1978-04-22 — Page 31

報日僑

【豆難

WAH KIU YAT PO

|

类及

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| ZAKSEK - ZI(FR) TEUERNE 【司董事長劉啓用宣佈加入利集團:此將更有 。爲配合未來之莱務發展計劃,讓字貿易有限公

KON¤VÆRET - BORS - KBKKEK

|及東南亚各國之各類超毗運象世界各國,以 環宇贸易有限公司創立不過兩年,選辦本

EB-RARKIINARE -

秀,粜務蒸蒸日上,最近召加入實力雄厚之利亞 洪宇贸易有限公司爲本港雄案出入口起之

「擴展遲及歐美南非澳洲各國 環宇貿易公司加入利豐集團

ABRE - (22-1 OKUY ,均以特價優舂各界人士,歡迎各界人仕,蒞臨

新穎之稽字紙 - 神奇之設計版,及其他文具用品 跳行於展先介紹期間,並將徹國名廠,宇

一品質精英,定衝康定,定爲本港各界人仕樂 顧色快勞,在素有早已錄工商界人生難使用, 且對科自及推案之分類,亦倍感方健告時,此髯 綠、藍、灰、黑等七種絕色,不低薪緻美觀,而 該獄快勞,讎萬悅,有紅、遼、黃、

黨本港各界人士推開。. 廠JEA之榮譽出品,「易得利」顏色快勞, 低座,舉行商品優嵬,將整行代理之世界大快勞 永信举行於昨日起至卅日止,在香港大會堂

昨日起大會堂展出

永信洋行商品展覽

入口商。

ONEKESLOVENACRENKELHE 阿南之窗來活動,最近國於十七日晚僇座貿易中

MAR - 10 | ZOENE - 37 } [82

六期星

日二十月四年八七九一公年七十六國民中

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• DK] BESEMÉ@SKERK KANG 咪 IBB

sample of Bodium carbon-

ate.

育教僑華 R

18

1978

中學會考試題預習專欄

AREA

化學

(廿九)朱宏林

Chemistry (29)

Question 43

(a) Study the following block dia- gram carefully and then answer the question which follows.

CHO

can give white steamy fumes with phosphorus(V)chloride. Qis a hydrocarbon which can

decolorize acidified potas- sium permanganate solution. (1) Give t

the names of comp- ounds P, Q and R and

write down their respec-H. tive structural formulae, (11) State the reagent(s) and

the conditions for the conversion of P to Q: Give an equation for the reaction.

(ii) Mention the reagent(8)

used in converting P to R.

Give an equation for the reaction,

(iv) What would be obtained when is heated under a high pressure and a high temperature with a little peroxide as the catalyst?

Using structural formulae show how the substance can be obtained from the compound Q..

(b) The following investigations were carried out on a sample of water X from a small town and the results were recorded in the table below:-

(1) distilled

vol of soap sol- ution to for a permanent lather

When, aqueous barium chloride solution is added to a solu- tion of sodium sulphite, a white precipitate ia obtained, What is this precipitate likely to be?

Give an ionic equation for

its formation.

(11) When dilute hydrochloric acid

la added to the precipitate,

it reacts and a pungent gas

is given off. What is this

gas? Give an ionic equation for its formation.

(iii) A solution of sulphur dioxide

in water is warmed with a little nitric acid. Barium chloride solution is added and a white precipitate is formed which does not dissol-

ve when dilute hydrochloric

acid is added. What happens. to the solution of sulphur

dioxide when it is acted upon by the nitric acid? Give the equation for the reaction concerned.

(iv) What would you observe when

a solution of sodium sulphite is shaken up with bromine solution in water?

Give an ionic equation for the changes observed. Question 45

(a) Ten beakers, each of which

containe 25 cm of silver nitrate solution, are prepared. Different volumes of a sodium chloride solution are then added separately into the beakers. The weight of the precipiate formed in each beaker is recorded, The read- ings are shown in the follow- ing table:-

wt. of the

precipitate/g

vol of NaCl Beakers added/cm2

(1)

01

0.052.

0.304

0.156

0,208

0,259

0.312

0.342

-0.342

0.342

Give an ionic equation for the formation of the precipitate.

(ii) What is the minimum vol-

ume of sodium chloride. solution required to re- act with all the silver nitrate in the 25 cm solution?

(iii) How many moles of silver nitrate are there in the solution?

(iv)

how many moles of sodium

water

(2) sample X

0.2 cm

35 cm

21 cm3

(v)

(3) boiled

sample X

བྱང་འཕྱ་སྐྱེ་གྱི་སྐུ་སྐྱོ

What is a hard water'?.

(11) What chemical species

is/are responsible for the hardness of water? (111) What is meant by the

*temporary hardness'?

(iv) What is meant by the

'permanent hardness?.

Do you think the sample

X consists of temporary hardness or permanent hardness or both?

(vi) Suggest a method suitable

to remove the permanent hardness.

Question 44 (a) 2.48 g of a sample of hydrated

sodium carbonate, of formula

of

Na CnH20, are dissolved in 50 om of M hydrochloric acid and the resulting solution,is made up to 250 m2. :25 m2 this diluted solution require 20 am of a 0.05M sodium hyd- roxide for neutralising the excess acid.

(at.wt.Na=23, C=12,0=16,01=35.5

K=1

(1) Write the aquation for

the reactions involved.

(ii) Calculate the value of n,

the number of water of crystallisation, in the

chloride are required to completely precipitate the silver nitrate

present?

what is the concentration

of the silver nitrate: 5 solution?

(vi) What is the concentration

of the sodium chloride solution?

