Study of Compounds — Ammonia
ICSE Class 10 · Chemistry · Chapter 9
What this chapter covers
- Laboratory preparation of ammonia from ammonium chloride
- Ammonia from nitrides and ammonium salts
- Manufacture of ammonia by Haber's process
- Density and solubility of ammonia
- Aqueous solution of ammonia
- Burning of ammonia in oxygen
- Catalytic oxidation of ammonia
- Reactions of ammonia gas
- Reactions of aqueous ammonia with acids and metal salt solutions
- Uses of ammonia
- Tests for ammonia
Key definitions
Ammonia is a compound of nitrogen and hydrogen with the formula NH3, in which one nitrogen atom is joined to three hydrogen atoms by single covalent bonds and still keeps one lone pair of electrons.
Downward displacement of air is the method of collecting a gas that is lighter than air by passing it upwards into an inverted jar, so that the gas pushes the air down and out.
A drying agent is a substance that absorbs water vapour from a gas without reacting with the gas itself.
A metal nitride is a compound of a metal with nitrogen alone, in which nitrogen is present as the nitride ion, N3-.
Haber's process is the industrial method of manufacturing ammonia by the direct combination of nitrogen and hydrogen in the ratio 1 : 3 by volume, at about 450–500 °C and high pressure, over a catalyst of finely divided iron.
A reversible reaction is a reaction in which the products can react to give back the reactants, so that the reaction proceeds in both directions under the same conditions.
A catalyst is a substance that changes the rate of a chemical reaction without itself undergoing any permanent chemical change.
A promoter is a substance that increases the efficiency of a catalyst, although on its own it has little or no catalytic action.
Liquid ammonia is ammonia gas that has been liquefied by cooling or by compression; it contains no water and is not the same as the solution of ammonia in water.
Vapour density is the ratio of the mass of a certain volume of a gas to the mass of the same volume of hydrogen, measured at the same temperature and pressure.
The fountain experiment is a demonstration of the very high solubility of a gas in water, in which water rushes into a flask of the gas through a narrow jet and forms a fountain.
Ammonium hydroxide is the aqueous solution of ammonia, a weak alkali that contains a low concentration of hydroxide ions because the dissolved ammonia is only slightly ionised.
Key points
- Ammonia, NH3, is a colourless, pungent, basic gas; the lone pair on nitrogen lets it accept protons.
- Laboratory preparation: heat ammonium chloride with slaked lime in a tilted flask; dry over quicklime; collect by downward displacement of air.
- Concentrated sulphuric acid, phosphorus pentoxide and anhydrous calcium chloride cannot dry ammonia because they react with it.
- Metal nitrides (Mg3N2, AlN) give ammonia with warm water; every ammonium salt gives ammonia when warmed with an alkali.
- Haber's process: N2 + 3H2 rightleftharpoons 2NH3, ratio 1 : 3, 450–500 °C, 200–900 atm, iron catalyst with molybdenum promoter; ammonia removed by liquefaction, unreacted gases recycled.
- Ammonia is lighter than air (vapour density 8.5) and extremely soluble in water, as the fountain experiment shows.
- The aqueous solution, ammonium hydroxide, is a weak alkali; liquor ammonia is its concentrated form, and liquid ammonia contains no water.
- Ammonia burns in oxygen to give nitrogen and water, but over platinum at 800 °C it is oxidised to nitric oxide, the first step of Ostwald's process.
- Ammonia gives white fumes with hydrogen chloride and reduces hot copper(II) oxide and lead(IV) oxide, being oxidised to nitrogen.
- With excess ammonia, chlorine gives ammonium chloride and nitrogen; with excess chlorine, it gives explosive nitrogen trichloride and hydrogen chloride.
- Ammonium hydroxide precipitates Fe(OH)3 (reddish-brown), Fe(OH)2 (dirty green), Pb(OH)2 (white); Zn(OH)2 and Cu(OH)2 dissolve in excess.
