ChemistryICSE Class 10 · Chapter 9

Ammonia ICSE Class 10: Preparation, Haber's Process, Properties and Tests

Updated 14 October 2026 · Fact-checked

Ammonia is prepared in the laboratory by heating ammonium chloride with slaked lime, dried over quicklime and collected by downward displacement of air. It is made industrially by Haber's process from nitrogen and hydrogen over iron. It is very soluble, forms a weak alkali, and reduces hot copper(II) oxide.

What Ammonia is about

Ammonia, NH₃, is a colourless gas with a sharp, pungent smell. It is lighter than air, extremely soluble in water, and the only common alkaline gas. Its lone pair (see Chemical Bonding) makes it a base, and its hydrogen makes it a reducing agent.

The CISCE 2027 syllabus covers: laboratory preparation from ammonium chloride (apparatus, diagram, procedure, observation, collection, identification); ammonia from nitrides (Mg₃N₂, AlN) with warm water and from ammonium salts with alkalis; manufacture by Haber's process; density and solubility (fountain experiment); burning in oxygen and catalytic oxidation; reactions with hydrogen chloride, hot copper(II) oxide, lead(IV) oxide and chlorine (both with chlorine in excess and with ammonia in excess); aqueous ammonia with sulphuric, nitric and hydrochloric acids and with solutions of iron(III) chloride, iron(II) sulphate, lead nitrate, zinc nitrate and copper sulphate; uses (fertilisers, explosives, nitric acid, refrigerant, cleansing agents); and tests for ammonia.

Weightage: CISCE publishes no chapter or unit weightage for ICSE Chemistry. Ammonia is in the 8. Study of Compounds B. Ammonia 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 from ammonium chloride

Reactants: ammonium chloride and slaked lime (calcium hydroxide), mixed and heated.
Equation: $2 N H_{4} C l + C a (O H)_{2} \to C a C l_{2} + 2 H_{2} O + 2 N H_{3}$
Apparatus: the hard-glass flask (or boiling tube) is clamped with its mouth slightly downwards, so that the water formed does not run back onto the hot glass and crack it.
Drying: through a tower of quicklime (CaO). Concentrated H₂SO₄, P₂O₅ and anhydrous CaCl₂ cannot be used, because they react with ammonia (the acids form ammonium salts; calcium chloride forms an addition compound).
Collection: by downward displacement of air (gas jar inverted), because ammonia is lighter than air (vapour density 8.5). Not over water: it is extremely soluble.
Jar full? Moist red litmus at the mouth turns blue, or a rod dipped in conc. HCl gives dense white fumes.

Worked example

Why is concentrated sulphuric acid not used to dry ammonia?

Try it first, then show the solutionSolution

Ammonia is a base; sulphuric acid is an acid.
They react: $2 N H_{3} + H_{2} S O_{4} \to (N H_{4})_{2} S O_{4}$ .
The ammonia would be absorbed, not dried.

Answer: It reacts with ammonia; quicklime is used instead.

Ammonia from nitrides and from ammonium salts

Nitrides with warm water (hydrolysis):

$M g_{3} N_{2} + 6 H_{2} O \to 3 M g (O H)_{2} + 2 N H_{3}$

$A l N + 3 H_{2} O \to A l (O H)_{3} + N H_{3}$

The products are the metal hydroxides (white solids), not oxides.

Any ammonium salt with any alkali (on warming):

$N H_{4} C l + N a O H \to N a C l + H_{2} O + N H_{3}$

$(N H_{4})_{2} S O_{4} + 2 N a O H \to N a_{2} S O_{4} + 2 H_{2} O + 2 N H_{3}$

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

This is also the test for the ammonium ion. Do not use ammonium nitrate for this in practice: it can decompose explosively on heating.

Worked example

Aluminium nitride is used to make ammonia in a flask with a dropping funnel. Name the liquid in the funnel and write the equation.

Try it first, then show the solutionSolution

Nitrides react with warm water.
$A l N + 3 H_{2} O \to A l (O H)_{3} + N H_{3}$

Answer: Warm water; aluminium hydroxide and ammonia form.

