Page 252 - Chemistry ICSE Class X

10 Study of Compounds–

Nitric Acid

Nitric Acid
CONTENTS
Molecular formula HNO 3
ͻ Occurrence Molecular mass 63 u
ͻ WƌĞƉĂƌĂƟŽŶ ŽĨ ŶŝƚƌŝĐ ĂĐŝĚ –1
ͻ KdžŝĚĂƟŽŶ ƌĞĂĐƟŽŶƐ ŽĨ ŶŝƚƌŝĐ ĂĐŝĚ Molar mass 63 g mol Structure of nitric acid
ǁŝƚŚ ƐŽŵĞ ĐŽŵƉŽƵŶĚƐ Basicity 1
ͻ KdžŝĚĂƟŽŶ ƌĞĂĐƟŽŶƐ ŽĨ ŶŝƚƌŝĐ ĂĐŝĚ
ǁŝƚŚ ƐŽŵĞ ŶŽŶŵĞƚĂůƐ Nitric acid was prepared by Johann Glauber in 1650 by distilling a mixture
ͻ KdžŝĚĂƟŽŶ ƌĞĂĐƟŽŶƐ ŽĨ ŶŝƚƌŝĐ ĂĐŝĚ of nitre (chemical name: potassium nitrate) and conc. sulphuric acid.
ǁŝƚŚ ƐŽŵĞ ŵĞƚĂůƐ Lavoisier in 1776 showed the presence of oxygen in this acid.
Cavendish in 1784 established that nitric acid contains nitrogen,
hydrogen and oxygen. Cavendish also prepared nitric acid by passing
electric spark through a mixture of nitrogen, oxygen and moisture.

Occurrence

ƒ In the free state, trace quantity of nitric acid is found in rain water.
ƒ In the combined state, nitric acid occurs in the form of nitrates, such
as nitre (potassium nitrate, KNO ), chile saltpetre (sodium nitrate,
3
NaNO ) and calcium nitrate [Ca(NO ) ].
3 2
3
Preparation of Nitric Acid
^ŽĚŝƵŵ ŶŝƚƌĂƚĞ ;EĂEK Ϳ ĐĂŶ ĂůƐŽ ďĞ
3
ƵƐĞĚ ĨŽƌ ƉƌĞƉĂƌŝŶŐ ŶŝƚƌŝĐ ĂĐŝĚ͘ Ƶƚ
ĐŽƐƚͲĨĂĐƚŽƌ ĚŽĞƐ ŶŽƚ ĨĂǀŽƵƌ ŝƚƐ ƵƐĞ͘ How is nitric acid prepared in laboratory
ƒ Reactants. Nitre (potassium nitrate, KNO ), Conc. sulphuric acid
3
ƒ Products. Potassium bisulphate, Nitric acid
ƒ Procedure. Nitric acid is prepared by heating nitre (potassium nitrate)
with conc. sulphuric acid, (1 : 1 mixture) at 180°C–200°C in a glass
retort. The vapour of nitric acid is condensed in a receiver which is
cooled by water. The apparatus used is shown in Fig. 10.1.
heat
ƒ Reaction: KNO (s) + H SO (conc.) o KHSO + HNO (l)
3
4
3
4
2

potassium sulphuric acid <200°C potassium nitric acid
nitrate bisulphate
ƒ Collection. The condensed nitric acid is collected as the
distillate in a glass receiver.
ƒ Precautions. The following precautions should be observed
during the preparation of nitric acid:
Š All glass apparatus should be used because nitric acid
attacks rubber and cork.
Š The reaction mixture should not be heated above 200°C.
At higher temperatures,
y nitric acid would decompose into nitrogen dioxide
Fig. 10.1 Laboratory preparation of nitric acid and oxygen.