1989-03-18 — Page 29

29 )育教 日一十月二年巳己磨買

Chemistry (25)

R: Chu

1989 中學會考預習專欄

明治出版社

Unit 14 (Continued)

MILL & DALE PRESS

3. Summary of chemical properties

Alkanes

#81 #

(b)With very reactive metals (e.g. K, Na)

and alkanel's act as weak acids.

Alkanol + Na.

sodium

alkoxide:

e.g. C2H5OH + Na: →→→→→ 0;

六期星日八十月三(九八九一)年八十七國民華中

Pydrogen gas is liberated:

sod um

(c)With chlorides of phosphorus (PCI, and

White misty fumes of HC1 (g) are obtained.

PC15)

-seen and

chloroalkane is

500+ HOT

1. Preparation By heating. sodium alkanoate with soda lime.

Rooo Na*

Sodium alkanoate

+

NaOH

A

RH + Na,CO,

·Sode line is a solid mixture of quicklime (CaO) and Nabil e.g. CH,COONa+ NaOH

CHÍCH, CƯỜNG + NACH

2. Reactions

+

CH,CH,Na,CO,

Alkanes are rather chemically unreactive. Under ordinary conditions, they are inert to acids, bases, reducing or oxidising agents, etc.

(a) Combustion burning in air with a slightly luminous flame, giving.

CO, and steam.

GO2+ (n+1)H2O

CO or C is formed if oxygen is insufficient.

Đ.3. CH + 20,

CD, - 2,0

e.g. C2H ̧ON + PC1 ̧ ——- * ̧H¿C1

chloroethene

(d)Dehydration-converting alkanols, to alkenes

Alkano

Dehydrating agent

conc H2S04 CH2

Alkeneh,0%

CH2+H20

180°C

(e)0x1dation

(0)

Alkanol

Alkanal

Oxidising agents commonly used are: (1)acidified KM0, (Chromic acid) (2)acidified K2Gr207

(3)copper at 250°C

g.CH,CH2OH + 2(0)

CH,COOH

Ethanoic acid

2CH 30,

CHA

(b)Substitution reaction.

Alkanes are saturated hydrocarbons, ie all their bonds are single bonds. The H-atoms in alkanes can be substituted by halogen atoms-in the presence of sunlight.

Alkane X,

e.g.

CH +Cl

Halogens alkanes

HX

direct sunlight

diffused light.

in darkness.

X: Cl, Br, explosive reaction

smooth reaction: no reaction

Thus, light is necessary for the reaction to take place, so, it is a

photochemical reaction. The reaction between CH, and Ci2 is given below..

CH2 + C], ~~• HE] + CHC (nonochloromethane)

CH,Cl + 01;

∙CHET, +1:

HCT4

· HCI +

(c) Thermal cracking.

(dichloromethane)

CHC (trichloromethang-

(tetrachloromethane)

large alkanes catalyst simpler.

A

alkanes N.B. This an important industrial

petroleum.)

1273k

But, CHA

C2H, (Pyrolysis!

Alkenes

Preparation By dehydration of alkarols.

Alkano

Danydrating agent

Alkene d

Dehydrating agents commonly used are:

(a)hot, unglazed porcelain (using alkang) sapnfir) (b)cont. 11,50, (excess, at 175°C to 180 C7

(c)hot alumina (A1,0%),

(d)phosphoric acid.

e.g. C4,CH2011

2. Reactions

(a)Combustion

cone H2SO

港

HONG

4. CH, = "CH, + H20°

burning with a smoky flame, giving

ጠር + nH 0

e.g. C4, CH2+ 30,→→→→ 200, +2420

Alkanoic acids:

1. Preparation By Oxidation of alkanals

Alkanol

Alkanoic acid + H20

(1)What is the function of the

broken porcelain?

(iii)(1)What happens to the bromine,

water?

(2)what type of reaction is this? (3)Write an equation of

reaction?

the

(iv)(1)What happens to the acidified potassium permanganate?

(2)What type of reaction is this?

Question 14.3

In the experiment below a mixture P. and a little of concentrated sulphuric acid

was refluxed using a waterbath. After

some while, ethyl propanoate, a sweet- smelling

liquid collected receiver,

in

the

Disting

flask

sture and..

—valer-baxt

Alkanoic acid

Oxidising agents used: KMnU ̧/H* or K ̧Cr ̧0,#H*

e.g. CH2CH2CH2OH + 2(0)

Propan-1-01

Reaccions

(a)As a weak acid

CH,CH,COOK

Propanoic acid:

Alkanoic acids, when dissolved in water, are slightly ionized to. give hydronins (1,0) that responsible for acidic properties.

pic scid + H2O A kandate ion +H,{

Thus, the

momobasic acids.