Haber's process

$N_{2} + 3 H_{2} ⇌ 2 N H_{3} + heat$

Raw materials: nitrogen (from liquefied air) and hydrogen, mixed in the ratio 1 : 3 by volume.
Temperature: about 450-500 °C.
Pressure: about 200-900 atmospheres (high pressure favours fewer gas molecules: 4 volumes → 2 volumes).
Catalyst: finely divided iron; molybdenum is added as a promoter to make the catalyst more effective.
Separation: the gas mixture is cooled; ammonia liquefies (it liquefies much more easily than N₂ and H₂), and the unreacted gases are recycled.

The reaction is reversible and exothermic, so the temperature chosen is a compromise: lower would give more ammonia but too slowly; the catalyst makes it fast enough.

Worked example

Give the conditions for Haber's process and say how ammonia is separated from the unreacted gases.

Try it first, then show the solutionSolution

N₂ : H₂ = 1 : 3; 450-500 °C; 200-900 atm; finely divided iron with molybdenum.
Cool the mixture: ammonia liquefies, N₂ and H₂ remain gases and are recycled.

Answer: As above; separation by liquefaction.

Density, solubility and aqueous ammonia

Lighter than air: collected in an inverted jar.

Fountain experiment: as for HCl, but with red litmus (or phenolphthalein) in the trough; the fountain is blue (or pink), showing ammonia is highly soluble and its solution is alkaline.

Aqueous ammonia (ammonium hydroxide) is a weak alkali:
$N H_{3} + H_{2} O ⇌ N H_{4} O H ⇌ N H_{4}^{+} + O H^{-}$

It neutralises acids to form ammonium salts:
$2 N H_{4} O H + H_{2} S O_{4} \to (N H_{4})_{2} S O_{4} + 2 H_{2} O$
$N H_{4} O H + H N O_{3} \to N H_{4} N O_{3} + H_{2} O$
$N H_{4} O H + H C l \to N H_{4} C l + H_{2} O$

With metal salt solutions it precipitates hydroxides:

$F e C l_{3} + 3 N H_{4} O H \to F e (O H)_{3} + 3 N H_{4} C l$ : reddish brown.
$F e S O_{4} + 2 N H_{4} O H \to F e (O H)_{2} + (N H_{4})_{2} S O_{4}$ : dirty green.
$P b (N O_{3})_{2} + 2 N H_{4} O H \to P b (O H)_{2} + 2 N H_{4} N O_{3}$ : chalky white, insoluble in excess.
$Z n (N O_{3})_{2} + 2 N H_{4} O H \to Z n (O H)_{2} + 2 N H_{4} N O_{3}$ : white, soluble in excess.
$C u S O_{4} + 2 N H_{4} O H \to C u (O H)_{2} + (N H_{4})_{2} S O_{4}$ : pale blue, dissolves in excess to an inky blue solution.

Worked example

What do you observe when excess ammonium hydroxide is added to (a) zinc nitrate solution, (b) iron(III) chloride solution?

Try it first, then show the solutionSolution

(a) White gelatinous precipitate that dissolves in excess to give a colourless solution.
(b) Reddish brown precipitate, insoluble in excess.

Answer: As above.

Ammonia as a reducing agent: CuO and PbO₂

Hot metal oxides are reduced by ammonia; the hydrogen of ammonia forms water and nitrogen gas is released.

Hot copper(II) oxide:
$3 C u O + 2 N H_{3} \to 3 C u + 3 H_{2} O + N_{2}$
Observations: the black copper(II) oxide turns reddish brown (copper); droplets of water collect on the cooler parts of the tube; a colourless gas (nitrogen) is given off.

Hot lead(IV) oxide:
$3 P b O_{2} + 4 N H_{3} \to 3 P b + 6 H_{2} O + 2 N_{2}$
Observation: the dark brown oxide is reduced to greyish lead; water droplets form.

These show the reducing property of ammonia (not its basic property).

Worked example

Ammonia is passed over heated copper(II) oxide. Name the gas evolved and give the colour of the residue.

