Introduction

Upon addition of hydrogen peroxide to Rochelle's salt (sodium potassium tartrate), the hydrogen peroxide decomposes and tartaric acid is oxidized.  This reaction proceeds very slowly at room temperature.  The addition of cobalt chloride as a catalyst produces a green cobalt-tartrate intermediate and copious evolution of oxygen and carbon dioxide.  The pink color of the regenerated catalyst is visible upon completion of the reaction.

HO2CCH(OH)CH(OH)CO2H + H2O2  →  HO2CCO2H + O2 + CO2

tartaric acid                             oxalic acid

 NOTE:  This reaction is not balanced --- other products are possible.

To Conduct Demonstration:

  1. Place the 600mL beaker containing 400mL of sodium potassium tartrate solution at 70oC into a large crystallizing dish on the overhead projector.NOTE:  The temperature must be very close to 70oC for the reaction to proceed at an appropriate rate. 60C works very well.
  2. Add 30mL of 30% hydrogen peroxide with stirring.  Point out that the reaction is proceeding very slowly if at all (no gas bubbles visible).
  3. Pour 50mL of 0.4M cobalt chloride solution into a beaker to demonstrate the color of the catalyst solution, then add it to the reaction mixture with stirring.
  4. Stand back!  The reaction will be vigorous and solution will overflow the beaker into the crystallizing dish if the temperature is high enough.  The green cobalt-tartrate activated complex will be visible for the duration of the reaction.
  5. Upon completion of the reaction, the solution will return to the pink color of the cobalt chloride catalyst, demonstrating that the catalyst was not consume in the reaction.

 Safety 

Goggles should be worn. Wear gloves when handling 30% hydrogen peroxide. Watch out for spattering during the catalyzed reaction.

Reference:

Summerlin and Ealy, Chemical Demonstrations: A Sourcebook for Teachers,1985.

Acknowledgment:

Margaret Asirvatham and Veronica Vaida, Spring 1991.