why is potassium iodide a good catalyst of hydrogen peroxide?
Tuesday, February 23rd, 2010 at
5:00 PM
i did the experiment "elephants toothpaste" or "foam column" with potassium iodide as the catalyst.
why did it work as a catalyst?
any info would be useful!
thanks
Filed under: Potassium Questions
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The mechanism of catalysis involves the I- ion only.
The mechanism is: H2O2 + I- –> IO- + H2O, then
H2O2 + IO- –> I- H2O O2
Second step regenerates the I- ion (thus acts as a catalyst). This reaction is first order with regard to both H2O2 and I-.
Notably exothermic reaction.
Must be in a medium which allows formation of I-, ie dissociation of KI. Water is a wonderful example. So we use a 30% H2O2 solution in the elephant toothpaste reaction, the ordinary household 3% H2O2 is too slow and not at all impressive.
Regarding why it worked…. it worked as a catalyst because it got involved in the process and immediately was regenerated so it never got consumed in the overall reaction. It also acted as a catalyst because of the spontaneous exothermic reaction it engaged in with the H2O2 so you could say it "sparked" the decomposition (foaming) reaction. The addition of the soap to the "toothpaste" is what the "foam" was.