Try it first, then show the solutionSolution

$3 C u O + 2 N H_{3} \to 3 C u + 3 H_{2} O + N_{2}$
The gas is nitrogen; the residue is copper.

Answer: Nitrogen; reddish brown copper.

Ammonia with chlorine and with oxygen

With chlorine, the products depend on which gas is in excess:

Ammonia in excess: $8 N H_{3} + 3 C l_{2} \to 6 N H_{4} C l + N_{2}$ . Greenish-yellow chlorine disappears and dense white fumes of ammonium chloride form.
Chlorine in excess: $N H_{3} + 3 C l_{2} \to N C l_{3} + 3 H C l$ . A yellow, highly explosive oily liquid, nitrogen trichloride, forms.

Burning in oxygen: ammonia does not burn in air, but burns in oxygen with a yellowish-green flame:
$4 N H_{3} + 3 O_{2} \to 2 N_{2} + 6 H_{2} O$

Catalytic oxidation (with platinum at about 800 °C):
$4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O + heat$
The platinum keeps glowing (the reaction is exothermic), and reddish brown fumes of NO₂ appear as nitric oxide meets more air: $2 N O + O_{2} \to 2 N O_{2}$ . This is the first step of Ostwald's process for nitric acid.

Worked example

Write the equations for the reaction of ammonia with chlorine when (a) ammonia is in excess, (b) chlorine is in excess.

Try it first, then show the solutionSolution

(a) $8 N H_{3} + 3 C l_{2} \to 6 N H_{4} C l + N_{2}$ (white fumes).
(b) $N H_{3} + 3 C l_{2} \to N C l_{3} + 3 H C l$ (yellow explosive liquid).

Answer: As above.

Uses and tests of ammonia

Uses:

Manufacture of fertilisers: ammonium sulphate, ammonium nitrate, urea.
Manufacture of explosives (from ammonium nitrate) and of nitric acid (Ostwald's process).
Refrigerant: liquid ammonia absorbs a lot of heat when it evaporates; it is used in ice plants and cold storage. It does not deplete the ozone layer, unlike chlorofluorocarbons (CFCs), and is one of the alternatives to them.
Cleansing agent: dilute ammonia solution removes grease and stains from glass and fabrics.

Tests:

Characteristic pungent smell.
Turns moist red litmus blue (only common alkaline gas).
Dense white fumes with a rod dipped in conc. HCl.
With copper(II) sulphate solution: pale blue precipitate dissolving in excess to an inky blue solution.

Worked example

Give two tests that confirm a gas is ammonia.

Try it first, then show the solutionSolution

Moist red litmus paper turns blue.
A glass rod dipped in concentrated HCl gives dense white fumes.

Answer: Red litmus blue; white fumes with HCl.

Chemistry in real life: Ammonia

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.

Refrigerant

Suppose an ice-cream factory is replacing an old CFC cooling system and the manager is told that ammonia is a good alternative.

Explain why ammonia works as a refrigerant and why it is preferred to CFCs for the environment.

Try it first, then show the solutionSolution

Liquid ammonia absorbs a large amount of heat from its surroundings when it evaporates, cooling them.
The gas can be compressed back to liquid and reused.
Ammonia does not deplete the ozone layer, whereas CFCs do.

Answer: High heat absorbed on evaporation; non-ozone-depleting.

Memory hook: Evaporating ammonia takes heat away, without harming the ozone layer.

Fertiliser from Haber's process

Suppose a fertiliser plant runs its ammonia converter and engineers ask why they cannot just run it at room temperature, where more ammonia would form at equilibrium.

Explain the choice of temperature and the role of the catalyst.

Try it first, then show the solutionSolution

The forward reaction is exothermic, so a lower temperature favours more ammonia.
But at low temperature the reaction is far too slow.
About 450-500 °C with a finely divided iron catalyst (molybdenum promoter) gives a reasonable yield quickly.

Answer: A compromise temperature with a catalyst gives an acceptable yield at a useful rate.

Memory hook: Too cold is too slow; the iron catalyst speeds things up.

