柯二張三等
日五十月二年申戊瑟夏
WAH KIU YAT PO
日
期塋
白三十月三年八六九一間公年七十五國民中
育教健康
育華僑華
1968
英文中學會考試題預習專欄
化學科 (二十)
•
王錦釗。
Chemistry (20)
2. Ammonia may be prepared in the laboratory by heating
any ammonium salt with any alkali; a mixture of
ཀ
smmonium chloride and calcium hydroxide is commonly 1 ed.
An intimate mixture of ammonium chloride and calcium hydroxide is heated in a round-bottomed flask fitted with a rubber bung through which passes a delivery tube. In order to prevent excessive sublimation of ammonium chloride, excess of calcium hydroxide is used. When the flask is heated gently, ammonia is evolved.
2NH ̧€1 + Ca(OH) ɔ ~~_CaCl2_†_283f +_250.
ciclu nor
In order to dry the gas, neither concentrated sulphuric acid can be used as dry ing agents.
Calcium chloride reacts with ammonia to forg CaCl. 48Hz while sulphuric acid reacts with the gas to form (NH4)250,. The drying agent used is quicklims. The quicklime is put into a drying tower. The wet gas is passed up the drying-towar where it is dried, and the dry gas is collected above the drying-tower by upward delivery (a) When ammonia solution is added to a solution.
of ferric chloride, a brown gelatinous precipitate of ferric hydroxide is formed.
or
·
FeCl3 + 3NH OH Fe(OH)36 + 3NHCL) F■*** + 30H”,
A
Fe(OH)36
(b) when ammonia' solution is adɑso carefully solution of copper sulphate, a pale-blue precipitate of copper hydroxide is first forad,
[CuSQ,*+ 2NH,CB} i» »Cu(OH)z! + (NH4) 30%
+
When ammonia solution is added in excess, the precipitate disṣalvas to give a deep blus solution
hcuprio, tetrammine.
tion
HO
1) When a solution of ammonia 10 neutralised
with hydrochloric acid, a colourlass
solution of ammonium chloride is obtained.
HOL + NH4OH
-
NHẠC ghi tinh
If the solution is evaporated to dryness, a white crystalline solid, ammonium chloride remains, Un heating the solid strongly, dense white fumes are given off as the ammonium chloride sublime, Eventually, on continued heating, all the namonium chloride will sublime, and ther will be no residue left in the dish.
(11) When a solution of ammonia is neutralised
with nitric acid, a colourless solution of ammonium nitrate is formed,
2. (a) The
•
HNO3 + NH2ON NHz NO3 + HAO
If the solution is evaporated to' dryness, a white crystalline solid, ammonium nitrate is left.
On heating amponium nitrate cautiously, part of the solid will sublime, and the remainder will decompose to form nitrous oxide and water.
NHNO
N20 + 2H2O.
Nitrous
oxide
Eventually there will be no residue left. Care must be taken not to overheat the solid, for the reaction is liable to be explosive,
'fountain experiment is a popular method of showing the extreme solubility of ammonia in water. Set up the apparatus as shown in the disgrAD.
Water, energing from Get (hlus C
fountain Experiment
üired. with.
To start the experiment, introduce a little water into the upper flask by blowing into the tuba connected to the lower flask. when some water reaches the upper flask, the pressure of the gas is lowered as some smmonia dissolves in the water. There is the no need to continue blowing. Atmospheric pressure will continue to push the water from the bottom flask into the upper flask. The water emerges from the jet in a spray, resembling a fountain,
The gas can be shown to be alkaline simply by adding red litmus solution to the bottom flask. As the water antera the upper flask, it will be noticed that the colour of the water turns blue.
a
(b) To show that ammonia i☐ reducing agent, it
is passed over heated cupric oxide, the
apparatus being set up as shown in the diagram.
Dry ammon la
+
...
cupris oxide
condensed. water
Nitrogen
As the ary gas la passed over neated cupric oxide, it will be noticed that the black oxide is reduced to metallic copper which is red in colour.
-
30u0+ NH3 30u +380 + N2 f
The water which is formed is condensed and is collected as a colourless liquid in a flask immersed in cold water. It can be showE to be water by testing it with anhydrous copper sulphate which will turn blue.
water
The gas collected in the gas jer over
can be shown to be nitrogen by testin
it with burning magnesium, The magnes 1 um reacts with nitrogen to form magnesim nitrida Which on addition of water liberates ammonia
348.
Questions for next week (21)
1. Outline the industrial method by which nitrogen my be converted into (a) ammonia, (b) nitrio svid.
2. Hoy, and under what conditions, does nitric aci
react with (a) hoppar, (b) sine, (c) irog
!
sulphur, (s) carbon, (f) ferrous sulphate,
sandust?
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