(1)CH,COOH + H20 →→

(2)2CH COOH Mg

(3)2CH,COOH + Na2CO,

(4)CH,COOH + NaOH

ing alkenes from

(b)Ester formation a

Alkanoic acid + Alkanol

4. Tests

.e. AC OR

many propert

CH,COO

are

圖

of acids. They are

Mg(CH,C00),

CH,000 Na +

condensation reaction

R* catalyst

Ester (fragrant smell)

ዛዕ

CH2O where A and

denotes, alkyl groups.. The reaction -is reversible. e.g_CH COOH + C2H2OH

CH, COOCH2

H', 3

Ethyl ethanoate

(c)with chlorides of phosphorus (PC1 or PC1,

White fumes of HCl(s) are seen and an alkanoyl chloride is formed:

Atkanoic acid' + "PC

C.g.CH2C - OH + PC15

no specific test.

Alkahoyl

chloride + POCT + HOT

CH,&-C1 + HCT

Ethanoy! chloride

(a)Rapid decolourization of bromine water (Br,/H,0) or bromine in tetrachloromethane (B/CC14),

Receiver

Colster

prpancate

(a)Give the structural formula of ethyl

propanoate.

(b)Name Two compounds which are most. probably contained in the mixture P. (c)Write an equation of the formation

of ethyl propanoate.

(d)State' TWO functions of. the concentrated sulphuric acid in this experiment.

(e)Give the name of the apparatus Ÿ in..

the diagram, 2-

(f)Which of the two openings, A and B,

is the water inlet?

(g)(i)What would be obtained on heating

some ethyl propanoate with sodium. hydroxide solution?:

(ii)Write an

reaction.

equation

of the

(What type of reaction is this?

(h)Why is the receive immersed in the

cold water?

Solution to Q.14.1

(a)P is an alkene.

Qis ar alkanoic acid. (b)X is propan-1-ol (CH,CH,CH,OH)

(It could not be propan-2-ol because this compound would not be oxidized to an acid having the same number of carbon atoms.)

Pis propene.

Q is propanoic acid.

Ris 1-chloropropane.

ethyl ethanoate.

Excess conc H2SO/Heat to 180°,

CHỊCH = CH, + H20

(ii)Acidified KMnO/Heat.

CH,CH,CH2OH+ 210) CH,CH2COOH + H,0~ PC15/No heating required.

CH2CH2OHPC)

ARIES

P can decolourize bromine solution tetrachloromethane.

Q can turn a wet pH paper ged.

LIBR

is a sweet-smelling konsoluble in water. (alState thegames

KONG PUBLIC

(b)Addition -- converting unsaturated compounds to saturated compounds.

AB

rapid decolourization. Forming oily drops.

X: C, Gry L. CHỈ XẾCH X

Examples

(1)With halogens (X,)

(2)With hydrogen halides (HX)

CH,CH2X

CH2 CI, 1.4

Ni or Pt.

A

CH,CH,

·CH2 = CH2 + Xz

·CH2 = CH2- HX

(3)Catalytic hydrogenation.

(D)Rapi decolourization

acid tas un pangriate

4.3Alkanols

(a)Smell e.g. CH2CH and C2,04. (b)Burning with a blue flame.

(c)Forming fruit-smelling ester with

an alkanoic acid.

(d)Evolving H, gas on adding sodium

metal.

4.4Alkanoic acids

homologous serier to wch Plana Q respectively

3b)entify and name, according to the TOP Systems, the compounds X,,

and S.

(c)State the reagents and conditions necessary for each of the following conversions. Write an equation of each conversion. (1)X

(11)X → Q

P

CH, CH, CH, CI + POCT + HOT

thanuic acid (CH,CрOH), conc 1250/Heat. CH,CH,CH2OH + CH, COCH

CH,COOCH,CH2CH + H2O

CH,CH&RCH,Br

{b}CH,CH_ = CH2+ Br

Solution to 4.14.2

(a)x is, 2-methylpropan-1-oi.

(ĐỊCHÍCH, CHÍCH CH

-Butan-1-01

CH,CH,CHCH

OH

Butan-2-31

CH,

CH1

(iv)X. 5

(d) Write

gas on adding Magnesium to the aqueous solution) of the acid.

between

an equation of P and bromine

reaction solution

(4)[volving H2

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CH=CH2

180°C

(4)With cone H2504

+ A - NISO CH2CH2HSO4

CH, CH2SO1 + H2O CH2CH2OH + H2SOA :

(c)Oxidation

Acidified KMnO is decolourized by alkenes. CH, = CHÍ + {0} + HỌ

(d)Polymerization.