Volumes when ammonia burns

Suppose 80 cm³ of ammonia and 100 cm³ of oxygen are sparked together in a sealed tube and cooled to room temperature: $4 N H_{3} + 3 O_{2} \to 2 N_{2} + 6 H_{2} O$ .

Find the volume of oxygen left over and the total volume of gas at the end (same temperature and pressure).

Try it first, then show the solutionSolution

NH₃ : O₂ = 4 : 3, so 80 cm³ NH₃ needs 60 cm³ O₂.
O₂ left = 100 - 60 = 40 cm³.
N₂ formed = 80 × 2/4 = 40 cm³; water is liquid.
Total = 40 + 40 = 80 cm³.

Answer: 40 cm³ O₂ left; 80 cm³ total.

Memory hook: Add the leftover reactant to the gaseous products.

Topics in this chapter

Ammonia formula sheet

Laboratory preparation: $2 N H_{4} C l + C a (O H)_{2} \to C a C l_{2} + 2 H_{2} O + 2 N H_{3}$; Heat; dry over CaO.
From magnesium nitride: $M g_{3} N_{2} + 6 H_{2} O \to 3 M g (O H)_{2} + 2 N H_{3}$; Warm water.
Haber's process: $N_{2} + 3 H_{2} ⇌ 2 N H_{3}$; 450-500 °C, 200-900 atm, Fe + Mo.
Reduction of CuO: $3 C u O + 2 N H_{3} \to 3 C u + 3 H_{2} O + N_{2}$; Black → reddish brown.
Excess ammonia with chlorine: $8 N H_{3} + 3 C l_{2} \to 6 N H_{4} C l + N_{2}$; White fumes.
Excess chlorine: $N H_{3} + 3 C l_{2} \to N C l_{3} + 3 H C l$; Explosive yellow liquid.
Burning in oxygen: $4 N H_{3} + 3 O_{2} \to 2 N_{2} + 6 H_{2} O$; Yellowish-green flame.
Catalytic oxidation: $4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$; Pt, about 800 °C.

Ammonia: diagrams to practise

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

Laboratory preparation of ammonia

Draw a labelled diagram of the preparation, drying and collection of ammonia.

Draw

A round-bottom (hard-glass) flask clamped with its mouth slightly downwards, containing NH₄Cl and Ca(OH)₂, heated by a burner.
A delivery tube to a drying tower packed with quicklime.
From the tower, a tube going up into an inverted gas jar (downward displacement of air).
Moist red litmus paper at the mouth of the jar.

Label

NH₄Cl + Ca(OH)₂
heat
drying tower (quicklime)
ammonia gas
inverted gas jar

Watch out: Show the flask tilted; label 'lighter than air'.

Catalytic oxidation of ammonia

Diagram showing ammonia oxidised over platinum.

Draw

A conical flask with concentrated ammonia solution; oxygen bubbled through it.
A heated platinum coil (or gauze) hanging in the flask above the liquid.
Reddish brown fumes at the mouth.

Label

conc. ammonia solution
oxygen in
glowing platinum
brown fumes of NO₂

Watch out: Note that the coil keeps glowing: exothermic reaction.

How the board asks Ammonia

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

Question type	How it is asked	Method
Laboratory preparation set-up	Diagram-based: reactants, why the flask is tilted, drying agent X, method of collection, why not over water.	Use the preparation checklist; quicklime, inverted jar.
Nitride preparation	Section A Question 2 (2025 style): reactant in the funnel, products, drying agent, why the gas is not collected over water.	Warm water; hydroxide + NH₃; CaO.
Haber's process	Match the columns or short answers: catalyst, promoter, temperature, pressure, ratio, separation.	Iron catalyst, molybdenum promoter; don't confuse with platinum (Ostwald) or V₂O₅ (Contact).
Reactions and observations	Ammonia over hot CuO, with excess chlorine or ammonia, burning in oxygen, catalytic oxidation.	Write the equation and one observation for each.
Gay-Lussac numericals	Volumes of NH₃ and O₂ reacting, excess oxygen and total volume.	Use the equation's coefficients; water is liquid.

