【四張五
日三初月一十年牛丙膺宴
WAM: KIU YAT PO
圖式英文中學會考試題預習專欄
物理科(七)
梁海明,
PHYSICS (3).M.Leung
Solution
生熱無他奶,至五時始盡弑散會。「港)
|優紛飽品,並由香港豆品公司報妨全校資
45
11.(a)(i)Thrust on the bottom of the vesseli
F=PxA
where P is the pressure of water,
*
期
日四十月二十年六六九一层公年五十五國民塞中
方
【倫敦城市工聯會學院
(b)
Pahˇx"d
•20 x 1
/ 201
A-150
A is the cross-sectional areal
of the vessel..
英文中學會考試題預習專欄
我年
[em/sq.cm,
g/ag.om.
.eq.cm.
化學科
·王錦釗.
CHEMISTRY (7),
...F- 20x150 gm.wt.
kgwt.
(ti)if a cubical block or wood of volume 150070.1
and s.g, 0.6 floats freely on the surface. the weight of block of wood is
1500.b.x0.6. gm/20. • 90 gm.wt
900.c. of water rises above the originals water level. Height of water increased ia 1900.00 0.6
150 bq.cm.
cm..
additional thrust"="0,6x150
490
gm.wt. gm.wt.
(Answer; varust on the bottom of the vessel
is 3 kg.wt. Additional thrust on the bottom of the vessel when a cubical block of wood floats freely on the surface is 90 gm.wt.
Pressure of water P1-bjxdı
12.3 G..!
sq.ca.
• 1 gm/c.c.
- 12.3 cm.)
em/cn2 gm/cm
Pressure of liquid P2ch
- 12.3 x 1
1
-:12.3
7.0.0.0.
= 7
ст.
1 sq.cm.
= 0.80
7.0x0.8 gm/cm
5.6
gm/cm
12.3 -5.6 6.7
water
fug
Pressure of water exceeding that of the liquid:
gm/cm gm/cm
this difference in pressure should be balance by the rising of mercury on the left limb. Let h cm be the height of mercury in the (left limb above that in the right limb.
Then 6.7 gm/sq.cm. -h x 13.6 g/0.0.
6.7 13.67
05༣...
CD
Gm
The difference in level between the surgaces the water and the liquid 16 12.3–(7+0,016m. e. 4.8 cm.
Answer: The difference in Burraces between
the water and the liquid 18 4.8 (c) The siphon is a bent tube made of glass,rub.
ber or plastic thbing with its short arm dipping: into the tank of liquid and its lower arm out. side. (fig.)
Let us consider conditions whilst the clip is closed.
The pressure at A or Bol atmospheric pressure +
( και
The pressure at C just
inside the clip-pressure at B♦ (h2xd)
catmospheri
Dressure + (h,xd)+(b2xd)
atmospheric
pressure+ +{h+h2Jxd..
Thus the pressure at
Siphon
just inside the clip is greater than the pressure just outside the clip, which 18 atmospheric pressure by y the depth of
C below the surface of liquid in the tank mul- tiplied by the density of the liquid. When the clip at C is opened, water will be forced out
Ci and runs with a continuous flow. We see that once it commences to flow, the pressure at Ç is always greater than the atmospheric pressure 60 long as C ie below the level of the surface of the liquid in the tank. the liquid continues to flow
2.(a)(1)Boyles! law: The volume of a fixed mass of
gas is inversely proportional to the pressure, provided the temperature remains constant. (11) From Boyles law: PVP2
let P128 lb/in2
-1000 cu.in.
P2-15p 7b/in?
1866
28 x 1000.
cu.ina
(b) The figure shows the
principle of a modern type of simple vacuum. pump. Each time, the⠀⠀ paston is at the bot-
•hand
tom of the cylinder.
