1970-03-11 — Page 23

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REFERE

11 MAR 1970

育教僑華頁三第張六第日四初月二年戌庚夏

FERIN YAT PO

郭日僑華

{ $C%$#TY3# [\#$%$#TA£#£#£##&%*#$%385#1#$#$%$&#2#2#$%$#$58#84′′

*#*#$%$#**£#THALA BASKIA 348# 77%£# 8%$#T%%$#*!38 3%#£# $%£L# $# $#$%$#$

The ferrio sulphate solution formed in pale. yellow in colour.

菠僑

#513 757367595 45 43 4541 #578 #5%8 #378 #5%3 #8%3 45%5 #2545 #353 4

170英文中學會考試題預習專欄

堅道英文書院主編

化學科

· CHEMISTRY (19)

SOLUTIONS FOR LAST WEEK.

(PA)

Weight of alum cystals = (9.306 – 7.780) gn.

1.526.

Weight of water or crystallisation in the simpse

(9.306-8.611) gm. 0.695 m

Therefore % by weight of water of crystallisation in alum

0.695

* 100

45.55

Molecular weight of alum crystals KAB (S0),--Ħ ̧0

39.1 + 26.97 + 2(32.06 + 4 x 16) + x(2 + 16) 258.2 + 18x

Thus

18x 258.2 + 18x

0.4555

0.4555 x 255.2 18: x 0.5445

12

Thus anaber of molsoules of water of crystalliz** tion per molecule of alum in 12, giving a formid of Kal(80,),.128,0

Co: tast for the presence of potaSSIUM IN BLUE, small amount of the salt is dissolved in cono. hydrochloric acid, a olean platir mm wire is dippoc into the solution and applied to the Bunsen flame. Potassium is indicated by a lilac flame.

Fo test for the presence of aluminium, ammonium hydroxide and ammonium chloridé ara added to a solution of the alum, & white g gelatinous precipitate of aluzinim hydroxide is formed. This dissolves to form an aluminate when sodium hydroxide solution is added. That this precipitation and dissolution is not due to sino hydroxids and the zincate is indicated by paskage of hydrogen sulphide into the resultant solution, when no precipitation of zino sulphide is observed.

A1

+30 41(OH),

Al(OH) + NaOH - NaALO,

To test for the presenes of sulphate, dil. hydrochloric acid and barium chloride solution are added to a solution of alum. A white precipitate of barium sulphate proves the presence of sulphate.

3. The four gases that may be prepared here are oxygen, ammonia, nitrous oxide and nitrogen. (1) Oxygen

Sodium nitrate is heated strongly in a bara-. glans tast-tube. The salt decomposes to oxygen and sodium nitrits. Tho gàs in collected over water.

2O3 = 2NaNO2+

(11) Ammonia.

Ammonium sulphate and exceum calcium hydroxide is mixed intimately, and heated in boiling tube, Ammonia is evolved and may be collected by upward displacement of air

(NH) 504 +

28H+

Ca(OH)2 - CaSO + 2NH.

(iii) Nitrous oxide

Ammonium nitrate is prepared in a slask by mixing and heating ammonium sulphate and sodium nitrate in the correct proportions, ammonium nitrate decomposes on heating, yielding nitrowe. oxide. The gas is collected over warm water.

Ng250 + 2020 ↑ + 48,0

2NaO+ (NH4)2S04

(iv) Nitrogen

The sodium nitrite obtained from (1) de dissolved in water and mixed with ammonium sulphate. The mixture is heated gently. Nitrog is evolved and can be collected over water.

2N«NO, + (HH) 50 - Na So +21

221 +420

The gases may be distinguished by the following tests:

(1) Oxygen

A glowing splint is introduced into a gas-jar of oxygen, it will be rekindled,AN

A gas-jar of oxygen is put into contact wita another gas-jar containing nitric oxide. The space occupied by the two jars will immediately. be filled with brown fumes of nitrogen dioxide. (ii) Ankonia

When a piece of damp red litmus paper is put in a jar of ammonia, it turns blue. Ammonia is the only common alkaline gas.

If a rod dipped in concentrated hydrochlorio acid is placed near the mouth of a gas-jar of ammonia, denne white fumes of ammonium chloride will be seen to form round the rod.

+ HCL - NE OL

(iii) #itrous oxide

A strongly glowing sprint will be rekindled by the gas. It is distinguished from oxygen, since it do not form brown fumes of nitrogen dioride with nitric oxide.

When the gas le panned over coated copper, the copper reduces sitrous oxide to nitrogen,

Cu + N2O - N2 + Cuo

(1v) Mitrogen

This gas is identified by its inertness and) negative teats for common gases.

When a strip of burning magnesium vire is cut into a gas jær of nitrogen, it continues to burn, yielding nagresium nitride which is hydrolysed by water to ammonia.

3Mg(OH), + 2N1

Ma32

1632 + 67,0

sulphur, aiz

mölten

and water

hot compressed.

water heated under. pressure

500-1500 ft of Olay and sand

三期星日一十月三年〇七九一座公年九十五國民華中

一起家具 中文中學會考試題預習專欄]

英文科 (1九)

LESSON NINETEEN

SECTION THREE

王淑方

11-3-1970.

