Experiment 5 - Qualitative Analysis

Objectives - To study the chemical properties of the three cations: Pb²⁺, Hg₂²⁺ and Ag⁺ and then use these properties to separate and identify which of these cations are present in an unknown solution.

Introduction

There are about 25 cations, which are commonly examined. From this group only three (Pb²⁺, Hg₂²⁺ and Ag⁺) form water insoluble chlorides. This chemical property is used as a basis for separating them from other cations. Differences in the chemical properties of the individual ions are then used as a basis for separation and identification.

If a solution contains several cations, it is possible to select a reagent that will form an insoluble product with one of the cations and not with the others. A technique known as centrifuging separates the precipitated cations (i.e. the solid) from the remaining ions in the solution. The solution, or known as the supernate, is then poured off and the analysis continues for the remaining cations in the solution.

Click on the following links and study the net ionic equations for the reactions you will observe:

1. Pb²⁺ ions reactions
2. Ag⁺ ions reactions
3. Hg₂²⁺ ions reactions

View the flow diagram which summarizes the analysis procedure that you will follow for the unknown solution.