Page 230 - Chemistry ICSE Class X

216 ICSE Chemistry – 10
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(c) Pb O (s) + 8HCl(aq) o 3PbCl (s) + 4H O + Cl (g)
4
3
2
2
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red lead lead chloride
Hydrochloric Acid [HCl(aq)]
Hydrochloric acid is obtained by dissolving hydrogen chloride
[HCl(g)] in distilled water.
How is hydrochloric acid prepared in laboratory
Hydrogen chloride gas is highly soluble in water. It cannot be
dissolved in water by dipping the delivery tube directly into it
because it is highly soluble in water. It dissolves rapidly and creates
a partial vacuum (or low pressure) in the delivery tube. As a result
of it, water is sucked into the apparatus. This is called back-suction.
To prevent back suction, the gas is dissolved by using a funnel
attachment as shown in Fig. 8.3.
The funnel arrangement
Fig. 8.3 Laboratory preparation of hydrochloric acid
ƒ RTGXGPVU VJG DCEM UWEVKQP QH YCVGT KPVQ VJG ƀCUM
ƒ provides larger surface area for the absorption of the gas in water.

Process: The hydrochloric gas is prepared by the action of hot conc.
sulphuric acid on sodium chloride (or common salt) as described earlier.
ĐŽŶƐƚĂŶƚ ďŽŝůŝŶŐ ŵŝdžƚƵƌĞ ŝƐ ĐĂůůĞĚ But instead of collecting the gas in a gas air, it is dissolved in water.
ĂŶ ĂnjĞŽƚƌŽƉĞ͘ Ŷ ĂnjĞŽƚƌŽƉĞ ďŽŝůƐ Ăƚ
Ă ĮdžĞĚ ƉŽŝŶƚ ĂŶĚ ĚŝƐƟůƐ ŽǀĞƌ ǁŝƚŚŽƵƚ Hydrogen chloride is made to dissolve in water through a funnel as
ĂŶLJ ĐŚĂŶŐĞ ŝŶ ŝƚƐ ĐŽŵƉŽƐŝƟŽŶ͘ shown in Fig. 8.3.
ͻ
, ů ĨŽƌŵƐ Ă ĐŽŶƐƚĂŶƚ ďŽŝůŝŶŐ ŵŝdžƚƵƌĞ
ǁŝƚŚ ǁĂƚĞƌ ;ϮϬ͘ϯй ďLJ ŵĂƐƐ , /Ϳ͕ What are the uses of hydrogen chloride or hydrochloric
ǁŚŝĐŚ ďŽŝůƐ Ăƚ ϭϭϬΣ ͘ dŚŝƐ ŵĞĂŶƐ ƚŚĂƚ acid
ƚŚĞ ŚLJĚƌŽĐŚůŽƌŝĐ ĂĐŝĚ ĨŽƌŵĞĚ ďLJ ƚŚŝƐ
ĚŝƐƐŽůƵƟŽŶ ŵĞƚŚŽĚ ĐŽŶƚĂŝŶƐ ϮϬ͘ϯй Following are the main uses of hydrogen chloride (or hydrochloric acid):
;ďLJ ŵĂƐƐͿ ŽĨ ŚLJĚƌŽŐĞŶ ĐŚůŽƌŝĚĞ͘ ƒ Industrial uses
ͻ
dŚŝƐ ƉƌŽĐĞƐƐ ŽĨ ĐůĞĂŶŝŶŐ ŵĞƚĂů ƐƵƌĨĂĐĞ Š For the manufacture of chlorine.
ďLJ ƵƐŝŶŐ ĂŶ ĂĐŝĚ ŝƐ ĐĂůůĞĚ ƉŝĐŬůŝŶŐ͘ Š For preparing glucose from starch.
dŚŝƐ ƐƚĞƉ ŝƐ ǀĞƌLJ ŝŵƉŽƌƚĂŶƚ ďĞĨŽƌĞ
ĞůĞĐƚƌŽƉůĂƟŶŐ ĂŶĚ ŐĂůǀĂŶŝƐŝŶŐ͘ Š For extracting glue from bones.
Š For the preparation of industrially important chlorides.
Š For the preparation of dyes, drugs, etc.
Š It is used in aqua-regia — a mixture of conc. HCl and conc. HNO
3
in the ratio of 3 : 1. Aqua-regia is used for dissolving noble metals
like gold and platinum.
Š HCl(aq) is also used for cleaning the surface of metals like iron and
steel. The surface layer of such metals contains oxides and other
impurities. HCl dissolves these oxides and renders the surface
clean.

Tests for Hydrogen Chloride and Hydrochloric Acid

Following tests may be used for testing or identifying both HCl(g) and
HCl(aq):
ƒ Odour. HCl(g) has a characteristic pungent and irritating odour.
ƒ With ammonium hydroxide. HCl(g) and the vapour of HCl(aq) give
dense white fumes when a glass rod dipped in ammonium hydroxide