真四第張七第 日八十月二年戌壬器

1982

中學會考試題預習專欄

(廿二)

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Chemistry (22)

Reginald W. Chụ

Mill & Dale Press Ltd.

Solution to

(1)

(ii)

Gas. Xi's nitroge

(1)brown Kis

copper and

magnesium: nitride

(2)2mHg+5CuO

*Ny+3Cu+3Wj0

Ny+3Mg→M&zNz

The:concentrated

sulphuric acid

is

to dry the gas X

and to absorb any. unreacted ammonia"

(ix) (1)W is magnesium

oxide:

Z is annonís.

gas

{2}NgzN2+6W¿0

-3Mg(OH),+2NH, According to the following equation 3Mg+Ng MEN (3x24)g of Mg forms 100g of MggN2

mass of

formed by 1.54g of Mg

1.54 #今x24×100g-

-2.14%

According to the equation below. Mg3NY+6H2O

100g

3Mg(OH)2 (3x58)g

+2NH3

2x22.4dm

WAH KIU YAT PO

formed by

2g of Mezo

*100*(3x58)g

(2) 100g Mg-N

2x22 hdm3

NH at

vol of NHy obtained from 2g of

at

100

x(2x22.4)dm3

=0.896dm)

(vii) Air consists of

(b)

nitrogen. When magnesium burns air, it also combines with the nitrogen in air to form magnesium nitride which, reacting with water gives off ammonia ges that is

on

alkaline in nature.

(1)Copper(II) oxide will

remain unchanged when. heated in. a current of air. When carbon powder is heated in gir, it will combine with the oxygen in air to give carbon.. dioxide. This gas can be identified by. paesing it into some: limewater which will turn milky. C+02

CO2+Ca(UII),→→CaCO3(s)

(2)Carbon does not have

any apparent reaction with hot dilute hydrochloric acid. When copper(II) oxide is heated with dilute hydrochloric acid, pale-blue solution of copper(11) chloride: will be obtained. CuO+2HC1 Cuc1.

Solution to 0.32.

100g of MN2 (

gives (3x58)g.

of

Mg(OH)2+

-mass of

Mg(OH)2

(1)x (2) 2. (3.) T

(4) 2.

(ii) The formula is

a

XY

報日僑單

(iii) (1) Ionic

(electrovalent) hond is present in P. and the covalent bond in Q

(2) The electronic

̇structure of

282

W

The electronic structure of q

(3) Q has a lower

melling paint. P consists of:: ions held strongly together:by electrostatic force while Q consists of: molecules held together by weak.van der: waals force only. So to melt P requires: more venergy: than to melt Q (4) P will conduct

electricity because it consists of ions which are mobile in liquid state

consists of convaleut

molecules which do not conduct electricity.

even in liquid state.

(iv) The atoms in X are

held together by fairly strong. metallic bond while

Y consists of molecules held together by weak van der waale force. So, more energy is required

to melt X which

thus has a higher

melting point.

六期星

same group of the Periodic Table have the same number of electrons in the outermost (or valeice) shell of. their atoms. As the chemical properties of an element are mainly determined by the electrons in the outermost: shell; so, the

elements in the Same grouy often have similar

chemical behaviour. when hydrogen. chloride dissolves in water, it, being a polar moleculer ionizes to give chloride ions and hydronium ions. The chloride ions. thus formed will react with silver ions to give a

white precipitate

of silver chloride

Ag*(aq)+61 ̄ ̄ (aq)

AgCl(s)

Tetrachloromethane, being: non-polar, does not mix with water at all.

(iii) Pure water has a

pH of 7. When hydrogen chloride dissolves in water it ionizes to give hydronium ion which is responsible for the acidity. As a "consequence, the

pit decreases from 7 to a smaller value indicating an inerease in acidity

HCl(g)+H20→1 Ethane is... saturated

日三十月三年二八九一公年一十七國民華中育教僑華

hydrocarbon, i.e. in ethane all the C-CandC-H bonds' are single covalent bonds. However, ethene, there is a

carhen-carbon.

double, C=C, Soy ethane and ethene

dioxide.

· (2) Cu+2H2SO,

CuSD,

+2H2O+SU2

(5)The pH of the

solution would

he smaller than 7 because

Sug

is acidic in

(iii) (1)It turns from

My vorange to green. (2)Yellow particles

of sulphur are seen.

^210+3S(a)

(3) Khite

precipitate of harium sulphite appeurs.

BaCl, +H 0 S

► BaSU2(s)+2][C1

(4)It is

decolourized.

Br2+2I10+502

► 2HBr+12SO4

(iv) When S0, dissolves

8

(ii)

shows different chemical behaviour.

Solution to §.22.

The white solid is anhydrous

(111)

copper(II) sulphate,

Elementa in the

(ii) (1)Gas X is sulphur

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in water, it ionizes to give

When

ut and sulphite ions, S05 NauSUf dissolves in water,it diasociates to forci Na and 30.

803 Since both solutions contain

24

503.

ions, 80, they

show similar reactions towards certain reagents

blue because it. contains hydrated copper(11) jons,

Formula mass of NaOH!=40. Molarity of solution A. 2.0 1000 40 250

mol dri

Molecular mass of

HS-98

Molarity of

solution, B

2.45-1000-

98 250 =0.1M

(1)The pll of the

solution would

increase to 7.

(2)No, of monor

WySoy present

25 1000*9.1

= 0.0025-

No. of mol of

NaOFT added

25 1000 =0.005

mole ratio. of NaOH:H2SO4 =0.005;0.0025

That is, 2 mol of NaUH has reacted with mol of

The salt X obtained should be the normal: 结婚美 sodium

aulphate,

According to the equation

NaOH+H1SO,

·Nan SOL

of hol of Na, S0, formed:

of mol of reacted

0025.

Vol. of solution -vol, of NaOn-

vol of

1504

=25cm ?+25cm?

50 cm.

molarity.

Na SO

1,0025

50

0.05 M

1000

of mul of NGO] 20

1000×0.1 05002

, of mol of H12SO1⁄2

1000.

* 0,2

mole ratio of

10.002

1:1

0.002

Hence, the salt

obtained: would be

sodium hydrogen

sulphate, NanSo.

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