Question

Explain the following: An all glass apparatus is used in the laboratory preparation of nitric acid.

Answer 1

Think about the reactivity properties of nitric acid. Generally mineral acids are present in the form of a gas. This gas is dissolved in water under pressure and a saturated solution is made to obtain a concentrated solution of acid. Think about the stability of acid and then draw a conclusion.

Complete answer:
- Nitric acid is an oxyacid of nitrogen. It has the molecular formula, $HN{{O}_{3}}$.
- Laboratory preparation of nitric acid involves distillation of sodium nitrate with concentrated sulphuric acid to form nitric acid and sodium hydrogen sulphate. The reaction is represented as,
$NaN{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\to NaHS{{O}_{4}}+HN{{O}_{3}}$
- Now, one of the reactants is concentrated sulphuric acid which is highly corrosive in nature. Sulphuric acid is a strong dehydrating and oxidizing agent. Concentrated sulphuric acid has the tendency to melt plastic apparatus and also reacts with metals to form metal sulphates. Therefore, glass apparatus is used for preparation of nitric acid since sulphuric acid doesn’t react with glass.
- Secondly, nitric acid that is formed by dehydration with conc. sulphuric acid is 98% concentrated. Therefore, it was called aqua fortis which means strong water because it attacks almost all metals except gold and platinum. Pure acid is unstable and therefore has high reactivity.
- Concentrated nitric acid is a strong oxidizing agent and therefore, it is capable of attacking almost all metals.
- The vapours of nitric acid are extremely corrosive and they melt the plastic. Therefore, while handling strong mineral acids like nitric acid, sulphuric acid, hydrochloric acid, glass apparatus is used since glass doesn’t react with these acids.
- Even for storage of these strong acids, glass bottles generally, dark brown bottles are used due to their inert nature.
- Hence, an all glass apparatus is used in the laboratory preparation of nitric acid.

Note:
Remember for handling strong acids like hydrochloric acid, sulphuric acid, nitric acid, only glass apparatus should be used. These acids are highly reactive and corrosive and therefore have the tendency to react with metals and plastic. While preparing dilutions of strong acids, care should be taken and only automated pipettes need to be used for pipetting out the required amount of conc. acid. Never mouth-pipette strong acids and alkalis like sodium hydroxide, bromine solution because they are highly toxic.