Question

What is the group reagent of V group? Why is it necessary to test for V group radicals in the order of $B{a^{2 + }},S{r^{2 + }}$ and $C{a^{2 + }}$ only?

Answer 1

In cation analysis, the cations that can be present in a mixture are divided into seven groups (zero to six) on the basis of the reagent used for their separation from a solution of the mixture. First of all, the original solution (O.S) is prepared to get the cations in solution form followed by their classification into groups.

Complete answer:
Group V cations are: $B{a^{2 + }},S{r^{2 + }},C{a^{2 + }}$
After the removal of group IV cations, it is necessary to concentrate the solution and remove the residual ${H_2}S$ gas. We have to evaporate the centrifugate from group four till its volume is reduced to one-fourth. We have to make this hot solution ammoniacal by addition of $N{H_4}OH$ followed by addition of saturated solution of ${(N{H_4})_2}C{O_3}$ . Formation of white precipitate indicates the presence of group V cations.
Thus , the reagent of group V cations is ${(N{H_4})_2}C{O_3}$ in the presence of $N{H_4}Cl$ and $N{H_4}OH$
It is necessary to test the group V cations in the order $B{a^{2 + }},S{r^{2 + }},C{a^{2 + }}$ only. This is because like $SrS{O_4}$, $BaS{O_4}$ is also insoluble in acetic acid and like calcium oxalate, $S{r^{2 + }}$ and $B{a^{2 + }}$ oxalates are also insoluble. As similar tests of $C{a^{2 + }}$ are given by $S{r^{2 + }}$ also. Thus, before confirming the presence of $S{r^{2 + }}$we have to show the absence of $B{a^{2 + }}$ and before confirming the presence of $C{a^{2 + }}$we need to confirm the absence of $B{a^{2 + }},S{r^{2 + }}$ .

Note:
It should be noted that the cations of group V are precipitated in the form of carbonates by adding ${(N{H_4})_2}C{O_3}$ solution to their hot ammoniacal solution in presence of a little $N{H_4}Cl$. The addition of $N{H_4}Cl$ is mandatory but if it is present in excess amount , the precipitation of group V cations is not complete.