ChemistryICSE Class 10 · Ammonia

Reactions of Ammonia: Basic and Reducing Properties (ICSE Class 10)

Updated 15 October 2026 · Fact-checked

Ammonia is basic: it forms white fumes of ammonium chloride with hydrogen chloride and ammonium salts with acids. It is also a reducing agent: it reduces hot copper(II) oxide to copper, giving nitrogen and water. With excess chlorine it forms nitrogen trichloride; it burns in oxygen to nitrogen and, over platinum, oxidises to nitric oxide.

Understand Reactions of Ammonia

Ammonia shows two kinds of chemistry, and exam questions usually ask which one a reaction shows.

1. Basic nature (ammonia accepts H⁺).

With hydrogen chloride gas: dense white fumes of ammonium chloride, $N H_{3} + H C l \to N H_{4} C l$ .
In water it forms a weak alkali, ammonium hydroxide, which turns moist red litmus blue: $N H_{3} + H_{2} O ⇌ N H_{4} O H$ .
Aqueous ammonia neutralises acids to give ammonium salts, for example $2 N H_{4} O H + H_{2} S O_{4} \to (N H_{4})_{2} S O_{4} + 2 H_{2} O$ and $N H_{4} O H + H N O_{3} \to N H_{4} N O_{3} + H_{2} O$ .

2. Reducing nature (the hydrogen of ammonia removes oxygen; nitrogen is set free).

Hot copper(II) oxide: $3 C u O + 2 N H_{3} Δ 3 C u + 3 H_{2} O + N_{2}$ . The black solid turns reddish-brown (copper), water droplets collect on the cooler part of the tube, and a colourless gas, nitrogen, comes off.
Hot lead(IV) oxide: $3 P b O_{2} + 4 N H_{3} Δ 3 P b + 6 H_{2} O + 2 N_{2}$ . The dark brown oxide gives greyish lead.
Chlorine: the products depend on which gas is in excess.
Ammonia in excess: $8 N H_{3} + 3 C l_{2} \to 6 N H_{4} C l + N_{2}$ . The greenish-yellow colour of chlorine disappears and dense white fumes of ammonium chloride form. (Chlorine first takes hydrogen to form HCl, which the excess ammonia turns into NH₄Cl.)
Chlorine in excess: $N H_{3} + 3 C l_{2} \to N C l_{3} + 3 H C l$ . A yellow, oily, highly explosive liquid, nitrogen trichloride, forms.

3. Reactions with oxygen.

Ammonia does not burn in air, but it 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: a mixture of ammonia and air passed over platinum at about 800 °C gives nitric oxide: $4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$ . The reaction is exothermic, so the platinum keeps glowing after heating stops, and reddish-brown fumes of nitrogen dioxide appear as NO meets more air ( $2 N O + O_{2} \to 2 N O_{2}$ ). This is the first step of Ostwald's process.

Gas volumes. Because these are gas reactions, Gay-Lussac's law lets you find the volumes of gases left; water is a liquid at room temperature and is not counted.

Reactions of Ammonia: formulas and key facts

With hydrogen chloride: $N H_{3} + H C l \to N H_{4} C l$
Reduction of hot copper(II) oxide: $3 C u O + 2 N H_{3} \to 3 C u + 3 H_{2} O + N_{2}$
Reduction of hot lead(IV) oxide: $3 P b O_{2} + 4 N H_{3} \to 3 P b + 6 H_{2} O + 2 N_{2}$
Chlorine with excess ammonia, and excess chlorine: $8 N H_{3} + 3 C l_{2} \to 6 N H_{4} C l + N_{2}; N H_{3} + 3 C l_{2} \to N C l_{3} + 3 H C l$
Burning in oxygen and catalytic oxidation: $4 N H_{3} + 3 O_{2} \to 2 N_{2} + 6 H_{2} O; 4 N H_{3} + 5 O_{2} P t 4 N O + 6 H_{2} O$
Observations to remember: Ammonia with HCl gas dense white fumes
Hot CuO black to reddish-brown, water droplets, nitrogen given off
Excess ammonia with chlorine greenish-yellow colour vanishes, white fumes
Excess chlorine yellow explosive oily liquid
Burning in oxygen yellowish-green flame
Over platinum wire keeps glowing, reddish-brown fumes

Ammonia with HCl gas	dense white fumes
Hot CuO	black to reddish-brown, water droplets, nitrogen given off
Excess ammonia with chlorine	greenish-yellow colour vanishes, white fumes
Excess chlorine	yellow explosive oily liquid
Burning in oxygen	yellowish-green flame
Over platinum	wire keeps glowing, reddish-brown fumes

How to solve Reactions of Ammonia questions

First decide which property the reaction shows, then write the equation and the observation.

