Organic Chemistry - Hydrocarbons Chapter Notes PDF Download

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12 Ł

Organic Chemistry

Issi11

(i)

Introduction to Organic compounds.

Unique nature of Carbon atom -tetravalency, catenation, formation of single, double and triple bonds, straight chain, branched chain and cyclic compounds.

(ii)

Structure and Isomerism.

Structure of compounds with single, double and triple bonds; Isomerism -structural (chain, position)

(iii)

Homologous series -characteristics with examples Alkane, alkene, alkyne series and their gradation in properties and the relationship with the molecular mass or molecular formula.

(iv)

Simple nomenclature.

Simple nomenclature -of the hydrocarbons with simple functional groups -(double bond, triple bond, alcoholic, ether, aldehydic, keto, carboxylic group) longest chain rule and smallest number for functional groups rule -trivial and /UPAC names.

(v)

Hydrocarbons : alkanes, alkenes, alkynes.

Alkanes -general formula; methane (green house gas) and ethane -methods of preparation from sodium ethanoate (sodium acetate), sodium propanoate (sodium propionate), from iodomethane (methyl iodide) and bromoethane (ethyl bromide). Oxidation of methane and ethane in presence of oxygen under suitable conditions reaction of methane and ethane with chlorine through substitution.

Alkenes -(unsaturated hydrocarbons with a double bond); ethene as an example. Methods of preparation of ethene by dehydro halogenation reaction and dehydration reactions.

Alkynes -(unsaturated hydrocarbons with a triple bond); ethyne as an example of alkyne; Methods of preparation from calcium carbide and 1, 2 dibromoethane ethylene dibromide ). Only main properties, particularly addition products with hydrogen and halogen namely Cl, Br and I; structural formulae of hydrocarbons. Structural formula must be given for : alkanes (up to butane); alkene (CH); alkynes (CH). Uses of methane, ethane, ethene, acetylene.

(vi)

Alcohols: ethanol -preparation, properties and uses

Preparation of ethanol :

•

hydration of ethene;

•

by hydrolysis of alkyl halide;

•

Properties -Physical : Nature, Solubility, Density, Boiling Points, Chemical : Combustion, Oxidation with acidified Potassium dichromate, action with sodium, ester formation with acetic acid, dehydration with conc. Sulphuric acid with reference to Ethanol

•

hydration of ethene;

•

by hydrolysis of alkyl halide;

•

Denatured alcohol :

•

Important uses of Ethanol

(vii)

Carboxylic acids (aliphatic -mono carboxylic acid) : Acetic acid-preparation, properties and uses of acetic acid. Preparation of acetic acid from Ethyl alcohol. Properties of Acetic Acid: Physical properties -odour (vinegar), glacial acetic acid (effect of sufficient cooling to produce ice like crystals). Chemical properties -action with litmus, alkalis and alcohol (idea of esterification) Uses of acetic acid.

12A. ORGANIC COMPOUNDS

12.1 INTRODUCTION

The word 'organic' means pertaining to life. When comparatively little chemistry was known, people thought that substances like sugar, starch, protein and acetic acid could be obtained only from living sources like plants and animals. So they called such substances organic compounds (the compounds

derived from living organisms) and the chemistry dealing with them was named organic chemistry. As against these compounds, substances like common salt, blue vitriol, nitrate, etc., which could be produced from minerals and non-living sources, were called inorganic compounds, and the chemistry dealing with them was called inorganic chemistry.

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Since these organic compounds were obtained straight from nature and there was no known method of preparing them in the laboratory, it was believed that they were the products of some "vital force" of nature.

compounds now applies to the compounds of carbon and organic chemistry is defined as the study of carbon compounds. This however excludes oxides of carbon, metallic carbonates and related compounds like metal cyanides, metal carbides, etc.

The vital force theory of organic compounds was soon discarded when, in 1828, a German chemist named Friedrich Wohler showed that it was possible to obtain an organic compound urea, from the laboratory process.

Sources of organic compounds

1.

Plants : Compounds like sugar, starch and cellulose, as well as several drugs, are obtained from plants.

2.

Animals : Urea, proteins, fats, etc., are obtained from animals.

heat ) CO(NH2)2 (Ammonium cyanate) (Urea) Inorganic compound Organic compound

3.

Coal : Destructive distillation of coal produces benzene, toluene, naphthalene, dyes, drugs, perfumes, etc.

In 1845, Kolbe prepared acetic acid (CH,COOH) from its constituent elements, carbon, hydrogen and oxygen. Berthelot, in 1856, synthesized methane gas (CH). In this manner, the old concept of organic chemistry was given up and it was accepted that organic chemistry is essentially the chemistry of carbon compounds.

