K953: Prep Notes

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.

Supplies

Short List

  •   Goggles and gloves
  •   190x100mm crystallizing dish
  •   600mL beaker
  •   100mL beaker
  •   Stirring rod
  •   Hot plate
  •   Thermometer
  •   Paper towels

Chemicals

  •   30g potassium sodium tartrate
  •   30mL of 30% hydrogen peroxide
  •   50mL of 0.4M CoCl2

Prior to Lecture  (prep time ~ 5 min.)

1.      Assemble the following equipment:

  1. 190x100mm crystallizing dish
  2. goggles
  3. gloves
  4.  paper towels
  5.   thermometer
  6.  hotplate
  7.  stirring rod
  8. 100mL beaker to display color of catalyst
  9. 600mL beaker for reaction

2.      Preparing the following chemicals:

  1. 30g potassium sodium tartrate in 400mL distilled water.
  2. 50mL of 0.4M CoCl2   (or 95.2g CoCl2.H2O/L)
  3. 30mL of 30% hydrogen peroxide

3.      At the start of lecture, set up a hot plate to about 135 oC. Place the potassium sodium tartrate in 600 mL beaker on the hot plate. The reaction works well if performed at 60 oC.

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 and Disposal

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