★教僑華
三第八
日二十月五年丑乙
WAH KIU YAT PO
報日僑華
六期星
mole ratio of
1985
中學會考試題預習專欄
=25cm3: 65cm3
化學科建議解答
明德出版社
提供資料
SUGGESTED SOLUTIONS TO
CHEMISTRY I
1. (b)(i)oxygen,
This is because
its intermole-
cular forces are
the weakest.
(ii)Chromium (Cr)
for mingabése
(Ma}},
(orange);
o. of Cris +6.
(or M:0,- (purple)
0. M. of Mn is +7).
(iii)The compound
formed by potassium and bromine has a bigher melting point because it
is an ionic
compound
The electronic structure of the compound is
K
(iv)Graphite.
Br
It consists of layera of hexagonal rings of carbon atomą and the force existing between. the layers ig the weak van der vogli force. The layers can slide on one another easily, thue having the
lubricating property..
(v)Carbon has the
reducing
property. One heating carbon CAR reduce copper(II): oxide
to copper. 2Cu0+C→→→2¢u+C
(1)Phosphorus
(yellow/white form).
It hurst in
flame sponta- neously on
coming in.
contact with sir Storingi tunder water would prevent it from coming into. contact with
(b)(i)Ammonia wan
decomposed to hydrogen and nitrogen. (2) Iran, wool
acted as a catalyst.
(ii)(1)The reaction
is atop II was:
(2)Copper(11)
eride is an oxidising sgent.
(iii)The residual goS
is nitrogen.
(iv)(1)Võl. of No
residual ges
in syringe 3
-23 cm3
Vol of Hy
-88-23
-65cm3
-1:3
-1:2.8
mole ratio of
mole ratio of
N:B in ammonia
Na Ho
-1:3
empirical formula
of
ammonia is
NII (2)Relative
molecular
mass (or vapour
density) of anim snin -
to
(v)(1)This was.
ensure that
there: was not
iron oxide on the
any
iron woo}
the
oxide
would react with ammonia.
(2)This was to
ensure there was not any oxygen/air inside the apparatus as the hot iron would be oxidized readily by air.
(vi)When there was
uot any further change in the. gas volume, the reaction was. completed.
2. (a)(i)Mercury electrode. (ii)Electrode P is
made of graphite which is inert
to chlorine gas. (iii)(1)at electrode
P
201 ̄(sq) →→ Cl2(8)+26 ̄
(2)At the mercury electrode:.
Nae--> Ni (iv)Place a wet blue
litmus paper in. the gas. If the Litmus paper turns first red and is ther bleached, it is chlorine gas. When chlorine
dissolves in water, it forma hydrochloric. acid and hypo chlorous acid (HC10) vhi ch bleaches the litmue paper by oxidation,íve....
HC10 dyes→→→ HCl + { dyes+0)
colourless (v)(1)The equation.
સં.
2Na+H20 2NaOH+H2
(2) Chlorine gas
dissolves and and reacts
with solution
S to give aodium
chloride, sodium hypochlorite and water.
NaCl+NaC10+0 (3)It can be
used, as a bleaching agent be cause
NaClO has a
bleaching
power.
(vi)Two, potential
hazards are:
(1)mercury
vapour is poisonous súd prolonged
inhalation of it would
cause mercury poisoning. (2)Chlorine gas is toxic.
(vii) dil NCT were
used, the gas.
collected at
electrode P
would be mainly oxygen ges; i.e.
408TM (aq)→29,0(4) +02 ( 8 ) + 4 *°
(b)(1)(1)The repeating
unit is
II
II.
(2)% by SA of
C in perspex by base of
C in a
repeating
unit
x100
- 60.
12x5
(ii)The Perspex
chipa melt.to a yellowish liquid and then слага проп
strong heating. (iii)Thin, is to
condense the monomer.
(iv)The experiment
should be carried out in. the fume cup- board, because part of the vapour of the monomer, which is toxic, may, have not been condensed.
(*)(1)
H CH
CC
·C
COCH
(2) It is
addition polymeriza tion.
(vi)This is because
the monone ris expensive(or Perspex is a thermoplistic).
(vii)It is used as
lens material because it is transparent and not-readily breakable.
-3.(a)(1)(1)Iron forms
iron(II) ions which combine with hexacy- anoferrate (III): to give a blue complex. Fe-> Fe426
(2)The hydroxide
ions (OH) are formed which then turns phenolphth lein pink. O2+ 2020+4¢ ~~> 4 (F (ii)Pink colour is observed first at the edges of
the drop because
this part
contains more
iron(III) oxide
The Fe" initially formed, is readily oxidized by
hir to Fe which then react with of ions to give
FеDz. 120 (#)N&C1 could
speed up the iron rusting. This is because the...
of. presence dissolved No and C1 ene increase the electrical conductivity. (3)6&lvainzing/ Tin-plating/. Electroplating/ painting/ greasing, etc... (b)(1)X à dilute
sulphuric acid and Z is dilute nitric acid. The reactión between X, and marble chips slows down because of the formation of the insoluble
calcium sulphate on the marble chips.
The reaction of Z with zine granules, gives yellow-brown. fumes because of the formation of nitrogen(TV)
oxide.
(ii)(1)Zīne' chloride
solution (2)A white.
gelatinous precipitate is formed which then dissolves in excess sodiu bydroxide
solution.
