1973-05-09 — Page 18

真二第張五第日七初月四年丑発歷

1973英文中學會考試題預習專欄

WA ME NKARENA

化學科

(廿九)

Chemistry (29)

Solution for last week

TI

AMAMO

6000000

T

HUCHU

O. R

No. of Hydrogen: No. of Carbon:

14.28 85.72

12

14.28 7.14

Therefore the empirical formular of X is CH2

(ii) Molecular weight

2 x Vapour density

2 x 21

42

Let (CH2) be the molecula

formula,

(12 + 2) =

Therefore the molecular formula is CH6.

The structural formula is

HHH

Its name is propylene

(iii) 203H6 + 90%

6002 + 6H20

• 9 = 10 c... : Y c.c. (y be the volume of oxygen

required)

(iv) a. It combines with hydrogen

when passed over a catalyst of heated platinum

CH6 H2

озна

It reacts with chlorine under sunlight to form an additional product.

C3H6 + Cl2 C3H6C12

dichloropropan

It also forms additional product when hydrogen chlor- ide is passed slowly over it. C3H6 + HCl →→→

HACL

d. It is absorbed by concent- rated sulphuric acid":

C3H6 + H2SO

Organic chemistry (2)

озн

C HHSO

The Monohydric Alcohols.

The term monohydric alcohol indicates an alcohol possessing one hydroxyl (OH), group.

The monohydric alcohols consti -tute a homologeous series of general formula C H.

OH

the

first four membergcohol)

Methanol (or mei yl

Сизон

Ethanol (or ethyl alcohol):

C2H5OH

C

CHOH

Propanols (or propyl alcohols,

normal or iso

Butenols (or butyl alcohols, four isomers) OH OH CHOH

Classification of monohydric alcohols

They are classified as primary secondary and tetrary alcohols. according to whether the carbon atom which is combined with the hydroxyl group, OH, is combined with one, two or three carbon atoms respectively.

General methods of preparation alcohols

1. Hydrolysis of alkyl halides

The alkyl halide is boiled under reflux with aqueous caustic alkali, e.g.,

-O E ̧Br + KOH —○2H5OH + KBr

Reduction of carboxylic acids or their eaters

WAH KIU YAT PO

報日僑華

三期星 ®

日九月五年三七九一层公年二十六國民華中 育教僑華

HSO

1978

CHHSOC2H4+ H2SO4

中文中纜會考試題預習專欄

英文科

(廿九)

徐有祿。

The reducing agent is lithium aluminium hydride. The acid or ester and the reducing agent are both used cold in dry ester as solvent, under reflux» Later, water is added to remove excess of hydride and ditute sulphuric acid to release the free alcohol from intermediate products. The reactions are complex but equivalent finally to:

RCOOH + 4(H) →→→→→RCH2OH + RCOOR, + 4(H)- RCH OH +

By fermentation

By the fermentation of glucose or sugar with a suitable organic catalyst (enzyme). The catalyst used is zymase (yeast)

yeast C126

20H OH + 200

The fermentation goes best at a temperature of 25° 30°C. The product is distilled, and the alcohol collected, dried over quickline and redistilled

Properties of the Primary Alcohols Physical -- The simple alcohols are liquids. They are very soluble in water and in organic solvents such as ether

Chemical

ethanol

illustrated by

properties of the hydroxyl group

a) with sodium or potassium

In the cold, effervescence occurs and hydrogen is evolved.

A deliquescent

white solid is left, sodium ethoxide,

200

OH + 2Na2CH2ONa + H2↑

b) Ester formation with acids. -The alcohol is heated under reflux with an anhydr ous organic acid and a little concentrated sulphur- ic acid, or dry hydrogen chloride, as catalyst. The product is an ester.

CH

CHCOO

COOH + HỌC, H,= GH COOC, H,

H2O

Action with phosphorus pentachloride -- Vigorous reaction occurs in the cold "Steamy" fumes of hydrogen chloride are evolved togeth er with an al-yl chloride.

C2H5OH + PC15

+POC1

+H01

phosphorus trichloride giver a similar reaction. 3C2H5OH + 2PC1302H01

2. Oxidation

203 3HC

Primary alcohol oxidises in two distinct stages, first to an aldehyde, then to a carboxy lic acid, with no less of carbon.

RCH OH + (0)

RCHO + H2O

RCOOR

RCHO + (0)

CHCH2OH + (0):

CH3

CHO + (O)

3. Dehydration

CH CHO + H2O

Acetaldehyde CH COOH Acetic acid

Ethyl alcohol can be made to dehydrate in two distinct ways by choice of conditions and these should be carefully noted.

a) To ether

Ethanol in excess Concentrated sulphuric

acid Heat to 145°C.

b) To ethylene

Ethanol

Concentrated sulphuric

acid in excess Heat to 180°C. First stage for both:

CHOH + H2SO

HSO4 + H2O

With excess ethanol: C2HHSO4 + CH5OH (C2H)20

4. Dehydrogenation

Primary alcohols can often coverted to aldehydes by passage over copper ganze

(Catalyst) at 30000. Hydrogen is removed as the element.

