Study of Compounds — Nitric Acid
ICSE Class 10 · Chemistry · Chapter 10
What this chapter covers
- Nitric acid at a glance
- Laboratory preparation of nitric acid
- Manufacture of nitric acid by Ostwald's process
- Nitric acid as an oxidising agent
- Acidic properties of nitric acid
- Tests for nitric acid
Key definitions
Nitric acid is an oxyacid of nitrogen with the formula HNO3, in which a hydrogen atom is joined through an oxygen atom to a nitrogen atom that also carries two more oxygen atoms.
A monobasic acid is an acid that gives one hydrogen ion per molecule when it ionises in water.
Fuming nitric acid is very concentrated nitric acid, close to 98% or more, which gives off visible fumes in air because its vapour combines with moisture in the air to form tiny droplets.
Ostwald's process is the industrial method of manufacturing nitric acid by the catalytic oxidation of ammonia with air, followed by the oxidation of nitric oxide to nitrogen dioxide and the absorption of nitrogen dioxide in water in the presence of air.
An oxidising agent is a substance that gives oxygen to another substance, or removes hydrogen or electrons from it, and is itself reduced in the process.
Nascent oxygen is oxygen in the atomic state at the moment it is set free in a reaction, before its atoms join to form oxygen molecules, which makes it far more reactive than ordinary oxygen.
The brown ring test is a test for nitric acid or a nitrate in which a brown ring forms at the boundary between the test solution mixed with freshly prepared iron(II) sulphate solution and a layer of concentrated sulphuric acid poured carefully beneath it.
Key points
- Nitric acid, HNO3, is a strong monobasic acid and a powerful oxidising agent.
- It is stored in brown glass-stoppered bottles because light decomposes it to nitrogen dioxide, which makes it yellow.
- Laboratory method: potassium or sodium nitrate with concentrated sulphuric acid, heated below 200 °C, in an all-glass apparatus with a cooled receiver.
- Concentrated sulphuric acid works because it is non-volatile and drives out the volatile nitric acid.
- Ostwald's process: 4NH3 + 5O2 → 4NO + 6H2O (Pt, about 800 °C, 1 : 10 ammonia to air); 2NO + O2 → 2NO2 (about 50 °C); 4NO2 + 2H2O + O2 → 4HNO3.
- Concentrated acid is reduced to reddish-brown NO2; moderately dilute acid with copper gives colourless NO, which browns in air.
- Concentrated nitric acid oxidises copper to copper(II) nitrate, carbon to carbon dioxide and sulphur to sulphuric acid.
- Only magnesium and manganese give hydrogen, and only with very dilute, cold nitric acid.
- Dilute nitric acid forms nitrates with oxides, hydroxides, carbonates, hydrogen carbonates, sulphites and hydrogen sulphites.
- Tests: copper turnings give reddish-brown fumes and a blue solution; freshly prepared iron(II) sulphate and concentrated sulphuric acid give a brown ring.
Questions answered
Define a monobasic acid and write the equation for the ionisation of nitric acid in water.
Write the equation for the laboratory preparation of nitric acid from sodium nitrate, stating the condition.
Give two reasons why the temperature in the laboratory preparation is kept below 200 °C.
Why is the apparatus for preparing nitric acid made entirely of glass?
Why is concentrated hydrochloric acid not used in place of concentrated sulphuric acid in the laboratory preparation?
Why does laboratory nitric acid often look yellow, and how can the colour be removed?
Write the equations, with conditions, for the three stages of Ostwald's process.
Why is no outside heating needed once the catalytic oxidation of ammonia has started?
Past board exam questions
ICSE 2027 sample paper · 5 marks
Write balanced chemical equations for the following: (a) Chlorination of chloroform in the presence of diffused sunlight. (b) Hydrated aluminium oxide is treated with caustic soda. (c) Zinc oxide is treated with caustic alkali. (d) Copper reacts with cold dilute nitric acid. (e) Laboratory preparation of nitric acid using sodium nitrate.
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ICSE 2026 board paper · 2 marks
Study the reaction given below and answer the questions that follow: NaNO₃ + H₂SO₄ (Conc.) ⟶ NaHSO₄ + HNO₃ (< 200°C) (a) Give one reason for maintaining the temperature below 200°C. (b) Why is concentrated Sulphuric acid used in the above reaction?
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ICSE 2026 sample paper · 2 marks
Identify the reactant and write the balanced equation for the following: Nitric acid reacts with compound Q to give a salt Calcium nitrate, water and carbon dioxide.
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ICSE 2026 sample paper · 2 marks
Give reasons for the following: (a) Nitric acid does not normally liberate hydrogen gas when it reacts with active metals. (b) Silver-plated cutlery is not considered as pure silver.
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ICSE 2026 board paper · 3 marks
Anil is a laboratory assistant in a college. He prepared nitric acid but stored it in a transparent container exposed to sunlight. After a few days, brown fumes were observed in the container and the acid turned slightly yellowish in colour. (a) What was the error made by Anil while storing the acid? (b) Why were brown fumes observed in the container? (c) How can the yellowish tinge in the acid be removed?
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ICSE 2026 board paper · 2 marks
Carbon reacts with an acid to form carbon dioxide, water and nitrogen dioxide. (a) Name the acid used in the reaction. (b) Write a balanced chemical equation for the reaction that occurs.
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ICSE 2025 sample paper · 2 marks
Identify the reactant and write the balanced equation for the following: Nitric acid reacts with compound Q to give a salt Ca(NO₃)₂, water and carbon dioxide.
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ICSE 2025 sample paper · 3 marks
Give balanced equations for each of the following: (a) Action of warm water on Aluminium nitride. (b) Oxidation of carbon with conc. Nitric acid. (c) Laboratory preparation of ethanol by using chloroethane and aqueous sodium hydroxide.