- Uses: fertilisers, explosives, nitric acid, refrigerant (an ozone-safe alternative to CFCs) and cleansing agents.
- Tests: pungent smell, moist red litmus turns blue, white fumes with concentrated HCl, brown precipitate with Nessler's reagent.
Questions answered
Write the balanced equation for the laboratory preparation of ammonia from ammonium chloride, naming the condition.
Why is the flask clamped in a slanting position, mouth slightly downwards, during the laboratory preparation?
Name the drying agent used for ammonia, and give one reason why concentrated sulphuric acid cannot be used.
Why is ammonia collected by downward displacement of air and not over water?
Give balanced equations for the action of warm water on magnesium nitride and on aluminium nitride.
State the temperature, pressure, catalyst and promoter used in Haber's process, and explain why a very low temperature is not used.
How is ammonia separated from unreacted nitrogen and hydrogen in Haber's process, and what happens to the unreacted gases?
In the fountain experiment, why does water rise into the flask, and why does red litmus in the water turn blue?
Past board exam questions
ICSE 2027 sample paper · 2 marks
Give one significant observation when: (a) Excess of chlorine gas reacts with ammonia. (b) Zinc nitrate is strongly heated in a test tube.
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ICSE 2027 sample paper · 3 marks
Identify the reactants P, Q and R in the following reactions: (a) Copper (II) oxide + P → Copper + Water + Nitrogen (b) Iron pyrite + Q → Iron oxide + Sulphur dioxide (c) Ammonia + R → Nitrogen + Water
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ICSE 2027 sample paper · 4 marks
Rohan has two test tubes, A containing sodium chloride and B containing ammonium chloride. He adds sodium hydroxide solution to both the test tubes and warms them gently. Answer the following questions: (a) In which test tube (A or B) will Rohan observe the evolution of a gas? (b) Name the gas that is evolved. (c) What will be the colour of the flame when this gas burns in oxygen? (d) Write an equation for the reaction that occurs in the test tube in which the gas has evolved.
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ICSE 2026 board paper · 5 marks
Given below is the industrial process for the manufacture of ammonia gas. In the schematic set-up: H₂ and N₂ enter a compressor (C); the compressed gases pass into a catalytic chamber containing the catalyst bed; the gases leaving the chamber pass through cooling coils, below which liquid ammonia collects; the unreacted gases are led to a recycler (R), which sends them back to the compressor. Study the set-up to answer the following questions. (a) Name the process. (b) Which catalyst is used in the above process? (c) In the above set-up, how is ammonia gas separated from the unreacted gases to obtain liquid ammonia? (d) Which two properties of ammonia gas can be demonstrated by the Fountain Experiment?
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ICSE 2026 sample paper · 2 marks
Give reasons: (a) When ammonia gas is passed over black copper oxide in a combustion tube a reddish-brown substance is left behind. (b) Quick lime is not used to dry hydrogen chloride gas.
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ICSE 2026 sample paper · 3 marks
Write balanced chemical equations for the following reactions: (a) Ammonium chloride reacts with calcium hydroxide. (b) Nitric acid reacts with zinc carbonate. (c) Concentrated sulphuric acid is added to hydrated copper sulphate.
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ICSE 2025 compartment paper · 1 mark
Which gas is evolved when ammonia gas is passed over buff yellow PbO?
- N₂O
- NO
- N₂
- NO₂
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ICSE 2025 compartment paper · 5 marks
Complete the following sentences by choosing the correct answer from the brackets: (a) The metal to be refined is kept at the ____________ during the process of electro-refining. [cathode / anode] (b) Dilute HCl and dilute H₂SO₄ can be distinguished by adding _________ solution. [NaNO₃ / BaCl₂] (c) Ammonia gas is collected by ___________ displacement of air. [upward / downward] (d) The gas formed when copper carbonate is heated is ___________. [O₂ / CO₂] (e) Excess ammonia reacts with chlorine to form ___________. [nitrogen / nitrogen trichloride]