1977-04-22 — Page 27

WAH KIU YAT PO

★教菌三第張七第日五初月三年巳丁感夏

1977中學會考試題預習專欄

明德社主編

(1) Let the current through

the battery be I, the current

11

through the voltameter be

物理(廿四)

魯榮家。

and the current through the

heater be In

Since

PHYSICS (24)

Answers to Exercise 12.

[1,(*)(i) Deuterrium goen

toward plate Q with an acce....

leration 1.5 x 101o/sec2

(11)

maas no.

no. of charge

deuteriuEBK

2

proton

I

1

-particle

From the above table,

Deuterium and proton have the

same no,

of charge. But pro-

ton will move faster in the

electric field because they

experience the same magnitude

of external force but proton

is lighter,

Since

deu

deu

2 x 1.5 x 1010 3 x 1010

(iii) Similarly,

Fden

m/sec2

(Ans.)

sit

8.91 x

3.3 x 10-7

* 1x 3600 0.75 A

The current I

oaken from the

battery is given by

10

10. 20

-2425 A

(ii) The A

(Anm.)

through

the heater 12 is given by

2.25

1.5A

0.75

Energy given out by the

hesting coil

12t

-(1.5)2 x 10 x 3600

#81000 J (anv.)

(iii) Let the rise in temp-

erature of copper vessel and

its content be @'

Total heat gained:

0.5x4200 x 0 + 0.5x420 x

23100 J

Heat gained by the

copper vessel and its content

deg

deu

- heat given out by the

heating coil.

23100 = 81000

(Ans.)

1.5x101om/sec2

8

* 10-16

500

-13

(Ans.)

(b) (4)

Kinetic energy gained.

➡ workdone by the electric

field

K.K.

K.B.

(ii

4x10-13

4 x 10

4(45x10-28),2

- 35

the rise in temperature

of the copper, vessel and its

content in 35 c

Corréations : Question 3

-Should be

3.(#) The 0,01-amp meter A

in the figure below has a

resistance of 4 ohms, what

wast. be the values of the

#

91 - 82 + 2x + (-1)y

日二十月四年七七九一圈公年六十六國民華中

報日僑華

五期星

Mis a 1-ma meter having

E - L(R

+B+

F

battery has an emf of 3 volts

+ R +

600

+

2900 + 100

10-3

'amp

rence of 100 ohms. The

and negligible internal resi-

stance. R is so chosen that

when the terminals a and. b

are shorted (R = 0) the meter

reads full scale. When a and

b are open (X = co ), the

meter reads zero. All inter-

mediate values of K will be

indicated by currents bet-

ween 0 and 1 ma.

(i) what should be the value

of the resistor R ?

(ii) what current would indic-

ate a resistance R of 600

ohas ?

(iii) What resistance R would

· be indicated when the meter

zrada 0.5 ma

Solution

(a)

CF0.01A

When the meter reads:5 amp

full scale :

0.01 amp

99amp

= 0.00802 ohr

(Ans.)

When the meter reads I amp

full scale:

■ 0.01 smp, 12

99amp

B

82-12

833 ma (Anu.)

(iii) When

Since R.

ر 9.5

x 10-amp

1(B+R+r)

E – 1(1 + r)

3 – 0,5x10°3 (2900+100)

0.5 x 10-3

3000 ohms (Ane.)

化眼(什四)・朱宏林

Chemistry (24)

Answer to Q. 38

D; because it can conduct ele- otricity even in the solid state.

b) 3 and C; because they have high

melting points and boiling po- ints and can conduct electric- ity only in molten state or in solution but do not do so in solid state. They are ionio. c) E; because it has low melting and boiling points and does not conduct electricity neither in solid nor molten states. So 15 must be a covalent compound. d) E; because its melting point is

lower than the room temperature. e) E; because it is covalent but

becomes an electrolyte on diss- olving in water showing the formation of ions..

D; because it is a metallic element and reacts with water to liberate hydrogen

6) A; because it is a covalent

compound but it has high mel- ting and boiling points. This could be possible unless it has a giant molecular structure. h) B; because its melting point is lower than 1000 C and its boil- ing point is higher than 1000 0.

}) 3 (8) →→ N2 (6) + 38(6)

b) According to the equation in

(a), 2 moles of Ni, decompose to give 1 mole of N2 and 3 moles of How

Hence, by Gay-Lussac's Law,

Nand give 50 om Ny 10 cm NH3

100 CHỈ NH

3.

150 cm, at the same temper

ature and pressure.

c) According to the equation for the combustion of hydrogen,

2H2(8) + 02(8) — 2H20(1)

2 moles ia 2 vols

1 moles

1 vols

150 cm3

75

Hence, the volume of air re- quired for the burning of

∙100

20

= 0.01 moles

e) **0.005 moles of. Fe reacts with

0.01 moles of Fell, to give

iron(II)chloride.

i.e.,1 mole of Fe reacts with

2 moles of Fecl, to give Iron(II)chloride.

the equation for the react- ion would be,

Fe(s)+2Fc3+(aq) →→→ 3Fe2+(aq) f) Iron(III) ions act as oxidising agent because its oxidation number decreases from +3 to +2.

