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Chemistry LibreTexts

Catalysts in Living Color

Chemical Concepts Demonstrated

  • Temperature's effect on reactions
  • Heat catalysis

Demonstration

  • Four beakers contain equal amounts of rochelle salt solution and 6% H2O2.
  • The beakers are heated to their respective temperature.
  • CoCl2 is added to each of the four beakers.
catalysts.gif

Observations

The beakers all change color from pink to green when the CoCl2 is added.  The solutions turn pink again, but at different times.  Typically, the beaker at 25C changes in 10 minutes, the beaker at 45C changes in 3 minutes, the beaker at 55C changes in 1 minute, and the beaker at 65C quickly flashes through the colors.

Explanation

Heat itself makes a fairly good catalyst in certain cases.  This demonstration can show this fact quite well.

CoCl2, in the presence of water, forms Co(H2O)62+, which is pink.  In the presence of both H2Oand tartrate ion, a green cobalt-tartrate-peroxide complex is formed, which can formally be assumed to contain Co(III).  With time, the Co(III) oxidizes one of the tartrate ligands to COand is itself reduced to Co2+; at this point, the pink color of the solution returns.  The rate at which the pink color returns depends on the temperature.

Contributors

  • Dr. George Bodner