1979-01-13 — Page 34

頁二第張九第日五十月二十年午戊膳夏

1979

10 of

WAH KIU YAT PO

of

報日僑華

35.com

moles of • moles of

35

of hydrogen

六期星

of chlorine

73 hydro-

日三十月一年九七九一屦公年八十六國民華中 育教僑華

hydroxide.

2NaOH+Zn(NO3)y - 2NaNOㄢ +Zn(OH)2

14(n

74

14(n-1)=74

28 28

中學會考試題預習專欄

化

墨 (十四)

明德出版社朱宏林提供資料

Chemiatry (14)

rrection for Chemistry(13)

Question 20 (a):

The residual gaa was then pumped into: water and all but 15cm of gas dissolved.

Solution to 0.19

(*) (1)

(1) sodium atoms; (2) sulphur molecule (3) sodium ions; Na

and chloride

ionz

(ii) (1) In sadius metal

electrons are free to move about while in sulphur electrons are allowed to move about freely.

(2) In solideste baithe

ions are strongly held together by: electrostatic att- raction and are

mobile. However, in molten state,: the ions are mobile and. therefore. cai conduct electricity. As a result, sodium ions are discharged at the cathode and chloride iona at the anode.

(b) (1)

hydrogen gasi chlorine gas; R: hydrogen gas; S: oxygen gas.

(ii) P. 28 +20 →→→ Hy

2C1→Cl2+2e

S: 40H

(iix)According to the

equations

2C1.

of chlorine gay

not

(iv) The litmus turns blue because the discharge

of Hions at the cathode will shift the following equil- ibrium to right and

Leave behind an excess.

of hydroxide ions,

OH, which are reapon- aible for alkalinity..

Yes; its concentration will. increase during

the electroi the electrolysis

(vi) (1) No. of moles od

gas obtained

48 24000

= 0.002

"Time = "Gx60+26 日期:386"sec.

According to

equation.

408

the

4 faradays will

liberate 1 mole of oxygen gas

of faradays used to liberate 0,002 moles of

2,4.20.002

0.008

quantity of ele- ctricity:

=0.008 x 96500

772.coulombs.

the current ased.

772 386

| Solution to 0.20

ampere a

(a) (i). It is because hydrogen

and chlorine will re- act explosively under bright:aunlight;

(ii) It is to catalyse the

reaction between hydr- ogen and chlorine: under diffused light.

)Vol of gaseous mirture.

after reaction

(50+ 35)

85 cm

Vol of unreacted

wol of gas left over water

CM

3

wol of hydrogen:

chloride gas formed

(85 15)

70 cm

4 moles of electrons.

will liberate 2 moles

or

moleaof oxygen gas.

vol of Cl ̧¡vel of U2

(iv) Vol of reacted hydroge

(5015)

35.cn

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gen chloride gas

vol of hydrogen

1 vol of chlorine

2 vol of hydrogen chloride:

molecules of hydro- gen + 1 molecules nf: chlorine

2 molecules of

hydrogen chloride molecules of hydrogen chloride consist of 2 H-atoms and 2 l-atoms

molecule of hydro- gen chloride cene sists of 1 H-atom. and 1 C1-atom

the formula of. hydrogen chloride is HCl.

-

Avogadro's law stat that..

Equal volumes-61 different gases under the same temperature and pressure will

contain the game. number of molecules!

(b)(1) Bluish-green precipitates

of copper(II)hydroxide are seen which are then decomposed to give black. powder of copper(II)oride. Cu$0, +2Na0]->¤u(OH)2(#)

Na2SO Cu(OH) - CaO(a)+HO

rty-green of precipites

iron(II)hydrazide

are seen which turna reddish-brown on heating because of the formation of iron(III)oxide FeS0, +2NaOH~~~Fe(OH), (s)

4Fe(OH)2+0g*

e203(a)

(3) Reddish-brown precipitates of iron(III)hydroxide: are observed.

FeCl−+3NaOH(s)->Fe(OH),

+3NaCl

(4) White precipitates of

calcium hydroxide are observed。

CaCl2+2NauR→→→Ca(OH) ̧

+2NaCl

(5) White precipitates of

zine(TI)hydroxide are: seen which vill

dissolve

in excess sodium

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Solution to Q.21

(a) (1) No, of moles of NaOlf

used: 25

0.05

(ii) According to the

equation below

(C#g?n=1 COOR+N&OE

Py0+粒(CH2)

n-1

COON

•. of moles of acid present in 2.3 g I nv. of moles of NaOH required for neutr- alization:

0.05 moles

the mass of 1 mole of X

2.3

0.0555

46

Hence, the relative molecular mass of X is 46.

Similarly, no. of moles

of T present in 3.7 g Y

no. of m

moles of NaOH required for neutra- lization T

0.05

(vi)

the value of

Hence, Y is propanoic

acid, CH3C CHCOOH, and Qis propan−1-01, CHCICH OH

The reagent required. is an oxidizing agent such as acidified

KyCr2O7 or KMnO ėt

Heat has to be applied.

(1) CH30日+2(0)---HC00H+H2

(2) CHỊCH,CH,0F 2(0)

>H2O+CH2CH2COOR (vii) (1) compound Zia

propene.

(2) CHţCH2CH OH CH CH=CH2

H20

(3) It is an addition

(b) (i)

the mass of 1 mole of Y

0.05 74

Hence, the relative molecular masa'of

is 74.

(iii)Let the molecular form.

代客徵婚

ula of X be H(CH2) n-1°

YCOOKS

Then, relative molecular mass of XA

46 + 14(n−1).

#46 (determined as above)

14(n-1)=46 - 46.

the value of is L

Hence, A is nethanoic acid, HCOOH, and P is methanol, CHOH.

CH GOM

(iv) Let the molecular

formula of T be

(CH2)n-1

COOR;

Then, the relavie

mass of Y is

reaction.

CHgCH=CH + Bry CH3CH-CH2

Br Br

(1) The forward react- ion is usually called: hydrolysia of ester,

(2) An aqueous solution

of an alkali can.. be used which will react with the zeid formed, thus shift- ing the equilibrium above to the right.

(ii) (1) Compound B belongs

to the esters homo- logous series. It is

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