A solution containing a mixture of metal cations was treated with dilute HCl and

Question

A solution containing a mixture of metal cations was treated with dilute HCl and no precipitate formed. Next, H2S was bubbled through the acidic solution. A precipitate formed and was filtered off. Then, the pH was raised to about 8 and H2S was again bubbled through the solution. A precipitate again formed and was filtered off. Finally, the solution was treated with a sodium carbonate solution, which resulted in no precipitation. Which metal ions were definitely present, which were definitely absent, and which may or may not have been present in the orginal mixture? Definitely present Definitely absentPossibly present

Explanation / Answer

Given that,

1) The solution of metal mixture on dil. HCl treatment donot form any ppt.

Test for Gr-I Basic radicals: If metal mixture solution trated with dil. HCl and ppt. forms (i.e. Halides of these radicals) then it indicates presence of Ag+ Pb+2 and Hg+ . But as no ppt. formed this indicates Absence of Ag+ Pb+2 and Hg+ (Hg2+2).

2) In this acidic solution if H2S is bubbled and ppt. formation occurs then this is (Gr.II Basic radical test) indicates the presence of Hg+2, Bi3+,Cd2+, Cu2+ (Gr-IIA) and As3+, Sb3+, Sn2+, Sn4+ (Gr-IIB). as these radical forms their sulphides and ppt. out from mixture and other remains in solution as their solubity product values are high.

As ppt. formation took place it indicates presence of, Hg2+, Bi3+, Cu2+, and Sn4+.

3) Now of the same metal mixture solution (remaining filtrate) is added with a base and the alkaline medium with pH 8 is made and this is (Gr-IV basic radical test) indicative of presence of Co2+, Ni2+, Zn2+, Mn2+. These basic radicals forms their sulphide which ppt. out from basic medium. This indicates presence of Ni2+, Zn2+.

4) Now the filtrate left over is basic and treated with Na2CO3(sodium carbonate) and no ppt. occurs. If ppt would have been appeared it is (Gr-V Basic radical test) indicative of Ba2+, Sr2+, Ca2+. But No ppt. formation indicates Absence of Ba2+ .

5)About the reamining basic radicals, Cr3+ (Gr-III Basic radical), and Na+, Mg2+ nothing can be said as the neccesarry reagent treatmment (NH4OH +NH4Cl) not given and no results or observation derived.

Hence Cr3+ (Gr-III Basic radical), and K+,and Mg2+ (Gr-VI) may or may not present.

Finally we can say,

Radicals Definitely present : Hg2+, Bi3+, Cu2+,Sn4+, Ni2+, Zn2+.

Radicals Definitely absent: Ag+ Pb+2 and Hg+ (Hg2+2), Ba2+

radicals May/ may not present:Cr3+ K+,and Mg2+

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