1970-05-30 — Page 16

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英中會考化學科答案

(續) 堅道英文書院撰答

H.K. Certifica

Juggested Answers,

Jor

of Education Examination (English)

CHEMISTRY

3.(a) Preparation er water from

us

A small quantity of fairly pure water may be prepared from pure ethanol utilizing the combustion reaction by atmospheric oxygen: C ̧¤ ̧OH + 301⁄2 = 2002 / + 3820 /

The ethanol is placed in a spirit lamp," and is Ignited at the wick. The ethanol burns with a non-luminoua flame, yielding carbon dioxide and team. The flame is directed on to the surface of a cold finger-constructed from a test-tube and cooled by running tap water. The whole arrangement is as showni:

water in

water out

spirit Tamp

test-tubi

watch glass

The steam condemes and may be collected on the watch glass

The simplest test for the presence of water is a chemical one, When white anhydrous copper sulphate (CuSO)-is added to a suspected Liquid, the appearance of a blue coloration Aue to formation of the pentahydrate (CuS0.58,0) indicates

However, any

aqueous solution will give this test and only physical properties provide good tests for its purity. Two simple physical tests that are... often perform are the boiling point and the freezing point determinations. For pure water. ander 760 mm, pressure, the boiling point: LOO C; the freezing point is. 0°C.

(b) Reactions of metals with water

Calcium

Sodium

Magnesium

Conditions

Observations

metal to: cold water

bubbles

heated sétal lin atean

Ime tal

metal to cold water

metal floats

slowly givancatches fire and melt due

formation of to violent oxide Mg0; faction; intense beat clear

off water

becomes

aloudy due

to slightly. soluble

Ca(OH)2

Relative fates moderate

Blow

報日僑罩?

六期星日十三月五年〇七九一曆公年九十五國民華中 育敎僑華

(接第四張第一頁)

ore

3.imestone coke

()

英中會考歷史科答案 堅道英交筈院選答,

flue gases

fire brick

300

200 + 3002

2Feo +

hot air blast

11600

200

Iron ore, nard coke and Ilmestone are powdered, mixed, preheated and then fed into the furnace at the top. A blast of hot air is blown in at the bottom. At the hottaat part, combustion of coke to carbon monoxide occurs. This carbon monoxide is the essential reducing agent. It reacts with ferric oxide in two different ways. Direct reduction to iron is an exothermic reversible process:

3

+ 300 278 + 342

and according to Le Chatelier's frinciple more. iron will be produced higher up the furnace

there it is coolers. The ferrio oxide is als

eduod irreversibly to ferrous oxide =

0203 + CO - 2FeO + CO,

the ferrous oxide ao formed 18 reduced by coke in an endothermic reaction further down. The iron formed is tapped 18 a melt from the

earth of the furnace. The limestone added le composes into quickline and serves to removë the earthy impurities as a silicate slag that float on top the iron, preventing the latter from being oxidised, The alag is withdrawn at intervals,

Cat

• Ca0 + 002

(b)(i) Keight or ngematite in 1000 leg of the iron

(1000 x 0.36)kg

Ora

360 kg·

Weight of iron obtainable from this amount of haematite

(360 = 2(1.W. of 20

(360 x

252 ke

M.W. of

(11) Weight of silica in 1000 kg of the izon

(1000 x 0,2) kg

* 200 kg

Number of gh. moles of siapa involved

1200 x 1000 NW. of

3102

From the stoichiometry or one reactions this is also the go. moles of CaQ and in turn of Caco required to form the fusible. slag

Thus weight of limestone required to oonvert all the ailic into slag

MW

200 x 1000 of Sio

× MW. of CaCO, (in go)

solution of NaOH

fast

200

3338

Russian ambition in Manchuria became a monace to Japan. In 1902, Japan joined an alliance with Britain against Russia which supported the open door policy in China. In 1904, in order to resist Russian. penetration into Korea and Manchuria, Japan fought Russie over Chinese soil. By the Treaty of Fortsmouth Japan obtained further rights in Yanchuria. In 1910, Japan formally annexed Korea and establish it as a base for further expansion into Manchuria.

In 1911, the Chinese Revolution broke but and the country was in state of civil war between the North and the South. Japan tried to further her interests in both regions by offering help to both the northern (Manchu) and the southern (revolutionary) factions. She also attempted to intervene in Manchuria to establish a permanent control there. However, the rise of Yuan Shib-kai, who was strongly anti-Japanese, thwarted all her designs. Japan therefore waited for a favourable opportunity to defeat Tuan Shih-kai and to extend her control over China.

