Page 239 - Chemistry ICSE Class X

Study of Compounds–Ammonia 225

How is ammonia prepared from metal nitrides
Ammonia can also be prepared from metal nitrides. Metal nitrides, such
as magnesium nitride and aluminium nitride, on hydrolysis with boiling
water/steam or an alkali give ammonia.

boil
ƒ Reactions: Mg N 2 + 6H O o Mg(OH) 2 + 2NH (g)
2
3
3
magnesium magnesium ammonia
nitride hydroxide
boil
AlN + NaOH + H O o NaAlO 2 + NH (g)
2
3
aluminium sod. meta-aluminate ammonia
nitride
ƒ Procedure. Small pieces of magnesium
nitride (Mg N ) are placed
2
3
KP C TQWPF DQVVQO ƀCUM ſVVGF YKVJ C EQTM ſVVGF YKVJ C
thistle funnel, and a delivery tube as shown in Fig. 9.1.
Warm water is dropped dropwise from the thistle
funnel.
The ammonia gas formed is dried and collected.
ƒ Drying of ammonia gas. Ammonia gas prepared by
this method contains some moisture. This moist gas
is dried by passing through a column of quicklime
(CaO).
ƒ Collection of ammonia gas. Ammonia gas is collected Fig. 9.1 An experimental set-up for preparing ammonia from
magnesium nitride
by the downward displacement of air because
Š Ammonia gas is lighter than air.
Š Ammonia gas is highly soluble in water. Therefore, it cannot be
collected over water. dŚĞ ŇĂƐŬ ŝƐ ŬĞƉƚ ŝŶ ƚŚĞ ŝŶĐůŝŶĞĚ
ƉŽƐŝƟŽŶ ƐŽ ƚŚĂƚ ĚƌŽƉůĞƚƐ ŽĨ
ĐŽŶĚĞŶƐĞĚ ǁĂƚĞƌ ĚŽ ŶŽƚ ƚƌŝĐŬůĞ ďĂĐŬ
Laboratory Preparation of Ammonia from ŝŶƚŽ ƚŚĞ ŚŽƚ ŇĂƐŬ ĂŶĚ ĐĂƵƐĞ ŝƚ ƚŽ
Ammonium Chloride ĐƌĂĐŬ͘

How is ammonia prepared in laboratory
Ammonia gas is usually prepared in the laboratory by gently heating a
mixture of solid ammonium chloride (NH Cl) and slakedlime [Ca(OH) (s)].
2
4
heat
ƒ Reaction: 2NH Cl(s) + Ca(OH) (s) o CaCl + 2NH OH o 2NH (g) + 2H O(l)
2
4
3
2
2
4
ammonium slakedlime calcium ammonia
chloride chloride
ƒ Reactants. Ammonium chloride, Slakedlime.
ƒ Products. Calcium chloride, Ammonia gas, Water vapour.
ƒ Conditions. Reaction takes place on heating.
ƒ Procedure. A mixture of solid ammonium chloride and slakedlime
TCVKQ D[ OCUU KU ſPGN[ ITQWPF CPF VCMGP KP C FT[ TQWPF
DQVVQO ƀCUM
Set the experimental set-up, as shown in Fig. 9.2. Heat the mixture
FKTGEVN[ QP NQY ƀCOG #OOQPKC ICU QDVCKPGF KU FTKGF CPF EQNNGEVGF
ƒ Drying of ammonia gas. Ammonia gas is dried by passing over
quicklime (CaO).
ƒ Collection of ammonia gas. Ammonia gas is collected by the
downward displacement of the air. Ammonia cannot be collected
over water because it is highly soluble in it. Fig. 9.2 Laboratory preparation of ammonia