In gold mining , cyanide solutions are often used to dissolve AuBr from ore samp
ID: 635174 • Letter: I
Question
In gold mining , cyanide solutions are often used to dissolve AuBr from ore samples. In the presence of cyanide ions, CN-, gold forms a soluble complex according to the following reaction: Au+ + 2CN- ? Au(CN)2-. The formation of this complex causes the AuBr in the ore to dissolve. The Au(CN)2- complex has a Kform = 2.0x1013 and the Ksp of AuBr is 5.0x10-13.
Write a balanced chemical equation for the dissolution of gold bromide in a sodium cyanide solution and calculate the overall equilibrium constant for this reaction
Explanation / Answer
4Au(s) + 8NaCN(aq) + O2(g) + 2H2O(l) ---->4NaAu(CN)2(aq) + 4NaOH(aq)
Given Kform = 2.0x1013
and the Ksp of AuBr is 5.0x10-13.,
Overall equilibrium constant for this reaction
as K = 4.0