1968-06-08 — Page 15

JUNE 1968

教育部

真三第四第

日三十月五年申戊溫夏

WAH KIU YAT PC

CITY HALL

六湖星

日八月六年八六九一曆公七十五國民

英中會考化學科答案

王錦釗。

{ Suggested Answers'

H.K. Certificate of Education Examination, 1968]

SECTION A (80 marks)

CHEMISTRY.

Answer ALL the questions in the spaces provided.` Chemical symbols are permitted only in equations.

1. Name:

(a) Two gases that support the combustion of

a candle

(i) Oxygen (11) Nitrous Oxide (b) Two acids that do not contain oxygeni

(1) Hydrochloric acid(11) flydrobromic acid

(c) Two reducing agente that contain oxygent

(1) Sulphur dioxide (11) Ferrous sulphate

(d) Two oxidising agents that do not contain

oxygeni

(i) Chlorine

(ii) Bromine

(e) Two elements that exhibit allotropy:

. (1) Carbon (11) Sulphur

2, Write chemical equations tofshow the following

reactions-

(a) Boil sulphur in concentrated sulphuric acid,

S+ 252504

3802

+

2820

(b) Place heated lead diuxude into a jar of

sulphur dioxide.

Pb02

+

-

Pb504

(c) Pase chlorine gas into a cold, dilute solution

of caustic potash.

C12

+

2 KOH

+

KC1 + KC10 +

(d). Heat calcium nitrate atrongly.

2Ca(NO3)2

20a0 4N02

+

3. Complete the following statements:-

(a) During the extraction of iron from ite ore,

limestone is added to the blast furnace in order to convert any silica, Sio, impurity in the iron ore to a slag of calcium silicate, which floats on the surface of the molten iron.

(b) Oxygen is manufactured by the fractional

distillation of liquid air.

(c) The simple chemical compound used to remove permanent hardness of water is washing soda

(Na2CO3 10420)

(d) Solder is an alloy of (1) lead (70%) and

(ai) tin (30%).

e) Straw hats, silk and paper gradually turn

yellow because they are oxidised back to their original colour on exposure to air and light.

4. (a) Define a Faraday A Faraday in the quantit

of electricity required to liberate in electrolysis the equivalent weight in gramo of any substance.

(b) What weight of copper will be liberated from a copper sulphate solution by a quantity of electricity that sete free 2 grame of oxygen? (0 - 16; Cu- 64)

+

Wt. of copper liberated: Wt. of oxygen i

- E.W. of Cu E, W. of O2

64/21 16/2

- 32 : 8

liberated

.*. Weight of copper liberated

8 gme.

5. Outline the steps to prepare pure samples ofi-

(a) Sodium sulphite from sodium hydroxide solution and sulphur dioxide gas.

(1) Saturate the alkali with sulphur dioxid.

until it is completely converted into sodium bisulphite.

(11) Add an equal volume of the original

sodium hydroxide solution

(111) Evaporate the solution and allow 10 0001.

(iv) Filter off the crystals obtained and dry

them with filter paper.

(b) Cupric oxide from copper sulphate and sodium

hydroxide solution.

(1) Mix the two solutiong and heat the

mixture until no further action occurs.

(11) Filter the mixture. Rinse the residue in

the filter with distilled water.

(111) Dry the residue and beat until a constant weight is obtained,

(6. (a) bow would you show whether a sample of

ethyl alcohol contains water”

Drop a few drops of the sample of alcohol

on to a lump of white anhydrous, copper sulphate. If the copper sulphate turne diue in colour, the sample of alcohol contains water if not, it is pure alcohol,

(b) How would you find out if a solution of salt

Я is unsaturated or supersaturated?

Add a tiny crystal of the salt X to the solution. If the crystal dissolves the solution 18 unsaturated. If more crystals of I form at once, the solution is supersaturated.

7. What would you observe whens-

(a) Chlorine gas is bubbled through potassium sodide solution then followed by addition .of carbon tetrachloride.

The colourlees solution turna brown."

a black ppt.. If chlorine is added in excess, of iodine will form. Op shaking the resulting solution with carbon tetrachloride, a purple layer will form on the surface of the solution.

(b) Freshly prepared concentrated nitric acid

is poured on hot sawduat.

The sawdust catches fire, burning strongly, and clouds of brown nitrogen dioxide fumes are evolved.

(c) Hydrogen sulphide gas is bubbled through an

acidified solution of potassium permanganate..

The purple potassium permangana te solution is decolorised, and a yellow precipitate is obtained in solution.

(d) Metallic sodium is added to ethyl alcohol.

Effervescence will occur, and a gas is evolved which, on mixing with air, will explode on applying a lighted tapar.

8. Underline the term or phrase that best completea

the statement or answers the question (a) A modium ionis different from a sodium

atom because the podium ion (1) is neutral, (ii) reacts with water, (111) carries one positive charge, (iv) carries one negativa charge.

←

(b) When ammonia reacts with chlorine, the (11) oxidised.

ammonia is (1) reduce displaced,

◄ (111) neutralised.)

