Analysis of group 1 cations

Silver identification tests

1) Reaction with diluted nitric acid HNO3 

Taking advantage of a simple acid-base reaction, the silver is moved in solution from its complex with the ammonia and the value of the concentration of [Ag +] in solution make exceed the value of the Kps of the silver chloride (Ksp = [Ag+][Cl-]). Basically, the nitric acid gives a proton to ammonia shifting the equilibrium of the complex Ag (NH3)2+ toward its dissolution:reaction

2) Reaction with potassium iodide (KI)

This assay (not surprisingly) is basically the same that we have shown to identify Pb2+. The silver that we suppose to identify is in the form of amine complex. Adding potassium iodide (a very soluble salt) we have precipitation of silver iodide, very similar to lead iodide but even less soluble. And right because of its great insolubility (very low Ksp, around 10-16) we get the precipitate even adding KI to the solution containing amine complex. Actually, the concentration of Ag+ left free from the complex of diamine silver is enough to exceed the value of the Ksp for silver iodide (at the same time the dissolution equilibrium of amine complex moves to the right, so that virtually all Ag+ is released from the complex and precipitated as AgI).

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