ChemistryICSE Class 10 · Chapter 10

Nitric Acid ICSE Class 10: Preparation, Ostwald's Process and Reactions

Updated 14 October 2026 · Fact-checked

Nitric acid is prepared in the laboratory by heating potassium or sodium nitrate with concentrated sulphuric acid below 200 °C in an all-glass apparatus. It is manufactured by Ostwald's process, the catalytic oxidation of ammonia. Concentrated nitric acid is a strong oxidising agent that attacks copper, carbon and sulphur, releasing reddish brown nitrogen dioxide.

What Nitric Acid is about

Nitric acid, HNO₃, is a strong monobasic acid that is also a powerful oxidising agent, because it readily gives up oxygen (decomposing to nitrogen dioxide or nitric oxide). This double character explains most of the chapter: as an acid it forms nitrates; as an oxidising agent it attacks even copper and non-metals, and it usually does not release hydrogen with metals.

The CISCE 2027 syllabus covers: the laboratory preparation from potassium nitrate or sodium nitrate (reactants, products, conditions, equation, apparatus, diagram, precautions, collection and identification); manufacture by Ostwald's process (only equations with conditions); nitric acid as an oxidising agent with copper, carbon and sulphur; its acidic properties with magnesium and manganese, oxides, hydroxides, carbonates, hydrogen carbonates, sulphites and hydrogen sulphites; and the test for nitric acid.

Weightage: CISCE publishes no chapter or unit weightage for ICSE Chemistry. Nitric Acid is in the 8. Study of Compounds C. Nitric Acid part of the 2027 syllabus and can be asked in both Section A and Section B of the 80-mark paper.Source: CISCE ICSE Chemistry (Science Paper 2) syllabus, examination year 2027

Key concepts

Laboratory preparation

Reactants: potassium nitrate (or sodium nitrate) and concentrated sulphuric acid.
Condition: heating below 200 °C.
Equations: $K N O_{3} + H_{2} S O_{4} \to K H S O_{4} + H N O_{3}$ ; $N a N O_{3} + H_{2} S O_{4} \to N a H S O_{4} + H N O_{3}$
Apparatus: an all-glass apparatus (glass retort with a glass stopper). Nitric acid vapour attacks rubber and cork, so these are not used.
Collection: the vapour distils over and is condensed in a receiver (flask) cooled by running water.
Why below 200 °C? At higher temperatures nitric acid decomposes, more fuel is used, the glass may crack, and the less soluble normal sulphate (K₂SO₄) forms a hard crust.
Why concentrated H₂SO₄? It is non-volatile and displaces the more volatile nitric acid.

The acid collected is often yellow because some decomposes, $4 H N O_{3} \to 4 N O_{2} + 2 H_{2} O + O_{2}$ , and the brown NO₂ dissolves in it. Bubbling dry air through the warm acid (or adding water) removes the colour.

Worked example

Why is an all-glass apparatus used to prepare nitric acid in the laboratory?

Try it first, then show the solutionSolution

Nitric acid vapour is highly corrosive and oxidising.
It attacks (oxidises) rubber and cork.
Glass is not attacked.

Answer: Nitric acid vapour attacks rubber and cork.

Ostwald's process (equations with conditions)

1. Catalytic oxidation of ammonia: ammonia and air (about 1 : 10 by volume) are passed over platinum gauze at about 800 °C:
$4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O + heat$
The reaction is exothermic, so once started it keeps the catalyst hot.
2. Oxidation of nitric oxide (on cooling, with more air):
$2 N O + O_{2} \to 2 N O_{2}$
3. Absorption: nitrogen dioxide with air is absorbed in water in an absorption tower:
$4 N O_{2} + 2 H_{2} O + O_{2} \to 4 H N O_{3}$

The nitric acid formed is dilute and is concentrated by further treatment.

Worked example

Write the three equations of Ostwald's process and name the catalyst.

