Ammonia — Part 2: Chemical properties, uses and tests: visual lesson, ICSE Class 10 Chemistry (Science Paper 2)

Lesson

Ammonia reacts

Part 2 — Ammonia burns in oxygen, is oxidised over platinum, reduces hot metal oxides, reacts with chlorine, and in water forms an alkali that precipitates metal hydroxides.

In this lesson you will

Compare the burning of ammonia with its catalytic oxidation, with equations and conditions
Write equations and observations for ammonia reducing hot metal oxides and reacting with chlorine
Predict the precipitates formed by aqueous ammonia with salt solutions
State the uses of ammonia, explain the move to ozone-safe refrigerants and describe tests for ammonia

Table of the reactions of ammonia studied in Part 2 and their main products
Reaction	Main products
Burning in oxygen	Nitrogen + water
Catalytic oxidation (Pt, 800 °C)	Nitric oxide + water
With hot CuO	Copper + water + nitrogen
With chlorine	NH₄Cl + N₂ or NCl₃ + HCl
Aqueous, with salt solutions	Metal hydroxide precipitates

Concept

Burning in oxygen

Ammonia does not burn in air and does not support combustion. But a jet of ammonia burns in oxygen with a greenish-yellow flame, forming nitrogen and water vapour.

\ce{4NH3 + 3O2 -> 2N2 + 6H2O}

Burning of ammonia in oxygen

Concept

Catalytic oxidation over platinum

Over a platinum catalyst at about 800 °C, ammonia is oxidised to nitric oxide instead of nitrogen. The reaction is exothermic, so the platinum stays red-hot. In air, nitric oxide forms reddish-brown nitrogen dioxide: 2NO + O₂ → 2NO₂. This is the first step of Ostwald’s process for nitric acid.

\ce{4NH3 + 5O2 -> 4NO + 6H2O}

Catalytic oxidation: platinum, about 800 °C

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