Tricks to remember Ammonia

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

Light and lime
Ammonia is Light (inverted jar) and dried with Lime (CaO).
Use it when: Collection and drying.
Catalysts: Fe for Fritz (Haber), Pt for Ostwald, V for Contact
Iron in Haber, Platinum in Ostwald, Vanadium pentoxide in Contact.
Use it when: Matching catalysts.
8-3-6-1: excess ammonia
8NH₃ + 3Cl₂ → 6NH₄Cl + N₂; ammonia wins, so you get its salt (white fumes).
Use it when: Chlorine reactions.
Hot oxide goes red, tube gets wet
Ammonia over hot CuO: black → red (copper), droplets of water, nitrogen gas.
Use it when: Reducing property questions.

Ammonia: board-level solved questions

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

Example 1: Reducing property · 1 mark · MCQBoard level

Ammonia passed over heated copper(II) oxide leaves a reddish brown residue. This shows that ammonia is:
(a) basic
(b) an oxidising agent
(c) a reducing agent
(d) highly soluble

Try it first, then show the solutionSolution

Ammonia removes oxygen from CuO, reducing it to copper.

Answer: (c)

Example 2: Collection · 1 mark · Assertion-reasonHarder board level

Assertion (A): Ammonia is collected by downward displacement of air.
Reason (R): Ammonia is highly soluble in water.
(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

Both true. Solubility explains why it is not collected over water; downward displacement of air is used because ammonia is lighter than air.

Answer: (b)

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

In the laboratory preparation of ammonia: (a) write the equation; (b) why is the flask tilted downwards? (c) name the drying agent and say why conc. H₂SO₄ is unsuitable.

Try it first, then show the solutionSolution

(a) $2 N H_{4} C l + C a (O H)_{2} \to C a C l_{2} + 2 H_{2} O + 2 N H_{3}$
(b) So that water formed does not run back onto the hot part and crack the flask.
(c) Quicklime; sulphuric acid reacts with ammonia to form ammonium sulphate.

Answer: As above.

Example 4: Haber's process · 4 marks · Short answerBoard level

State (a) the catalyst and promoter, (b) the temperature, (c) the ratio of reactants in Haber's process, and (d) write the equation.

Try it first, then show the solutionSolution

(a) Finely divided iron; molybdenum.
(b) About 450-500 °C.
(c) N₂ : H₂ = 1 : 3 by volume.
(d) $N_{2} + 3 H_{2} ⇌ 2 N H_{3}$

Answer: As above.

Example 5: Chlorine reactions · 4 marks · Long answerHarder board level

Chlorine is passed into ammonia. State the products and one observation when (a) ammonia is in excess and (b) chlorine is in excess. Write both equations.

Try it first, then show the solutionSolution

(a) $8 N H_{3} + 3 C l_{2} \to 6 N H_{4} C l + N_{2}$
Observation: dense white fumes; greenish-yellow colour of chlorine disappears.
(b) $N H_{3} + 3 C l_{2} \to N C l_{3} + 3 H C l$
Observation: a yellow, explosive oily liquid forms.

Answer: As above.

Example 6: Catalytic oxidation · 3 marks · Short answerHarder board level

Ammonia and air are passed over red-hot platinum. (a) Write the equation. (b) Why does the platinum continue to glow without heating? (c) What is seen at the mouth of the vessel?

Try it first, then show the solutionSolution

(a) $4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$
(b) The reaction is exothermic; its heat keeps the platinum hot.
(c) Reddish brown fumes of NO₂, as NO reacts with air: $2 N O + O_{2} \to 2 N O_{2}$ .

Answer: As above.

Example 7: Mass from an equation · 3 marks · Short answerHarder board level

What mass of ammonium chloride and of calcium hydroxide is needed to prepare 4.48 L of ammonia at S.T.P.? (N = 14, H = 1, Cl = 35.5, Ca = 40, O = 16)

Try it first, then show the solutionSolution

Moles NH₃ = 4.48 ÷ 22.4 = 0.2.
NH₄Cl : NH₃ = 2 : 2, so 0.2 mol × 53.5 = 10.7 g.
Ca(OH)₂ : NH₃ = 1 : 2, so 0.1 mol × 74 = 7.4 g.