CH2CH2OM

OH

ethane-1,2-dibl

Since an alkene molecule: consists of carbon-carbon double bond, so, under high temperature and pressure it can join to one another to form long chains of polymer by addition reaction.

e.g. nCH, CH2 →→

a little 0, as catalyst 4 CH2- CH2 heat, high pressure

polythene

Alkanols

CH,CH2 - HS0

CH_CH2OH + H2504

Preparation

(a)By hydration of alkanes

e_g. (CH2 = CH2 † H250,

CH,CH2

(b)By fermentation of sugar. to give ethanol

Sugar Hydrolysis glucose Yeast

2. Reactions

Enzymes

(a)Combustion

Ethanol + CO, + energy

or

26°C - 36°C

fructose

(n+1)

e.g. C2H2OH + 302

200; 38.0

(b)Forming fruit-smelling ester with

an alkanol.

5. Uses

5.1Alkanes

(a)as fuels.

(b)as organic solvents:

(c)as grease, oils, wax, etc."

(d)as a source of raw material's of

plastics.

5.2Alkenes

As raw materials of many plastics, e.g. ethene for making polyethene. 5.3Alkanols

(a)Ethanol in alcoholic drinks, (b)As organic solvents, e.g. CH2OH for points and dyes; C,50 for cosmetics and perfumes, etc. (c)AS fuels in spirit lamps. (d)In manufacture of

synthetic.

fibres; ethanoic acid and esters.

5.4Alkanoic acids.

(1)Ethanoic acid n vinegar.. (2)In manufacture of esters, dyes artificial silk, drugs, etc. (3)Congulation of rubber latex.

Question 14.1

A simple alkanol X has a molecular formula C,H,0. On suitable treatments X can be converted separately to compounds P, Q, R and S-in one step. 8, Q and R contain the same number of carbon atoms as X.

Q

Ρ

· Intefr"chloromethane.

Question 14:2

An organic liquid X has the structural formula as shown below.

CH

X: CH, CH - CH2OH.

(a)Name the compound X according to the

IUPAC systems.

(b)There are THREE other compounds. isomeric to X and having many properties similar to X. Write: out their structural formulae and name them according to the IUPAC systems. (c)Describe what would you observe and write an appropriate equation of the reaction on adding the following substances separately into X.

i)A small piece of sodium metal. (ii)A few drops of phosphorus (v)

chloride

(d)In the experiment as shown below, compound X is vapourized and passed Cover some hot broken porcelain. A colourless gas. Y is formed and passed separately into the bromine water and the acidified potassium. permanganate solution by means of a 3-way tan.

jatron, maga [with kyond %

Acid:

A chloroalkane

(1)(1)What is gas Y?

(2)Write an equation.

formation.

of its

2-methylpropan-2-91

(c)(i)Effervescence occurs as H2

given off.

2(CH)¿CHCH2O + 2Na

2{CH,}_CH,CH20 ̄Na+ H2

(1)White fumes of hydrogen chloride.

are seen...

(CH), CHCH2ON + PC15

(CH3)2CHCH2C+ POC], + HC!

(d)(1)(1)Y is 2-methylpropene.

(2)(CH)CHCH2OH."

(CH,1,CH CH2+ H20.

(ii)ft dehydrates the alkanot X.

(iii)(1)Bromine water is decolourized.

(2)It is an addition reaction. (3)(CH)CH CH2 + Br2

(CH,), CHBYCH,Br

(iv)(1)The solution is decolmurized.

(2)It is an oxidationi.

Solution to 4.14.3.

(a)The structural formula of ethyl

propanoate is CH CH2COOCH,CH,

(b)The two compounds are propanoic acid

and ethanol.

(c)CH,CH,COOH + CH2CH2OH→→→→→→

> CH2CH2COOCH2CH2+ H2O ((d)Conc H250, acts as a catalyst and

dehydrating agerit..

(e)y is the Liebig condenser,

(f)B is the water inlet.

(9)(i)Sodium-propanoate and ethanol are

obtained.

(ii)It is the alkaline hydrolysis of

ester.

(111)CH, CH, COUCH, City N&CH.

CHÍCH C00 Ha + CHCHOI.

(h)This is to reduce the vapourization:

af liquid ethyl propanoate,

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