Try it first, then show the solutionSolution

$4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$ (Pt, about 800 °C)
$2 N O + O_{2} \to 2 N O_{2}$
$4 N O_{2} + 2 H_{2} O + O_{2} \to 4 H N O_{3}$

Answer: Equations above; platinum gauze.

Nitric acid as an oxidising agent: copper

Copper is below hydrogen and does not react with dilute HCl or dilute H₂SO₄, but nitric acid oxidises it.

Concentrated nitric acid: $C u + 4 H N O_{3} \to C u (N O_{3})_{2} + 2 N O_{2} + 2 H_{2} O$
Observations: reddish brown gas (NO₂) and a blue (green when very concentrated) solution of copper(II) nitrate.

Dilute nitric acid: $3 C u + 8 H N O_{3} \to 3 C u (N O_{3})_{2} + 2 N O + 4 H_{2} O$
Observations: colourless nitric oxide, which turns reddish brown at the mouth of the tube as it meets air ( $2 N O + O_{2} \to 2 N O_{2}$ ); blue solution.

In both, nitric acid oxidises Cu to Cu²⁺ and is itself reduced (to NO₂ or NO). No hydrogen is formed.

Worked example

Copper turnings are added to a concentrated acid P and a reddish brown gas is evolved. Identify P and write the equation.

Try it first, then show the solutionSolution

Copper reacts only with an oxidising acid; reddish brown gas is NO₂.
P is concentrated nitric acid.
$C u + 4 H N O_{3} \to C u (N O_{3})_{2} + 2 N O_{2} + 2 H_{2} O$

Answer: Concentrated nitric acid; equation above.

Oxidation of carbon and sulphur

Hot concentrated nitric acid oxidises non-metals to their highest oxides or oxyacids, and is itself reduced to NO₂:

Carbon → carbon dioxide: $C + 4 H N O_{3} \to C O_{2} + 4 N O_{2} + 2 H_{2} O$

Sulphur → sulphuric acid: $S + 6 H N O_{3} \to H_{2} S O_{4} + 6 N O_{2} + 2 H_{2} O$

In each, reddish brown fumes of NO₂ are seen. Note the products: carbon gives a gas (CO₂), but sulphur gives sulphuric acid, not SO₂.

Worked example

What is formed when sulphur is heated with concentrated nitric acid? How could you show that sulphuric acid has formed?

Try it first, then show the solutionSolution

$S + 6 H N O_{3} \to H_{2} S O_{4} + 6 N O_{2} + 2 H_{2} O$
Add barium chloride solution to the cooled, diluted product: a white precipitate of BaSO₄, insoluble in acid, shows sulphate.

Answer: Sulphuric acid, NO₂ and water; BaCl₂ test.

Acidic properties of dilute nitric acid

Dilute nitric acid is a strong acid: $H N O_{3} + H_{2} O \to H_{3} O^{+} + N O_{3}^{-}$ .

Metals: because it is oxidising, it usually does not give hydrogen. Only very dilute (about 1%) nitric acid gives hydrogen with magnesium and manganese:

$M g + 2 H N O_{3} \to M g (N O_{3})_{2} + H_{2}$
$M n + 2 H N O_{3} \to M n (N O_{3})_{2} + H_{2}$

Oxides and hydroxides: $C u O + 2 H N O_{3} \to C u (N O_{3})_{2} + H_{2} O$ ; $N a O H + H N O_{3} \to N a N O_{3} + H_{2} O$
Carbonates and hydrogen carbonates: $C a C O_{3} + 2 H N O_{3} \to C a (N O_{3})_{2} + H_{2} O + C O_{2}$ ; $N a H C O_{3} + H N O_{3} \to N a N O_{3} + H_{2} O + C O_{2}$
Sulphites and hydrogen sulphites: $N a_{2} S O_{3} + 2 H N O_{3} \to 2 N a N O_{3} + H_{2} O + S O_{2}$ ; $N a H S O_{3} + H N O_{3} \to N a N O_{3} + H_{2} O + S O_{2}$

Worked example

Why does dilute nitric acid generally not give hydrogen with metals?