ENGLISH LANGUAGE

ANSWERS. TO PREVIOUS EXERCISES

EXERCISE

(1)

concern enables

own

types pedestrians

construction

sub-ways reclaimed

circulate

(2) The reason given for the crowding of buses and

trans is the tremendous growth of population. in recent years.

(3) The rise in the standard of living which enables

more and more people to own cars shows that people are now better off.

(4) In order to keep the roads safer, pedestrians

should be more careful and they should not wander off the pavement.

(5) The widening of roads and the straightening of

dangerous corners are the two ways in which present roads are being improved,

(6) The construction of new carriage4ways and fly- overs for cars and of sub-ways for pedestrians being done to speed up the flow of traffic. (7) The group of town planners, architects and

engineers studied traffic problems overseas,

(8) There would be less danger for pedestrians if the reclaimed area in the Central District were built as suggested. It was because traffic and pedes- trians were kept apart, The former would circulate it the ground level while the latter would be free to go safely at the higher level.

EXERCISE 25

formerly

interrupted terrified

searching possessions

(b) widespre

main

(d); fatal-

adults

(2) The two natural disasters were earthquake and the

violent eruption of the volcano,

(3) In the main town of the island, the earthquaks |

caused the greatest damage.

(4) The number of casualties was small and there were]

four casualties.

(5) only

Wooden buildings suffered most.

(6) The nearby villages camped out in the surrounding!

countryside.

(7) The townspeople were searching for their possess=j

ions in the

When the..volcano

(8) As a result of the two natural disasters, all the

islanders had to leave and were resettled on one other island.

+ Ba

BaSO

When onlorine water and carbon tetrachloride are added to potassium bromide solution with shaking, an orange layer of liquid nettles to the bottom. This is due to extraction of bromine by

carbon tetrachlorids, the bromine being generated from reaction in the aqueous layer. The reaction is explained as a displacement by the more reactive chlorines

C1, + 2KBr - 2KG1 + Br ̧ /

(li) Rød lead may be considered to be amaized ozide of litharge, PbQ, and lead dioxide, Fb0, having a stoichiometry of Pb 0 - Upon heating, it decomposes and liberatas oxygen, which is a colourless gas. The residus, litharge, is an orange-red liquid in the molten state. When cool it sets to a yellow solid.

6F60 + 0;

(iii) When ferrous sulphate solution is heated with nitric acid in the presence of sulphuric Bold, it first reduces the nitric acid to nitrio oxide and i§ itself oxidized to ferric aulphates

6FeSO+ 2HNO + 3H2SO - 3F,(SO)3 + 2NO +

Nitric oxide readily combines with the remaining ferrous sulphate to sield a brown compound, nitroso-ferrous surplate, with the formula FeSO, NO. The heat however, is sufficient. to cause the compound to decompose with the liberation of nitric oxide. The nitric oxide is. oxidized by the oxygen in the air to fora nitrogen dioxide,

210+

brown

·gant.

210

sulphur deposite

Fraach's process is an industrial method of extraction of sulphur that occurs in beds at a depth of some 500-1500 feet below the surface of the earth. The proosas yielde sulphur in fairly pure form.

A system of three concentric pipes are drilled through the ground into the sulphur deposites. Superheated water at 170°C under pressure is. pumped down the outer pipe whilst hot compressed air is forced down the innermost. The sulphur melts at 115C, and the molten liquid is forced to the surface through the central pipe. The sulphur flows out of the pipe as a frothy mixture with water and air, it is allowed to solidify in large wooden tanks where the water is run off.

Sulphur is obtained as a by-product from both the petroleum industry and the coal gas industry. Sulphur. is extracted from crude petroleum as hydrogen sulphide gae. The hydrogen sulphide ia burnt in a limited supply of air to give sulphur.

25 + 0 2H 0 + 25

foxide

Sulphur may also be obtained from the apen

which is recovered from the purifiers in the gas works. During manufacture of coal gas, hydrogen sulphide is removed in the purifier by reaction with moist ferric oxide

зн

3H - Fe2S +3,0

When all the oxide is used up, the spent oxide' is exposed to air and moisture. It is reconverted; to ferric oxide and sulphur ia formed.

NEXT WEEK

2F%2 302 - 21620 + 68

Exercises in multiple choice objeotive: TORTH,

EXERCISE 26

put up dainty

ale

(c) roamed

veritable

e) smothered

opportunity gossip .book

(2)

Sonning is situated on a river.

(3)

It is because of its natural beauty and every house is smothered in roses which we bursting forth in clouds of dainty splendour. (4) The author and his companions visit Sonning in

early June.

(5) It is because of its beautiful scenery. It is

an old country inn, with green square courtyard in front: with low, quaint rooms and latticed windows, and awkward stairs and winding passages.

They wandered about the village for an hour or so. (7) They were going to put up for the night on one of

the Shiplake islands.

(8) George decided to make a stew because he wanted ti show his companions what could be done up the river in the way of cooking

EXERCISE 27

(1)

fresh

attracted

(e)

importance Establishing teenagers

(2)

resettled fanciful fundamental

i) bias

broad-mindedness

The founding of a children's village in Switzerland was the reason for ceremony (b) Immocent victims of World War II feel that

they were chosen to live in the village.

fo) It was because they had never lived a normal.

life.

(d) The education of the village children helped

them to be useful citizens of the countries. to which they belong.