在

fel Sodium hydroxide is manufactuEO

(1) Biketrolysis of bine una alatinum cathode, (ii) electrolysis of brine using mercury cathode, (iii) electrolysis of sodium sulphate using a platinum cathode, (iv) electrolysis of sodium sulphate using a mercury cathe

(a) The most s

(i) conce (ii) p hydr

(*) Zir

19. (*)

80%

for ammonia iá

calcium

(ii) an oxide

illustrate

very

series, oxygen to

t produced

tely.

by reduction,

fused chloride.

(b) How would you show by means of a simple chemical reaction that zing is more

·electropositive than lead?

vi)

育僑華

接第四張第二頁

英中會考數學(一)答案

(50)

歐陽鎰文。

•

No.

100

360° 2.5561

ts

360

77

0.49 71

15 m

1-6732

Y #

360 IST

~ 7.640(m)

Exp. 0.8831

OR. by making use of the formula,

AB=10'

= 4 ***

HE

RI

50.00 P

No.

109

2

0.3010

24

1.3801

zo

1.3010

001 671°

7.5878

Exp. 2 $650

360

As shown in the figure

• QRP = 45* + £ of #S^=6} { "

I AQAP: • QRP = 673

KQ # 24 0 m

RP=200 mi

By cosine formula,

Pq* = #Q1 + RP ̃— 2RQ · RP.

= *4*+ 24*– 2824X70x

Cos 67**

= $76+400 – 782

rc =

·· PQ = Jaz4 ~ 14.97 (mi) dishree beburen P+ Q je 14.97 nu

21

19

65 5 x

45 1. 3r 20 af

0.70 1.00 1.43 214 ten X 0.09 0.18, 0.27036047

43 1.00 470 0.47 cot X* (1.43| 5.67 3.73 2.75 214

2-13 =-63 11.52| 5.85 4.00 | 3-11 45

2.00 2.13 2.6)

70

75 ३० 85 2.75 3.73 5-67 41-43 10.36 0.27 0.18 0.09 3-114.00 5.85 11.53

the graph by using the above data, we find that the graph is a parabola, of which the least value of y is 2. And the graph is also symmetrical about x=45

For the equation, 35 tan xt 33_cet X*= 2* we find tan goc cotx s

Adding the graphi

diagram.

we

of y = 2x to the origin can then solve the regal aga:

the linear graph y=27. "We have 110 35

૩.

2

The intersection of this linear graph and the original curve gives the rega solutioness.

BR

ARIE

When zinc is added to a solution of a ad salt, such as, lead nitrate, metallic Thad is obtained as zinc. will displace lead from solutions of lead salta zing nitrate will be left in solution

10. Using the paraffins a examples, show FOUR characteristics of homologous series. (4) They can be represented by a general

formula, Ha

n2n + 2

(b) They show a regular gradation of physical

properties; the sp. gravity increases as n increases,

(c) Each paraffin has a molecular weight 14 greater than the preceding paraffin. (d) They have similar chemical properties; they

all form substitution products,

nfs ser

++ተ

++CH20

11. Complete and balance the following equations:-

+ 10Fe (a) 16H* +

20+10Fe** 2ln* (b) 4H*.+ MnO2 + 201 ̃ → Mn ́ 212 2H20 12. (a) In the space provided below, draw a diagram

+

+

to illustrate the atomic structure of each of the atoms named.

20

6 Atomic No. Atomic Wt. e 12

62

6 protons

Nucleus 6 neutrong

6 electrons

(2

•

4)

Carbon atom

Atomic No. - 8 Atomic Wt. - 16

8 protons

Nucleus & neutrons

8 electrons

(2

6 )

Oxygen atom

(b) Complete the following statements:-

(1) Isotopes are atoms of an element which

have the same chemical properties but a with different atomic weights. (ii) The atomic number of an element is the

ordinal number of that element in the periodic table arrangement and is equal to the value of the positive charge on the nucleus.

(iii) The atomic weight scale is drawn up

basing on isotope of carbon 12c as a standard,

13. The solubility of a substance at 20°C, is known'

to be 25 gm/100 gm of water, What weight of the Bubstance is present in 100 grams of its eaturated solution at 20°C.?

Calculation

Wt. of substance in 125 gms of ite saturated solution - 25 gme.

Wt. of substance in 100 gms of its saturated solution 100

x 25 gma.

-

125

20 gms.

14. State THREE differences between esterification

and neutralisation.

(a) Neutralisation involves an ionic reaction,

aterification does not.

(b) In esterification, the reaction is reversible

in neutralization, it is not,

(c) In neutralisation, the reaction is immediate in esterification, the reaction is slow,

15. Select from the following list of substances only.

sodium, hydrogen sulphide, sulphur dioxide, sodium hydroxide, methyl alcohol.

(a) Two substances which react to give a gan

with reducing properties;

(i) Sodium (ii) Methyl alcohol

b) Two substances which react to give a eslt

with reducing properties;

(i) Sulphur dioxide (ii) Sodium hydroxide

(0) Two substances which react to give an

element which exhibits allotropy.

(1) Hydrogen sulphide (ii) Sulphur dioxide

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日三十月五年申戊麼長

WAH KIU YAT PO