Oxidation / Reduction and lewis acid/base

[MCAT guy]

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• so CN- was listed in the purification of gold and it appears to be an oxidizing agent, but they just say it is a lewis base
  • Au + CN- + O2 + H2O --> Au(CN)2-

I had the reaction above with the following choices:

CN in the first reaction has the role of:

A. reducing agent
B. oxidizing agent
C. Lewis acid
D. Lewis base

this was in the electrochem chapter, I'm wondering why I can't say that it was an oxidizing agent, the correct answer being D. Au is oxidized here, but I guess CN is oxidized a bit too? The charge of AuCN2 is -1.

 

[loveoforganic]

Nothing is oxidized or reduced. You start with one gold (neutral) and two cyanides (-1 each for -2 total).

You end with Au(CN)2-. Gold is still in oxidation state 0 here. 0 + -2 = -2

The cyandies just act as ligands to complex the gold and make it soluble.