Answer: 10.7 g NH₄Cl; 7.4 g Ca(OH)₂.

Example 8: HOTS: identify from reactions · 4 marks · Long answerHOTS / competency

Gas A is alkaline. When passed over a heated black solid B, it gives a reddish brown solid C, a colourless liquid D and a neutral gas E. Identify A to E and write the equation. Why is E collected over water although A is not?

Try it first, then show the solutionSolution

A = ammonia, B = copper(II) oxide, C = copper, D = water, E = nitrogen.
$3 C u O + 2 N H_{3} \to 3 C u + 3 H_{2} O + N_{2}$
Nitrogen is almost insoluble in water, so it can be collected over water.
Ammonia is extremely soluble, so it would dissolve.

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 2 + 1 + 1 + 1 marks.

Ammonia from a nitride

Suppose a student puts magnesium nitride in a conical flask fitted with a dropping funnel, adds a liquid from the funnel, passes the gas through a drying tower Y, and collects it in an inverted gas jar.

(i) · 2 marks
Name the liquid in the funnel and write the equation.
Answer
Answer: Warm water: $M g_{3} N_{2} + 6 H_{2} O \to 3 M g (O H)_{2} + 2 N H_{3}$
(ii) · 1 mark
Name the substance in tower Y.
Answer
Answer: Quicklime (calcium oxide).
(iii) · 1 mark
Why is the gas jar inverted?
Answer
Answer: Ammonia is lighter than air (downward displacement of air).
(iv) · 1 mark
How many litres of ammonia at S.T.P. can 10 g of Mg₃N₂ give? (Mg = 24, N = 14)
Answer
Answer: M = 100; 0.1 mol gives 0.2 mol NH₃ = 4.48 L.

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.

Give two tests for ammonia gas. (2 marks) (2 marks)

Step	Marks
Moist red litmus turns blue	1
Dense white fumes with a rod dipped in conc. HCl	1

Ammonia is passed over hot copper(II) oxide: write the equation and two observations. (3 marks) (3 marks)

Step	Marks
$3 C u O + 2 N H_{3} \to 3 C u + 3 H_{2} O + N_{2}$	1
Black solid turns reddish brown	1
Droplets of a colourless liquid (water) form on the cooler part of the tube	1

80 cm³ of ammonia is burnt in 100 cm³ of oxygen: $4 N H_{3} + 3 O_{2} \to 2 N_{2} + 6 H_{2} O$ . Find the oxygen used, oxygen left, nitrogen formed and total gas volume (water liquid). (4 marks) (4 marks)

Step	Marks
O₂ used = 80 × 3/4 = 60 cm³	1
O₂ left = 100 - 60 = 40 cm³	1
N₂ = 80 × 2/4 = 40 cm³	1
Total = 40 + 40 = 80 cm³	1

