24 APR 1968
百三第張四第
日七廿月三年申戊贏复
168英文中學會考試題預習專欄
化學科
(二十六) ·王錦釗. (a) To test for a carbonate in solution, add
magnesium sulphate solution. A sarbonate will
give a white pracipitate of magnesium carbonate, wherwas a bioaròcante will not give any precipitata.
co
from carbonate
solution
SOL
-}
#ECO2+ 30%
in solution
Sulphate ions
To test for a bicarbonate in solution, also add magnesium solution. On boiling the resulting ́aixture, a white precipitate of angnesium carbonate will be formed. At the same tims carbos Moxide will be evolved.
2HCO3*
+ ME
from bicarbona te
solution
soj
2NCO2+ 30**
Hagnesium Sulphate ions bicarbonate remain in
solution
#g†† • 20003 ̄→→→ MgCO3 ↓ + co
(b) To test for a sulphite, add dilute hydrochloria acid and heat the mixture. Sulptrar dioxide gas, which will decolorise purple potassium parmanganate solution, will be evolved. Hydrochloric acid tas no actión on a sulphate,
503.
from sulphite
28*C1° ~~~902 ↑ + k20 + 201−
chlorine 1098 remain i solution.
To test for a sulphate, first dissolv the sulphate in water, then acidify with dilute hydrochloric acid, and finally áði barium chloride solution. A heavy white precipitate of barium chloride will be votained. A sulphite will give no precipitats. 90,
+ Ba++
201~→→ Ba30, ↓ + 201′′
·
Chlorine ime in solution
(◊) To test for potassium chlorate, mix it with somo manganese dioxide and heat the sixture gantly. A gas, oxygen, will be evolved, which will rekindle a glowing splint, No chemical change takes place with potassium chloride
163
catalyst)
2XC1 + 302 ?
test for potassium chloride, add conc. o acid to some of the solid chloride,
in moist air is evolved. Th hloride also riz A white
bydro
KHSO
e solution
HNO
WAH KIU: YA-
日
with bydrogen sulphide. This confirms that A is either leic copper, mercury or silver, since all the soluble salts of these metals will give a black insolble sulphide with hydrogen sulphide, (iv) The solution of the nitrate gives a white, precipitate with sodium hydroxide, the precipitate being soluble in excess of sodium hydroxide. A must be lead, since lead nitrate will give a white precipitate of lead hydroxide with sodium hydroxide solution. Lead hydroxide › is amphoterit. It will dissolve in sodium hydroxide forming sodium plumbite. Equations for the reactions:
{1} 3Pb + HNO3
1
(dilute
nitric acid)
(11) Pb(NO3)2 + H
3Pb(NO3)2 + 2N0† † 4820
PBS ! + 2HNO
black ppt.
(111) Pb(NO3)2 + NaOH
Po(OH)2
lead hydroxide (insoluble i
water)
Hence A is LEAD,
M
Pb(OH)2 + 2NaNO3
t white
ppt.
† 2NaOH - Na2Pb02+2H20
sodium plumbite (soluble
in water)
(b) B is a bicarbonate or an insoluble carbonate,
for bicarbonates and insoluble carbonates will, on heating yield a gas which turns lime-water milky, The gli is obviously carbon dioxide.
CO2+ Ca(OH)2
lime
wator
•
CaCO2 + H2O.
The rasida obtained is probably sing oxide, for sine oxide is yellow when hot and turns white when coll
ca ročna te
240
Co
# 100 oxide
The residue dissolves in hydrochlori and the solution formed produces a whiteɑ precipi tate with ammonium sulphide. This confirms that the metal is zine..
HONG KO
white ppt.
(insol. in nitric acid)
test for coal, put some powdered soul 17
ube, add pyridine and shake thoroughly
(about 40%) of the coal observed to
and" disappear. Cole
oxide
túras reuX,
with
becau
and the
owing to the formstá Cupric oxide is not goal contains vary
cake
C
CO2+ 200.
add dilute
To test for ferrous sulphia. A gas, which
hydrochloric acid to the
Bolls like rotten egga, and which will give a black precipitate with lead acetate will be evőlvad,
Fes + 2HC3
"Po**-2CH3000~~ + H2S
1
શ
hydrogen). sulphide
but.
PbS/+ 2H*CH300***
ms will also be evolved with zinc, was no smell, and has no action on lead te solution.
2HC1 - ZnC1, + H2 f
for zinc, put some. sine powder -tube, containing copper sulphate and shake the mixture throughly. The our of the copper sulphate solution
and the gray zinc powder turns rea In colour, sim tallic copper in displaced by the wine Ferrous sulphide has no action or
jopper sulphate solution.
2n + CUSUL
blue
dier" solution
the
the
-
ZaC12 + H2O
orige dissolved in hydrochlorie ar sine chaurus in solution. Zine
ANTONpni. Precipitate of sine
samonium sulphide
• 203 / + 201,01
colour
ueous solutions of Sluble wil
ition: 911**
remains in Solution)
insoluble in nitrie
in ammonia
lt for potassiu
三期
日四十月四年八六九一灣公年七十五國民基本
何玉柱·
| 中中會考英文科(廿六 )
8.
