Question

Write the equation for the reaction of Zinc metal/Zinc salt with each of the following

(i) Ammonium hydroxide

(ii) Sodium hydroxide and ${\mathrm{H}}_2$ is evolved

Answer 1

Part 1: Reaction with Ammonium hydroxide:-

1. Ammonium hydroxide is a weak base, as a result, it is written as Ammonia (${\mathrm{NH}}_3$) plus water.
2. Zinc interacts with ammonia to generate Zinc hydroxide, which dissolves with the addition of more ammonia.
3. $\underset{\mathrm{Zinc}\mathrm{ion}}{{\mathrm{Zn}}^{+2}\left(\mathrm{aq}\right)}+\underset{\mathrm{Ammonia}}{2{\mathrm{NH}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Zinc}\mathrm{hydroxide}}{\mathrm{Zn}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Ammonium}\mathrm{ion}}{2{{\mathrm{NH}}_4}^{+}\left(\mathrm{aq}\right)}$

Part 2: Reaction with Sodium hydroxide:-

1. When Sodium hydroxide combines with zinc, Sodium zincate, a salt, is formed, and hydrogen gas is released.
2. When Zinc is added to the solution, it rises to the surface and forms bubbles, indicating that gas has developed
3. $\underset{\mathrm{Sodiun}\mathrm{hydroxide}}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}+\underset{\mathrm{Zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}\to \underset{\mathrm{Sodium}\mathrm{zincate}}{2{\mathrm{NaZnO}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrogen}\mathrm{gas}}{{\mathrm{H}}_2\left(\mathrm{g}\right)(\uparrow )}$.

Therefore, the balanced equations are:-

1. $\underset{\mathrm{Zinc}\mathrm{ion}}{{\mathrm{Zn}}^{+2}\left(\mathrm{aq}\right)}+\underset{\mathrm{Ammonia}}{2{\mathrm{NH}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Zinc}\mathrm{hydroxide}}{\mathrm{Zn}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Ammonium}\mathrm{ion}}{2{{\mathrm{NH}}_4}^{+}\left(\mathrm{aq}\right)}$
2. $\underset{\mathrm{Sodiun}\mathrm{hydroxide}}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}+\underset{\mathrm{Zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}\to \underset{\mathrm{Sodium}\mathrm{zincate}}{2{\mathrm{NaZnO}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrogen}\mathrm{gas}}{{\mathrm{H}}_2\left(\mathrm{g}\right)(\uparrow )}$