Potentiometry with an Oscillating Reaction

Principles of potentiometry are illustrated in a fascinating manner by oscillating reactions in which chemical concentrations oscillate between high and low values. An example is the Belousov-Zhabotinskii reaction  

During this reaction, the quotient [Ce ]/[Ce ] oscillates by a factor of 10 to 100. When the Ce concentration is high, the solution is yellow. When Ce predominates, the solution is colorless. 

To start the show, combine the following solutions in a 300-mL beaker  

160 mLof I.5MH2SO4 40 mL of 2 M malonic acid 30 mL of 0.5 M NaBrOa (or saturated KB1O3) 

4 mL of saturated ceric ammonium sulfate, Ce(S04 2 2(NH4)2S04 2H2O 

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