Try it first, then show the solutionSolution

Nitric acid is a strong oxidising agent.
Any hydrogen formed is at once oxidised to water, and the acid is reduced to oxides of nitrogen.
Only very dilute acid with Mg or Mn releases hydrogen.

Answer: It oxidises the hydrogen to water.

Test for nitric acid

Heat the acid with copper turnings: reddish brown fumes of nitrogen dioxide are given off and the solution turns blue (copper(II) nitrate).

$C u + 4 H N O_{3} \to C u (N O_{3})_{2} + 2 N O_{2} + 2 H_{2} O$

This distinguishes nitric acid from hydrochloric and dilute sulphuric acids, which do not react with copper. Nitric acid also gives no precipitate with barium chloride or silver nitrate solution (unlike sulphuric and hydrochloric acids).

Worked example

Distinguish between dilute nitric acid and dilute sulphuric acid using barium chloride solution.

Try it first, then show the solutionSolution

Sulphuric acid: white precipitate of BaSO₄: $B a C l_{2} + H_{2} S O_{4} \to B a S O_{4} + 2 H C l$ .
Nitric acid: no precipitate (all nitrates are soluble).

Answer: White precipitate only with sulphuric acid.

Chemistry in real life: Nitric Acid

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Test for nitric acid

Suppose a laboratory assistant finds an unlabelled bottle of colourless acid and must decide whether it is hydrochloric, sulphuric or nitric acid, with only copper turnings, barium chloride and silver nitrate available.

Plan tests to identify it.

Try it first, then show the solutionSolution

Add copper turnings and warm: only nitric acid gives reddish brown NO₂ and a blue solution.
If no reaction, add BaCl₂: a white precipitate shows sulphuric acid.
If not, add AgNO₃: a white precipitate shows hydrochloric acid.

Answer: Copper (nitric), BaCl₂ (sulphuric), AgNO₃ (hydrochloric).

Memory hook: Copper reveals nitric; barium reveals sulphate; silver reveals chloride.

Why stored acid turns yellow

Suppose a school's bottle of concentrated nitric acid, kept on a sunny window sill, has turned yellow.

Explain the colour and suggest how the acid should be stored.

Try it first, then show the solutionSolution

Light and heat decompose nitric acid: $4 H N O_{3} \to 4 N O_{2} + 2 H_{2} O + O_{2}$ .
The brown NO₂ dissolves in the acid, giving a yellow colour.
Store it in dark brown bottles in a cool place.

Answer: Dissolved NO₂ from decomposition; store cool and dark.

Memory hook: Light breaks nitric acid; brown gas makes it yellow.

Ostwald's process

Suppose an engineer at a fertiliser plant wants to convert 100 L of ammonia into nitric oxide by catalytic oxidation (all gases at the same temperature and pressure).

What volume of oxygen is needed, and what volume of nitric oxide forms? Name the catalyst.

Try it first, then show the solutionSolution

$4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$
O₂ = 100 × 5/4 = 125 L.
NO = 100 × 4/4 = 100 L.
Catalyst: platinum gauze at about 800 °C.

Answer: 125 L of O₂; 100 L of NO; platinum.

Memory hook: Four ammonia, five oxygen, four nitric oxide.

