第二第張八第日一廿月四年申庚腦 WAH KIU YAT PO
1980
中學會考試題預習專欄
electropositive or
reactive than copper,
reduces copper(11)oxide to copper metal and is itself oxidized to
zinc(II)oxide,
SHUKS*** (*) The black solid A might
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Suggested Solutions to
Chemistry 1980
Gas X is hydrogen
chloride (HOL).
(11) KC1 MgCl2 6E, 0+3H2SOμ
3HC1+K][S0, +Mg(IISO, ),
(iii) The part of apparatus te
be used is shown as below.
ras
beaker
very tube
rubber connector
-Inverted
funnel
distilled water
(iv) The indicator is methyl
orange which changes
colour from red
acid) to yellow
alkali), or
(in::-
phenolphthalein which
changes from colourless
(in acid) to pink colour
(în alkali).
The ionic
equation for
neutralization is
H*(sq)+0H (8q) → H20(2)
(vi) No. of moles of NaOH
8
reacted
1000
=0.045
X
According to the equation below
HC1+NaOH→→→→→→ NaC1+H2O
No. of mules of HC1 present in 25cm-
solution Y
of
-no. of moles of NaOH
reacted
-0.045
molarity:
solution
0.045
x1000
25
-1.8 mol da #1.8M
Hence, the molarity of solution y is 1.BM
The set-up of apparatus for carrying out test 1 is shown as below,
porcelain
Doa
black solid A
Lown ga flame-
-stream of
lass wool:
jet
leat
glass Wool
combustion tube.
(1) Town gas is poisonous
and forma explosive mixture with air, hence any unreacted town vas must be burned off completely at the exit jet.
(2) When the reaction is
complete, the heat gource is removed and the hot metal Bis allowed to cool down in an atmosphere of town gas, i.e., let the town gas keep on passing over the metal
B when it cools; otherwise, the hot metal B will be.
oxidized again by the air.
(i) That the mixture continues to glow red-hot even after the heat source has been removed shows that reaction is taking place which is exothermic and gives out sufficient beat to keep the mixture glow. The yellow solid C is zinc(II)oxide (200). This is because zinc,being more
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be copper(II)oxide (Cuo).
The solid pelleta could be sodium hydroxide or potassium hydroxide
(ii) Grease is actually a kind
of estera. It is hydrolysed in warm alkaline medium to give an alkanol and a metal salt of an alkanoic acid; both of which are "soluble.
in water and hence. can be removed by washing with water
(111) The creamy yellow solid
is a sodium alkanoate, ie a sodium salt of a large alkanoïc acid. (iv) The equation for the
reaction is
CH CHOOC
CHOOC
CH OOC
000
3NaOH
CH, OH
CH2
CHOH
CH2OH
COO Na
creamy yellow solid
(v) The solid can be uge, as
a kind of soaps for cleaning purposes.
The crys
iron(111)chloride (FeC1-)
(ii) Solid X could be
anhydrous calcium chloride.
It prevents the moisture in air from entering into the combustion
(iii) No. of moles of Fe used
2.8
-0.05
According to the equation below 2Fe+301
2 moles 0.05 moles
2FeCl3
2 moles moles
10. of moles of
FeCl, obtained
=no. of moles of
iron used -0.05
molar mass of FeCl3 #56.0+3x35.5
-162.5 g mol
theoretical mass
crystals (FeCl3)
obtained
=0.05 mol x 162,5gmol7: -8.125 € Hence, the theoretical mass of crystals obtained is 8.125g
(1v) Iron(III) chloride
sublimes readily, since the combustion tube at the exit end is quite hot, so; part of the vapour of
iron(III) chloride night not be able to deposit at that place and passen into the drying bulb. a result, the mass of iron(III) chloride
As
actually obtained is much smaller than the theoretical mass. The set-up for improving the yield of crystals of iron(III) chloride is shown below..
trying huth, glass wool
ron filings
chlorine
anhydrous
/calcius
chloride
一期星
2Cu
2F
2 moles
0.0236, moles
Quantity of electricity
passes
crystals
=2Fx
-0.0236 moles
2 moles
According to the equation
-0.0236F
below
Flag yt]
heat
receivër
201
cuministi on tube
The experiment is done in a fume cupboard because- chlorine gas is poisonous and any unreacted chlorine. will be removed appropriately,
(vi) If dry hydrogen chloride
gas is used, the products would be iron(II)chloride (FeCl,) and hydrogen gas (¤, ).
Fe(s)+2HC1(g)
• FeC1, ( 8 ) +H2 ( 8 ).
fron, being more reactive
than hydrogen, displaces hydrogen from hydrogen chloride, That
iron(II)chloride is formed only because hydrogen chloride is a reducing agent, preventing the formation of any iron(III)chloride.
