9 MAR 1973
育教僑華頁三第張五第日四初月二年五穾曆駸
WAH KIU YAT PO
2H010
2H01 +0%
罗希
1973英文中學會考試題預習專欄
興酒英女院主編
化學科(二十)
unemistry (20)
solution for last week
Part
CARAÐ
→ પા
67800
Chlorine is prepared commercia -ly by the electrolystals of brim convenient type of cell is the liaphram 'cell,
Brime
(e) when a mixture of equa.
volumes of chlorine and hydrogen
are
exposed to direct sunlight, the two gases will combine explos- ively to hydrogen chloride.
H2
Cl2
2HC1
(f) When chlorine is passed over molten sulphur, a yellow liquid asulphur dichloride is formen.
25+ C12
S2012
2.(a) Chlorine reacts with ammonie by replacement of the hydrogen. Thus in presence of excess chlor-
ine, hydrogen chloride and nitro- gen trichloride are formed:
301, 73H01 + NO1,
NH
H2O
However, in the presence of excess ammonia, the nitrogen tri- chloride is decomposed:
NH OH + NC13
+ ЗНО + Н20
So that the over all reaction
IS
301
UNH OH
6NH C1
HO
d僑華
四期星
extracted the hydrogen from the turpentine, leaving the carbon.
1016 + 8015 — 100+ 16HCI
1) When chlorine is passed through a solution of ferrous
hloride, the colour of the solut- ion changes from pale green to. rellow, showing that the ferroua.
hloride has been oxidised to erric chloride.
2FeC12
+ 012
Hydrogen chloride Preparation
2Fe01:
1. Hydrogen chloride is usually made by the action of concentrated sulphuric acid on common salt.
cane this 04
•Hear
kystrafen Chloride
NaCl + H2SO
below 500°C.
NaHSO
3八月三年三七九一届公年二十六國民華中
A white precipitate
Ammonia dissolves
indication Action on
Action on Mg, Zn, Fe
Action on carbonate
Action on
ammoni
Toluene solution
It does not conduct electricity
with carbonates": It does not react
It does not form hydrogen
It conducts electricity
¿queous solution
It turns the colour of indicator
Hydorgen liberated
Carbon dioxide produced
Electrical
conductivity
No effect
-Abbaator diaphram -Steel chod
steel contamer
The anode is of carbon and the cathode is a mesh of steel. Two o the products, sodium hydroxide and chlorine, are kept apart by a porous diaphram separating the anode and cathode compartments.
The chloride ions are dischang- ed in preference to the hydroxyl Long at the anode and chlorine 19 Solved:
201
2e
201
At the cathode, hydrogen ions are discharged in preference to the sodium ions and hydrogen is
+ 2e.
hydroxide is formed in region of the cathode, dripe the diaphram and cathode be collected and concent-
Reactions of chlorine.
(a), When chlorine is passed inte potassium iodide solution, the latter turns brown at first when more chlorine is passed, a black precipitate of iodide is obtained
C12+ 2K1
2KC1 + 12
(b) wien gas jars of chlorine and ammonia are placed mouth to mouth, dense white fumes of ammonium chloride appears with less of the yellowish green colour of chlorine
Ammonia is first oxidized by chlorine to nitrogen, where chlorine is reduced to hydrogen chloride
3012 ŎNH
DNH
With excess chlorine, an explo 1ve compound nitrogen trichlor ide, NC1, will be formed
(c) when chlorine is passed into purple litmus solution, the latte.
red and is then bleach
first turns
|-ed to a colourless solution.
Chlorine dissolves in water form ang a mixture of hydrochloric aci and hypochorous acid which turn purple litmus red. The hypochlor ous acid bleaches red litmus to a colourless substance.
HC10
+ H2O
HC1+ HC10
HC1 + (0)
Dye + (o)- (Dye + 0)
colourless
colour ((d) · Chlorine reacts with waUEL and dissolving in it to hydro- chloric and hypochlorous acids. On starting, the hypochlorous acid slowly decomposes to hydro- johloric acid and oxygen.
(b) Chlorine combines directly with tin to form stannic chloride, however the reaction is catalysed by a trace of water.
Sn
2012
Sn01
(e) Aluminium is a strongly reducing metal, it combines very
igorously with chlorine yielding he chloride.
2A1 + 3012
→→2ATC13
(a) If chlorine is passed into an aqueous solution of sulphur 11oxide, 1.e. sulphrous acid, sulphuric and hydrochloric acids are formed:
502
+ 01 (e) Carbon monoxide will unite, with chlorine, in sunlight or in presence of heat animal charcoal to form carbonyl chloride COC12.
