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Letter 217
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(ie. CN- + H2O : : > OH- + HCN)?? This doesn't make since HCN : : > H+ + CN- as pH rises. Can someone tell me or describe why the KOH accumulates as gold is plated in an acid gold bath. I appreciate any comments. (This is probably a simple question; please excuse my ignorance) Thank-you Vaclav
Leshchenko |
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This phenomenon occurs with many acid baths, including those that do not contain cyanide. Nickel is a well known example, where boric acid is added to buffer the solution to try to minimize the effect.
It's the hydrolysis of water that causes it: 2H20 : : H2^ + 2OH-
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Please excuse this stupid question, but isn't cyanide a base??? I mean KAuCN is basic, is it not??? If so, then why do you refer to it as an acidic solution? Or am I just misinterpreting you answer?
Scott Ksobiech
Milwaukee WI
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- I know it sounds weird -- and it should sound dangerous if you have been properly warned about the danger of poisonous hydrogen cyanide gas evolving when acid and cyanide are mixed. But, yes, there are acid gold cyanide plating baths (as well as neutral gold cyanide and alkaline gold cyanide plating baths). The gold is so tightly bound to the cyanide that the cyanide does not independently participate in many chemical reactions. It is a 'radical' (along the lines of SO4) that tends to stay bonded together in most situations.
++++++ I was working in a company manufacturing nickel stampers.
There we used to do nickel electroforming. We used to put
boric acid in nickel baths because the temperature of the
solution near the cathode used to increase as a result of
which H-OH bond gets weak. And if this OH is not neutralised
by boric acid it used to combine with nickel forming burnt
deposits. Probably the same funda you can apply here. Anant Chavan
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