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

Lesson

Hydrochloric acid at work

Part 2 — In water, hydrogen chloride ionises completely, so hydrochloric acid is a strong acid. It shows all the typical reactions of acids, plus some special ones of its own.

In this lesson you will

Write balanced equations for hydrochloric acid with metals, oxides, hydroxides, carbonates, hydrogencarbonates, sulphides and sulphites
Describe the dense white fumes formed with ammonia
State the composition and use of aqua regia
Use silver nitrate and lead nitrate to identify hydrochloric acid and chlorides

Table of the classes of substance that react with hydrochloric acid and the main products
Reacts with	Main products
Ammonia	Ammonium chloride (white fumes)
Active metals	Metal chloride + hydrogen
Oxides and hydroxides	Metal chloride + water
Carbonates, hydrogencarbonates	Chloride + water + carbon dioxide
Sulphides	Chloride + hydrogen sulphide
Sulphites	Chloride + water + sulphur dioxide

Concept

With ammonia: dense white fumes

Hydrogen chloride and ammonia gas combine directly to form tiny solid particles of ammonium chloride, seen as dense white fumes. This is used to identify either gas, and to check whether a jar of either gas is full.

\ce{NH3 + HCl -> NH4Cl}

Dense white fumes of ammonium chloride

Concept

With active metals

Metals above hydrogen in the activity series displace hydrogen: metal + hydrochloric acid → metal chloride + hydrogen. Iron gives iron(II) chloride. Metals below hydrogen (copper, silver, gold) do not react.

Table of the reactions of zinc, magnesium, iron and copper with dilute hydrochloric acid
Metal	Equation	Observation
Zinc	Zn + 2HCl → ZnCl₂ + H₂	Effervescence; gas burns with a pop
Magnesium	Mg + 2HCl → MgCl₂ + H₂	Vigorous effervescence
Iron	Fe + 2HCl → FeCl₂ + H₂	Pale green solution
Copper	No reaction	No change

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