Evalve A
some air from the
vessel to be evacuated oil
expands-inside the
space of the cylinder
To vessel to be evacuate
On each upstroke the
air above the piston
Q.1. Dalton's Atomic Theory may be summed up briefly ́as/
follows:
(a) Matter 19 made of small particles called atoms », (b) Atoms are indivisible and indestructible and can
not be created,
c) The atoms of a particular element are all exactly alike in every way, and are different from the atoms of all other elements.
(a) When chemical combination takes place between,
elements, the atoms join up in simple whole numbers to form new substances in which they lose. their own characteristic properties.
SAHE
Q.2. The Law of Constant Composition states that the pure
chemical compound, however made, contains the same elements in the same fixed proportions by weight. To show how the truth of this statement may be ex- plained by means of balton's Atomic Theory.
cons GAS
If one atom of the element, copper," mass a gms.,com- bines with one atom of the element,'oxygen, mass b ga, to form the compounu, cupric oxide, then it follows from Dalton's Theory that one molecule of cupric oxide will always have a weight of (a+b)gms,,being made up of the weight of one atom of copper (a gms. which is fixed) and the weight of na atom of oxygen (bems which is fixed) 2.3.(a) Black copper oxide may be prepared from copper,
by first converting the metal to the nitrate,which decomposes easily on heating
3C + 8HNO3.
3: (NO3)2 + 2NO + 2° Cu(NO3)2 = 2 CuO + ↳ NO2 Black copper oxide may be obtained by the thema 1 decomposition of copper carbonate,
CuO + CO2
Cu C03
(c) Black copper oxide may be obtained from copper
sulphate by first converting it to the hydroxide which decomposes easily on heating.
Cu 50 + 2NaOH
Cu (OH)
· Cu O
Na2 50, + Cu(OR),
+ H2 O
oxide
and oxide
20 gms.
gms..
20 100% 20+5 - 80% 20%
Weight of oxide
2 gms Weight of copper in oxide 1.6 gms. Weight of oxygen in oxide 0.4 gms. Percentage of copper in oxide 10x 100%)
=80%
Percentage of copper in oxide 20% The percentage of each element in each oxide is found. to be constant. Hence these figures illustrate the Law of Constant Composition which states that the same pure chemical compound, however made, contains the same elements in the same fixed proportions by weight.
The law of Multiple Proportions states that 1 two elements A and B combine to form two or more compounds, then the several weights of A which wil combine with a fixed weight of B in each compound are in a simple whole number ratio. Experiment to illustrate the Law
(a) Two clean, dry porcelain boats are carefully
weighed,
(b) One boat is filled with cupric oxide, and the
other with cuprous oxide. The boats containing the oxides are again weighed.
c) The boats are then put into a combustion tube
A stream of coal was is passed over the oxides
top of the pistop acta y
not only as a lubricant
Vacuum Pump
and air seal but also fills the dead space bel tween piston and valve at the top of the stroke and all air trapped there is removed. (c) Force on the handle 28 1b.wt..
Since the mechanical advantage is 10.
force acting on the smaller plunger 28·10 lb.wt
280
lb.wt.
pressure on the smaller plunger 280 lb wt.
sq.in.
280 lb.wt./6q.10.
maximum weight that the larger plunger can sustain 280x20/
5600 12.5/
1b.wt. ton wt)
Answer: The maximum weight that the larger,
plunger can ustain.18.2.5.ton.
Topics for revision this weeke
Mercury and alcohol, thermometers - ventigrade" and Fahrenheit scale.
2: Thermal expansion of solids, 1iquide and gases.
Coefficient of linear expansion. Coefficient a apparent expansion of liquids.
Maximum density of water.
Questions”
13. (a) Describe the construction and action of "arcom-
bined maximum and minimum thermometer.
Leather сир
(b)
•Ool valve
is carried out through c valve A The oil on
Find the ratio of the lengths of two rods of different metals X and Y at 0°C if, the differ
and the gas is burnt at the Jet. Each oxide za then heated gently by means of a bunsen bumer Both oxides are gradually reduced to metallic copper. The process is continued until each boat until its contents have a constant weight. The weight of each boat is then recorded."