4.

Petroleum : A large number of organic compounds, like gasoline, fuel gases, petrol, naphtha, etc., are obtained from petroleum.

5.

Fermentation : Compounds like ethyl alcohol and acetic acid are obtained by fermentation.

12.2 ORGANIC COMPOUNDS

6.

Wood : Methyl alcohol, acetone, etc., are obtained by destructive distillation of wood.

Based on the fact that all organic compounds essentially contain carbon, the term organic

7.

Synthetic Methods : Most organic compounds are synthesized in the laboratory.

12.2.1 Comparison between organic and inorganic compounds

Characteristics

Organic compound

Inorganic compound

1. Presence of

carbon

Carbon is a necessary element in every organic compound.

Carbon is not an essential element in

inorganic compounds.

2. Solubility in water

They generally do not dissolve in water.

Ł

They generally dissolve in water.

3. Solubility in the

organic solvents

They dissolve in organic solvents like alcohol, benzene and chloroform.

All inorganic compounds do not dissolve in organic solvents.

4. Melting and

boiling point

They have low m.p. and b.p. and easily decompose on heating.

They have high m.p. and b.p. and usually do not decompose on heating.

5. Combustibility

They are inflammable, i.e., they catch fire easily.

They do not burn easily.

6. Bonding

They form covalent bonds.

I

Most of them form ionic bonds.

7. Conductivity

They are non-electrolytes.

-I

Only those that form ionic bonds are good electrolytes.

Ł 8. Isomerism

They show the phenomenon of isomerism

No such phenomenon is shown by inorganic compounds.

9. Colour and smell

Organic compounds have characteristic colour and odour.

Most of them are colourless and odourless.

10. Reactions

Molecular reactions are slow, due to the presence of linkages. These reactions never proceed to completion.

Ionic reactions are fast and covalent reactions

are slow.

Application of Organic Chemistry

Organic compounds are extremely useful to us in our daily life.

The soaps and shampoos we use while taking bath, the powders, perfumes, etc., we apply on the body, the clothes we wear, food we eat i.e., carbohydrates, proteins, fats, vitamins, etc., fuels we use, natural gas, petroleum products, medicines, explosives, dyes, insecticides, etc., are all organic compounds. There is hardly any walk of life where we do not need organic compounds.

-C-C-C-C-1 I I I -C-C-C-1 I I -c-l (Straight chain) (Branched chain) Ł Ł 2 >cc< ł="" ł="" (cyclic="" or="" closed="" chain)="" ł="" />

12.3 UNIQUE NATURE OF CARBON ATOMS

Carbon shows some unique properties like tetravalency and catenation, which are discussed below.

(i)

Tetravalency of the carbon atom: Carbon has four valence electrons (At. no. of C = 6; Elec. Config. = 2, 4). Since it can neither lose nor gain electrons to attain octet, it forms covalent bonds by sharing its four electrons with other atoms. This characteristic of the carbon atom, by virtue of which it forms four covalent bonds, is called the tetravalency of carbon.

X I xCx -C-x I

(ii)

Catenation : Carbon atom possesses an unique property to link together (self linking) to form very long chains. This property is referred to as catenation.

The carbon-carbon chain can be very long. Organic molecules containing as many as seventy carbon atoms joined together, one after the other, are known to exist.

(b)

Formation of single, double and triple covalent bonds : The valency of carbon is four, i.e. it is tetravalent. In order to satisfy its valency, it forms single, double and triple covalent bonds by sharing one, two or three pairs of electrons respectively between two carbon atoms as well as with other atoms like oxygen, nitrogen etc.

I I I I -C-C-C = c I I I I -C = C Ł (single bond) (double bond) (triple bond) 0 II -C-C--c=N I

The property of self-linking of atoms Ł of an element through covalent bonds in order to form straight chains, branched chains and cyclic chains of different sizes is known as catenation.

The property of catenation is shown by other elements also but carbon exhibits this property to maximum extent. This is due to greater strength of carbon-carbon bond and due to tetra-covalency of carbon. In this process of catenation carbon atoms form straight, branch and cyclic chains of atoms, and can involve single (-), double (=) or triple (=) covalent bonds.

(a)

Formation of straight, branched and cyclic chains of carbon atoms : The combination of carbon atoms with one another gives rise to straight or branched or cyclic chains.

(double bond with oxygen atom) (triple bond with nitrogen atom)

This unique nature of carbon atom (catenation and tetravalency) gives rise to the formation of a large number of compounds. More than 5 million organic compounds are known today and thousands of new compounds are added every year to the existing lot.