1Ammonia gaining H⁺ to form NH₄⁺ (with acids, HCl, water) shows its basic nature.
2Ammonia losing hydrogen and giving nitrogen (with CuO, PbO₂, Cl₂, O₂) shows its reducing nature.
3With chlorine, check which reactant is in excess before writing the products.
4For burning, distinguish 'in oxygen' (gives N₂) from 'over platinum' (gives NO).
5Give the colour change or appearance as the observation, not just the product names.
6For gas-volume questions, use the coefficients (Gay-Lussac's law) and remember that unused excess gas stays in the mixture.

Reactions of Ammonia in real life

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.

Never mix ammonia and bleach

Suppose someone cleaning a bathroom mixes an ammonia-based glass cleaner with a chlorine-releasing bleach in a small closed room, so that chlorine is present in excess over ammonia.

Using the reaction of ammonia with excess chlorine, explain why this is dangerous.

Try it first, then show the solutionSolution

With chlorine in excess: $N H_{3} + 3 C l_{2} \to N C l_{3} + 3 H C l$ .
Nitrogen trichloride is a yellow, oily, highly explosive compound, and HCl and leftover chlorine are corrosive, choking gases.

Answer: Excess chlorine converts ammonia into explosive nitrogen trichloride and corrosive HCl, so the two cleaners must never be mixed.

Memory hook: Too much chlorine makes trouble: NCl₃ explodes.

Tricks to remember Reactions of Ammonia

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

Basic takes H⁺, reducing gives N₂
If NH₄⁺ forms, ammonia acted as a base. If N₂ (or NO) forms, ammonia acted as a reducing agent.
Use it when: MCQs that ask which property is shown.
Black to brown means reduced
CuO black → Cu reddish-brown: something took the oxygen away, so the gas is a reducing agent.
Use it when: Ammonia over hot copper(II) oxide.
Excess decides
Excess ammonia: Ammonium chloride (A for A). Excess chlorine: nitrogen triChloride (C for C).
Use it when: Chlorine and ammonia questions.

Reactions of Ammonia: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Which property? · 1 mark · MCQBoard level

When ammonia is passed over heated lead(IV) oxide, greyish lead is formed. This reaction shows that ammonia is:
(a) basic
(b) an oxidising agent
(c) a reducing agent
(d) a dehydrating agent

Try it first, then show the solutionSolution

PbO₂ loses oxygen to become Pb: it is reduced.
The substance that reduces it is the reducing agent.

Answer: (c) a reducing agent.

Example 2: Copper oxide: gas and residue · 2 marks · Short answerBoard level

Dry ammonia is passed over hot copper(II) oxide and the products are led through a U-tube cooled in ice. (a) Write the balanced equation. (b) Name the liquid that collects in the U-tube and the gas that passes on through it.

Try it first, then show the solutionSolution

(a) $3 C u O + 2 N H_{3} \to 3 C u + 3 H_{2} O + N_{2}$ (the black oxide turns reddish-brown as copper forms).
(b) Water condenses in the cooled U-tube (it turns anhydrous copper sulphate blue); nitrogen, which does not condense, passes on.

Answer: (a) As above. (b) Water collects; nitrogen passes on.

Example 3: Chlorine and ammonia, both ways · 3 marks · Short answerHarder board level

Write the balanced equation and one observation when chlorine reacts with (a) excess ammonia, (b) ammonia when chlorine is in excess.

Try it first, then show the solutionSolution

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

Answer: (a) Ammonium chloride and nitrogen, white fumes. (b) Nitrogen trichloride and HCl, yellow explosive liquid.

Example 4: Two ways to oxidise ammonia · 3 marks · Short answerHarder board level

Compare the burning of ammonia in oxygen with its catalytic oxidation over platinum: give the equation, the nitrogen-containing product and one observation for each.

