Question

Consider the insoluble compound nickel(II) carbonate , NiCO3 . The nickel ion also forms a complex with cyanide ions . Write a balanced net ionic equation to show why the solubility of NiCO3 (s) increases in the presence of cyanide ions and calculate the equilibrium constant for this reaction. For Ni(CN)42- , Kf = 1.0×1031 . Use the pull-down boxes to specify states such as (aq) or (s). + + K =

Answer 1

balanced equation :

NiCO_3(s) + 4CN^-_(aq) -------> Ni(CN)₄^2-_(aq) + CO₃^2-_(aq)

NiCO_3(s) <----------> Ni²⁺_(aq) + CO₃^2-_(aq) Ksp = 1.3x10^-7

Ksp = [Ni²⁺][CO₃^2-]

net ionic equation :

Ni²⁺_(aq) + 4CN^-_(aq) -------> Ni(CN)₄^2-_(aq)

Kf = [Ni(CN)₄^2-] / [Ni²⁺][CN^-]⁴ = 1x10³¹

the balanced reaction we have:

NiCO_3(s) + 4CN^-_(aq) -------> Ni(CN)₄^2-_(aq) + CO₃^2-_(aq)

Kc = [Ni(CN)₄^2-] [CO₃^2-] / [Ni²⁺][CN^-]⁴

Kc =  ([Ni(CN)₄^2-] / [Ni²⁺][CN^-]⁴) *  [Ni²⁺][CO₃^2-]

Kc = Kf x Ksp

Kc = 1x10³¹ x 1.42 x10^-7

Kc = 1.4 x10²⁴

equilibrium constant Kc = 1.4 x10²⁴