Where students lose marks in Ammonia

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

Mistake: Confusing the reason for downward displacement
CISCE examiners' comments, 2024: candidates confused the collection of ammonia with that of HCl, choosing 'heavier than air' or a solubility statement.
Wrong working
Ammonia is collected by downward displacement of air because it is soluble.
Right working
Because it is lighter than air.
Do this: Collection method depends on density; 'not over water' depends on solubility.
Usually costs: 1 mark.
Mistake: Wrong products from nitrides
CISCE examiners' comments, 2025: for ammonia from aluminium nitride, candidates wrote water only or conc. H₂SO₄ as the reagent, aluminium oxide instead of hydroxide, and conc. H₂SO₄ or Ca(OH)₂ as the drying agent.
Wrong working
2AlN + 3H₂O → Al₂O₃ + 2NH₃
Right working
$A l N + 3 H_{2} O \to A l (O H)_{3} + N H_{3}$ (warm water); dry with CaO.
Do this: Nitride + warm water → hydroxide + NH₃.
Usually costs: 1 mark each.
Mistake: Mixing up catalysts
CISCE examiners' comments, 2025: in a match-the-columns item, candidates confused platinum with nickel as catalysts.
Wrong working
Haber's process: platinum catalyst.
Right working
Haber: iron (Mo promoter); Ostwald: platinum.
Do this: Fe-Pt-V for Haber-Ostwald-Contact.
Usually costs: 1 mark.
Mistake: Wrong products over hot CuO
CISCE examiners' comments, 2025: candidates named the gas as NO₂, NO, H₂ or water and gave random colours (blue, pink, black) for the residue.
Wrong working
Gas: hydrogen; residue: black.
Right working
Gas: nitrogen; residue: reddish brown copper.
Do this: Ammonia's N goes to N₂; its H goes into water.
Usually costs: 1 mark each.
Mistake: Ignoring the excess gas
CISCE examiners' comments, 2024: in an ammonia-burning volume question, candidates found the oxygen used but not the excess oxygen, and ignored unused oxygen in the final mixture.
Wrong working
Total volume = N₂ formed only.
Right working
Total = N₂ formed + excess O₂.
Do this: Always list every gas left after the reaction.
Usually costs: 1-2 marks.
Mistake: Excess chlorine versus excess ammonia
CISCE examiners' comments, 2024: candidates confused the excess chlorine and excess ammonia reactions.
Wrong working
Excess ammonia: NCl₃ formed.
Right working
Excess ammonia: NH₄Cl + N₂; excess chlorine: NCl₃ + HCl.
Do this: The gas in excess 'wins': excess NH₃ gives its salt NH₄Cl.
Usually costs: 1 mark.

Practice questions on Ammonia

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
The drying agent used for ammonia is:
(a) concentrated H₂SO₄
(b) phosphorus pentoxide
(c) anhydrous calcium chloride
(d) quicklime
Hint
Base dries base.
Answer
(d)
Q2 · 1 mark · MCQBoard level
In Haber's process, molybdenum acts as:
(a) catalyst
(b) promoter
(c) reactant
(d) drying agent
Hint
It helps the iron.
Answer
(b)
Q3 · 1 mark · MCQHarder board level
Statement I: Ammonia burns in air with a yellowish-green flame.
Statement II: Ammonia burns in oxygen to form nitrogen and water.
(a) Both true
(b) Both false
(c) I true, II false
(d) I false, II true
Hint
Air or oxygen?
Answer
(d)
Q4 · 3 marks · Short answerBoard level
Write equations for the reaction of aqueous ammonia with (a) dilute sulphuric acid, (b) iron(III) chloride solution, (c) lead nitrate solution.
Hint
Neutralisation; precipitates.
Answer
(a) $2 N H_{4} O H + H_{2} S O_{4} \to (N H_{4})_{2} S O_{4} + 2 H_{2} O$ (b) $F e C l_{3} + 3 N H_{4} O H \to F e (O H)_{3} + 3 N H_{4} C l$ (c) $P b (N O_{3})_{2} + 2 N H_{4} O H \to P b (O H)_{2} + 2 N H_{4} N O_{3}$
Q5 · 2 marks · Short answerHarder board level
Write the equation for ammonia with hot lead(IV) oxide and state the property of ammonia shown.
Hint
Like CuO.
Answer
$3 P b O_{2} + 4 N H_{3} \to 3 P b + 6 H_{2} O + 2 N_{2}$ ; reducing property.
Q6 · 3 marks · Short answerHarder board level
Give reasons: (a) Ammonia is not collected over water. (b) Liquid ammonia is used in ice plants. (c) Ammonium nitrate is not used to prepare ammonia in the laboratory.
Hint
Solubility; heat; explosive.
Answer
(a) It is extremely soluble in water. (b) It absorbs a large amount of heat on evaporating. (c) It may decompose explosively on heating.
Q7 · 2 marks · Short answerHarder board level
How is ammonia separated from unreacted nitrogen and hydrogen in Haber's process? Why are the unreacted gases recycled?
Hint
Liquefaction.
Answer
By cooling: ammonia liquefies easily, N₂ and H₂ do not. Recycling uses the unreacted gases, improving the overall yield and saving raw materials.
Q8 · 2 marks · Short answerHarder board level
Calculate the volume of oxygen needed to oxidise 100 L of ammonia catalytically, and the volume of nitric oxide formed (same temperature and pressure).
Hint
4 : 5 : 4.
Answer
$4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$ : O₂ = 125 L; NO = 100 L.
Q9 · 3 marks · Short answerHOTS / competency
A white crystalline salt X, warmed with NaOH solution, gives a gas that turns moist red litmus blue. X's solution gives a white precipitate with barium chloride, insoluble in HCl. (a) Identify X. (b) Write the equation with NaOH. (c) Suggest one use of X.
Hint
Ammonium + sulphate.
Answer
(a) Ammonium sulphate (b) $(N H_{4})_{2} S O_{4} + 2 N a O H \to N a_{2} S O_{4} + 2 H_{2} O + 2 N H_{3}$ (c) Fertiliser.
Q10 · 3 marks · Short answerHOTS / competency
Ammonia and hydrogen chloride are released at the same time from opposite ends of a long glass tube. A white ring forms closer to the HCl end. Explain, and name the white solid.
Hint
Lighter molecules move faster.
Answer
Ammonia (molecular mass 17) is lighter than HCl (36.5), so it diffuses faster and travels further before meeting HCl. They react to form ammonium chloride: $N H_{3} + H C l \to N H_{4} C l$ .
Q11 · 2 marks · Very short answerBoard level
Give two uses of ammonia and two tests for it.
Hint
Fertilisers, refrigerant; litmus, HCl.
Answer
Uses: making fertilisers; refrigerant (also nitric acid, explosives, cleaning). Tests: moist red litmus turns blue; dense white fumes with conc. HCl.