The oxygen in air is resposible for the conversion of iron(II)

ions to iron(III) ions,

b) The conversion can be avoided

keeping the solution of iron

(II) salts in contact with some iron powder.

Answer to 0.4

A

Let x Be the no. of moles of C, y be the no. of moles of K,

z be the no. of moles of 0. Then,

XY : Z

+

58,8 2,8 31.4

12

16

4.9 9.8 1.96

= 2.5 51

5:10:2

51002

Hence, the empirical formula of the compound is CE b) Molecular mass =2 x V.D

= 2 x 51

102

o) Let the molecular formula of

the compound be (CH2002)n• Then, the molecular mass is,

nx (12x5 + 10x1 + 16x2} =1020

a)

=102

in = 1

Hence, the molecular formula 151002

It belongs to the esters group. The possible structural form-. îla la

ондон воси

ethyl propanoate

The other compound obtained is sodium propanoate.

8) CH_CH,000C, H + NaOH

CHÍCH CHONG Ý

A is sodium sulphate;

B is sodium sulphite

C is sodium carbonate;

D is sulphur dioxide;

E is carbon dioxide.

b)‚Ba2+(aq)+502 ̄(aq)→→→BaS0 (e) An 2+ (q) +50

Ba

2+

(aq)BaSO, (9)

Ba (aq)+CO, (aq)) Ba00,(s)

c) BaSO2+2HNO BaCl2+?

+2HNO.

(NO3)2+H2O+S©g

d) CO2+ Ca(on),

•CaCO3(3)+H2O

= 375 cm3

Vol. of Ny from decomposition

2 of NH 50 cm2

ie 75 cm3

0.00802

obas

Then the meter reads 0,1 amp

fall scale :

** 0.01 amp, l2

12 (81 Bry + Big)

- 0.09

x 107 m/s

(Ans.

(c) Let the no, of

Th

alpha-de

cays be x, the no. of

beta-decays be y

208 Ph

resistors

By and Hz

nected as shown in the ding-

ram, to convert the meter

сод

0.0 - 0.00802

+

He

91

82

to one having the ranges 0.1

ap,

lamp and 5 amp ?

0.0324

-0,404 - ohm - (Anw.)

32 208 + 4x Oy

(b)

S=100.9

E.=3V

Since B. 1(B+ x)

Therefore

E- ir

Rw

3 - 10~32100

10-3

- 2900 ohms.. (Ans.) (ii) When R - 600 ohms

Vol. of N left by the air

used up 375 cm x 80%

= 300 om

the total volume of nitrogen: obtained at the end of the, combustion = 50 on +300 em2 -350

Answer to Q, 32

Cim

a) The hydrated iron(II) ions are responsible for the pale-green colour. Yes, all soluble iron (II) salts will give solutions with this colour.

b) The hydrated iron(III) ions

are responsible for the yellow brown colour, Yes, all soluble iron(III) salts will give sel- utions with similar colour,

B.

a) The reaction will proceed at

a higher rate on heating..

b) The mass of iron used up by

the solution (0.628+ 0.348.8

0.280 g

S

c) No. of moles of iron represen-

ted in 0.280 g of iron powder is

9.280

moles 56. -0.005 moles

d) No. of moles of FeCl in 50 on

of 0.2 solution is,

50

10000

x 0.2 moles

Answer to Q.

a) Anhydrous copper(II) sulphate

would turn from white to bluet while linewater would turn from clear to milky.

b) The changes observed indicate the presence of water and car bon dioxide respectively, c) The come from the burning

candle.

d) Water and carbon dioxide are formed during the combustion of the candle.

The elements are carbon and hydrogen because they form wa- ter and carbon dioxide respec- tively on burning.

f) The pump is used to pump the

air through the apparatus. “ g) They are carbon paricles which

are formed by incomplete com- bustion of carbon.

h) A luminous flame is one which has a yellow colour. The hot unburnt carbon is responsible for the yellow colour of the candle flame.”

A is hydrochloric acid)

· B is ammonium chloridej

C is sodium chloride;

D is calcium chloride;

E is sodium carbonate. b) 1) 2 (aq) +000

2-

11) CO2+28,0

OH + NE

111) Ca2+

+ 002

2

+

82CO2+201

· B29 + NH3

CaCO

I

6

y = 3.

Azim

The no. of alpha-desays

DIA

is 6 times and the no..

of beta-decays is 3 times

ZCA

(b) The circuit of a common

type of ohmmeter is shown in

the figure below i

(1) When R

x

fion

.8

11//../ Bathery

Rx