Topics in this chapter

Nitric Acid formula sheet

Laboratory preparation: $K N O_{3} + H_{2} S O_{4} \to K H S O_{4} + H N O_{3}$; Below 200 °C, all-glass apparatus.
Ostwald step 1: $4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$; Pt gauze, about 800 °C.
Ostwald step 2: $2 N O + O_{2} \to 2 N O_{2}$; Cooling, more air.
Ostwald step 3: $4 N O_{2} + 2 H_{2} O + O_{2} \to 4 H N O_{3}$; Absorption tower.
Copper + conc. HNO₃: $C u + 4 H N O_{3} \to C u (N O_{3})_{2} + 2 N O_{2} + 2 H_{2} O$; Reddish brown gas.
Copper + dilute HNO₃: $3 C u + 8 H N O_{3} \to 3 C u (N O_{3})_{2} + 2 N O + 4 H_{2} O$; Colourless NO.
Carbon + conc. HNO₃: $C + 4 H N O_{3} \to C O_{2} + 4 N O_{2} + 2 H_{2} O$; Hot acid.
Sulphur + conc. HNO₃: $S + 6 H N O_{3} \to H_{2} S O_{4} + 6 N O_{2} + 2 H_{2} O$; Sulphuric acid formed.

Nitric Acid: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

Laboratory preparation of nitric acid

Draw a labelled diagram of the laboratory preparation of nitric acid.

Draw

A glass retort with a glass stopper, containing KNO₃ (or NaNO₃) and conc. H₂SO₄, on a wire gauze over a burner.
The long neck of the retort leading into a round-bottom receiver flask.
The receiver kept under a stream of cold water (or in a trough of cold water).
Liquid nitric acid collecting in the receiver.

Label

glass retort
KNO₃ + conc. H₂SO₄
heat (below 200 °C)
receiver
cold water
nitric acid

Watch out: Write 'all-glass apparatus' as a note.

Ostwald's process flow chart

Outline the manufacture of nitric acid.

Draw

Box 1: NH₃ + air (1 : 10) → converter with platinum gauze, about 800 °C → NO.
Box 2: cooling chamber: NO + O₂ → NO₂.
Box 3: absorption tower: NO₂ + water + air → HNO₃.

Label

converter (Pt gauze)
cooler / oxidation chamber
absorption tower
nitric acid

Watch out: Write each equation under its box.

How the board asks Nitric Acid

The question patterns to expect, and the method that works for each.

Question type	How it is asked	Method
Laboratory preparation	Equation, temperature limit, why all-glass, why concentrated H₂SO₄, why the acid is yellow.	Learn the preparation checklist and the decomposition equation.
Ostwald's process	Write equations with conditions; identify the catalyst; table of industrial processes.	Three equations; platinum gauze at about 800 °C.
Oxidising reactions	Balanced equations for conc. HNO₃ with Cu, C, S; dilute HNO₃ with Cu; name the gas.	Conc. → NO₂ (brown); dilute → NO (colourless). Balance O carefully.
Acid properties	Equations with Mg, Mn, oxides, carbonates, sulphites; why most metals give no hydrogen.	Very dilute acid for H₂ with Mg and Mn only.
Distinguish / test	Distinguish HNO₃ from H₂SO₄ or HCl using BaCl₂, AgNO₃ or copper.	No precipitate with BaCl₂ or AgNO₃; brown gas with copper.

Tricks to remember Nitric Acid

Short memory aids. Say each one aloud once, then use it on a question the same day.

Concentrated = brown NO₂, dilute = colourless NO
Strong acid, strong colour; weak acid, no colour (until it meets air).
Use it when: Copper reactions.
1-4-1-2-2 and 3-8-3-2-4
Cu + 4HNO₃ (conc.) and 3Cu + 8HNO₃ (dilute): learn the coefficients as two number strings.
Use it when: Balancing copper equations.
Only Mg and Mn make H₂
'M and M' (magnesium, manganese) are the only metals that free hydrogen, and only from very dilute nitric acid.
Use it when: Hydrogen MCQs.
Glass only for nitric
Nitric acid eats rubber and cork, so its apparatus is all glass.
Use it when: Precautions.

Nitric Acid: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Example 1: Gas from copper · 1 mark · MCQBoard level

The gas evolved when copper reacts with concentrated nitric acid is:
(a) hydrogen
(b) nitric oxide
(c) nitrogen dioxide
(d) nitrogen

Try it first, then show the solutionSolution

Concentrated nitric acid is reduced to NO₂ (reddish brown).