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.Drying agent for ammonia?Show answer
Quicklime (CaO).
2.Catalyst in Haber's process?Show answer
Finely divided iron (molybdenum promoter).
3.Temperature for Haber's process?Show answer
About 450-500 °C.
4.Colour of the flame when ammonia burns in oxygen?Show answer
Yellowish green.
5.Product with excess chlorine?Show answer
Nitrogen trichloride (and HCl).
6.Colour of the fountain with red litmus?Show answer
Blue.
7.Ammonia + hot CuO: gas formed?Show answer
Nitrogen.
8.Why is ammonia used as a refrigerant instead of CFCs?Show answer
It absorbs much heat on evaporation and does not deplete the ozone layer.

Best order to study it

Learn the lab preparation checklist and diagram.
Learn nitride and ammonium salt equations.
Learn Haber's process conditions as a table.
Learn reactions: HCl, CuO, PbO₂, chlorine (both cases), oxygen, catalytic oxidation.
Learn aqueous ammonia with acids and the five salt solutions, uses and tests.

Quick revision checklist

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

Can you write the lab equation and explain the tilted flask, drying agent and collection?
Can you write the equations for Mg₃N₂ and AlN with warm water?
Can you state all the conditions of Haber's process?
Can you write the excess-ammonia and excess-chlorine equations?
Can you write the burning and catalytic oxidation equations with conditions?
Can you predict what aqueous ammonia does to Fe²⁺, Fe³⁺, Pb²⁺, Zn²⁺ and Cu²⁺ solutions?

Ammonia: frequently asked questions

What pressure should I write for Haber's process?

Write 'about 200-900 atmospheres' (high pressure). The direction matters most: high pressure favours ammonia because 4 volumes of reactants form 2 volumes of product.

Is ammonia from nitrides new in the 2027 ICSE syllabus?

Both Mg₃N₂ and AlN with warm water are named in the 2027 syllabus, and the 2025 paper set a question on preparing ammonia from aluminium nitride.

Why does ammonia not burn in air?

Air contains only about one-fifth oxygen; ammonia needs pure oxygen to keep burning.

Why is ammonium hydroxide a weak alkali?

Ammonia dissolves readily but only a small fraction reacts with water to form NH₄⁺ and OH⁻ ions; most remains as dissolved molecules.

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