potassium or sodium nitrate with concentrated sulphuric acid. KNO + H SO KHSO + HNO The temperature is kept as low as possible to avoid decomposition of nitric acid. The acid condenses to a fuming liquid which is coloured brown by the presence of a little nitrogen dioxide which is formed due to the decomposition of nitric acid. 4HNO 4NO + 2H O + O Commercial method of preparation Nitric acid prepared in large scales using Ostwald's process.
In this method ammonia from Haber’s process is mixed about times of air. This mixture is preheated and passed into the catalyst chamber where they come in contact with platinum gauze. The temperature rises to about K and the metallic gauze brings about the rapid catalytic oxidation of ammonia resulting in the formation of NO, which then oxidised to nitrogen dioxide. 4NH + 5O 4NO + 6H O + kJ 2NO + O 2NO The nitrogen dioxide produced is passed through a series of adsorption towers.
It reacts with water to give nitric acid. Nitric oxide formed is bleached by blowing air. 3NO + H O 2HNO + NO Properties Pure nitric acid is colourless. It boils at °C.
The acid is completely miscible with water forming a constant boiling mixture ( % HNO , Boiling point . °C). Fuming nitric acid contains oxides of nitrogen. It decomposes on exposure to sunlight or on being heated, into nitrogen dioxide, water and oxygen.
4HNO 4NO + 2H O + O Due to this reaction pure acid or its concentrated solution becomes yellow on standing. In most of the reactions, nitric acid acts as an oxidising agent. Hence the oxidation state changes from + to a lower one. It doesn’t yield hydrogen in its reaction with metals.
Nitric acid can act as an acid, an oxidizing agent and an nitrating agent. As an acid: Like other acids it reacts with bases and basic oxides to form salts and water ZnO + 2HNO Zn(NO ) + H O 3FeO + 10HNO 3Fe(NO ) + NO + H O