When

In 1914 the First World War, came as the favourable opportunity when the Powers were occupied in Europe. Japan made use of the opportunity and took over, the German garrisons in Shangtwig, China demanded her withdrawal she presented the 21 Demands which demanded from China further rights in Shangtung, South Manchuria, Fukien and the Han-yeh~) ping Company. In addition she demanded som political and economic control of China Yuan Shin- Kai was unable to resist Japan without foreign support and

most of the demanda".

after the War, China sent delegates to the k Versaileed Conference calling for the abolition of unequal treaty rights and the return of Shangtung and the abolition of the 21 Demands. However, Japan had obtained previous secret agreement with France and

Britain and was able to obtain all German rights Shangtung. This led to widespread anti-Japanese "feelinge in China and led to widespread boycott of

Japanese products. In 1922, when the Washington Conferende was convened, China again demanded ther abolition of the 21 Demands and the return of Shangtung. Under the pressure of the Allies Japan ais .

forced to return Shangtung to China but the 21 Demands was not abrogated.

To conclude, Japan's policy towards China during this period was directed mainly to achieving two endaj first, to establish a permanent control of Manchuria and secondly, to extend political and... economia influence in China. China's policy, on the other hand, was to rely on foreign help to resist Japan's aggressive designs, since she had not the strength herself to resisit it. As a result, the Sino-Japanese relations during this period was one of increasing hostility. On the one side was a strong. and aggressive netion intended on extending her intereste on the expense of the other one the other) side was a weak but wakening nation of increasing. national congicousness. The increasing strength and unity of China in the next decade brought further: olashes between the two countries.

Correction I

Answer to Question 4 of the Far Eas Sections

When the Sino-Japanese. War ended in the Treaty of .Shinonogat

Order Order of decreasing reactivityz Na, Ca, Mg.

(c) Reaction between sodium and ethanol

Ethanol contains two distinct types of hydrogan attached to the carbon skeleton of the molecules. Namely the hydrogen atoms that are covalently bondad direct to carbon, as well as a hydrogen atom bonded to oxygen. The latter combination is known as a hydroxyl function and possesses certain interesting features. Sodium is a highly electropositive metal and is capable to displace the very weakly acidic hydrogen of the hydroxyl function from ethanolt 2008 → 2#

2

This rsaults in the liberation of hydrogen and formation of an electrovalent compound known as Bodium ethoxide.

The reaction is actually or similar type that of sodium with water:

+2Na 2NaOH +

220+

#21

..

However, comparatively speaking, water is maah stronger acid than ethanol and its reaction with sodium is hence much more

vigorous. This is further. indicated by the fact that when water is added to sodium. ethoxide the latter readily hydrolyses, to Bodium hydroxide and the weaker acid, ethanol

+ NÃO

1

5

4. (a) Industrial extraction or iron from its ores. includes smelting of the oxide to the crude metal and refining to the pure metal. Smelting is carried out in the Blast Furnaces

5.(a)(i) Deduction of formula or reaction product

Let volume of hydrogen added to the unknown gas be 2V Thus volume of the unknown gaseous element ward is 7, and total volume of the mixture beti before and after Teration 10 3V,

When the reaction mixture is placed ovar water,.. of the volume of gases dissolved,

..3 Thus volume of the gaseous product formed fe 27 and volume of the residual hydrogen in V. The volume of hydrogen that has reacted must

olume of

Thus V volume of hydrogen reacts with V volume of the unknown gas to yiela 27. volumes of gaseous produet.

As a corollory of Avogadro's Hypothesis states that for the same temperature and pressure equal volumes of different gasea contain the same number of molecules, it cần be suggested that one molecule of hydrogen reacts with one molecule of the b unknown to form two molecules of product. Given that hydrogen is distomic, and that the unknown is an element of atomicity ny the reaction may be represented stoichiometrically as

2EX0.50

where X represent the molecular formula

the unknown elementi

According to Dalton's atomic theory, the atom ie the smallest entity that can ba involved in chemical combinations. Thus must be 2 or a multiple of 2.

From the know fact that hydrogen combines with a válancy of 1, i.e. 1 atom of it can combine with only 1 atom at a time — the product must be HX Thus n, the atonicity of molecules of X 19 2.

B

2HX

(ii) As wat blue litmus paper is turned red in

presence of the gaseous product HX, the gar is capable of yielding hydrogen ions in aqueous solution. Compounds of hydrogen with other elements are often covalent (except certain hydrides) and water is. required to act as & bago (the proton. acceptor) on HX to yield its conjugate acid (H30) which has an effect on litmus.

HX + H ̧0 - 8 ̧0′′

(b) Carbon monoxide and carbon dizu may no

separated from a mixture of the two by making. use of the acidic property of the dioxide. Carbon dioxide is readily absorbed by sodium hydroxide solution to form the soluble sodiun carbonate

+2NaOH

Na COHO

Thas to obtain fairly pure carbon monoxide, the mixture is bubbled through a cold. concentrated solution of sodium hydroxide and collected over water. If moisture is to be removed, the emergent gas is passed

through

cono. B250 before collecting by displacement of memoury.

22

The carbon dioxiɑs in readily regenerated by adding excess of dilute 2,504 to the resulting sodium carbonate solution in a flask, the Darbon dioxide evolved is removed from moistura by passing through conc. 30, and collecting,

24 by displacement of mercury

Ja, C

B:90