1972-12-20 — Page 27

MEFERENCE LIBRARY

20 DEC 1972

青教僑望頁一第張七第日五十月一十年子壬龍WAH RIO YAT PO

1973英文中學會考試題預習專欄

化學科

(九)

Chemistry (9)

Solution for last week

(a)

740 x 1400

760 V.

2003~1900-273~

707070

(b): 760 x 287

1,283 0.0. 735 V1

273

288760 x 287

7352 273

593272

191100

313 0.0

2.(a) 1) Gay Lussac's Law stetes that whon gases react, they do s in volumes which bear a simple ratio to one another, and to the volumes of any gaseous products. All volumes must be measured at, or corrected to, the same temper ature and pressure.

11) Avogador's. Hypothesis states that qual volumes of all gases under the same conditions of temperature and pressure con- tain equal numbers of molecules.

(b) By definition,

fapour density of a gas

of volume of the res of an equal volume of hydroge Applying Avogadro's Hypothesis,

V.D.

t of nmol

the cas

wo of n mol. of hydorgen

wt.

of 1 mol, of the gas.. wt of 1 mole of hydrogen

But hydorgen is diatomic ther

1 mol, of hydorgen

wt. of 1 atom of hydrogen

SO V.D. -

wt. of 1 mol, of the

xwth of 1 atom of hydrogen kultiplying throughout by

2 x V.D.

wt of 1 mol of the cas

of atom of hydrogen molecular weight of the g erefore Molecular Weight

2x V.D

(c) Before explosion, 20 of CO + 20 c.c. of: 0,

After the treatment with NaOH, remaining volume 30.0.0.

Volume of CO

produced

= 50 0.0 - 30 c.c. - 20 Excess Oxygen = 30 c.c... So volume ofr

-ion = 40

Therefore,

used in the explos

30 c.c. = 100.c. in explosion 20 c.c. of 00 + 10 c.c. of yield 20 c.0.

Thus, the volumes of une reacting gases and the gaseous product are in a simple ratio to one another. 2

The molar volume

By experiment, it has beer found that 1 litre of hydrogen at N.T.P. weighs 0.09 gm. There fore, 2.016 gm of hydrogeo

O eight of hydrogen=1,008)

016 litres, or 22.4 11t

at N., P. This volume is called the grava-molecular volume of hyd rogene

Suppose that 22.4 litres of hydrogen contain n molecules. Then by Avogadro's Hypothesis 22.4 litres of any other gas will con- tain n mclecules.

Suppose that 22.4 litres of ery gas at N. 7. P. weigh w gi.. Each molecule of it will therefore weigh w go, and a hydrogen sole-

gule will weigh ag

The weight of a mol-ulle ui

The Weight of a moledÜLE

hydrogen

--

weight of a molecule

The weight of an atom of

hydrogen

銀日僑茶

三期星

日十二月二十年二七九一圈公年一十六國民華中

That is, the molecular weight of

ages is equel to the weight in grars of 22.4 litres of the cas measured at 1.7.P.

The gran-molecular volume or gas is the volume occupied at H.T.P. by its gran, moleculare weight and is 22.4 litres at N.TE

This is a most important and

uzeful result because it means that if we write the molecular formule of eny gas, ard agree to work in grams ae weight, units, 11 those molecular formula re- present 22.4 litres of the gas a

Chust

31

444

Hi

Molieut 22

dei tes fet bee bee bee bee

A

[(b) Yaban

Motar Vol.

(litre)

Tetermination of formulae of som

cec

(1) The formula of hydrogen

chloride

The apparatus consists of two bulbs of equal volume Falt

{]h A with hydrogen and B withi stry chlorine. Oper the centre tap so that the gases mix. Leave the

pparatus in diffused sunlight for about two days. Place one end of the apparatus, under mercury and open the tap; no gas escapes ard ro mercury enters. This shows that the volume of residual gases is the same as that of the origin n) gogos. Closes the tap. Now

place one end of the apparatus. undor water containing potassium rodide

and then open the tap. water enters and fills both tubes completely, therefore, all the Hydrogen was used up. No, brown colour due to lodine 18 seen, Therefore all the chlorine war used up. The only product as very soluble-tydrogen chloride, which dissolved completely in the water.

