When solid ammonium chloride (NH_4Cl) is heated with aqueous sodium hydroxide (NaOH), a ch… — JAMB UTME

When solid ammonium chloride ( $NH_4Cl$ ) is heated with aqueous sodium hydroxide ( $NaOH$ ), a characteristic gas is evolved. Which of the following observations correctly identifies the gas liberated and demonstrates a key chemical property of bases?

Ammonia gas ( $NH_3$ ) is liberated, which turns damp red litmus paper blue.Answer
B
Hydrogen gas ( $H_2$ ) is liberated, which turns damp blue litmus paper red.
C
Chlorine gas ( $Cl_2$ ) is liberated, which bleaches damp litmus paper.
D
Nitrogen(IV) oxide ( $NO_2$ ) is liberated, which turns lime water milky.

Answer

Heating an ammonium salt with a soluble base (alkali) liberates ammonia gas (

NH_3

), an alkaline gas that turns damp red litmus paper blue.

A defining chemical property of bases (alkalis) is their ability to react with ammonium salts when heated to displace and liberate ammonia gas (

NH_3

). Ammonia is alkaline in aqueous medium and turns damp red litmus paper blue.

Step-by-Step Solution

Identify the chemical reaction taking place

The reaction between ammonium chloride and sodium hydroxide is represented by:

NH_4Cl(s) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l) + NH_3(g)

Reaction of ammonium salts with strong bases upon warming is a general chemical property of bases used to test for ammonium ions and liberate ammonia.

Determine the nature and testing method of the evolved gas

Ammonia (

NH_3

) is a alkaline gas soluble in water forming

NH_4^+(aq)

and

OH^-(aq)

ions.

Because it produces hydroxide ions in moisture, damp red litmus paper turns blue when exposed to the gas.

Key Concept

Chemical reaction of bases with ammonium salts to liberate ammonia gas

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