Chapter 17 Principles of Chemical Reactivity: Other Aspects of Aqueous Equilibria - 17-6 Equilibria Involving Complex Ions - Review & Check for Section 17-6 - Page 672: 1

B

First, assume all iron goes to the complex form: $[Fe(CN)_6^{4-}]=0.0025\ mol/1.0\ L=0.0025\ M$ $[CN^-]=0.500\ M-6\dot{}0.0025=0.485\ M$ Then assume that some of the complex ion dissociates: $Fe(CN)_6^{4-}\leftrightarrow Fe^{2+}+6\ CN^-$ $1/Kf=[Fe^{2+}][CN^-]^6/[Fe(CN)_6^{4-}]$ $1/10^{35}=[Fe^{2+}]\dot{}0.485^6/0.0025$ $[Fe^{2+}]=1.92\dot{}10^{-36}\ M$