Chemistry - Salt Analysis Question with Solution | TestHub

Question Explanation:

${\mathrm{HNO}}_3$ oxidizes ${\mathrm{Fe}}^{2+}$ to ${\mathrm{Fe}}^{3+}$ (Group III) and removes the Group II precipitating reagent $\left({\mathrm{H}}_2\mathrm{S}\right)$.

Concept:

Group III Pretreatment.

Solution:

The Group II filtrate must be boiled to remove the excess ${\mathrm{H}}_2\mathrm{S}$.

Then, a few drops of concentrated ${\mathrm{HNO}}_3$ are added and the solution is boiled again to ensure that all ${\mathrm{Fe}}^{2+}$ (which would be precipitated in Group IV) is oxidized to ${\mathrm{Fe}}^{3+}$ so it precipitates completely as $\mathrm{Fe}(\mathrm{OH}{)}_3$ in Group III.

Final Answer: Options (B & D)

After boiling 2-3 drops of ${\mathrm{HNO}}_3$ is added and boiled again.

Group II filtrate has to be boiled first and then after adding 2,3 drops of conc. ${\mathrm{HNO}}_3$, it is boiled again to remove ${\mathrm{S}}^{2-}$ (group II reagent).