Try it first, then show the solutionSolution

Burning in oxygen: $4 N H_{3} + 3 O_{2} \to 2 N_{2} + 6 H_{2} O$ ; product nitrogen; yellowish-green flame.
Over platinum at about 800 °C: $4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$ ; product nitric oxide; platinum keeps glowing and reddish-brown fumes of NO₂ appear.

Answer: In oxygen: N₂, yellowish-green flame. Over Pt: NO, glowing platinum and brown fumes.

Example 5: Gas left after burning · 3 marks · Short answerHOTS / competency

60 cm³ of ammonia is burnt in 60 cm³ of oxygen: $4 N H_{3} + 3 O_{2} \to 2 N_{2} + 6 H_{2} O$ . Find the composition and total volume of the gases left after cooling to room temperature (all volumes at the same temperature and pressure).

Try it first, then show the solutionSolution

O₂ needed for 60 cm³ NH₃ $= 60 \times \frac{3}{4} = 45$ cm³; ammonia is used up and O₂ left $= 60 - 45 = 15$ cm³.
N₂ formed $= 60 \times \frac{2}{4} = 30$ cm³; water is a liquid and is not counted.
Total $= 15 + 30 = 45$ cm³.

Answer: 15 cm³ oxygen + 30 cm³ nitrogen = 45 cm³.

Example 6: Masses in the copper oxide reaction · 4 marks · Long answerHOTS / competency

2.4 g of copper(II) oxide is completely reduced by ammonia: $3 C u O + 2 N H_{3} \to 3 C u + 3 H_{2} O + N_{2}$ . Calculate (a) the mass of copper formed, (b) the mass of ammonia used, (c) the volume of nitrogen at S.T.P. (Cu = 64, O = 16, N = 14, H = 1)

Try it first, then show the solutionSolution

Moles of CuO $= 2.4/80 = 0.03$ .
(a) Cu $= 0.03$ mol $= 0.03 \times 64 = 1.92$ g.
(b) NH₃ $= 0.03 \times \frac{2}{3} = 0.02$ mol $= 0.34$ g.
(c) N₂ $= 0.03/3 = 0.01$ mol $= 0.01 \times 22400 = 224$ cm³.

Answer: (a) 1.92 g (b) 0.34 g (c) 224 cm³.

Where students lose marks in Reactions of Ammonia

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

Mistake: Calling the CuO reaction 'basic' or 'oxidising'
In 2024 (Q1(x)) candidates confused the reducing property of ammonia with its oxidising or basic property.
Do this: Copper oxide loses oxygen, so ammonia is the reducing agent.
Usually costs: 1 mark.
Mistake: Wrong gas or colour in the CuO reaction
In 2025 (Q5(ii)) examiners found NO₂, NO, H₂ or water given as the gas, and blue, pink or black as the residue colour.
Do this: Gas: nitrogen. Residue: reddish-brown copper.
Usually costs: 1 to 2 marks.
Mistake: Not saying which reactant is in excess
In 2024 (Q3(i)) candidates added 'aqueous' instead of 'excess' ammonia and confused the two chlorine reactions.
Wrong working
Ammonia reacts with chlorine to give ammonium chloride and nitrogen.
Right working
Excess ammonia reacts with chlorine to give ammonium chloride and nitrogen.
Do this: Always state 'excess ammonia' or 'excess chlorine'.
Usually costs: 1 mark.
Mistake: Ignoring unused oxygen
In 2024 (Q7(iii)) candidates found the oxygen used and the nitrogen formed but left out the excess oxygen in the final mixture.
Do this: Final gas = excess reactant + gaseous products; water is liquid at room temperature.
Usually costs: 1 mark.

Exam tips

Pair every reaction with its observation; 'state what you observe' items are very common.
Write 'heated' or 'hot' copper(II) oxide: cold CuO does not react.
For burning in oxygen, nitrogen is formed; for catalytic oxidation over platinum, nitric oxide is formed.
Keep a catalyst list: iron (Haber), platinum (catalytic oxidation of ammonia), vanadium pentoxide (Contact process).