Answer: (c)

Example 2: Hydrogen from nitric acid · 1 mark · Assertion-reasonHarder board level

Assertion (A): Zinc does not liberate hydrogen with dilute nitric acid.
Reason (R): Nitric acid is a strong oxidising agent.
(a) Both (A) and (R) are true, and (R) is the correct explanation for (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation for (A).
(c) (A) is true and (R) is false.
(d) (A) is false and (R) is true.

Try it first, then show the solutionSolution

Any hydrogen formed is oxidised to water by the nitric acid.

Answer: (a)

Example 3: Laboratory preparation · 3 marks · Short answerBoard level

In the laboratory preparation of nitric acid: (a) write the equation using sodium nitrate; (b) why is the temperature kept below 200 °C? (c) how is the acid collected?

Try it first, then show the solutionSolution

(a) $N a N O_{3} + H_{2} S O_{4} \to N a H S O_{4} + H N O_{3}$
(b) Higher temperatures decompose nitric acid, waste fuel, and may crack the glass (a hard crust of Na₂SO₄ forms).
(c) The vapour is condensed in a receiver cooled by running water.

Answer: As above.

Example 4: Balancing oxidations · 3 marks · Short answerHarder board level

Write balanced equations for concentrated nitric acid with (a) carbon, (b) sulphur, (c) copper.

Try it first, then show the solutionSolution

(a) $C + 4 H N O_{3} \to C O_{2} + 4 N O_{2} + 2 H_{2} O$
(b) $S + 6 H N O_{3} \to H_{2} S O_{4} + 6 N O_{2} + 2 H_{2} O$
(c) $C u + 4 H N O_{3} \to C u (N O_{3})_{2} + 2 N O_{2} + 2 H_{2} O$

Answer: As above.

Example 5: Ostwald's process · 3 marks · Short answerBoard level

Give the equations, with conditions, for the conversion of ammonia to nitric acid.

Try it first, then show the solutionSolution

$4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$ (platinum gauze, about 800 °C)
$2 N O + O_{2} \to 2 N O_{2}$ (on cooling)
$4 N O_{2} + 2 H_{2} O + O_{2} \to 4 H N O_{3}$ (absorption in water)

Answer: As above.

Example 6: Acid properties · 4 marks · Long answerHarder board level

Write equations for dilute nitric acid with (a) magnesium, (b) sodium hydrogen carbonate, (c) sodium sulphite. Which condition is needed for (a)?

Try it first, then show the solutionSolution

(a) $M g + 2 H N O_{3} \to M g (N O_{3})_{2} + H_{2}$
(b) $N a H C O_{3} + H N O_{3} \to N a N O_{3} + H_{2} O + C O_{2}$
(c) $N a_{2} S O_{3} + 2 H N O_{3} \to 2 N a N O_{3} + H_{2} O + S O_{2}$
(a) needs very dilute (about 1%) nitric acid.

Answer: As above.

Example 7: Volume of gas from copper · 3 marks · Short answerHarder board level

3.2 g of copper reacts completely with concentrated nitric acid. Calculate the volume of NO₂ at S.T.P. and the mass of HNO₃ used. (Cu = 64, H = 1, N = 14, O = 16)

Try it first, then show the solutionSolution

$C u + 4 H N O_{3} \to C u (N O_{3})_{2} + 2 N O_{2} + 2 H_{2} O$ ; moles Cu = 3.2 ÷ 64 = 0.05.
NO₂ = 2 × 0.05 = 0.1 mol = 2.24 L.
HNO₃ = 4 × 0.05 = 0.2 mol × 63 = 12.6 g.

Answer: 2.24 L NO₂; 12.6 g HNO₃.

Example 8: HOTS: concentration decides · 4 marks · Long answerHOTS / competency

Two students add copper to nitric acid. Student A sees reddish brown gas immediately; student B sees a colourless gas that turns brown only at the mouth of the tube. Explain both, with equations, and say which acid was more concentrated.

