Analytical Chemistry — Question 5

(a) When hot concentrated caustic soda solution is added to zinc, soluble salt of sodium zincate [Na₂ZnO₂] is formed and hydrogen gas is liberated.

The balanced equation is:

$\text{Zn} + \underset{\text{hot and conc.}}{2\text{NaOH}} \longrightarrow \underset{\underset{\text{colourless}}{\text{sodium zincate}}}{\text{Na}_2\text{ZnO}_2} + \text{H}_2↑$

(b) When hot concentrated caustic soda solution is added to aluminium, soluble salt of sodium meta aluminate [NaAlO₂] is formed and hydrogen gas is liberated.

$2\text{Al} + 2\text{NaOH} + 2\text{H}_2\text{O} \longrightarrow \underset{\underset{\text{colourless}}{\text{sodium meta aluminate}}}{2\text{NaAlO}_2} + 3\text{H}_2↑$