ICSE Class 10 Chemistry Chapter 10 Nitric Acid

Chapter 10: Nitric Acid

Important Points To Remember

Nitric acid is commonly called as aqua fortis, i.e., strong water. Glauber first prepared Nitric acid by distilling mixture of nitre and concentrated Sulphuric acid.

Traces of Nitric acid come on to the earth in the form of Acid rain.

In laboratory, Nitric acid is prepared by distilling either Sodium nitrate (NaNO₃) or Potassium nitrate (KNO₃) with concentrated Sulphuric acid (Fig.1)

The reaction equations are:

KNO₃ + H₂SO₄ (conc.) -[below 200°C]-> KHSO₄ + HNO₃

2KNO₃ + H₂SO₄ (conc.) -[above 200°C]-> K₂SO₄ + 2HNO₃

NaNO₃ + H₂SO₄ (conc.) -[below 200°C]-> NaHSO₄ + HNO₃

2NaNO₃ + H₂SO₄ (conc.) -[above 200°C]-> Na₂SO₄ + 2HNO₃

Laboratory Preparation Setup

The apparatus used for the preparation of Nitric acid must be made of all glass as the vapours of Nitric acid are corrosive, therefore, it damages the rubber and cork.

Vapours of nitric acid get condensed into pale yellow liquid by cooling the receiver with the cold water in this way the nitric acid gets collected.

The reaction mixture should not be heated beyond 200°C because Nitric acid decomposes at higher temperatures. Above 200°C sodium sulphate forms a hard crust which sticks to the wall of apparatus and is very difficult to remove and apparatus gets damaged.

The decomposition equation is: \[4\text{HNO}_3 \to 4\text{NO}_2 + 2\text{H}_2\text{O} + \text{O}_2\]

Pure Nitric acid is colourless however commercial sample of Nitric acid is pale yellow in colour due to the presence of dissolved Nitrogen dioxide.

Teacher's Note

The careful control of temperature in laboratory preparation mirrors industrial processes where heat management is critical for product quality and worker safety.

Industrial Manufacture - Ostwald's Process

Overview

Nitric acid is manufactured by Ostwald's process (Fig. 2).

Process Steps

Catalytic oxidation of Ammonia: The gases entering the catalytic chamber must be absolutely pure otherwise it would poison the catalyst. Only the initial heating of the catalyst is required as the reaction is exothermic.

\[4\text{NH}_3 + 5\text{O}_2 \xrightarrow[\text{800°C}]{\text{Pt}} 4\text{NO} + 6\text{H}_2\text{O}\]

Oxidation Chamber: Before entering the oxidation chamber the gases must be cooled so that complete oxidation of Nitric oxide takes place.

\[2\text{NO} + \text{O}_2 \xrightarrow[\text{50°C}]{} 2\text{NO}_2\]

Absorption Tower: The water slowly trickles down through the absorption tower, which is packed with quartz and nitrogen dioxide slowly rises up and get merged with water to form nitric acid. The quartz packing provides a greater surface area in which nitrogen dioxide comes in contact with water.

\[4\text{NO}_2 + 2\text{H}_2\text{O} + \text{O}_2 \to 4\text{HNO}_3\]

Teacher's Note

Ostwald's process demonstrates how industrial chemistry optimizes natural reactions through temperature control and catalyst selection, similar to how biological systems use enzymes.

Key Reactions During Acid Rain Formation

In the atmosphere, nitrogen oxides from pollution undergo a series of reactions:

\[N_2 + O_2 \xrightarrow[\text{thunder/lightning}]{} 2\text{NO}\]

\[2\text{NO} + \text{O}_2 \to 2\text{NO}_2\]

\[4\text{NO}_2 + 2\text{H}_2\text{O} + \text{O}_2 \to 4\text{HNO}_3\]

Teacher's Note

Acid rain formation directly connects laboratory reactions to real environmental consequences, showing how classroom chemistry impacts our water systems and ecosystems.

Properties of Nitric Acid

Physical State

Nitric acid is unstable and it decomposes slightly even at room temperature.

\[4\text{HNO}_3 \to 2\text{H}_2\text{O} + 4\text{NO}_2 + \text{O}_2\]

Acidic Nature

Nitric acid is a typical monobasic acid. It gives all the properties of a dilute acid.

Dilute nitric acid shows characteristic colour change with indicators:

Reactions with Metallic Oxides and Hydroxides

It reacts with metallic Oxides and metallic Hydroxides to form salt and water (neutralization).

\[\text{CuO} + 2\text{HNO}_3 \to \text{Cu(NO}_3)_2 + \text{H}_2\text{O}\]

\[\text{ZnO} + 2\text{HNO}_3 \to \text{Zn(NO}_3)_2 + \text{H}_2\text{O}\]

\[\text{NaOH} + \text{HNO}_3 \to \text{NaNO}_3 + \text{H}_2\text{O}\]

Reactions with Metallic Carbonates and Bicarbonates

It reacts with metallic Carbonates and metallic Bicarbonates to liberate Carbon dioxide.

\[\text{NaHCO}_3 + \text{HNO}_3 \to \text{NaNO}_3 + \text{H}_2\text{O} + \text{CO}_2\]

\[\text{Na}_2\text{CO}_3 + 2\text{HNO}_3 \text{(dil.)} \to 2\text{NaNO}_3 + \text{H}_2\text{O} + \text{CO}_2\]

Pure nitric acid is colourless however the commercial sample of nitric acid is pale yellow in colour due to the presence of dissolved nitrogen dioxide.

Teacher's Note

Testing acids with indicators connects abstract chemistry to practical laboratory skills used in water quality testing and environmental monitoring.

This is a preview of the first 3 pages. To get the complete book, click below.