1973-05-03 — Page 17

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頁一第張五第 日一初月四年丑癸歷夏 WAH KIU YAT PO

四期星

日三月五年三七九一番公年二十六國民華中

くくし

Structural isomerism in the paraffins is caused by the ability of a carbon atom to use any number

of its valency bonds to combine.

with other carbon atoms, up to

the maximum of 4, e.§.,

||molecular |

formula Structurnal formula.

chloride

B. pt. is

chemical

1050. at 760 mm.

CH2C1

CHC12

+

Name

1913英文中學會考試題預習專欄

harmat

butune

CHC1

012

HCI + CCLA

Catho

紫道英文書院ま編

CH; CHICHTS IC

carbon tetra- chloride

化學科

(廿八)

HC1+CH, CL

methylene chloride

-HOL + CHC13

chloro- form

Combustion when a light is applied to it, ethylene burns in air with a luminous, smoky flame, and leaves carbon dioxide

200, + 2H 0

2. Addition Reactions -- most of the reactions of ethylene are addition reactions of the type. CH2

CH2A

AB

(A and B are

CH2

CH B

univalent

radicals)

Chemistry (28)

Solution for last week!

Part

B

B

A

A

5. E

Part II

00:00 RAS

Pig iron, or in moulded form cast iron, contains from 2.2 4.5% carbon and about 1% each of sulphur, manganese, silicon and phosphorus. It is very hard and brittle and is used mainly for casting, since it has a comparatively low melt- ing point and expands slightly. on cooling, thus taking up the shape of the

Wrought iron

virtually

pure iron, containing only a very small amount of carbon and little fibrous slag. It has high tensile strength and can be welded by hammering at red heat. Corresion resistance is excellent and it is used for ship's chains, bollards, ora- mental iron-work and so on.

alloy of iron, 5%

A simple type of steel is an

or mild

carbon. A low

steel is relatively soft and ductile, but increased carbon content improves tensile streną -th and hardness, at the expen- se of ductility. Heat treat- ment also affects the properti- es of steel and a medium carbor steel heated to redness and 7 quenched in cold water becomes

very hard. Chromium, nickel,

steel

etc; are added to

certain properti-

onion resistance,

hardness and toughness.

16. Organic Chemistry (1

Organic chemistry is the

study of the compounds of the element. carbon. Some important ideas which occur constantly in organic chemistry must now be considered.

Homologous Semes

A homologous series is a group of organic compounds with the following characteristics:

411 members may be represented by a general formula, e.g.,

alcohole

2.

pas, C

n2n

OH

Each member differs from the next by the group,

-CH2

The members of the series have the similar chemical properties e.g.; alcohols react with

sodium.

20 H

12n+1

OH + 2Ña

20 H2n+ 10Na +

Physical properties of members usually very by steps in the same general direction, e.g., in the paraffins, as the number of carbon atoms per molecule. increases, boiling-points rise, densities increases, heats of combustion increase.

. All members can be prepared by

general methods, e.g., any paraffin can be prepared by the reaction:

H2n+1000Na + 2NaOH

Isomerism

Na2CO2 + C H2n + 2

Isomerism is the occurrence. of two or more compounds with the same molecular formula but differ- eut structures and, therefore, different properties.

pintine".

•CH2 CHACHCHO

CH2

CHS

The paraffin hydrocarbons

The paraffins constitute a homologous series of compounds of general formula CuH

The 2n+2.

first five paraffins, of which methane is by far the most import- ant, are:

Substitution:

A substitution reaction is one which occurs between an organic.. compound containing hydrogen and a substance of the type, X.Y, where X and Y are univalent atoms or groups, X enters the organic molecule, replacing a hydrogen atom, which combines with Y to. form the compound HY, 18.,

RH

XY

=

RX HY

Substitution is the typical behaviour or a saturated organi compound.

The Olefines. Ethylene

Ethylene has the molecular

is the first formula, CH, and member of the homologous series of olefine hydrocarbons, which have the general formula, C

a, CH. They are characterised by possessing, at one point in the carbon chain, a double bond between a pair of carbon atoms, ie, the structure

Methods of prepar

(and othe Olefines)

Methane.

Ethane

H

Propane

C2Hg

Butanes,

Pentanes,

mal and iso

iso-and

-neo-

0512

CH3 сион

HO

The first four of these are gases; the peutanes are volatile liquids. Genera method of preparation of paraffins:

1. By heating the sodium salt of

a carboxylic acid with soda- line:

2n

COONa + NaOH

CnH2n+ 2 + Na2CO3.

