1973-02-28 — Page 20

日八十月二年三七九一屦公年二十六國民華中育教坻割

郭日僑華

三期星

四笑張五第二日六廿月正年丑癸屬

WAH KIU YAT PO

2A1 + 301,

2A101

菠橋

1913英文中學會考試題預習專欄

That

化學科

(十九)

Valse To rimossan. Comme mi

Today you

Chemistry:

Solution for last week Part

10.

Part II: [16: (a) L (1).

Concentrated sulphuric acid has oxidising properties, which increase in power as the concent- ration of sulphur trioxide in- creases, Thus hot concentrated acid will oxidises sulphur to sulphur dioxide, while the acid itself is also reduced to sulph dioxide:

SO: →3502 2H20

(11) Sulphiaric acid in the con- centrated state has a great affinity for water. Organic comp ounds that contain the elements of water are easily dehydrated. For sugar, , action of concentrated acid will cause the formation of a spongy mass of carbon:

122201

120↓ + 118,0

(removed by conc

(111) Concentrated sulphuric acid like the dilute acid also process -es acidic properties. The acid, being dibasic will react with bases in two stages, forming firstly an acid salt, then with excess base to a neutral salt:

Zno+H SO

(b)

NaHSO+NaC1

Hydrogen chloride gas. NaCl + H SO

NaHSO HOL

Na 50+ HC1]

higher temperature required).

(11) Nitric acid vapour, the pour is coloured somwhat brown due to decomposition of nitric acid to nitrogen dioxide and oxygen.

BENO

BaHSO

+H2SO

NaNO

NaHSO HINO

Na SO+ HNO (higher

temperature. required).

(111) Carbon monoxide

HCOONa 30

HCOOH + NaHSO

as an

acid)

CO (coc. H2SO as

4

dehydrating agent)

(iv) Carbon monoxide and carbon

dioxides.

9202

10. Chlorine

Preparation:

H2C204 (H2SO4

2

acid).

NaHSO

aa an

CO2

HSO

conc.

as a dehydrat

b) from common sait:

Instead of using hydrochioric acid and manganese dioxide a mixture of salt, manganese dioxide, and sulphuric acid may be heated.

MnO 4NaCl + 48, 50

4NaHSO

MinCi

11) Instead of manganese dioxide, lead dioxide (Pb0) may be used

PbO2 + 4HC.

PbC1+ 28-0

0121

111) Red lead acts on concentrated

hydrochloric acid

8HC1

3PbC1

012

iv) Oxidation of concentrated

hydrochloric acid by potassium [permanganate.

No heat is required, and the facid can be added to the flask containing the permanganate by means of a dropping funnel.

+16HC1 →→2KC1 + 2MnC1

8H 0 + 501 ↑

By electrolysis of hydrochloric acid (conc.

Cathode of carbon or platinum Anode of carbon 2H01 At anode

Thin copper leaf also takes fire spontaneously:

Action on non-metals

Chlorine attacks all non-metals except carbon, oxygen and nitro- gen. The last three elements. combine with chlorine only in- directly.

a. White phosphorus, in a derlag- rating spoon, takes fire in chlorine, forming white clouas which are partly phosphorous trichloride (liquid) and phosphorus peutachloride(solid) 12P+ 3012

2PC1

2P

5012

Sulphur.

2PC15

When dry chlorine is passed over molten sulphur in a distilling flask connected to

a condenser, a reddish liquid distils over:

129

Sulphur monochloride

Priser opagising agent

Oxygen imparted to another substance Sulphites are oxidised to sulphates

HSO

H2O + Na2SO2

2HOT

2H01

Chlorine imparted to another substance Ferrous Chloride is oxidised to fermic chloride

2 FeCl + Cl

2FeC1

Hydrogen 18 oxidised to hydrogen chloride.

2H

201

2017 2e volume of chlorine liberated At Cathode: H ion discharge

012

H2 C12

2H + 2e

volume of hydrogen liberate, Properties Physical

Greenish yeaslow gas with punget smell, attack- ing mucous membrane, poisonous, diatomic molecules, soluble in water.

Chemical ---

ion of chiomne on nya roge Hydrogen elegant H2 C1-

ዘር

(Porus stehin

Tumes of. nyorogen

6. Compounds containing nyd roger react with chlorine, giving up their hydrogen to form nya rogen chloride

Waru turpentine,

8012 16H01

Candle wax

111) Ammonia

| 2NH

iv)

6H01

6HC1

3022 Hydrogen sulphide" HS

Cl

2. Action on metals

2H01

Chlorine attacks and directly. combines with all metala forma pa the highest chloride.

a. Sodium burns if heated 107

chlorine

21a

ga

ing agent ).

