Chemistry - Salt Analysis Question with Solution | TestHub

Question Explanation:

Identify the mixture of cations that can be separated by adding excess ${\mathbf{NH}}_3$ solution.

Concept:

Ammonia Complex Formation and Precipitation.

Solution:

Separation by excess ${\mathrm{NH}}_3$ requires one ion to precipitate (insoluble hydroxide) and the other to dissolve (ammonia complex).

(1) Zn (Dissolves as $[\mathrm{Zn}({\mathrm{NH}}_3{)}_4{]}^{2+}$). Mn²⁺ (Precipitates as $\mathrm{Mn}(\mathrm{OH}{)}_2$). 

(2) Both ${\mathrm{Zn}}^{2+}$ and ${\mathrm{Cd}}^{2+}$ form soluble complexes in excess ${\mathrm{NH}}_3$ solution.

(3) ${\mathrm{Zn}}^{2+}$ form soluble complex while ${\mathrm{Pb}}^{2+}$ precipitates out as $\mathrm{Pb}(\mathrm{OH}{)}_2$.

(4) Zn²⁺ (Dissolves as $[\mathrm{Zn}({\mathrm{NH}}_3{)}_4{]}^{2+}$), Cu²⁺ (Precipitates as $[\mathrm{Cu}({\mathrm{NH}}_3{)}_4{]}^{2+}$).