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Demonstration Experiment on Video

Belousov-Zhabotinsky-Reaction

Objective: Mechanism of an Oscillating Reaction

Peter Keusch




German version




Chemicals:
malonic acid
potassium bromate
potassium bromide
conc. sulfuric acid
ferroin solution


Ferroin solution:  0.35 g of ferrum sulfate heptahydrate and 0.88 g of 1.10-phenanthroline hydrochloride are dissolved in 35 ml dist water. The solution is made up to 50 mL with dist. water.


Apparatus and glass wares:
magnetic stirrer
magnetic stirring bar
stirring bar remover
crystallizing dish d = 115 mm, h = 65 mm
beaker 50 mL
4 beakers 100 mL
measuring cylinder 100 mL


Hazards and safety precautions:

Potassium bromate is a strong oxidizer - contact with combustible materials may cause fire. Harmful if swallowed. Possible human carcinogen. Eye, skin and respiratory irritant.
Conc. sulfuric acid is highly toxic. Causes severe burns.
Malonic acid is harmful if swallowed, inhaled or absorbed through the skin. High concentrations are very destructive of mucous membranes.

Safety goggles and protective gloves must be worn. Effective ventilation!


Experimental procedure:

Four solutions are prepared:
Solution A:   6.75 g of KBrO3 in 80 mL of dist. water
Solution B:   15.6 g of malonic acid in 100 mL of dist. water
Solution C:   1.3 g of KBr in 70 mL of dist. water
Solution D:   14 mL of conc. H2SO4 in of 65 mL dist. water. The mixture is allowed to cool to room temperature.

The four solutions are poured into a crystallizing dish containing 400 mL of dist. water while stirring on a magnetic stirrer. After the yellow-brown color (bromine) has disappeared, 2 mL of ferroin solution are added to the mixture.


Result:

Ferroin-indicator added creates a red color. After approximately 75 seconds the color of the solution turns to a blue, that will disappear after a short time and a red color will appear again. Thus the color oscillates between red and blue.











   

Video clip
(Download RealPlayer .rm Datei)


Discussion:

Casey R. Gray: An Analysis of the Belousov-Zhabotinskii Reaction


Reference:
  Demonstration Experiment on Video   Briggs-Rauscher Oscillating Reaction


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