A number of slightly soluble salts do not dissolve readily in acids. eg. AgCl will not dissolve in nitric acid. In order to dissolve AgCl, the equilibrium of AgCl(s) <=====> Ag+(aq) + Cl-(aq) must be shifted to the right. Two things can do this: NH3 or CN- form co-ordinate bonds with the Ag+ ions and remove them from the solution. They create complex ions that are even more insoluble then the original AgCl. The ammonia solution has Ag(NH3)2+ in it, and the cyanide solution has the Ag(CN)2- ion in it. These two polyatomic ions are weakly dissociated. The part of the ion which attaches by a co-ordinate bond is called a ligand. eg. AgCl(s) + 2 NH3(aq) <======> Ag(NH3)2+(aq) + Cl-(aq) AgCl(s) + 2 CN-(aq) <=======> Ag(CN)2- + Cl-(aq)