H2t

RCH OH ) RCHO

e.g. CH2CH2OH

5. Burning

-- CH CHO + H

Ethyl 1 alcohol burns in air, and in oxygen:

e•E• CH CH2OH + 302

Saturated Monocar (Fatty acids)

3H 0 + 2002 (4 His

ylic acids

Saturated monocarboxylic acids form a homologous series of which the general molecular formula is CHCOOH, where

n is 0,1,2,3, etc

Formic acid

Acetic acid

CH3C

HCOOH соон

Propionic acid C2HCOOH

Method of prepara

By oxidation of primary alcohols

All the simpler primary alcohols and aldehydes are oxidis- ed readily to the corresponding. carboxylic acids.

RGH2OH + (0)- PCHO + H2O

ROHO+ (0)

RCOOH

CH_CH OH + (0) →→ CH CHCH2O

сна сно (0)

CH3CHO + H2O CH COOH Acetic acid

Properties of the fatty acids

Physical The first two fatty

acids are liquids in ordinary conditions. Both of these acids mix with water in any proportions. With lengthen- ing of the carbon chain, the acids become solid and the solubility in water decreases

Chemical --

Acidic properties -- All the fatty acids are weak,

a) production of colour change in indicators, e.g., litmus from blue to red

b) Neutralisation of a base to produce a salt and water only, e.g.,

RCOOH + KOH- RCOOK + H2O

c) Liberation of hydrogen with strongly electropositive metals.

2(CH,COOH) + Mg

Mg(CH, COO)2 + H2↑

d) Liberation of carbon dioxide with carbonates and bicarbon -ates.

e.g.

NaCO3 + 2CH3COOH →→→→

2CH COONE +H2O

Ester formation

+ CO

The anhydrous acid is boiled under reflux with an alcohol and with concentrated sulphuric acid or dry hydrogen chloride as catalyst. RCOOH + ROH

RCOOR + HO

CH3COOH + CHOH

CH COOCH

+ H2O

3. Action with phosphorus

pentachloride, and trichloride.

Phosphorus pentachloride. reacts quite rapidly at ordin- ary temperature with the simpler acids, liberating hydrogen chloride and forming the corresponding acyl chloride

RCOOH PO15 →→RCOC1 + POC13

+HC1

Phosphorus trichloride gives the acyl chloride and hydrogen chloride, too, but less rapidly. and usually requires steam-heat 3RCOOH + 2P0133RC001 + P203

(未兆明日續)

3HCL

English (29)

The answers to last week's exer

cise are as follows:

(a) postponed

(b. it will start.

(c) takes

(d) neither did I

(g) s

somewhere else

on

spend

0000000

Read the following passage care- "fully and write down suitable

prepositions for (a), (b), (c) etc. Do not copy the passage.

The chairman turning (a), the secretary, told him to put the

Then he proposal (b) record. asked whether anyone (c) the meet-

He ing had any objection (a) it. was surprised (e) the show. (f); hands (g) response and he rose (h) his seat to count them. Still determined to have the proposal passed, he said he would repeat. it (i) the benefit (j) those who could not understand its importance.

Write out the correct tenses, active or passive, of the verbs in brackets in the following sentences:

(a) The accident not (occur) if

he (check) the brake of his car before going for a ride. (b) The unfortunate man, who

(fall) from the tenth storey, (catch) halfway by a canopy extending from the window. (c) If you (be) the director of

the department, what you (do) (d) In two more hours our car

(complete) its trip round the New Territories and the sun.. (set) by that time.

(e) Every evening he (visit) the

theatre but never (buy) a ticket.

Insert "helping verbs" to complete the following questions: (a) Why

you not tried to persuade him to join us? (b) Where

(c)

he leave the pen- cil case yesterday?

he quite happy with his present job?

the boy holding the tray when he slipped? (e) Who: take care of the baby when she is gone?

(a) How

(£)

(e)

the girl shown any interest when you showed her the necklace?

the dog playing in the garden when it bit you? (h) Why

the pupils being detained now? (1)

your brother like straw- berry jam?

we been told of the regulations of this school?.

Combine each of the following group of sentences into ONE sentence:

(a) Mr. Jacob attended a village

school in Scotland.

He was the author of this book.

He died recently.

(b) He saw the big fish in the

stream.

He sat down on a rock on the bank.

He tried to think of a way to catch it.

Put the first sentence (a) into Indirect speech and the second (e) into Direct speech: (d) Before going out, Mr. Banner

said to his wife: "If I am not home by 11 o'clock, tele- phone me at the office.": (e) The bus conductor told the

passengers to wait till the bus had stopped before they got off.

Candidates may find the exercises in this week's column somewhat different from those in previous weeks columns, but they are not simpler. They are just

Candidates as full of pitfalls. are therefore warned that they must approach every question with the same caution although they maj find one question simpler than another on the surface. They should bear this in mind when they are doing the exercises, as well an attempting the questions in Paper.