Question

Write the balanced chemical equation for the following reaction.

(a) Zinc is heated with sodium hydroxide solution.

Answer 1

Zinc$\left(\mathrm{Zn}\right)$ is an amphoteric metal that on heating with sodium hydroxide solution $\left(\mathrm{NaOH}\right)$ liberates hydrogen gas $\left({\mathrm{H}}_2\right)$ with the formation of sodium zincate $\left({\mathrm{Na}}_2{\mathrm{ZnO}}_2\right)$.

The skeleton reaction is as follows:

$\mathrm{Zn}\left(\mathrm{s}\right)+\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}_2{\mathrm{ZnO}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\uparrow$

In the above unbalanced reaction, there are $2$ sodium $\left(\mathrm{Na}\right)$ atoms on the product side while $1$ sodium atom on the reactant side. So, to write complete a balanced reaction one must add a stoichiometric coefficient of $2$ in front of $\mathrm{NaOH}$. This will balance the other atoms too. Thus, the balanced chemical equation will be as follows:

$\mathrm{Zn}\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\stackrel{\mathrm{Heat}}{\to }{\mathrm{Na}}_2{\mathrm{ZnO}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\uparrow$