Question

What is the equilibrium constant for the reaction of AgCl(s) with concentrated HCN? The Ksp of AgCl is 1.8 × 10−10 and the Kf of Ag(CN)2− is 1.0 × 1021.

Answer 1

The equilibrium constant for a reaction is simply the product of the solubility constant of the solute and the formation constant of the product, that is:

Keq = Ksp * Kf

Keq = 1.8 × 10^−10 * 1.0 × 10^21

Keq = 1.8 x 10^11

Answer 2

We have to determine equilibrium constant for given reaction

AgCl (s)  + 2HCN ---> Ag(CN)⁻²  + 2HCl    K = ?    ..............  (i)

We are provided with

AgCl  ---> Ag⁺  + Cl⁻   Ksp = 1.8 X 10⁻¹⁰   .................(ii)

Ag⁺ + 2CN⁻  --------> Ag(CN)⁻²    Kf= 1 X 10²¹   ...........(iii)

we can obtain equation (i) from (ii) and (iii) as

K = Kf X Ksp

K =  1 X 10²¹ X 1.8 X 10⁻¹⁰ = 1.8 X 10¹¹