Try it first, then show the solutionSolution

A used concentrated acid: $C u + 4 H N O_{3} \to C u (N O_{3})_{2} + 2 N O_{2} + 2 H_{2} O$ ; NO₂ is brown.
B used dilute acid: $3 C u + 8 H N O_{3} \to 3 C u (N O_{3})_{2} + 2 N O + 4 H_{2} O$ ; NO is colourless.
At the mouth, NO meets air: $2 N O + O_{2} \to 2 N O_{2}$ , turning brown.
A's acid was more concentrated.

Answer: As above.

Case-study practice (Section B style)

Read the situation, then answer every part. In the board paper this is a 5-mark question split into 1 + 1 + 1 + 2 marks.

The all-glass retort

Suppose a teacher sets up a glass retort containing potassium nitrate and concentrated sulphuric acid, heated gently, with its neck leading into a flask kept under a stream of cold water.

(i) · 1 mark
Write the equation for the reaction in the retort.
Answer
Answer: $K N O_{3} + H_{2} S O_{4} \to K H S O_{4} + H N O_{3}$
(ii) · 1 mark
Why is the flask cooled?
Answer
Answer: To condense the nitric acid vapour into a liquid.
(iii) · 1 mark
Why is the retort stoppered with glass, not cork?
Answer
Answer: Nitric acid vapour attacks cork and rubber.
(iv) · 2 marks
The collected acid is pale yellow. Why, and how can it be made colourless?
Answer
Answer: Some acid decomposes to NO₂, which dissolves in it; blow dry air through the warm acid (or dilute it with water).

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Write the equation for copper with dilute nitric acid and name the gas. (2 marks) (2 marks)

Step	Marks
$3 C u + 8 H N O_{3} \to 3 C u (N O_{3})_{2} + 2 N O + 4 H_{2} O$	1
Nitric oxide (NO), colourless	1

Give the three equations of Ostwald's process. (3 marks) (3 marks)

Step	Marks
$4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$ (Pt, about 800 °C)	1
$2 N O + O_{2} \to 2 N O_{2}$	1
$4 N O_{2} + 2 H_{2} O + O_{2} \to 4 H N O_{3}$	1

State two precautions in the laboratory preparation of nitric acid, give the equation, and explain the yellow colour of the product. (4 marks) (4 marks)

Step	Marks
Temperature below 200 °C	1
All-glass apparatus (no cork or rubber)	1
$K N O_{3} + H_{2} S O_{4} \to K H S O_{4} + H N O_{3}$	1
Dissolved NO₂ from $4 H N O_{3} \to 4 N O_{2} + 2 H_{2} O + O_{2}$	1

Where students lose marks in Nitric Acid

The slips examiners see most often, and what to write instead.

Mistake: Dilute-acid products for concentrated acid
CISCE examiners' comments, 2024: for copper with concentrated nitric acid, candidates wrote the dilute-acid product (NO) instead of NO₂.
Wrong working
Cu + conc. HNO₃ → ... + NO
Right working
$C u + 4 H N O_{3} \to C u (N O_{3})_{2} + 2 N O_{2} + 2 H_{2} O$
Do this: Concentrated = NO₂; dilute = NO.
Usually costs: 1 mark.
Mistake: Not saying 'concentrated'
CISCE examiners' comments, 2025: identifying the acid that gives a reddish brown gas with copper, candidates wrote HCl or H₂SO₄, or nitric acid without 'concentrated'; some wrote copper oxide for copper nitrate.
Wrong working
Acid P: nitric acid; product: CuO
Right working
Concentrated nitric acid; product copper(II) nitrate.
Do this: Name the concentration whenever it decides the product.
Usually costs: 1 mark.
Mistake: Confusing NO and NO₂
CISCE examiners' comments, 2025: naming gases from reactions, candidates confused nitrogen dioxide with nitric oxide, or wrote hydrogen.
Wrong working
Gas from copper + conc. HNO₃: nitric oxide
Right working
Nitrogen dioxide (reddish brown).
Do this: NO is colourless; NO₂ is reddish brown.
Usually costs: 1 mark.
Mistake: Wrong BaCl₂ result for nitric acid
CISCE examiners' comments, 2024: distinguishing acids with barium chloride, candidates did not state that nitric acid gives no precipitate, or claimed a brown precipitate.
Wrong working
Nitric acid + BaCl₂: brown precipitate
Right working
No precipitate (barium nitrate is soluble).
Do this: All nitrates are soluble: nitric acid never gives a precipitate with BaCl₂ or AgNO₃.
Usually costs: 1 mark.
Mistake: Mixing up industrial processes
CISCE examiners' comments, 2024: in a table about an industrial acid process, candidates confused the Contact process with Ostwald's or Bayer's process.
Wrong working
Ostwald's process uses V₂O₅.
Right working
Ostwald: platinum, NH₃ → HNO₃. Contact: V₂O₅, SO₂ → H₂SO₄.
Do this: Pair each process with its acid and catalyst.
Usually costs: 1-3 marks.

