1977-04-02 — Page 22

真二第張六第日四十月二年巳丁屦爱

-1977中學會考試題預習專欏

1 明德社主編

化學(二十)·朱宏林·

Cheng

Answer to W032

· (20)

Apparatus G is glass retort. The pale-yellow liquid Lis pure nitrið acia.

YKONO3 + H2SO4g KHNO3

+ HNO d) It is because nitric acid is

volatile but concentrated sul- phuric acid is non-volatile. a) Liquid I la pale-yellow in.

colour because it contains dissolved nitrogen dioxide which is formed by the thermal decomposition of nitric acid. f) The yellow colour can be re-

moved by either adding water so as to dissolve the nitrogen, dioxide or blowing air into the nitric acid so as to re- move the nitrogen dioxide.

It is gently heated in order. to reduce. the thermal decompow Esition of the nitric acid, h) The receiver is cooled in ord-

er to cool down the nitric acid vapour which distils over. i) It is because nitrio acid can

attack any cork or rubber sto- ppers.

j) (三) Brown fumes containing ni−

trogen dioxide mainly are evo- Ived and a blue solution of copper(II)nitrate is obtained. Cu + 4-NOg>Cu(NO3)2+2NO2+2H2O On strong heating, cooper(II) nitrate decomposes to give wa- ter and black powder of copper. (IT)oxide and brom fumes. 2Cu(NO3)2

→2CuO + 480g + 02

(2) Brown fumes containing mem inly nitrogen dioxide are ob- seived and the S disappear. because they are oxidised by nitinic acid to sulphuric acid, S+ 6HNO3H_S04+60g+2H2O

So when barium chloride solutm ionis added, white precipitate: of barium sulphate is observed.

+ 201 H2SO4 + BaClg BaSO

4

The precipitate obtained is Insoluble in the apid,

Answer to 33

The formula of ethyl propanoate

is CH.

CH-CH COOCH CEL.

| b). The mixture. M consists of eth-

WAH KIU YAT PO

anol and propannic acid. d) It acts as a catalyst and as.

a dehydrating agent.

d). It is cooled in order to con-

dense the ester, ethyl, propa noate, which is volatile.

e) No, because concentrated hyd-

rochloric acid is volatile and does not act as a dehydrating agent.

[F) CH CH COOH + CHCH2OH

CH CHR COOCH CH3.

g) Apparatus A. is called Liebig

Condenser,

h) Opening Y is the water inlet while opening X is the water youtlet.

1) apparatus. A is used to conden-

se the vapour of the firoduct. 3) Sodium propanoate and ethanol.

would be the products.

a)

CHCH2 COOGH, CH2+ NaOH --

CTㄢ CH2COCNa + CH CH OH +CH CH2OH

A colourless gas is evolved which can turn the potassium dichromate paper from orange to creen, so it is sulphur di- oxide; at the same time, white solids of copper(II) sulphate ere obtained in the test-tube. Concentrated sulphuric acid, on heating, oxidizes copper to. copper(II)oxide which at once is neutralised by the acid to give the salt, copper(II)sul- phate.

* 250 CuSO D4+2H2O+$0. The propan-1-ol is oxidised by potassium dichromate first to propanal and finally to propai noic acid while the potassium ddchromate is reduced, so it. turns from orange to green due

to the formation of chromium

(III) ions, Cr

CHỊ CHI CHO OUT OI, CHI CHO LEO

CH2CF CHOCH CH COOM

A bluish precipitate is at first observed which is (II)hydroxide.

28 Copper

Cu2+(aq) + 20H(aq) → Cu(08)。 The precipitate then dissolves in the excess ammonia solution because it forms complex ions with excess ammonia. The ions impart an intense blue colour to the solution.

Cu(OH)2+4NH,→→ Cu(NH,

+ 2DHT

Answer to n34 Formula mass of sodium carbon- ate = 23x2 + 12 + 3x16 = 106 Therefore, the molarity of so- dium carbonate solution is,

22 moles per litre ≈ 0.5 M

53 106.

報日僑業

b) BaCl2+Na2C03-

六期星

• BaCO3 + 2NaCl Na2CO3+2HCl-2NaCl+H2O+CO2

c) Formula mase of BaCl,*xi,019

(137 + 35.5x2 + 18) 208 + 18x

Moles

no. of moles of BaCl2 xH20

2.44 208418x According to the 2nd equation in (b), no. of moles of Na2 CO2

left unused

x(no, of moles of hydrochloric acid)

0.2) moles

25

100

=0.0025 moles.

But, the original amount of so- dium carbonate added is,

1250 x 0.5 moles=0.0125 moles:

1000

no, of moles of sodium carbo- nate used up in precipitation is, (0.0125 0.0025) moles

-

= 0.01 moles (1 Now, according to the 1st equi tion in (b), no. of moles of barium chloride present

no. of moles of sodium carbo- nate used in precipitation

= 0.01.

