Chemistry - Salt Analysis Question with Solution | TestHub

Question Explanation:

${\mathrm{Fe}}^{2+}$ is oxidized to ${\mathrm{Fe}}^{3+}$ (Group III) before precipitation, so the initial salt could contain ${\mathrm{Fe}}^{2+}$ or ${\mathrm{Fe}}^{3+}$.

Concept:

Group III Pretreatment $\left({\mathrm{Fe}}^{2+}\to {\mathrm{Fe}}^{3+}\right)$.

Solution:

The reddish-brown precipitate in Group III is $\mathrm{Fe}(\mathrm{OH}{)}_3$, indicating the presence of ${\mathrm{Fe}}^{3+}$.

Since the typical procedure before adding the Group III reagent involves adding ${\mathrm{HNO}}_3$ to oxidize all ${\mathrm{Fe}}^{2+}$ to ${\mathrm{Fe}}^{3+}$,

the original salt could have contained ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ both.

Final Answer: Options (1, $2\&3$ ) ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ both

In group III reagent, first we boil with little conc ${\mathrm{HNO}}_3$ which converts ${\mathrm{Fe}}^{+2}$ to ${\mathrm{Fe}}^{+3}$, so if we obtain ${\mathrm{Fe}}^{+3}$, it may be $+2,+3$ or both.