The three conditions required in step I are:- (1) relatively high
pressure (about 200- 350 atmospheres), (2) relatively high ~~ temperature (about 500-550 C);
(3) the presence of a
catalyst such as iron. (ii) Substance A is oxygen or
air
(iii)-Platinum (or copper
can be used as a catalyst In-step II
(iv) The equation for the
reaction in step:11fs
4NO2+
2+2H20+0 ̧———4HNO,
(v) The oxidation number of
nitrogen 19.
(1) -3 in ammonia (NH;);
(2) +5 in nitric acid (HNO-).
(vi) Nitric acid is used in
industry for
(1) manufacturing nitrates
which are often used as fertilizers,
explosives, etc.; (2) preparing organic
nitro-compounds.
(vii) This is because one of
the raw materiala, hydrogen, is not readily available in Hong Kong. (c) Add sodium and sodium
carbonate solution separately into the three colourless liquids, X, Y and Z respectively, The liquid which gives off gas bubbles with sodium but not with sodin carbonate solution is an alkanol, The liquid which gives off gas bubbles with both sodium and sodium ⠀⠀⠀ carbonate solution is an alkanoci acid.
(a)
The Liquid which has no ~ apparent reaction with both sodium and sodium: carbonate solution is an ester.
(1) Gas X is chlorine (C12). (ii) The ionic equation is
2c1 —C12+2e
(iii) Molar mass of
Cu63.5g mol
No. of moles of Cu deposited 1.5g)
-0.0236
According to the foblowing equations
8
日三月六年〇八九一圈公年九十六國民華中有教備
nitrogen(IV)oxide for
nitrogen dioxide) and
oxygen gas, and leave
hehind a greyish-black solid of metallic silver as the residue.
ZAgNO3 ---> 2A6+2N0g+On
The catalyst is used to speed up the reaction. (11) This could be achieved by heating the hydrogen peroxide solution as the rate of the reaction is increased by an increase.
emperature,
The
graph is shown as
below.
Volume of gas
G()/cm3
0,02362
in
Volume of gas X (C112) liberated at room
temperature and. pressure
202361
24 dm
0.2835dm 283.5cm-
The pli of the solution near the anode during. "electrolysis is smaller
than 7. This is because. the chlorine gas liberated can dissolve in water to
give hydromium ions (H,0). C12+3H, 0¬→2H_0*+C1 ̄+C10 ̄
The brown fumes are nitrogen(IV)oxide (or
nitrogen dioxide), (ii) The brown fumes are
formed when a redox. reaction takes place. between ·
nitric acid and sulphur, with nitric acid as oxidising agent.
HN0 ̧+S—H250,+6NO2+2H20
They are also formed by the thermal decomposition of nitric acid;
4HNO — 28,0+4N0, +0%
(ii) The brown fumes have all
(iv)
been dissolved because they are very soluble in
Acidified üflute potasalur permangauate solution would be decolourized because subphur dioxide which is also formed in tube A, is a strong reducing agent, (v) Conduction of electricity
through a liquid depends
8
(ii
(11
on the presence of mobile inus. When brown fumes dissolve in water, nitric acid (HNO2) and nitrous acid (HNO,) are formed which ionize readily in water to give hydronium ions (H,01), nitrate ions (NO2) and nitrite iong (NO,, ̄), thus increasing
the electrical
conductivity of water.
Iron(III) ions (F 3+)
solution A is responsible for the brown colour,
The reddish-brown precipitate C is
iron(III)hydroxide.
(Fe(OH)).
The ionic equation for reaction II is
Fe
e3*(aq)+3011" (ag)
Fe(OH),(8)
The equation for the formation of precipitate
B (silver) is
Ag*(aq)+Fe2*(aq).
Ag(s)+Fe2*(aq)
and that for the formation of precipitate E (silver chloride) 18
(iv) When solution D is
-AgCl(s)
evaporated to dryness, Colourless crystals of silver nitrate are
obtained hai
futher strong heating. decompose to give off brown gaa of
at which Time the catalyst is added
(iv) The set-up of apparatus.
for preparing gas G from hydrogen peroxide
solution is shown as below.
hydrogen separating peroxide (or dropping). solution Funnel
dry gas
drying hulb
suction flask
glass wool
ga's
piston syringe
anhydrous calcium chloride:
manganese(IV) oxide
(v) The equation is
28,02 (ag) — 28,0(()+02(E) (vi) According to the
following equation- 28,02
20
02
moles
mole
25dm
1.00cm
no. of moles of H2O2
contained in 4dm solution
100 25000
21
0.008
But, molar mass of H10-34g nol-
mass of Hole
contained in 4dm solution
=0.008mol x 34g mol
0.272g
(vii) The molarity of the
hydrogen peroxide solution
8
0.008 mol
=0.002 mol du
=0.002M
The IUPAC name for X i 2-methylpropan-1-ol,
(ii) The structure of the
isomer is
B-C-G-
-C-C-OH
HHHH
butan-1-ol
H-C-H
H-CC-
H OH
2-methylpropan-2-ol They have similar chemical properties because they contain the same functional group,
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