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Chemistry LibreTexts

Catalysts in Living Color

  • Page ID
    2972
  • 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 25o C changes in 10 minutes, the beaker at 45o C changes in 3 minutes, the beaker at 55o C changes in 1 minute, and the beaker at 65o C 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 H2O2 and 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 CO2 and 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