Silver chloride has a Ksp value of 1.8 x 10-10. The solubility can be increased (AgCl can be dissolved) by adding NH3 which will complex with Ag+ ions to form Ag(NH3)2+. The equation for the formation of Ag(NH3)2+ from AgCl(s) is:
When NH3 is added to a saturated solution of AgCl there are two reactions that are competing for the Ag ions in equilibrium with the reactions listed below. The large Kf value for the formation of Ag(NH3)2+ makes it possible for NH3 to remove Ag+ ions in equilibrium with AgCl(s). The equations add as follows:
The Keq for the dissolving of AgCl with NH3 is equal to Kf x Ksp = Keq or 1.0 x 108 x 1.8 x 10-10 = 1.8 x 10-2. The Keq expression for the overall reaction is written as
Consider a case where the NH3 concentration is 1.0 M. To solve for the concentration of Ag+ in solution let x = Ag(NH3)2+, x = Cl- and let 2x = NH3 that has reacted.
Taking the square root of both side gives x/1-2x = 0.13 and then solving for x, we obtain 0.10 moles/L. The concentration of the complex ion Ag(NH3)2+ in equilibrium with AgCl(s) indicates that silver choride has considerable solubility in 1 M NH3.
