Question

Q2.

(a) Name a yellow monoxide that dissolves in hot and concentrated alkali. Give equation

(b) Name a white insoluble oxide that dissolves when fused with caustic soda or caustic potash.

(c) What is the reaction of freshly precipitated aluminium hydroxide with caustic soda solution? Give equation.

(d) Identify the blue solution that turns deep blue on addition of excess of ${\mathrm{NH}}_4\mathrm{OH}$.

(e) Name the hydroxide which is soluble in excess of ammonium hydroxide.

Answer 1

(a) Lead oxide is the yellow monoxide that dissolves in hot and concentrated alkali. The reaction:

$\underset{\mathrm{lead}\mathrm{oxide}}{\mathrm{PbO}}+\underset{\mathrm{sodium}\mathrm{hydroxide}}{2\mathrm{NaOH}}\to \underset{\mathrm{sodium}\mathrm{plumbate}}{{\mathrm{Na}}_2{\mathrm{PbO}}_2}+\underset{\mathrm{water}}{{\mathrm{H}}_2\mathrm{O}}$

(b) Auminium oxide is a white insoluble oxide that dissolves when fused with caustic soda or caustic potash.

The reaction of aluminium oxide $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ with caustic soda $\left(\mathrm{NaOH}\right)$ is

$\underset{\mathrm{aluminium}\mathrm{oxide}}{{\mathrm{Al}}_2{\mathrm{O}}_3}+\underset{\mathrm{caustic}\mathrm{soda}}{2\mathrm{NaOH}}\to \underset{\mathrm{sodium}\mathrm{aluminate}}{2{\mathrm{NaAlO}}_2}+\underset{\mathrm{water}}{{\mathrm{H}}_2\mathrm{O}}$

(c) When aluminium hydroxide is added with caustic soda we get a salt of sodium meta aluminate $\left({\mathrm{NaAlO}}_2\right)$

The reaction:

$\underset{\mathrm{aluminium}\mathrm{oxide}}{{\mathrm{Al}}_2{\mathrm{O}}_3}+\underset{\mathrm{caustic}\mathrm{soda}}{2\mathrm{NaOH}}\to \underset{\mathrm{sodium}\mathrm{aluminate}}{2{\mathrm{NaAlO}}_2}+\underset{\mathrm{water}}{{\mathrm{H}}_2\mathrm{O}}$

(d) The blue solution is Copper sulphate $\left({\mathrm{CuSO}}_4\right)$. The reaction is,

$\underset{\mathrm{copper}\mathrm{sulphate}}{{\mathrm{CuSO}}_4}+\underset{\mathrm{ammonium}\mathrm{hydroxide}}{2{\mathrm{NH}}_4\mathrm{OH}}\to \underset{\mathrm{copper}\mathrm{hydroxide}(\mathrm{deep}\mathrm{blue})}{\mathrm{Cu}{\left(\mathrm{OH}\right)}_2}+\underset{\mathrm{ammonium}\mathrm{sulphate}}{{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4}$

(e) Copper hydroxide $\left[\mathrm{Cu}{\left(\mathrm{OH}\right)}_2\right]$ is the hydroxide soluble in excess of Ammonium hydroxide.