Question

(a) (i) Explain, why only all glass apparatus should be used for the preparation of nitric acid by heating concentrated acid and potassium nitrate.
(ii) Write a chemical equation to illustrate the acidic nature of nitric acid.
(iii) Name the products formed when ammonium nitrate is heated.

Answer 1

(i) The preparation of nitric acid involves the use of concentrated sulphuric acid, which is heated with potassium nitrate. Also, vapours of nitric acid are formed during this reaction. Since all these chemicals are corrosive in nature, the use of glass apparatus is required.
(ii) Reactions depicting the acidic nature of nitric acid are given below:

Nitric acid converts basic metal oxides and hydroxides into nitrate salts. For example, consider the reactions stated below:

$$\begin{gathered} \mathrm{CaO}+2{\mathrm{HNO}}_3\to \mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Mg}{\left(\mathrm{OH}\right)}_2+2{\mathrm{HNO}}_3\to \mathrm{Mg}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{H}}_2\mathrm{O} \end{gathered}$$

Metal carbonates and bicarbonates are also converted to nitrate salts along with the evolution of carbon dioxide. For example, consider the reactions given below:

$$\begin{gathered} {\mathrm{PbCO}}_3+2{\mathrm{HNO}}_3\to \mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2 \\ \mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2+2{\mathrm{HNO}}_3\to \mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{H}}_2\mathrm{O}+2{\mathrm{CO}}_2 \end{gathered}$$

Nitric acid converts metal sulphites into nitrate salts along with the evolution of sulphur dioxide. For example, consider the reaction given below:

${\mathrm{Na}}_2{\mathrm{SO}}_3+2{\mathrm{HNO}}_3\to 2{\mathrm{NaNO}}_3+{\mathrm{SO}}_2+{\mathrm{H}}_2\mathrm{O}$

(iii) Ammonium nitrate, on heating, evolves dinitrogen oxide and water vapour. The equation for this reaction is shown below:

${\mathrm{NH}}_4{\mathrm{NO}}_3\stackrel{\mathrm{\Delta }}{\to }{\mathrm{N}}_2\mathrm{O}+2{\mathrm{H}}_2\mathrm{O}$