9.
answers to sxercise XXI:
2.
3.
7hen he WAS a student, he never came. Lace. (A past tense should be used and as" come" is a vero, only auxiliary "did* if needed, can be used--ne did not come late.)
►
poys, are often dirtier than girls. (a. "boys" is plural commou noun used in a general sense;
therefore no artiske is used. "boys isthe subject, "they" is excessive, do not repeat the subject. "dirty" is positive degres, bere it 18 & comparison, a comparative degree should be used.)
C..
This book is still better than that. ("better" is comparative degree, there 18 ad need to use "more". if it is used, it is called a double comparison.
However, "still" may be used if desired.)
(As it is a
Do you really want to go? question not beginning with a question word, the auxiliary "ão"--subject is "you". --should be used.)
5. I am interested in whether he can pass or or not. (After preposition "in" a noun of poun equivalent is needed. Here we need a noun clause and it is a question "Can be_pass?". Therefore we should add. "whe-
ther".
English is aliicult, but on the other hand, it is very useful. ("difficulty" is a noun, but we need an adjective, Students often confuse the noun and the adjective.
the other band" means" on the other side" "in the other hand' means "within the lim-
it of the other palma)
He is a good makes trouble, person though he sometimes
"people" is a plural noun, when it is used as a collective
it means "tribe" "race" The Chinese are
noun
a people of fine culture. b. as the subject is "he", the verb should agree in person and dumber with "he".)
We would have helped them if they had, told us their trouble, but they just did not want to let us know, (a. This la some- thing that did not happen in the past, and we suppose that it had happened, in other words, we are making a past condi*. tionalclause in which a past perfect tc. cense is used. the main clause there-
should be with would or should, etc. and a perfect infinitive, that is, have, past particiile. b. After "let", we must use infinitive without "to", unless "let" is used in passive voice.
Even the children were lat to join.)
He works very hard to earn his living. worka" 1a, in agreement with "be"
to earn a living" means to get daily supply of food, clothes and so forth.) 10. my foot hurts very much, I fell over
stone and twisted it yesterday, ("päin" la a noun, we may either say "is painful
hurts" which means exactly the same His face is like a mon avis(face The face cannot be like a monkey with body, a head and limbs. We say "He 18 like his father. or Fia face is like
is fatherte 42.
IBX
rous salt, singe ferrous BOLU Lon-of D in water
a pale grsen
green precipitate
•(OH)2+ 2+
green
(remins in solution)
ydroxide turns from pale green to inally brown when shaken with compound being oxidised by air to form borun farris
brom solid
sinse sälutions of sulphates chloride solution, a white sulphate insoluble in
201
To18 book 18 very familiar to familiar with" means know
ow quite wells while "be familiar to" means "be seen by, therefore not look strange
His mistake is similar to mine. (si lar to, not "similar" as")
15.
14. That type of flower ie as pretty as
this. OT: That type of flower is the заще as this. (We may use any adjec in comparison but if it ie 'same" "the same as”.
15.
use
Bure
Surprised, the touriste uttered a cry of joy. (a. The subject is "touri sta", they are not causing surprise but are prised, now, it is a past participle to qualify the subject. b. After preposition we use noun or noun equivalent,"joyfulmiş an adjective.)
Exercise XXII:1
Use a suitable phrasal verb to complete each of the following sentences
1.
Several children were unexploded grenade,
it did not t
236 with an
• it was mere luck that
2. I thought I was all alone in
eign country but then I was ov
I
super-market.
ን፡
BS04+2C2
(remins in #olution)
5.
"sulphata
ZnSO4 colourless, solution
Cu
for next visk (27)
reddish-brown'
powder
4. (a) In w
Since A is not acted upon by dilute
ric acid, it must be lead or a metal} than hydrogen is the electrochemical}
soluble
dilute nitric acid,
lying between lead and
he electrochemical als are attacked by
dilution, KS
son found in natura? teh or a blast furnace, and reaétions that take plase
6.
steal, and describe that go j they are used.
8.
#olútions of a coppeme,
9.
We haven't.
my old clar
any deci
to bow long giris skirts should As the school Certificate Exam
proaching, we'd better start
our lessons right now.
T
Here are all the letter 1 found in his drawer, please
there's the one you need.
them to see if
The headmaster has promised to
the matter so that nobody would be wrons 19 judged.
"I remember it cost only $1.50, why do does it cost $1.80 now?”
"Don't you know that everything bas
thirty cente?"
It's quite normal that people
those who have had prominent accompa ments but valueless to the society.
those who are
elephone di ri
I could not find his telephone number
even when I-
eatprjar að me
Would you
do not want to
the
the Lamp sò, th
darkes
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