(b) The following experiments were

carried out, in order to study the conditions for rusting of iron to take place:-

nail

Call bolled water salty acidified

we tor

water water The following results were

obtained:-

Tubes

Resulta

.(A)...

no corrosion(rusting)

(b)

no corrosion

(0)

(a)

(e)

(1)

rusting

extreme corrosion

extreme corrosion

What are the necessary conditons for rusting to take place?

(11) Give an ionic equation

to show the changes the iron has undergone during rusting.

(iii) What

happens

to

the rate

of rusting in the presence of salt or an 'acid?

Explain why this is so.

(iv) Do you expect a car parked near sea will rust faster?

Rusting is in fact a redox reaction during which iron loses electrons. Using - this idea try to explain (1) why iron plated with

tin is easy to rust when the tin coat is broken?

物理

(2) why iron plated with

zinc is not easy to rust even when the zinc coat is broken?

(廿九 ) 香榮家

PHYS ICS (29)

Answers to Revision Exercise

SECTION A * - MECHANICS AND.

"PROPKUTIES OF MATTER 1.(a)(i)The graph of linea speed against time is as

follows:

Time in second

(ii) The linear ace

slope of the graph

2

ma

(Ans.)

(iii) Apply | 8. fat

100- 3(2)+2

t10 s (Ans.) (iv) Let the coefficient of

sliding friction between the

hody and the inclined plane

be u, the mass of the body be m and the angle of inclination of the plane Al be

flence the net force acting

on the body is

ngs ine ungcon8

m(gaine uge na6)

Apply Newton's 2nd Law

P ma

(gsine

3(5)2 + (3m)(5)2

50m J

+

The fraction of energy lost

200m 50m 200m

(Ans)

(i) The energy lost in this

impact will be dissipated mainly in the form of heat and little in the form

sound.

2(a) The conditions are

1. The resultant of the forces

must be zero.

2. The lines of action of the

forces must be concurrent. for, equivalently, the re- sultant moment about any point

is zerpa

Since, the non-uniform Tad AB is in equilibrium, ánd

there are three forces acting

on the rod, they are the ten

sions of the strings and the

weight of the rod, Therefore;

the forces must be concurrent

Hence the centre of masa nf

the rod can be found graphical

ly as he low

75

The Lines of action of tension Tand. Tz dre.... produced and wizeť at 0.

& must, on Ake vertical, like thresho

Ans: The centre of mass of

the rod AB is 2,5m from A. (Note : AG : GB = 1 : 3)

(c) let the reactions at P and

Che B and B respectively. (*) An shown in the force

diagram below

n = mass of the man - 75kg

mass of the planck-50kg Since the planck is in equi-

librium, the resultant of

forces acting on the planck

iszRTO

B+ B - mg - μg - 0

R1 + Ry - 750- 500 = 0

Roy

1250 (1): Also, the sun of moment about

nge one)

but

відн

Cras

10ms 80

any point must be zero,

TOU

to

100

•((10)(276) ~ u(19) (100)

Take moment about P.;

B(6) mg (5) - Mg(3); = 0) R2 (5)-(75)(10)(5)–(50)(10)(3)

6

= 0.5 (Ans.)

(b)(i)Take the direction to-

wards right as positive, lat the velocity of the body at B be v.

Apply 12

= 2A8.

= 2(2)(100)

-1

400

Y = 20 ma

Momentum before impact -m(20)

Movientam after Impact

(n +

3m)v!

where v' is the final velocity

20m2 « (m43m) v.*

5 ma (Ana.)

-1

(ii) Total energy before

impact m(20)2. - 200m J Total energy after impact

875 N

{ans.)

From (1),

M

1250 1250

H2

www

875

375 N (Ans.)

(ii) Suppose the planck will tilt when the man is x meters from B. Hence, the reactio

Fon

at P, By = 0.

Take moment about Q

R1=0

Mg (3) mg (QB (50)(10)(3)-(75)(10) (3-x)-

* 1

Annt. When the man ia 1 m

from B.

(i) The

velocity

ratio of

the system is 8.

(11) weight of the block

-(7200) (0.01) (10) = 720N The efficiency of the system

M.A. V.R.

x 100

= 90% (Ang.) (iii) since.

by Load Workdone

Workdone by effort

efficiency = 90%

720 x 4 Workdone:

720

100

x 100%

8

100%

x 100% 90%

Workdone by effort

3200 J (Ans.)

The M.A, of the system

720

-7.2

-100

The tension in the cord

connected to the iron block

7.2 x 75N

540. N

The tension in the cord is

less than that in (a) because

of bouỹant farer.

Houyant force,

720N - 540N.

180N

(density of liquid) x 8

x (volume of the iron block) (density of liquid) x (10) x (0.01).

-(0.1) x(density of liquid)

Density of liquid 1800 kg m-3

SECTION B

HEAT, LIGHT SOUND AND WAVE MOTION

4(a) Quantity of heat absorbed by the alloy of mass (M+2}}kg if the temperature is incre- ased by 1 c

≈ 1000M + 550 (2M)

Joules

Heat required to raise the

temperature of the alloy per

kg through-1°c ·

(Specific heat capacity

the alloy)

2100M

73H

- 700 J

The specific heat capacity

of the alloy

alloy

■ 700 J kg

(Ans.)

(b) Let the temperature of

the bunsen burner flame be t°C.

Heat energy given out by

the sphere

(0.3)(700)(t = 35)'' ́s

llent energy gained by water

and calorimeter

= (1.98)(4200) (35-15) (0,2)(420)(35-15) 168000 J

(0,3)((700)(t-35)

168000

t = 835 (áns,).

the temperature of the bunsen burner flame is 835€