(iii) (1) CaCO2+2INO
Ca(NO3) y+HD+Câg
(2) Zn+4ING Zn(NO3)2 + 2H2O+2N0p
(c)(1)This is to allow
the glass
syringes and the contents to reach attain a uniform
temperature and to allow the systems to
attain chemical équí librium. (ii)The following
equilibriumi system exists in the glass syringes at 25°c. Ng3⁄44 (8) −2N01(6) pale yellow
brown (1)When the
syringe A is cooled down to 9 C, the gas become s pale yellow and, the plunger moves in. This is because the equilibrium is shifted to the "left; thus forming more N
dissolved oxygen.
(2)When the.
(Hi)(1)Rust is
hydrated
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syringe C is
warmed to
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75°C, the gas becomes dark- brown and the plunger moves out. This is because the equilibrium is shifted to the right,
thus forming
more Nog.
4,{¤)(i)A is barium
sulphite
B is harium
chloride solution. The ioni c equation is:
BaSO, (9)+2}*(on) ' (41)(1)G could be
carbon dioxide (2)Pase & and 50,
suparately into some KMnO solution. G does not react with
KMnO4 while $02
decolorizes
it.
(iii)(1)502 cat be
used for bleaching the wood pulp. It is because So bleaches it by reduction.
(2)S0, blénches wond pulp by reduction. When the.
paper is in .contact with
air, the bleaching effect of S02
is reversed
by oxidation by by air.
(b)(i)The breding of
epparatus, is as shown below
Cotton wool soaked with CH,CH,09
heat
delivery
CH-CH
Broken porcalỀU
(ii)A colourless.
gos in evolved and sodiùm metal gradually dissolves.
(ii)(1)Reagenta:
ethanoic acid. (CIL COOL) cone H,SO, Conditions heat is
applied. (2)It may be,
delected by ita pleasant, fruity smell when the product is added to a
large audunt of vater.
(iv)If alcohol were present, the mixture would.
turn from orange. to green. This is. because Acidified K2Cr20 oxidizes alcohol to an
alkanic acid and.
is itself reduced to cr3 (ag).
i)In aqueous
ammonia, solution
the following.
equilibrium
exists.
NB2 (g) +120(l)=
日九廿月六年五八九一圈公年四十七國民華中
NH, *(aq)+01! (sq)
The equilibrium
lies well over
to the left, 30, the concentra- tion of OH ions is low and it is a weak alkali. (ii)on the initial
addition of
NH(aq) to copper(II) sulphate solution, a blue precipitate
Been This Was copper(II) hydroxide.
{ng)+20U" (sq)→→
Cu(OH)2(B)
Wes
The precipitate was dissolved in excess NHL (aq) to form blue solution
*
deep
due to the formation of a complex ion.
1 Cu(OH)2 ( s ) + 4NH2(sq)→→→
.2+
Cu (NB2), **(sq)+2011 (aq)
(iii)The solution
become lighter in blue colour. and blue precipitate appeared. This was due to the shifting to the left of the equilibrium
Cu(OH)2+
24
+NH(aq)
Cù (NH 3 ),2 * ( × q) +2017TM (@q). when dil 1,504
reacted with NH. with excess dil
the
precipitate dissolved
be cause copper(II). hydroxide was neutralized. by dil H2SO Cu(OH)2(3)+2SO4(aq)--
€USD, {8q) +2B ̧¤(£)
5. (a)(i)Brown fumes are
་------་་
несп.
The colourless crystals turns to an orange solid.
(ii)2pb(NO3)2 ?
2pb0+4N+02 (iii)(1)Nitrogen(IV)
oxide (NO2)
(2)2N012+28a0U-->
NONO+NaN@+I ̧0
\\(iv){1}n(NaOH)
originally
-present
20
x 0.50 1000
NaOH + HCl
mol.
-0.010 mol
According to the equation below
Nac1+H2O
1 mol n(Naon) is
ексева
(HCI)reacted
with exceas
NaOH
20.
10009.10 =0.002 mol
(NOR) reacted withi dissolved No
=07010-0,002 -0.008 mot
(2)According to
2N02+2Naor
2mol
2001
the equation below
N&NO2+N®NO2+H2O
n(NOg)
dissolved
(Natl)
reacted with
NO
=0.008mol
According to
the equation he law.
2pb(No03)2+ 2Pb0+4NO2+by
2 mol
Amol
_n{Pb(NOx)g)
decomposed
(NO)dis
solved
* 0.008
=0.004 mol
M(Pb(NO3)2)
551g vol
.m(Pb(NO3)2)
decomposed
1 x 0,004 -1.34
(v)The delivery. tube
should be lifted above the NaOH solution in test-tube B before removing the heat source. This is to pr preeast the sucking back of NSOR slution from the
test-tube B into the test-tube A.
(b)(i)(1)Nitrogen(IV)
oxide and,
Sulphur dioride (or hydrogen sulphide). 50 is contained in smokes form
factories.
NO 502 is
contained in smokes from factorica. NO 18
contained in car exhanets. (2)ŽNO,+i0
[NO+NO
11,90 (ii)Calcite would.
dieselve in acid rain. (iii)Aluminium
This is bechuse aluminium is covered with layer of
aluminium oxide which prevent it from further corrosion.
(c)(i)The reactions.
were completed when there was no more, gus being evolved: (ii)Ethanoic acid is
BD,
a weak acid, so it consists of- a lower concent tration of {* ìó ions. Since the rate of reaction is proportional to the lion concentration,
LLs rate is Blower. (iii)The time required
required is sho shorter because sulphuric acid is dibasic and there is a hig higher concey- tration of H* in 50cm of 1M
(N.B. The answer suggest- ed here is, in most cases, ly one of the possible-
solutions: to the question.)
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