Q.2
其三第六
日千初月一十年午丙慈煲
"WAH KIH YAT PO
英文中學會考試題預習專欄
化學科
(A). 王錦釗
育教僑華
英文中學會考試題預習專欄上
(A).
·梁海明·
PHYSICS (8) H.M.Leung
CHEMISTRY (8)
Two soluble carbonates are
(1) Sodium carbonate, (ii) potassium carbonate
Four insoluble carbonates are
(1) Calcium carbonate, (11) magnesium carbonate, (iii) lead carbonate, (iv) copper carbonate.
Two bicarbonates which exist as solids are- (1) Sodium bicarbonate, (li) potassium bicarbonate Two bicarbonates which exist in solution only are (1) Calcium bicarbonate, (ii) magnesium bicarbonate Q.3 (a) Heat some limestone strongly in a bunsen
flame until it has a constant weight. The lime- stone decomposes, giving off an invisible gas, carbon dioxide, and leaving a white solid residue quicklime.
CaCO 3
+
Ca O limestone quickline carbon dioxide
(b) Add water slowly to some freshly prepared quick-
lime until no further action takes place. The quicklime absorbs water to form a white solid, blaked lime. During the feaction, the quicklime swells up and much heat is given out.
CAO
quicklime
H2O
water
=
Ca(OH)2
slaked lime c) Slaked lime is dissolved in water to form 1109
water. Carbon dioxide is bubbled through some line water. At first, the solution turns milky. But on passing carbon dioxide through the solu- tion for a longer period, the solution eventually becomes clear again. The clear solution so pre- pared is a solution of calcium bicarbonate which exists only in solution.
Ca(OH)2 + 002
Time water
carbon dioxide
CaCO3 + H2O
002
Ca CO3 + H2O
chalk
Ca (HCO3)2
calcium bicarbonate
Q.4 (1) Dilute hydrochloric acid is poured on to calcium.
carbonate, effervescence occurs and carbon dioxide gas is evolved. The gas contains hydrochloric acid vapour and water vapour as impurities. The hydrochloric acid vapour is removed by passing the impure carbon dioxide through water. The hydrochloric acid vapour is absorbed by the water The damp carbon dioxide is then dried by passing the gas through U-tubes containing anhydrous ga chloride. As carbon dioxide is heavier than air. it may be collected in gas Jars by downward deliver
THISTLE FUNNEL
DILUTE
HYDROCHLORIC
ACID
DRECHSEL BOTTLE
CONTAINING
m
CALCIUM CARBONATE
DILUTE ACID
U-TUBE CONTA IN ING CALCIUM CHLORIDE
Equation for the reaction:-
CaCO3 + 2HCl = CaCl2 + CO2!
GAS JAR CONTAINING CARBON DIOXIDE
物理科
Solution.
13.(a) The thermometer consists of a fairly large
cylindrical bulb A full of alcohol, connected by a U-shaped stem to a second bulb nearly full of alcohol (fig.). The bend of the U stem contains a thread of mercury. Two scales are marked, one against each limb of the tube so that the tem- perature may be read ageinst either of the mer- oury levels. On each
of the mercury sur--.
faces, there are small Alcohol
steel indexes provided with light springs to
MIN.
MAX
L120
20
hold them in position Minimum 40, in the stem. Expansion temp. 60
or contraction of the alcohol in A causes a movement of the mercury. thread. Consequently one or other index is pushed forward by the mercury and left in
Fico Steal index
४०
60
Maximum
Ba
100
40 temp.
Mercury
the extreme position reached. The lower end or the index on the left indicates the minimum temperature and that on the right the maximum. After readings have been recorded a small magnet is used to bring the indexes back into contact with the mercury.
be the length of
Let
rod X
the length of rod
be the length of rod Y at
ly, be the length of rod Y at t. C. n, 1,1 (1+0.000047)
1 (1+0.00002t
(1)-(2) 1. 1 −1 +0.00002€ (21 ̧−1_)
(1) (2)
Since the difference in length is always the Bame,i,e. 1
21-1-0.
11
Answer: The ratio of the lengths of two to
of different metals I and Yat
From V1 =V [1+(+ =t, }}}]
21.
where V2 is the volume of liquid at t.
V1 is the volume of liquid at t
is the coefficient of apparent pangion of milk.
60°C.
15°C...
10000.c.
0.00038-0.000025
☐ 0.000355
on substitution,
1000 V, E 1+0.000355(60-15)]
1000 11.01598
984c..
c.c.
點
日一廿月二十年六九一曆公五十五
BTem
from Verh
0.00009-JTx(x0.3
2 0.00f2
d =
04 0.0195
20.2%
CM..
Answer: The diameter of the circular bore of the
stem is 0.2 mm approximately.
b)(i) As the temperature is lowered from 20°c,
the volume of water contracts and reaches its minimum at 40. In other words, the density
of water increases as the temperature is lower.. ed and reaches its maxinum at. 40. But if the temperature is lowered further.
then the volume of water
from 40 to 0°C decreases! again. This can beil- lustrated by the graph shown.
O
Temperature in!!
(ii) As the temperature of a deep pond falls
the water contracts,becomes denser and sinks. A circulation
15 set up until all the water reaches its maximum density at 4°C. If further cooling occurs any water below 4 0 will remain at the top owing to its lighter density. Therefore, ice forms
on the top of the water, and after this the lower layers of water at 4°C can lose heat by conduction only. Therefore in deep ponds, there will always be water beneath the ice (o) Let meters be the true length of the steel
tape at that temperature. Then,
1-100(1+0.000011+ L+0,016=100(1+0.0000191)
From (1)
put (3) into (2)
ta
'L - 100 .0011
1-100- 0.016 +
BL
72.743
0.0019.