Practice questions on Nitric Acid

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Nitric acid is prepared in the laboratory in an all-glass apparatus because:
(a) it is volatile
(b) its vapour attacks rubber and cork
(c) it is a strong acid
(d) it decomposes on heating
Hint
Corrosive vapour.
Answer
(b)
Q2 · 1 mark · MCQBoard level
Which metal liberates hydrogen with very dilute nitric acid?
(a) Copper
(b) Zinc
(c) Magnesium
(d) Iron
Hint
M and M.
Answer
(c)
Q3 · 1 mark · MCQHarder board level
Statement I: Carbon is oxidised to carbon dioxide by hot concentrated nitric acid.
Statement II: Sulphur is oxidised to sulphur dioxide by hot concentrated nitric acid.
(a) Both true
(b) Both false
(c) I true, II false
(d) I false, II true
Hint
Sulphur goes to its highest oxyacid.
Answer
(c): sulphur gives sulphuric acid.
Q4 · 2 marks · Short answerBoard level
Write the equation for the decomposition of nitric acid by light and state how this affects storage.
Hint
Brown bottles.
Answer
$4 H N O_{3} \to 4 N O_{2} + 2 H_{2} O + O_{2}$ ; store in dark brown bottles in a cool place.
Q5 · 3 marks · Very short answerBoard level
Name the gas formed in each case: (a) copper + dilute HNO₃; (b) carbon + conc. HNO₃ (two gases); (c) sodium sulphite + dilute HNO₃.
Hint
NO, CO₂ + NO₂, SO₂.
Answer
(a) Nitric oxide (b) Carbon dioxide and nitrogen dioxide (c) Sulphur dioxide
Q6 · 2 marks · Short answerHarder board level
Explain why concentrated sulphuric acid, not concentrated hydrochloric acid, is used to prepare nitric acid from potassium nitrate.
Hint
Volatility.
Answer
A non-volatile acid displaces a volatile one. H₂SO₄ is non-volatile; HCl is itself volatile and would distil over with the nitric acid.
Q7 · 3 marks · Short answerHarder board level
Write equations for dilute nitric acid with (a) copper(II) oxide, (b) calcium carbonate, (c) manganese.
Hint
Normal acid reactions.
Answer
(a) $C u O + 2 H N O_{3} \to C u (N O_{3})_{2} + H_{2} O$ (b) $C a C O_{3} + 2 H N O_{3} \to C a (N O_{3})_{2} + H_{2} O + C O_{2}$ (c) $M n + 2 H N O_{3} \to M n (N O_{3})_{2} + H_{2}$ (very dilute acid)
Q8 · 3 marks · Short answerHarder board level
Calculate the volume of nitric oxide at S.T.P. formed when 9.6 g of copper reacts with dilute nitric acid. (Cu = 64)
Hint
3Cu : 2NO.
Answer
Moles Cu = 9.6 ÷ 64 = 0.15; NO = 0.15 × 2/3 = 0.1 mol = 2.24 L.
Q9 · 2 marks · Short answerHarder board level
Calculate the mass of nitric acid obtained from 20.2 g of potassium nitrate in the laboratory preparation. (K = 39, N = 14, O = 16, H = 1)
Hint
1 : 1.
Answer
M(KNO₃) = 101; 0.2 mol → 0.2 × 63 = 12.6 g HNO₃.
Q10 · 3 marks · Short answerHOTS / competency
In the reaction $S + 6 H N O_{3} \to H_{2} S O_{4} + 6 N O_{2} + 2 H_{2} O$ , identify the oxidising agent and the substance oxidised. Explain how you know.
Hint
Who gains oxygen?
Answer
Sulphur is oxidised (it gains oxygen to become H₂SO₄). Nitric acid is the oxidising agent: it gives oxygen and is itself reduced to NO₂.
Q11 · 3 marks · Short answerHOTS / competency
A colourless gas X forms when copper reacts with an acid; X turns reddish brown in air. The solution left is blue and gives no precipitate with BaCl₂. Identify the acid and its concentration, X, and the blue compound.
Hint
Not sulphate.
Answer
Dilute nitric acid; X = nitric oxide (NO); copper(II) nitrate.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Reactants for lab preparation of HNO₃?Show answer
KNO₃ (or NaNO₃) and concentrated H₂SO₄.
2.Catalyst in Ostwald's process?Show answer
Platinum gauze.
3.Gas from copper with dilute HNO₃?Show answer
Nitric oxide (NO).
4.Product of sulphur with conc. HNO₃?Show answer
Sulphuric acid (with NO₂ and water).
5.Metals giving H₂ with very dilute HNO₃?Show answer
Magnesium and manganese.
6.Why is lab nitric acid yellow?Show answer
Dissolved NO₂ from its decomposition.
7.Basicity of nitric acid?Show answer
1 (monobasic).
8.Test for nitric acid?Show answer
Warm with copper turnings: reddish brown fumes and a blue solution.