This is usually illustrated by heating sodium acetate (anhydro -us) with its own weight of

flask soda lime in a hard-glass

and collecting the gas over. water.

→→ CH 1+ Na2CO3 CHCOONa + NaOH

Sodium acetate.

Wurtz's method -- this produces

higher hydrocarbons.

Two Well dried alkyl iodides in dry ether as solvent react with sodium. The reaction is usual- ly spontaneous at room temperat -ure, e-£•;

C2HI + 2Na + ICH-

2NaI + C5H12

A single alkyl halide may also be used, as in: 20H I ÷ 2Na

2NaI + C4H10

Chemical imperties (a) Combustion -- The paraffins burn readily in air wher ignited by a flame, forming. carbon dioxide and water.

CO2 + 2H20

(b) Action with chlorine

1) A mixture of methane and

chlorine explodes when placed in bright sunlight or when sparked: CH4 + 2012

4HCLO

ii) paraffins react slowly with chlorine at ordinary temper -ature. The reactions are catalysed by light. With methane:

СЕД

➤ HC1+ CHCL

methyl

of Ethylen

1. By Dehydration of the corresp- onding Alcohol:

The usual dehydrating agent employed in the laboratory is concentrated sulphuric acid. required conditions are:

ethenal

The

conc. sulphuric acid in excess temperature of 180oC.

For the preparation of ethzYT- ene, conc. sulphuric acid is added slowly to ethanol with shaking

The and cooling under the tap. mixture is heated to about 180°0.

+ HHSO

4

HOH +

CHHSO

with chlorine or bromine At ordinary temperature, ethylene dichloride is rapid- ly produced.

H2O + CH

C1—CH2 01

СН2СІ

(and corres -pondingly

for Br

Ethylene

With halogen acid reacts rapidly with hydrogen iodide at ordinary temperat- ure to produce ethyl iodide

HC=

CH CHI CH + HI

At

With chlorine water

room temperature, ethylene. produces ethylene chlorhydrin H2O + Cl

HCI HOCI

CH2OHCH2C1

H2C = CH2 + HOC1:

a) With hydrogen Ethylene

and hydrogen are passed over nickel at about 200°C. The product is ethane

H2C = CH2 + H2− → CH ̧CHỤ

With conc. sulphuric acid Ethylene is absorbed by fum ing sulphuric acid in the cold. Paraffin hydrocarbons. are not so absorbed. CH2

CH

50

CH

CHHSO

The reaction is reversed at about 180°0. and ethylene is liberated.

CH

CH3

HOH

CHHSO

CH2O

OH + H2

SO

H2O

C2H1f+ H2SO

The principal impurity is ulphur dioxide, produced by oxidation of ethanol in side-

on of reaction:

CHOH + 2H SO

20 + 2502

+5H20

This impurity is removed by caust- ic soda solution.

and Crt's OH.

Canetic soda sol

-Ethylene

From the corresponding alkyl halide

The alkyl bromides are usual-

the essential change

RCH

ly used in theons and.

CH2Br

HBr

CH

The reagent usually used is a boiling conc. solution of caustic potash in alcohol. The alkali immediately neutralises the hydrogen bromide, to give the total reaction.

RCH

RCH

KOH

Br

+ XBr + H20 CH2

Properties:

physical Ethylene is a colour-

less gas, almost insoluble in water, slightly less dense than air, with a faint smell and anaesthetic properties. Its

With potassium permanganate solution

i) If neutral, the permangan- ate solution is decoloris- ed with a brown precipit- ate in it (Mino,);

ii) if acidic, it is decoloris

-ed.

iii) if alkaline, the solution is turned green, and contains a manganate,

+ H2O + (0) CH2OHCHOH

Tests for unsa

glycol

With Bromine Vapour -The reddish-brown vapour is rapidly decolorised, by formation of an addition compound between the hydrocarbon and bromine,

R.CH

- CHR + Br2RCHBT.CHBIR

With acidified potassium permanganese solution-- The purple solution is rapidly decolorised with formation of

a dihydroxy -- alcohol. RCH = CHR + H20 + (0)

RCH(OH)CH(OH)R

3. Polymerisation

At about 1,000 atmos, press- ure, with a trace of oxygen present, ethylene polymerises. to polyethylene or polythene. Heat is required to start the polymerisation.

=

3n (HC CH)(-CH-CH2-

CH2 CH2 CH2 CH2-)n.

Where n is about 200.

Structure of nylon,

Nylon is synthetic protein,

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