Question

hint: 5 rans use 3, lworth 5pts). solution that is .500 molar HCN, K= 6.2 x 10-10, is in equilibrium with solid silver (1) de, Ksp = 2.2 x 10-16. However, it is known that silver (1), Ag, can complex under certain ons with CN to produce the silver (1) dicyano complex, [Ag(CN)2]', log Kr=20.48. what are all of the equilibrium reactions that are occurring in this solution? Is there a single overall reaction that can describe the equilibria in this solution?

Answer 1

The equilibrium reactions happening in this system are:

• Acid-base equilibrium of HCN:

$HCN_{(aq)}\leftrightharpoons H^{+}_{(aq)}+CN^{-}_{(aq)}$

• The precipitation equilibrium of AgCN, which is actually composed of two equilibriums:

$AgCN_{(s)}\leftrightharpoons AgCN_{(aq)}$

$AgCN_{(aq)}\leftrightharpoons Ag_{(aq)}^{+}+CN_{(aq)}^{-}$

And the complexation equilibrium:

$Ag_{(aq)}^{+}+2CN_{(aq)}^{-}\leftrightharpoons Ag(CN)_{2(aq)}^{-}$

(Of course, the autoionization of water is an ubiquitous equilibrium in all aqueous systems):

$H_{2}O_{(l)}\leftrightharpoons H^{+}_{(aq)}+OH^{-}_{(aq)}$

A single reaction that could sum all of the equilibriums would be:

$2AgCN_{(s)}+CN^{-}_{(aq)}+H^{+}_{(aq)}\leftrightharpoons Ag(CN)_{2,(aq)}^{-}+HCN+Ag^{+}$