Question

In Gr (V), ${\left( {N{H_4}} \right)_2}C{O_3}$ is added to precipitate out carbonates. What happens when $N{a_2}C{O_3}$ is added instead of ${\left( {N{H_4}} \right)_2}C{O_3}$ ?
(A) $CaC{O_3}$ will be soluble in $N{a_2}C{O_3}$
(B) $MgC{O_3}$ will be precipitated out
(C) $N{a_2}C{O_3}$ will increase the solubility of fifth group carbonates
(D) Both (A) and (B)

Answer 1

The salt analysis for the basic radicals (cationic part of salt) and acid radicals (anionic part of salt) is done separately. The basic radicals are divided into various groups on the basis of their chemical properties and solubility. Each group has a different group reagent which helps the basic radicals to separate out in the form of their insoluble salt.

Complete answer:
We know that the salt analysis for the basic radicals (cationic part of salt) and acid radicals (anionic part of salt) is done separately. The basic radicals are divided into various groups on the basis of their chemical properties and solubility in group reagents. Every group have different set of reagents known as group reagents which help the basic radicals to separate out in the form of their insoluble salt.
The group V basic radicals are $C{a^{2 + }},B{a^{2 + }}$ and $S{r^{2 + }}$ .
Now, the group V reagent is ${\left( {N{H_4}} \right)_2}C{O_3}$ in presence of $N{H_4}Cl$ . If we use $N{a_2}C{O_3}$ instead of ${\left( {N{H_4}} \right)_2}C{O_3}$ then, due to the high ionization of $N{a_2}C{O_3}$ the concentration of $CO_3^{2 - }$ ions increase and hence, it will exceed the solubility of group V basic radicals as well as that of $M{g^{2 + }}$ . So, Magnesium (which is group VI cation) will also get precipitated in the form of its carbonate.
Hence, the correct option is (B) $MgC{O_3}$ will be precipitated out.

Note:
Each group has different group reagents in salt analysis such as group I is dilute HCl and group II is Hydrogen sulphide in presence of dil. HCl. For group III, it is $N{H_4}OH$ in presence of $N{H_4}Cl$ and for group IV it is Hydrogen sulphide in ammoniacal medium. For group V, the group reagent is ${\left( {N{H_4}} \right)_2}C{O_3}$ in presence of $N{H_4}Cl$ and for group VI it is $N{H_4}OH$ and $N{a_2}HP{O_4}$ .