1 vol. of hydrogen 1. vol. of chlorine

2 vols of hydrogen

chloride

Therefore, by Avogadro's Hypothesi18:-

mol, of hydrogen + 1 mol. Chlorine

mols. of hydrogen

chloride.

Hydrogen and chlorine are both

herefore diatomic,

2 atome, of hydrogen + 2 atoms of

orine

mols. of hydrogen

chloride

1 atom of hydrogen of chlorine

of hydrogen chloride

Bulls of equal Volieine

五

The formula of steam

atom mol.

The formula of hydrogen chloride

3 HOT

The formula of steam

acchol Vapour out

Wicted to intuction

merewny

The apparatus is a U-tube or chack glass closed at one end and sur

round get. The closed

tube

Two platinum wires are sealed into the glass, with a small gap oetween them.

ent

Pass vapour from boiling amyl alcohol through the jacket; the steam formed during the experime bill not condense, Add x al. oxygen to the apparatus: make the mercury levels equal before reading this volume is made at atmospheric pressure and 131°C. Add 2x ml. of hydrogen. Run mercury out of the tap to reduce the pressure of the gases and therefore to lessen the risk of damage to the apparatus by the explosion. Cork the open lim

to prevent being forced out. Con- nect the two platinum wires to an induction coil and pass an electri spark across the gap between the wires. The gases explode and form steam. Allow the product to cool to 131°C. and make the mercury levels equal. Note the volume of gas in the apparatus, it is 2x ml, Allow to cool below 100°C. The mercury rises to the top of the graduated tube, showing that all the oxygen and hydrogen have react -ed and that the gas formed is steam.

2 vols of hydrogen + vol of oxygen

2 vols. of steam

Therefore, by Avogadro's

Hypothesis:

2 mols. of hydrogen 1 mol. oxygen,

2: mols. of steam

mola. of hydrogen and

oxygen are diatomia

2 atoms of hydrogen + 1 atom of oxygen

mol of steam.

Graphite

Плаво скудел flanne

mercury

The formula of steam is there- fore 120

(3) The formula of carbon dioxide: Place a tiny piece of graphit in a boiling-tube, Arrange the apparatus as in the diagram, but without the mercury. Pass dry oxy- gen from a cylinder into the tube, then close the clip, pour mercury into the U-tube, open the clip until the mercury levels are equal then close it again. That the car- bon with a small flame, being careful that expansion of the gas does not drive mercury out of the U-tube. When the reaction has finished, let the apparatus cool. Excess carbon remains, showing that all the oxygen has reated The mercury returns to its origina levels, proving that carbon dioxid contains its own volume of oxygen. carbon + 1 vol. of oxygen

1 vol. of carbon dioxide Therefore, by Avogadro's

Hypothesis, carbon + 1 mol. of oxygen.

1 mol of carbon dioxide The molecule of exygen is diatomic, therefore carbon + 2 atoms of oxygen

mol, of carbon dioxide. The formula of carbon dioxide 19 0.0. Its molecular weight is therefore 12x + 32. The vapour density of carbon dioxide is 22, and therefore its molecular weigh 18 2 x 22

12x 32)

The formula of carbon dioxide is

(4) The formula of sulphur dioxida Repeat the previous experiment using sulphur powder: instead of

·不過,鋼然录岸個有讓說的環境,但仍不可

BR-VFDZFFWEEKITE ANDKOR BESENHEERECEKS

DS

KORS-REFS-REEGEE 0-

KAT-FAFEX÷B-BBYEF 在學校生活的地位,而各等于秘,其整如下:未來健康生活的根基,已在補強而出,

本人 談說。本人以身!設科還包括一些區 號碼節目,位語有中國舞蹈,歌就等,均禸盟一方做得好;在路途实,做人方面,能 活,所以,正義而會,所調無術教育,就基宿必一網規,絕非局辏於堅持就行那些預早編排的工作,無論他所担任的科目是什麼,對於某巴材