This may Also known as phosgene.
be considered as an addition
- 2H2O — >H2SO + 2HC;
Reaction:
(a)
COM
[NACI
COCI
The apparatus was set up as shown above: A mixture of communi salt and manganese dioxide was put in the flask and then covered with
concentrated sulphuric acid. On gentle heating a greenish yellow gas was seen to evolved:
2NaCl + MnO2 + 2H SO
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4
0121
The gas was passed through the first washing bottle containing water, which was used to absorb any hydrogen chloride that might. have been carried over. The second washing bottle containing concentrated sulphuric acid, which was used to remove any water vap vapour grom the gas. The gas was dollected by downward delivery. The fulness of the jar was tested With moist litmus paper
(b) The simplest laboratory preparation of chlorine withou heat is by the action of potass. permanganate or concentrated hydrochloric acid.
2KMnO +
2K01 + 2MnC1
8H0+ 5012
(0) Uniorane is a greenish yellow gas with a choking, un- plwasant smell. It is heavier than air, and easily liquefied.
(d) 1) If a filter paper soaked with warm turpentine is dropped into a jar of chlorine, there is a vigorous reaction and clouds of Boot are formed. The chlorine has
or 2NaC1
above 500901
Ta 50+ 2HC1
It is heavier than air, and so pan be collected by downward de- Livery.
b. The large quantity is now made by direct synthesis from hydrogen and chlorine. These are both obtained by the electrolysis of brime solution in the manufactur of caustic soas. The hydrogen is then burnt in an atmosphere of
hlorine in silica vessels.
H2 + Cl2
2HC1
A solution of hydrogen chloride in water is called... hydrochloric acid, This cannot be made by leading hydorgen Chloride directly into water by an ordinary delivery tube, The gas is so soluble that water would fill the tube and suck back" into the flask. An Inverted funnel is attached to
the tube and arranged so that itı rim is just below the surface of water in a beaker.
Properties
Physical - It is a colourless gas, when breathed, the hydrochloric acid formed gives it a choking, irritating smell. It is very soluble in water, heavier, than air.
hemical
1. Dry hydrogen chloride is noT
acidic and will not affect Iry litmus paper.
It neither burns nor supports combustion.
With ammonia, white clouds of ammonium chloride smoke are immediately formed.
NH3+HC1
NHC1
With reactive metale un beating to give the anhyurons chloride.
In + 2HC1
Fe + 2HCT
Hydrochloric acid and hydrogen chloride in toluene.
We know that hydrogen chlem ide is a covalent compound, but that when it dissolves in water. it Losises, giving hydroxonium Lons and chloride ions.
HCL+H20
→ H20 + 01
Hydroxonium ions are present n all solutions of acids.
Hydrogen chloride does not Lonize in dry toluene, and is present as a covalent compound.
ie toluene solution differs fro Le aqueous solution as follows:
West for hydrochloric acıd
Added a solution of silver nitrate into the hydrochloric aci (or any of its salts). A white- precipitate of insoluble silver Chloride is at once obtained. precipitate dissolves again very easily in a dilute solution of ammonia.
HC1 + AgNO
Chlorides
AgC1+ HNO
Tat
Hydrochloric acid forms only one series of salts known as the chlorides. All of these are freely soluble with the exceptioni of lead, silver and mercury (1) chlorides..
Preparation.
1. By neutralisation of an acid
with an alkali, e.g. potassiu sodium and ammonium chlorides NaOH + HCL
NH OH | HOI
HO+NaC1
21,0 + NHẠC.
By the action of the acid
a metal, e.g. zinc and Ferrou chlorides.
ZnCl + H2
Zn + 2HC1
Fe HOL
By the action of the acid on metallic oxide or carbonat
e.g. Calcium chloride
Caco
2HC1 ———→→Ca¤T ̧ + H2O + Co
By double decomposition (pre- cipitation method) e.g. lead and silver chlorides.
+2H01 →PBC1
Agno + HCl →→ AgC1
HNO 3
15 By direct combination or une metal with chlorine, e.g. Copper and ferric chlorides/
Cu + Cl2
2Fe + 3C12-
Properties
72red13
1. Most metallic chlorides yiela"
hydrogen chloride with concent- rated sulphuric acid. Chlorine is evolved on heating a mixtur of chloride, manganese dioxide, and sulphuric acid.
Some chlorides decompose un heating to give either the elements or a lower chlorid 8.g.
CuCl
Other chordes Torm the corFUI -ponding oxides and chlorine when heated in air,
4FeCl2 + 302 -->2F205 3+ 4012 T
When it is heaven ammunzun chloride dissociates into two simpler gaseous compounds, ammonia and hydrogen chloride, when cooled, these gases re- combine to fom solid ammonium chloride. This sort of deo om→→ position is called therma? dissociation.
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