Practice questions on Reactions of 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 product formed when ammonia reacts with excess chlorine is:
(a) ammonium chloride
(b) nitrogen
(c) nitrogen trichloride
(d) hydrazine
Hint
Chlorine replaces all the hydrogen.
Answer
(c) nitrogen trichloride (with HCl).
Q2 · 1 mark · Very short answerBoard level
What is seen when a rod dipped in concentrated HCl is brought near ammonia gas? Write the equation.
Hint
A white solid in the air.
Answer
Dense white fumes; $N H_{3} + H C l \to N H_{4} C l$ .
Q3 · 2 marks · Short answerBoard level
Write balanced equations for the reaction of aqueous ammonia with (a) dilute nitric acid, (b) dilute sulphuric acid.
Hint
Ammonium salt + water.
Answer
(a) $N H_{4} O H + H N O_{3} \to N H_{4} N O_{3} + H_{2} O$ (b) $2 N H_{4} O H + H_{2} S O_{4} \to (N H_{4})_{2} S O_{4} + 2 H_{2} O$ .
Q4 · 1 mark · Very short answerHarder board level
In the catalytic oxidation of ammonia, why does the platinum continue to glow after the burner is removed?
Hint
Is the reaction exothermic?
Answer
The reaction is exothermic; the heat released keeps the platinum red hot.
Q5 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Ammonia shows basic nature when it reacts with hydrogen chloride.
Reason (R): Ammonia accepts a proton to form the ammonium ion.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
NH₃ + H⁺ → NH₄⁺.
Answer
(a).
Q6 · 2 marks · Short answerHarder board level
30 cm³ of chlorine reacts completely with excess ammonia: $8 N H_{3} + 3 C l_{2} \to 6 N H_{4} C l + N_{2}$ . What volume of ammonia is used and what volume of nitrogen is formed at the same temperature and pressure?
Hint
Ammonium chloride is a solid.
Answer
NH₃ used $= 30 \times \frac{8}{3} = 80$ cm³; N₂ formed $= 30 \times \frac{1}{3} = 10$ cm³.
Q7 · 2 marks · Short answerHarder board level
40 L of ammonia is oxidised over platinum: $4 N H_{3} + 5 O_{2} \to 4 N O + 6 H_{2} O$ . Find the volume of oxygen required and of nitric oxide formed at the same temperature and pressure.
Hint
Ratio 4 : 5 : 4.
Answer
O₂ $= 40 \times \frac{5}{4} = 50$ L; NO $= 40$ L.
Q8 · 3 marks · Short answerHOTS / competency
A colourless gas X turns moist red litmus blue. When X is passed over a heated black solid, a reddish-brown solid and a colourless liquid form, and a gas that is neither acidic nor basic is given off. Identify the gas X, the black solid and the neutral gas, write the equation and state the property of X shown.
Hint
The liquid turns anhydrous copper sulphate blue.
Answer
X is ammonia; the black solid is copper(II) oxide; the neutral gas is nitrogen. $3 C u O + 2 N H_{3} \to 3 C u + 3 H_{2} O + N_{2}$ . Reducing property.

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.Colour of the flame when ammonia burns in oxygen?Show answer
Yellowish-green.
2.Gas given off when ammonia reduces CuO?Show answer
Nitrogen.
3.Products of excess ammonia with chlorine?Show answer
Ammonium chloride and nitrogen.
4.Catalyst for oxidising ammonia to nitric oxide?Show answer
Platinum (at about 800 °C).
5.Which property of ammonia forms white fumes with HCl?Show answer
Its basic nature.

Reactions of Ammonia: frequently asked questions

Why is ammonia called a reducing agent?

It removes oxygen from hot metal oxides such as CuO and PbO₂ (its hydrogen forms water) and is itself oxidised to nitrogen.

What happens when ammonia reacts with chlorine?

With excess ammonia, ammonium chloride and nitrogen form (white fumes). With excess chlorine, explosive nitrogen trichloride and HCl form.

Does ammonia burn in air?

No. It burns only in oxygen, with a yellowish-green flame, forming nitrogen and water.

What is the catalytic oxidation of ammonia used for?

It is the first step of Ostwald's process: the nitric oxide formed is oxidised to NO₂ and absorbed in water to make nitric acid.