莫二第張七第日一十月三年未已歷夏
1979
中學會考試題預習專欄
化
(tha)
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Chemistry: (26)
(Reginaled W CHU)
Solution to 0.37
(ii
Gas X is nitrogen.
(1) The reddish-brown:
powder is copper
and the yellow solid is the magnesium nitride.
2NHz+3Cu0
2+3Cu+3H20
(iii) The concentrated
(文)
3
(-)
sulphuric acid is to dry the gas X and to absorb. ony unreacted: ammonia gas,
(1) Wis magnesium
oxide,
Z in ammonia: gas. (2) Mg2N2+611¿?
→3Mg(OH)2+2NT13
According to the following equation 3Mg+Ng →→→ M&qNo2 (5x24)g of Hg: form (3x24+2x14.)g of ME-No-
ammount of Mg-No.
obtained from 3g of magnesium
(3x24+2x14)g
x100g
WAH KIU YAT PO
報日僑華
六期星
(2) 100g MgzNo2 811
2x22.4dm-
volume of Niz
formed from 2g of
at s.t.p
100年
(2x22,4)dm
=0.896dm-
(vii) Air consists of nitrogen
nitrogen. When
magnesium burns in air, it also combines with the nitrogen in air to form magnesium nitride which; on、adding water drops, gives off ammonia gas that is alkaline in nature.
Copper(II)oxide will remain unchanged when heated in a current of air When carbon powder in
heated in air, it will
in.as combine with the oxygen inair to give carhon. dioxide; this.gas can be identified by passing it into some limewater which will turn milky
CO2+Ca (0II ),→→CaCO3(s)+l ̧0_
(2) Carbon does not have any
"apparent reaction with
hot dilute hydrochloric acid.
When copper(II)oxide is heated with dilute
hydrochloric acid, a pale- blue solution of
copper(II)chloride will
be obtained.
•CuO+2AC1-→CuCl.
Solution to 0.38
(vi).
According to the equation: below
8
100g
→3Mg (011) 2+2NH3
(3x58) g
(1) 100g of HggNo give
(3x58)g of Mg(OH),,
mass of Mg(OI),
formed from 2g.
MEN2 •
(3x58)g.
-100
-3.48%
裝繄修 東窗萬
英印
X; (2) Z;
【(3) T; (4):2.
(ii) The formula is (111)
Tonic
(electrovalent) bond is present in P and the covalent bond
(2) The electronic structure of p
The electronic
structure of Q is:
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(3) Q has a lower
C
melting point. consists of ions
P
held strongly.
together by
electronstatic force. while Q consists of molecules held together by weak van der vaals force" only. So: to melt P requires more energy than to me It
P will.conduct, electricity because
it consists of ions which a are mobile in
puid. state whilen
consists of
covalent molecules which do, not conduct electricity even in liquid state,
(iv) The atoms in X are held.
together by fairly strong metallic bond while Y consists of molecules held together: by weak van der waals force. So, more energy is required to melt which thus has a higher
melting point.
bi
Elements in the same group in the: Periodic Table have the same number of electrons in the outermost
(or valence) shell of their atoms. As the chemical properties of an element are mainly determined by the
electrons in the outermost shell, so the elements in the
same group often have similar chemical behavious. behaviour.
(ii)When hydrogen chloride
dissolves in water, at, being a polar molecuee ionizes to give chloride ions, and hydronium ions. The chloride ions thus formed will react with silver ions to give a white precipitate of silver chloride.
Ag*(aq)+c1 (aq)→AgCl(n)
rachloromethane, being non-polar, does not mix with water at all. (iii)Pure water has a pH of
7. When hydrogen chloride dissolves in water, it
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日七月四年九七九一曆公年八十六國民華中 育教僑華
consequence, the pil
decreases from 7 to a
smaller value, indicating:
an increase in acidity.
HC 1 ( g ) +E2 0 ~~~#30 +C]
Ethane, is a saturated: hydrocarbun, i.e. in ethane all the C-C and C-H bonds are single covalent bonds. However, in ethene, there is a carbon-carbon double,
•
CC present. So, -ethane and ethene shows differe chemical behaviour,
Solution to (0.39.
(11)
The white solid is anhydrous
copper(II)sulphate. (1) Gae X in sulphur
dioxide.
(2) Cu+2H2SO
→CuS0+2H2
(3) The pH of the
solution: would be smaller than 7 because Sug
acidic in nature. (111) (1) It turns from orange
to green,
(2) Yellow particles of
sulphur are precipitated. 212S+S02
→2HQ0+3$(3)
(3) White-precipitate:
of barium sulphite appears.
BaCl,+H20+S02
→BaSOţ(3)+2HCl
(4) It is decolorized.
Bro+2HQ0+S0g ⇒2HBr+H2S04
(iv) When 50
(v)
00
(ii)
As a
Lonizes to give hydronium ion which is responsible for the acidity
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disanlves in
water, it ionizes to give H and sulphi te
ions. Soc. When
2
Na¿50, dissolves in water, it dissociates to form Na and 50
Since both solutions. contain SU2 lone, so
they show similar reactions towards certain reagents. The solution is blue because it contains hydrated copper(TI)ions:
Formula mass of NaOH-40
Molarity of solution A
-270 1000
40 25001 dm
-0.2M
Holecular mass of
# SO-98
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Molarity of solution B
2,45 1000
.98
-0.1M
.dm
(1) The ph of the solution.
would increase to 7.
(2) No. of moles of
present
25 "1000" -0.0025
0
No. of moles of Naof: added:
1000
·molar ratio of
Su
NaoH:HSU
≈0.0050:0.0025
2:17
That is, Zmoles of NaOH have reacted with 1 mole of H2504.
The aalt X obtained: should be the normal
sodium gulphate
(3) According to the equation
below
2NaOH+HQSO
of moles of salt X
(NaS0) obtained
of moles of H_S0,
originally present,
25
1000
720.1
-0.0025
But, the volume of the final solution
=25cm)+25
-50cm3
molarity of the salt
0.0025 50 -0.05M
1000
(iv) Molar ratio of NaOH:II,SO,
20
10
1000*0.2006
=0.004:0;001
all the gulphuric
acid has reacted with NaOH -to form the normal salt,
Na
while some NaOll are
left behind Sin
excess.
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