(2) .(3)
0.0011-(1-100)
1. 11⁄2 100,022 metres.
Answer: The true length of the steel tape is
100.022 metres.
Topice for revision tale weeks'
PRESSURE VOLUME-TEMPERATURE relationship for the rae equation, absolute temperature. Questions
(a) Describe an experimental method of measuring
the coefficient of expansion of tant pressure.
b) A faulty baromet
[6.(a)
a
gas at cons
the space
containing air above the mercury, reads 750 mm. at O. C. when 485 reer pressure 18 760 mm, - her space above- the mercury having a volume of 20 c,c. What will the real atmospheric pressure be if the tem perature rises to 20 C and the reading of the faulty barometer remains constant?
An air bubble at the bottom of a lake 240 ft. deep has a volume of 0.3 cu.in. What will be 11 volume on reaching the surface, if the atmos pheric pressure is 30 ins of mercury? (8.g. of mercury is 13.6)
PUBLIC LIBRA
Volume of the
Ο
is
calcium dilute calcium carbon water carbonate hydro- chloride dioxide
chloric acid
(1)(a) Burning magnesium will react with carbon
dioxide, when a piece of magnesium ribbon 18 lit in a bunsen flame and lowered into a jar
of carbon dioxide, the magnesium
copt Inuse tat burn with some difficulty. A white ash, mag- nesium oxide, is obtained at the bottom of the gas jar, and black specks of carbon are found on the sides.
2Mg magnesiumn
CO2 carbon
dioxide
21g0 magnesium.
oxide
carbon
(b) When carbon dioxide gas is passed over rød,
hot carbon, the cabin reduces the gas to another colourless gas, carbon monoxide.
CO2
200 carbon monoxide.
(c) When carbon dioxide gas is bubbled into an
aqueous solution of sodium carbonate, a white sludge is formed. This is the acid salt of carbonic acid, sodium bicarbonate, which is one of the few relatively insoluble salts of sodium.
Na2CO3 sodium
carbonate
HO CO 2Na HCO,
sodium bicarbonate
(iii) Four commercial uses of carbon dioxide are -- (a) It is used in making derated waters.
(b) Solid carbon dioxide commonly called "dry ice"
is used for refrigeration, particularly in the case of ice cream containers.
(c) It is used in certain types of fire-ext inguishers (d) It is used in the Solvay Process for the manu facture of sodium carbonate, and sodium bicar- bonata.
1000-982 c. = 16
0.0.
at 15°c
Answer: Volume of the empty space in the bottle
at the new temperature 28 16 c.c.
14.(a) Since the mercury moves 3 mm. in the atem ror each degree centigrade rise. The volume of mer- cury at 0°C 25 0.5 c.c. The volume increased at 1°C = 0.5 x 0.00018 x 1 c.c..
= 0.00009
c.c.
Let d cm. be the length of the diameter of the
(iv) Carbon dioxide is taken in by living plants and is
built up into substances of high molecular weight, which form the tissue
sue of plants.
Carbon dioxide + water + other substances + energy from the sun plant substance
The plant substances built up in this way are called carbohydrates. At important part in this process
is played by chlorophyll, the green substance pre- sent in the leaves of plants- The simplest carbohydrate is glucose which is made is follows-
chlorophyll energy + 6 CO2 + 6 H2O
C6H1206 +6:02
glucose
Inside the plant, other more complicated carpony drates such as starch or cellulose are built up.
'n 06 H129 = (C6H1205), + nH20
starch,cellulose,
etc.
A solid which gives off water vapour and carbon- dioxide when heated is a solid bicarbonate. A must be a bicarbonate.
ZNA HCO3 2K H C03
Na2CO3 + CO2 + K2003 + CO2
H2O
Draw and label a constant-volume air thermo meter. State two advantages of such a thermometer as compared with a mercury thermometer, (b) A constant volume air thermometer recorde a
pressure of 75 cm, when immersed in melting ice 105 cm. when in water at its normal boiling point, and 112.5 cm when in a boiling liquid. What is the Centigrade temperature of the boiling liquid?
A flask of capacity of 10000.c. 18 slowly ex- hausted of air by means of a pump. The cylinder of the pump has an internal area 10 eq.cm, and the length of the stroke is 15 om. If the in- itial air pressure in the flask ia 77 om, of mercury what will be the pressure afteri (1) one stroke. (11) two strokes?
The white residue-evolves more carbon dioxide on the addition of hydrochloric acid. The residue, therefore, must be a solid carbonate, which does not decompose on heating. The only white solid carbonates which are not, decomposed by heat are sodium carbonate and potassium carbonate,
2NAC1 + CO2 + H20 2KC1 H2O
Nã2 CO 3*2HC1
+2KC3
Hence substance A must be either Sodium on potassium bicarbonate.
QUESTIONS FOR NEXT WEEK.
10 gm of quickiume are dissolved in water. What weight of precipitated chalk will be obtained when the correct amount of carbon dioxide is passed into the solution?
2. 1 gram of a mixture of chalk and quicklime when treated
with an excess of acid gave 190 c.c. of carbon dioxide, at 15°C. and 74 a pressure. Calculate the percentage of quicklime in the mixture.
3. Give one conclusive experiment to distinguish between
(a) chalk and anhydrous sodium carbonate,
(b) washing soda ar baking soda,
(c) sodium carbonate monohydrate and slaked lime How would you prepare a specimen of (a) sodium
bicarbon
ate,
and (b) sodiul carbonate from caustic soda.
5. How is sodium carborate prepared from sodium chloride?: