6th edition, 14.119

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Hai-Lin Yeh 1J
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6th edition, 14.119

Postby Hai-Lin Yeh 1J » Sat Mar 09, 2019 9:52 pm

One stage in the extraction of gold from rocks involves dissolving the metal from the rock with a basic solution of sodium cyanide that has been thoroughly aerated. This stage results in the formation of soluble Au(CN)2- ions. The next stage is to reduce gold to the metal by the addition of zinc dust, forming Zn(CN)42-. Write the balanced equations for the half- reactions and the overall redox equation for both stages.

Can someone explain how to write the half-reactions and the overall redox equation for both stages? I don't understand how they decided which reaction they decided to use for oxidation & reduction.

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Re: 6th edition, 14.119

Postby Chem_Mod » Sun Mar 10, 2019 10:18 pm

In the first stage, Au becomes Au(CN)2 - in the anode and O2 + H2O become OH- in the cathode,
In the second stage, Zn becomes Zn(CN)4 2- in the anode and Au(CN)2- becomes Au in the cathode.

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