Question

Write the equations for the reaction of zinc with each of the following:
(a) sodium hydroxide solution.
(b) dilute sulphuric acid.
(c) copper sulphate solution.

Answer 1

(a) Zinc reacts with an aqueous solution of sodium hydroxide and forms sodium hydroxy zincate, with the evolution of hydrogen gas.

$$\begin{gathered} \mathrm{Zn}+2\mathrm{NaOH}+2{\mathrm{H}}_2\mathrm{O}\stackrel{}{\to }{\mathrm{Na}}_2\mathrm{Zn}(\mathrm{OH}{)}_4+{\mathrm{H}}_2 \\ \mathrm{Zinc}\mathrm{Sodium}\mathrm{hydroxide}\mathrm{Solu}.\mathrm{Sodium}\mathrm{hydroxy}\mathrm{zincate}\mathrm{Hydrogen}\mathrm{gas} \end{gathered}$$

(b) Because zinc is more reactive than hydrogen, it reacts with dilute sulphuric acid and the displaced hydrogen from the acid, forming zinc sulphate and liberating hydrogen gas.

$$\begin{gathered} \mathrm{Zn}+{\mathrm{H}}_2{\mathrm{SO}}_4\stackrel{}{\to }{\mathrm{ZnSO}}_4+{\mathrm{H}}_2 \\ \mathrm{Zinc}\mathrm{Sulphuric}\mathrm{acid}\mathrm{Zinc}\mathrm{sulphate}\mathrm{Hydrogen}\mathrm{gas} \end{gathered}$$

(c) Because zinc is more reactive than copper, it displaces copper from its salt solution. On adding zinc, the blue colour of copper sulphate solution becomes colourless and a reddish brown copper metal is formed.

$$\begin{gathered} \mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\stackrel{}{\to }{\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+\mathrm{Cu}\left(\mathrm{s}\right) \\ \mathrm{Zinc}\mathrm{Copper}\mathrm{sulphate}\mathrm{Zinc}\mathrm{sulphate}\mathrm{Copper} \end{gathered}$$