PORCELAIN BOAT
CONTAINING CUPROUS
OXIDE
PORCELAW BOAT! CONTAINING CUPRIT
OXIDE
Results:
Weight of empty boat. Weight of boat and oxide Weight of boat and copper.
Weight of copper in the oxide W
Weight of oxygen the oxide Wz - W2
Weight of copper that combines W2-W1. with 100 gms. of oxygen
HARD GLASS COMBUSTION, TUBE
· EXCESS
QAS
BURNIT JET
+
HEAT
HEAT
Cupric oxide"
พา
"Cuprous oxide
W2
W21
W3
W1
W3 - W2 W3'
-2x 100 13
* 100
Wz-W2
KI
K2
K2
1 : 2
=
It will be found that K1 Hence the figures illustrate the Law of Multiple Pro- portions.
N.T.P.
Volume of nitrogen in nitrous oxide at 2.24 litre
↑ Gram-molecule of N2
- 28 gm
Weight of nitrogen in nitrous oxide 2.8 gms. Weight of oxygen in nitrous oxide = 1.6 gms. lume of nitrogen in nitrogen dioxide at NTP= 1.12 litre
dioxide
Weight of nitrogen in nitrogen Weight of oxygen in nitrogen dioxide
of nitrogen in oxide
Nitrous oxide
1.6
-> 1.4 2025 •
3.2 zins Nitrogen Diox
3.2 gma.
3.5qm.
√t of oxygen in oxide Wt of nitrogen that will combine with 8 gms of oxygen
2.8 x these weights are in the ratio of = 14am Hence these figures illustrate the Law of Multiple Pro- portions.
Question for next week
4
1. Name two soluble and four insoluble carbonates. 2.Meme two bicarbonates which exist as solids, and two-
which exist in solution only.
Describe briefly, giving equations now you would convert limestone into (a) quicklime. (b) slaked lime.. (c) calcium bicarbonate.
(1) Describe in detail the laboratory preparation of purc dry carbon dioxide from calcium carbonate.
(ii) How and under what conditions does carvon aloxide react with:
(a) magnesium; (0) Carpon; (c) sodium carbonate? (iii) State four commercial uses of carbon dioxide. (iv) Explain briefly why carbon dioxide is important to living plants.
5.A white substance A gave Dii water vapour and carbon
qioxide when heated, After heating for a long period, a white residue was left which, when cold, evolved some more carbon dioxide on the addition of hydrochloric acid What can you say about the chemical nature of A? Give reasons for your answer.
enos of their lengths is the same at all tem peratures. The coefficients of linear expansion of X and Y may be taken as 0.00002 Der G and 0.00004 per C
(c) A litre bottle rull of maik which has just
been pasteurised at 60 C is sealed and cooled to 15 C. Find the volume of the empty space in. the bottle at the new temperature, assuming that) the coefficients of cubical expansion of milk and glass are 0.00038 and 0.000025 ser degree respectively.
14(a) A thermometer nas a pul or volume 0.5 ..
and the mercury in the stem moves 3mm for 1 rise in temperature. If the coefficient of cubical expansion of mercury is 0.00018 per degree C.,calculate approximately the diameter of the circular bore of the stem, neglecting. the effect of the expansion of the glass. (b)(1) How does the density of water change as the temperature is lowered from 20°C to freezing point? (11) How wousu you expect the temperature or the
water in a deep pond to vary with distance below the surface during a long period of hard frost?
(c) A brase tape snu steel tape are botn ivu mevres
long at 0°C. On a warm day it was found that
the
one.
ss tape was 1.6 cm longer than the steel
• What was the true length of the sieel tapel coefficient of linear expansion of bras8
0.000019 coefficient of linear expansion of steel 0.000071).
ENĎ
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