Redox and redox equilibria
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In the iodine clock reaction, are copper 2+ ions used as copper is in the d-block and it has a split d-shell, so electrons can jump between the two?
Igloo writes ...
Most metal ions in the d-block do have incomplete d-shells, but the "split shell transitions" to which you refer are not responsible (they are linked with colour instead). Many of their reactions are to do with the fact that they are able to lose or gain d-electrons relatively easily to form ions with different charges. In the case of copper(II) ions, the structure is 4s03d9 (incomplete d-shell, hence coloured blue), but, by gain of one electron they are reduced to copper(I) ions with a structure of 4s03d10 (filled d-shell - hence colourless). This isn't a d-d shell transition, of course. It involves a complete gain of one electron from an external source, e.g. from I- as they are oxidised to I2.
In the reaction between Cu2+ and I-, the products are I2 and solid CuI, since copper(I) ions are unstable in solution and precipitate out with the iodide ions. I am not sure why you are calling this an iodine clock, since it takes place almost instantaneously and the copper(II) ions are certainly not catalysts, since they are permanently destroyed as I have explained.
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updated: 23 February 2007
