Question

Q13. Which one of the following salt solution on reaction with excess of ammonium hydroxide gives a deep blue solution?

• A. ${FeCl}_3\left(aq\right)$
• B. ${CuSO}_4\left(aq\right)$
• C. ${Al}_2{\left({SO}_4\right)}_3\left(aq\right)$
• D. ${ZnSO}_4\left(aq\right)$

Answer 1

The correct option is B

${\mathrm{CuSO}}_4\left(\mathrm{aq}\right)$

Explanation for the correct option:

Iron(III) Chloride solution $FeC{l}_3\left(\mathrm{aq}\right)$ reacts with Ammonium Hydroxide ${\mathrm{NH}}_4\mathrm{OH}$ to give a reddish brown precipitate of Ferric hydroxide $\mathrm{Fe}{\left(\mathrm{OH}\right)}_3$.

${\mathrm{FeCl}}_3\left(\mathrm{s}\right)+3{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{l}\right)\to \mathrm{Fe}{\left(\mathrm{OH}\right)}_3\downarrow \left(\mathrm{s}\right)+3{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{l}\right)$

Explanation for the incorrect options:

Copper(II) Sulphate solution ${\mathrm{CuSO}}_4\left(\mathrm{aq}\right)$ reacts with Ammonium Hydroxide ${\mathrm{NH}}_4\mathrm{OH}$ to give a deep blue solution.

$$\begin{gathered} {\mathrm{CuSO}}_4\left(\mathrm{s}\right)+2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{l}\right)\to \mathrm{Cu}{\left(\mathrm{OH}\right)}_2\downarrow \left(\mathrm{s}\right)+{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4\left(\mathrm{l}\right) \\ \mathrm{Cu}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)+{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4\left(\mathrm{l}\right)+\underset{\mathrm{Tetramine}\mathrm{copper}\mathrm{sulphate}\{\mathrm{deep}\mathrm{blue}\}}{\underset{\mathrm{excess}}{2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{l}\right)}\to \left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]{\mathrm{SO}}_4\left(\mathrm{s}\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)} \end{gathered}$$

Aluminium Sulphate solution ${\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3\left(\mathrm{aq}\right)$ reacts with Ammonium Hydroxide ${\mathrm{NH}}_4\mathrm{OH}$ to give a colourless solution.

Zinc Sulphate solution ${\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)$ reacts with Ammonium Hydroxide ${\mathrm{NH}}_4\mathrm{OH}$ to give a white gelatinous solution.

Hence option (b) is correct.