Question

Leaching of gold with dilute aqueous solution of $NaCN$ in presence of oxygen gives complex [A], which on reaction with zinc forms the elemental gold and another complex [B]. [A] and [B], respectively are :

Answer 1

Cyanide process which is also known as the Macarthur-forest process is widely used in extracting gold or silver from the ores by dissolving them in a dilute solution of potassium cyanide or sodium cyanide.

During leaching the following reactions take place:
$4Au+8C{N}^{–}+2H_{2}O+O_2\to 4\left[Au\right(CN{)}_2{]}^{–}+4O{H}^{–}$
$2\left[Au\right(CN{)}_2{]}^{–}+Zn\to \left[Zn\right(CN{)}_4{]}^{2–}+2Au$