Best order to study it

Learn the laboratory preparation checklist and diagram.
Learn Ostwald's three equations with conditions.
Practise balancing the copper (conc. and dilute), carbon and sulphur equations.
Learn the acid properties, including the Mg/Mn exception.
Learn the test and how to distinguish the three mineral acids.

Quick revision checklist

The night before the exam: can you do each of these without looking?

Can you explain why the apparatus is all glass and the temperature below 200 °C?
Can you write all three Ostwald equations with conditions?
Can you balance copper + conc. HNO₃ and copper + dilute HNO₃?
Can you write the oxidation of carbon and sulphur?
Can you explain why most metals give no hydrogen with nitric acid?
Can you distinguish HNO₃ from H₂SO₄ and HCl?

Nitric Acid: frequently asked questions

How much of Ostwald's process do I need for ICSE 2027?

The syllabus asks for 'only equations with conditions where applicable': the three equations, the platinum catalyst and the temperature.

Which metals must I know for the acid properties of nitric acid?

The 2027 syllabus names magnesium and manganese (which give hydrogen with very dilute nitric acid), plus reactions with oxides, hydroxides, carbonates, hydrogen carbonates, sulphites and hydrogen sulphites.

Why is nitric acid stored in brown bottles?

Light decomposes it to NO₂, water and oxygen; brown glass cuts out the light.

Is the brown ring test required?

The syllabus asks for 'test for nitric acid'; the copper test (brown fumes, blue solution) is the standard one to give.

Based on: CISCE ICSE 2027 Chemistry (Science Paper 2) syllabus; CISCE ICSE 2027 Chemistry (Science Paper 2) specimen question paper and marking scheme; CISCE Analysis of Pupil Performance, ICSE Chemistry (Science Paper 2), 2025; CISCE Analysis of Pupil Performance, ICSE Chemistry (Science Paper 2), 2024