Chapter 17, Problem 17.140MP

Gold metal is extracted from its ore by treating the crushed rock with an aerated cyanide solution. The unbalanced equation for the reaction is

     $\text{Au}\left(s\right)+{\text{CN}}^{-}\left(aq\right)+{\text{O}}_2\left(g\right)\to \text{Au}{\left(\text{CN}\right)}_2{}^{-}\left(aq\right)$

1. (a) Balance the equation for this reaction in basic solution.
2. (b) Use any of the following data at 25 °C to calculate Δ G° for this reaction at 25 °C: K_f for Au(CN)₂^– = 6.2 × 10³⁸, K_a for HCN = 4.9 × 10^–10, and standard reduction potentials are

     $\begin{array}{l}{\text{O}}_2\left(g\right)+4{\text{H}}^{+}\left(aq\right)+4{\text{e}}^{-}\to 2{\text{H}}_2\text{O}\left(l\right)E^{\circ }=1.229\text{ V}\\ {\text{ Au}}^{3+}\left(aq\right)+3{\text{ e}}^{-}\to \text{Au}\left(s\right)E^{\circ }=1.498\text{ V}\\ {\text{ Au}}^{3+}\left(aq\right)+2{\text{ e}}^{-}\to {\text{Au}}^{+}\left(aq\right)E^{\circ }=1.401\text{ V }\end{array}$