Find the composition of a saturated solution of AgCN containing 0.10 M KCN adjusted to pH 12.00 with NaOH. Consider the following equilibria and use Davies activity coefficients.


Suggested procedure: Let [CN-] be the master variable. We know [H+] from the pH, and we can find [Ag+] = Ksp /[CN-]. (i) Use equilibrium expressions to find [OH-], [HCN], [AgOH],
[Ag(OH)(CN)'], [Ag(CN)-2 ], and [Ag(CN)32-] in terms of [CN-], [Ag+], and [H+]. (ii) Key mass balance: {total silver} + [K+] = {total cyanide}. (iii) Guess that ionic strength = 0.10 M and compute activity coefficients. (iv) Compute . (v) Guess a value of [CN-] and compute the concentrations of all species in the mass balance. (vi) Use Solver to vary [CN-] to satisfy the mass balance. (vii) Compute [Na] from the charge balance. (viii) Compute the ionic strength and perform several iterations of the entire process until the ionic strength no longer changes.