Hi, I was curious.

 

In chemistry class we did a lab involving an aqueous solution of hydrogen peroxide being catalyzed with potassium iodide to decompose. The solution turned yellow. Why is that?

The iodine in the potassium iodide makes it yellow, I think. Don't quote me on that, though.

 

Ok thanks for the info XD

The KI is not *catalyzing* the decomposition of the H2O2. It is being oxidized to yield I2, which is the source of the brown color. This reaction is a stoichiometric redox and it is the basis for most quantitative redox titrations (usually using starch as an indicator).

 

Catalytic decomposition of peroxide can be seen with enzymes (see catalase) or metals (Fe, Mn, W). Here, a small trace of the catalyst will, over time eventually lead to the near complete exhaustion of the peroxide (decisively non-stoichiometric).

 

For example, peroxide plus Mn yields oxidized Mn and O2 (sometimes quite vigorously); Fe2+ yields -OH, .OH and Fe3+, and W is used in the titrimetric assay for H2O2.

 

Cheers,

 

O3

The KI is not *catalyzing* the decomposition of the H2O2. It is being oxidized to yield I2, which is the source of the brown color.

 

If it yields I2, can the Iodine be separated from the solution through evaporation ?

 

Ken

Ah, sounds like those concepts are a bit beyond me right now ozone. But thanks for the reply. *will now go look them up ^^; *