lonic acid, trans­form­ing into the com­plex of iron +2 (red col­or).

4[Fe(phen)₃]³⁺ + BrCH(COOH)₂ + 7H₂O = 2CO₂↑ + 5H₃O⁺ + Br⁻ + HCOOH + 4[Fe(phen)₃]²⁺

The reagents are dis­trib­uted in the so­lu­tion un­even­ly, so the col­or changes in waves. Red-blue waves form in the so­lu­tion, like on the sur­face of wa­ter. The Be­lousov-Zhabotin­sky re­ac­tion is one of the most fa­mous chem­i­cal re­ac­tions in sci­ence, and many sci­en­tists and groups from dif­fer­ent sci­en­tif­ic dis­ci­plines all over the world have stud­ied it. Thou­sands and books have been pub­lished, and many doc­tor­al dis­ser­ta­tions have been de­fend­ed on the top­ic. The dis­cov­ery of the re­ac­tion es­sen­tial­ly gave im­pe­tus to the de­vel­op­ment of such branch­es of mod­ern sci­ence as syn­er­get­ics and the the­o­ry of dy­nam­ic sys­tems and de­ter­mined chaos.