QUALITATIVE ANALYSIS OF CATIONS

In a laboratory environment, the method of qualitative analysis of cations is often required. The objective of qualitative analysis is to separate and identify the cations present in an unkonwn solution. Cations are first separated into five main groups depending on their solubilities  

Group I contains Ag , Pb and Hg ions. These cations form precipitates by adding HCl. 

Group II includes Bp+, Cu , Sn, Hg, Sb8+, and Cd ions. They give insoluble sulfides by adding H2S to the solution. 

Group III cations form more soluble sulfides than those in group 11. Thus, they don t precipitate in an acidic medium. After the addition of OH ions hydroxides of the following ions will precipitate Ni, Ca, Fe, Mn2+, Zn, AP , Cr . 

Group IV. So far, all the cations have been precipitated. Ca, Ba, Mg ions in the solution need to be extracted through the formation of insoluble compounds with CO ions. 

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Experiment 14 Separation and Qualitative Analysis of Cations and Anions... 

Chatteijee R, Dey AK (1967) Schematic qualitative analysis of cations by the ring oven technique. Microchem J 12 151-156. 

Separation and qualitative analysis of cations and anions test tubes, beaker, evaporating dish, funnel, watch glass, mortar and pestle, centrifuge, Pt or Ni test wire... 

Note that the qualitative analysis of cations by selective precipitation involves all the types of reactions we have discussed and represents an excellent application of the principles of chemical equilibrium. 

Another step in the qualitative analysis of cations (see Exercise 28) involves precipitating some of the metal ions as the insoluble sulfides (followed by subsequent treatment of the mixed sulfide precipitate to separate the individual ions). Write balanced net ionic equations for the reactions of Co(ll), Co(lll), Fe(ll), and Fe(lll) ions with sulfide ion,... 

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