Mg

С12

1) 8) oxidation of concentrated.

hydrochloric acid by manganese dioxide

Mno

+ 4HC

MnCl2 2820

01.10

2NaC1

2401

Acid radical imparted to another substance

Ferrous sulphate oxidised ferric sulphate

2Feso

C12

Fe (S0) + 2HC1

Hydrogen taken from a substanc Hydrogen sulphide is oxidised to sulphur H2S + Cl2

2HC1

Chlorine Water or moist chlor- ine gas as an tleaching agent

· For bleaching action, chlorine first reacts with the water and forms hypochlorous zeid, HC10, this acid readily yield up its oxygen. It is this oxygen which causes the bleaching, the oxygen combines with the dye and forms a colourless compound material is bleached,

Cl2 + H2O

HC10+ Dye

hence the

ОТОН + ТОН

HC1 + (Dye + O

colourleas

The action is an oxidation of the dye

6. As a displacing element

Chlorine displaces bromine or iodine from solutions of potass= ium bromide or iodide.

2KBг + 012

2K1 + C12

2 KC1

2KC1

Br2 12

7. The action of chlorine on

Alkalis

a. Cold dilute sodium or potass->

ium hydroxide solution gives a mixture of chloride and hypochlorite

C12 + 2KOH

KC1 +

KC10

H2O

Magnesium burns in chlorine

b. Hot concentrated sodium or

potassium hydroxide solution gives a mixture of chloride and chlorate. 1301 6KON

► MgC12]

Zinc also burns in chlorine gas

ZaC1,

Tron or aluminium is beated chlorine

2PeC1

\270 + 3012

Ca(OH)2 Ca001

Manufacture of hydrochlore acid.:

2. Water purification, because

chlorine is a powerful killer

of

germs in the prevention or cholera, typhoid, etc. 3. As a bleaching agent, buc 19

too destructive to use in bleaching wool, silk, etc. 4. Manufacture of many organic compounds or chlorinat ed products, e.g. chlorogorm, D.D.T. carbon tetrachloride and synthetic rubber, synthal ic plastic and weed killer etc. Exercise Part 1

1. When chlorine is passed into solution sulphate and sulphuric acid, the salt undergoer

A. reduction

B. neutralisation)

C. oxidation

D. decomposition

E. double decomposition

2. Chlorine is usually added to pater which is going to be provid- ed in a town. This is in other to

dissolves the impurities in the water

precipitates all suspended matter in the water. softens the water

kill germs

E decolourise.it

3. Chlorine will turn moist blue litmus paper red. This is becaus chlorine water.

A. reduces litmus dye B: oxidises litmus dye

C. contains chloride ion

D. contains hypochlorous acid E. contains hydrochloric acid

4. The majority of chlorine used

industry is

A. Water purification

B. bleaching agent

C. manufacture of D.D.T.

D. manufacture of hydrochloric

acid.

manufacture of carbon tetrachloride

Chlorine is made commerically

rom

A. the action of mangenese

dioxide on sodium chloride and concentrated sulphuria acid

the action of mangenese “dioxide on concentrated/

hydrochloride acid

the oxidation of concentrated hydrochloric acid by sir, using a surface catelyst the electrolysis of dilute) hydrochlomo acid

the electrolysis of rused sodium chloride..

6. When chlorine is bubbled through a cold, dilute potassium hydroxide solution, the products formed are potassium chloride, water and

potassium hypochlorite potassium chlorate

R. potassium chloʻrite »

potassium perchlorate none of the above

Chlorine reacts directly, with, all non-metals except:

1. carbon

2. nitrogen

oxygen silicon

sul phu 17

which of the following aloernatīv

es is correct?.

P. 1, 2, and 3 only

Q.

R

S

A

and S only

* 53, and 4 only

2, 3, 4 only

none of these combination

8. When chlorine is passed into » cold dilute solütion of sod 1 um hydroxide it forma

P. perchlorate only

Q. chlorate only

R. chloride only

5KC1 + KC103

3.

+ 3H20

When chlorine is passed for a long time over solid slaked line, bleaching powder is formed.

a mixture of chlorate chloride q

1. a mixture of hypochlorite

"and chlorad s

(朱宪明日籤)

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