·卲祐宮司何雅爾於致詞中,以「館與弦育」:洛加各項基法生活,我們就可肯定地說,至屯門 | 微沉略其中的價值和食要件的一些活動和意見。一。其實,由於鎮康改可與學生們的日常生活,底把那些習慣,碧固地所養起來的。領一位師 可致詞,所生致詞後,即做縠族。唔務,亦塔校聚,能够把有空我的工作,按照到己的維,使增資們龍成熱制身心,以铜花得健康的中一棟的合作。所以,在敦們方面來說,健康致聲的,有關個人資燊方面的就是。不過,假如,倍 ,他阿雅阴夫人而發區及品,何雅版 心奥康福的。如教他們自一般人士,濟現無礙致肾的首婆目的,就是要時更要提起终生的興趣和獲得他們對鐵後有關儷,內,將某因替,但有此的製的屬會,例如 「艾亨尼婚的教會,致事自日的家見和冊感,以及須給各可以用實例遠出來,使天生們四格爾底,而地需要將那生們自動參加的活動,加以行 實,都未鯤身笈力行,那麼,是難實求易生们 現在欹將餘 康教育的蹀座,略予,且有實實感的活動,應該是絕無困難的, 呲科特别重健康習慣和獲發健。 憑相,所以,教師對於換需要昂生合作而交都必須了解,本身對健康方面需度正織與否

(1) WAREMCEKUSE.

全性性來心

**

橋

300

くくり

活談

地健教

舉聖

|舉行畢業禮

|聖心中學校

授學致

頒生

A

禮校

她,华三個目檫就是對成宮的習慣,

康接有關的門號線。舉例而證,證育團體 對健,他所作所需,了然於胸,租們是不會把在校裏, 一康方研的正確熊安!以及得有隔 那我的船雅,在家中扮實踐的。而且,除事遊戲,家政,以及生物科在學校里程中的地位,一境。關於區校所在的區 朊 康發育,在團校生活中,也常 多種的想,登以及觀感,他們在樱所以後是一關保的,只不過是周一艘人士-

分認識而已。在地举人搞的地

副教育司何雅明致詞

活之地位 何夫人授憑頒 談「健康教育」在學校生 兩角的話,默就階於既不當值又不智的了。後 想而言,每一位都該是健康立育致,的影响程涩,在乎激師們對理京福利的因煤而定,

-CX-CHERKESKIRES USOS •

AKCHILAKEREREK 明夫婚主持。然會職鶇有教會人士及學生家長準明即起,清新空腻,作息四恊得官,都足以很一钟跳察迥然不同的。一方面雷橏因概舘料對學生 在理論 本身的特質,所以,它是夙其他各 方面而食,餘康發會,具有其 細。潸然,我們可以顾想到在心間聽玛低,用。到估織,它是必須由变瑛相础而行的,而做一行的原則,以期使到健康教育的訓練及乎習資料點交的任何工作,其馈行的成功與否。

褟備權和口

環排竄 作汁釐 面即個

有療部則智到一的展上

的們,開健語米激活生

歡迎歡

B

謝合

福雞

用了生一此的的壓顧

|磨加密的

graphite. The same result is obtaiî

-ed. Sulphur dioxide contains its ɔwn volume of oxygen.

Sulphur + 1 vol. of oxygen

1 vol. of sulphur dioxide By the same reasoning as above, the formula of sulphur, dioxide is 50. Its molecular weight is therefore 32x + 32. The vapour density of sulphur dioxids is 32, and therefore its molecular weight is 2 x 32 = 64.

Exercise.

64

sulphur dioxide is

1. Calculate the maxinum volume

of oxygen, measured at N.I.P. evolved when 12.25 gm. of patassium chlorate are heated, A compound contains 15.8 per cent of carbon and 84.2 per cent. of sulphur. Calculate its empirical formula. Its vapour density is 38; what is ita molecular formula?

Comprehension.

Choosing the right word is very important here. In an interview with a reporter, a government official was asked whether a pro- posed development plan in his country had any link with politicr His answer was