Page 238 - Chemistry ICSE Class X

9 Study of Compounds–

Ammonia

Ammonia
CONTENTS
Molecular formula NH 3 Nature Covalent
ͻ KĐĐƵƌƌĞŶĐĞ ŽĨ ĂŵŵŽŶŝĂ
ͻ &ŽƌŵƐ ŽĨ ĂŵŵŽŶŝĂ Molecular mass 17 u
ͻ 'ĞŶĞƌĂů ŵĞƚŚŽĚƐ ŽĨ ƉƌĞƉĂƌĂƟŽŶ ŽĨ Molar mass 17 g mol –1 Dot structure
ĂŵŵŽŶŝĂ
3
ͻ >ĂďŽƌĂƚŽƌLJ ƉƌĞƉĂƌĂƟŽŶ ŽĨ ĂŵŵŽŶŝĂ Liquid ammonia NH (l)
ĨƌŽŵ ĂŵŵŽŶŝƵŵ ĐŚůŽƌŝĚĞ Liquor ammonia NH OH(aq) Structural formula
4
ͻ /ŶĚƵƐƚƌŝĂů ƉƌĞƉĂƌĂƟŽŶ ŽĨ Liquor ammonia fortis NH OH(sat.)
ĂŵŵŽŶŝĂͶ,ĂďĞƌ͛Ɛ ƉƌŽĐĞƐƐ 4
ͻ WŚLJƐŝĐĂů ĂŶĚ ĐŚĞŵŝĐĂů ƉƌŽƉĞƌƟĞƐ ŽĨ
ĂŵŵŽŶŝĂ Occurrence of Ammonia
Free ammonia occurs near decaying organic matter or near a toilet.
Ammonia is formed due to the bacterial decomposition of urea present in
urine.
bacteria
NH .CO.NH (aq) + 2H O(l) o 2NH (g) + H O(l) + CO (g)
2
2
3
2
2
2
ŵŵŽŶŝĂ ĂŶĚ ĂŵŵŽŶŝƵŵ ƐĂůƚƐ ĂƌĞ urea (in urine) ammonia
ŚŝŐŚůLJ ƐŽůƵďůĞ ŝŶ ǁĂƚĞƌ͘ ^Ž͕ ƚŚĞLJ ĚŽ In combined form, ammonia occurs as ammonium sulphate,
ŶŽƚ ŽĐĐƵƌ ĂƐ ŵŝŶĞƌĂůƐ͘
ammonium chloride and many other ammonium salts.
Forms of Ammonia
Ammonia is a gaseous compound at room temperature. It can, however, be
NKSWGſGF CV TQQO VGORGTCVWTG D[ CRRN[KPI C RTGUUWTG QH Ō CVOQURJGTG
Most common forms of ammonia are
ƒ Gaseous ammonia NH (g)
3
ƒ Liquid ammonia NH (l)
3
ƒ Concentrated solution of ammonia in water NH OH(aq)
4
The saturated solution of ammonia in water is called liquor ammonia
fortis (NH OH (sat. QT COOQPKC
4
General Methods of Preparation of Ammonia

How is ammonia prepared from ammonium salts
Ammonia can be prepared by heating ammonium salts with a caustic alkali,
such as sodium hydroxide (or caustic soda), slakedlime, or potassium
hydroxide (or caustic potash).
heat
KĨ Ăůů ƚŚĞ ĂŵŵŽŶŝƵŵ ƐĂůƚƐ͕ 2NH Cl(s) + Ca(OH) (s) o CaCl (s) + 2H O(l) + 2NH (g)
4
2
2
2
3
ĂŵŵŽŶŝƵŵ ŶŝƚƌĂƚĞ ;E, EK Ϳ ŝƐ ŶŽƚ ammonium chloride slakedlime ammonia
4
3
heat
ƵƐĞĚ ĨŽƌ ƉƌĞƉĂƌŝŶŐ ĂŵŵŽŶŝĂ ŐĂƐ͘ (NH ) SO (s) + Ca(OH) (s) o CaSO (s) + 2H O(l) + 2NH (g)
4
3
4
4 2
2
2
dŚŝƐ ŝƐ ďĞĐĂƵƐĞ ĂŵŵŽŶŝƵŵ ŶŝƚƌĂƚĞ ammonium sulphate slakedlime ammonia
heat
ĚĞĐŽŵƉŽƐĞƐ explosively ĨŽƌŵŝŶŐ (NH ) SO (s) + 2NaOH(aq) o Na SO (aq) + 2H O(l) + 2NH 3
2
4 2
4
2
4
ŶŝƚƌŽƵƐ ŽdžŝĚĞ ;EKͿ ĂŶĚ ǁĂƚĞƌ ǀĂƉŽƵƌ͘ ammonium sulphate sodium hydroxide ammonia
(caustic soda)