2.44 208+18x

·0.01(208 + 18x) 1.e. 2.44: 1.9. 244 = 208 + 18x 1.e,18x=244 208 = 36

d) Formula mass of Bacog is.

(137 + 12 + 16 x 33 = 197

no. of males of Baictog

no. of moles of Badlg•2H2O

= 0.01 moles

mass of barium carbonate is, 0.01 x 1976 1.978

a) B is carbon dioxide; C is car-

bon monoxide; D is carbon,

b) It is used to absorb the: excess.

unreacted carbon dioxide.

c) 1) 2HC1+CaCO =CaCl2+H2O+CO2

ii) CO + C 200 (iii) CO2+2NaOH WaCO3 + H2O

CO2+Na_COg+E_O 2NaHCO3

d) Noy it is because the slightly

soluble calcium sulphate obtain ned form a coat on the unreact- ed marble chips thus preventing further reaction and the react- ion will cease..

Gae C can combine with haemom globinto form-carboxyhaemog1- obin thus preventing it to

carry out lta normal function.

of delivering: oxygen..

f) 3) Carbon dioxide has no reacto ion with copper(II)oxide but

日二月四年七七九一屦公年六十六國民華中 ★教僑華

it will be reduced by carbon morioxide to copper.

CuO + COC + CO2

iiii) A burning magnesium will be extinguished in carbon mono xide as this gas does not suppTM ort combustion but it will con- tinue to burn in carbon dioxide. eg the heat given off. by:the. burning magnesium can décompose carbon dioxide to carbon and oxygen which can be used for burning. Black particles of carbon are also observed. 2Mg + CO2

2189 + C Corrections for Chemiatry(19) 234 Part (A) of this

question should read as follows:

2.44 g of barium chloride cry- stale:of formula BaC1.

are dissolven in water trô the

solution is added 25 cm of a solution of sodium carbonate containing 53 g of sodium car- bonate per litre, and the pre- cipitate formed filtered, car- efully washed, and dried. The excess sodium carbonate in the filtrate requires. 25 cmdf 0.2M hydrochloric acid for complete neutraliz: tion,

a) what is the molarity of the

eodium carbonate" "

There are no corrections for

(b), (c) and (d).

物理(廿一)

PHYSICS (2))

魯榮家

Exercise The Flectricity

(a) As_figure shown, a rect angular coil of wire sivated.

symmetrically bout a vertical,

axim-XY is placed in a uniform.

borizontal magnetic

with

its plane parallel to the

field,

N⋅

if a current

the coil

determine the magnitude of the deflectión of the coil. (b) If a moving esil anmeter.

b. tacâle.

gives a

deflection

for a current of 1o milli-

resistance

amperes and has

of: 2.5 hma, how would von adopt on that it could be used **(i) an ammeter reading to 1.0

ampere

voltmeter, reading up to

0 volt

As figure ch wn

紅

15.2.

w

(a) Find the equivalent:

tance of the external cireui (h) Pind the reading inf.the

amme teru

(e) the reading of the volt-

3. (a) Two resistors By and H

are in narallel with

one.

other and in series with a

-ohm resistor and a dry

cell whose enf is 1.5 volts

and whose internal resistence.

is negligible. The resistance

of B2 is 100 chos. When disconnected from Rys

itional resistance

d

50 ohms:

must be inserted in the cir-

cuit in order to keen the cur-

rent through N, unchanged.

Pind the resistance of R, (b) 10 minutes are repuired

to heat a certain mass of

water to its boiling point by a coil A, 20 minutes are

Find "required", by a

the time ree-2...

to boil the

same quantity of water if

connected in

(i) A and Bare nt throngh

(i) Explain what happens

(ii)State the factors which · ·

評好致一論輿西中 奖仙嘉姫歌耄。丹施⁑尼安⁑片威公歐

ㄨㄨ

•童兒

主紅

演星

寶莉蓮奴連昆東

頭浪拋

尼斯

大衛

尼雲

蜜馬 彼尼大拉尼亞斯彼福

馬彼 史 絲~姬“福得雲衛*斯歷*拉得

低案奇能探五 宴共 鉿面 橋闖 !較謀!比大 「赴!對!道

高破 偵

奪迷

高華參戰挑款智超高的你向

gu

series.

(ii) A and B are connected

in parallel.

水司洲慶

良好

餐 五塲請早

要週第

街北 國

ㄜ

總

V心

第三

華盛

賓華統頓

影電門奇部一第

感耆 場夜午開加桟全晚今

宜幼

隰映献塲六日今 Murder by Death