Question

Write the balanced chemical equation for the following reaction.

(b) Zinc oxide dissolves in sodium hydroxide

Answer 1

Zinc oxide $\left(\mathrm{ZnO}\right)$ is an amphoteric metal oxide that reacts with sodium hydroxide $\left(\mathrm{NaOH}\right)$ to form sodium zincate $\left({\mathrm{Na}}_2{\mathrm{ZnO}}_2\right)$ and water $\left({\mathrm{H}}_2\mathrm{O}\right)$.

The skeleton reaction is as follows:

$\mathrm{ZnO}\left(\mathrm{aq}\right)+\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}_2{\mathrm{ZnO}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

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 a complete 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 is as follows:

$\mathrm{ZnO}\left(\mathrm{aq}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}_2{\mathrm{ZnO}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$