All this demands a separate branch of chemistry, i.e., organic chemistry.

Organic chemistry may be defined as the chemistry of hydrocarbons and their derivatives.

Features of covalent bonding involving carbon

•

Carbon atoms can join to each other to form long chains. Atoms of other elements can then attach to the chain.

[ 195]

•

The carbon atoms in a chain can be linked by single, double or triple covalent bonds.

•

Carbon atoms can also arranged themselves in nngs.

The open chain compounds or aliphatic compounds are further sub-divided into saturated compounds and unsaturated compounds.

Saturated Compounds

12.4 TYPES OF ORGANIC COMPOUNDS

The organic compounds have been classified as hydrocarbons whereas their derivatives are classified as alcohol, aldehydes, carboxylic acids, ethers, halides, etc. These compounds may contain any number of other elements, including hydrogen, nitrogen, oxygen, the halogens as well as phosphorus, silicon and sulphur.

Table 12.1 : Organic Compounds

Ł

Types of compound

Identified by the presence of

Example

1.

Hydrocarbon

(a)

alkane

(b)

alkene

(c)

alkyne

CC-bond

Ethane HC-CH,

,

-C = C- bond

Ethene HC = CH,

-C = C-bond

Ethyne HC =CH

2. Alcohol

--OH group

Methanol CH0H

3. Aldehyde

-CHO group

Ethanal CH,CH0

4. Ketone

Ł C = 0

Propanone CH,COCH,

5. Carboxylic acid

-COOH group

Ethanoic acid

CHCOOH

6. Ether

COCgroup

Dimethyl ether

HC-O

CH,

7. Halide

-X (F, CI, Br, I)

Chloroethane C"H,CI

12.5 HYDROCARBONS

Hydrocarbons are compounds that are made up only of carbon and hydrogen atoms.

Classification of Hydrocarbons

Hydrocarbons are sub-divided into two main groups, the aliphatic (open) and cyclic (closed) chain compounds.

C"H2n + 2,

The simplest open chain hydrocarbon is alkane. It is represented by the formula where n represents natural number.

It is a saturated hydrocarbon, as all the four valencies of carbon are satisfied by a single covalent bond. (For further details refer section 12B).

Unsaturated Compounds

Open chain compounds where all the four valencies are not satisfied by single covalent bonds, double or triple bonds are required to satisfy the valencies. These compounds are known as unsaturated compounds e.g., Alkenes are the hydrocarbons with double bond and Alkynes are the hydrocarbons with triple bond between two carbon atoms. (For further details refer sections 12C & 12D).

Comparison of Saturated and Unsaturated Hydrocarbons

Saturated organic compounds

Unsaturated organic compounds

1. All the four valencies of each carbon atom are satisfied by forming single covalent bonds with carbon and with hydrogen atoms.

1.

The valencies of at least two carbon atoms are not fully satisfied by the hydrogen atoms.

2.

Carbon atoms are joined by double covalent bonds

Ł C = C Ł or by triple covalent bonds.

-C = C

3.

They are more reactive due to the presence of electrons in the double or the triple bond, and therefore undergo

addition reaction**.

2. Carbon atoms are joined only by a single covalent bond.

I I

-C -C Ł

1 I

3, They are less reactive

due to the non­

availability of

electrons in the single

Ł covalent bond, and therefore they undergo

substitution reaction*.

Aliphatic or open chain compounds Hydrocarbons I I I Saturated Unsaturated alkanes (paraffins) I Cyclic or closed chain compounds C"H2a +2 [ I Alkenes (Olefins) Alkynes C"H2n C"H2a-2

* Substitution reaction : A reaction in which one atom of a molecule is replaced by another atom (or group of atoms) is called a substitution reaction. e.g. CH4 + Cl Ł CH,CI + HCI.

** Addition reaction : A reaction involving addition of atom(s) or molecule(s) to the double or the triple bond of an unsaturated compound so as to yield a saturated product is known as an addition reaction, e.g. CH4 + Bra Ł CH4Bra.

Cyclic or closed chain hydrocarbons contain three or more carbon atoms in their molecules. These have properties similar to open chain hydrocarbons. They are also called carbocyclic compounds.

Examples : (i) Cyclic compounds containing single bond are called cycloalkanes.

CH, /\ H,C CH, Cyclopropane (C,H<) ch,="" h,c="" ch="" \="" i="" 2="" h,c-ch,="" cyclopentane="" (c,ho)="">

(ii)

Cyclic compounds containing double bond are called cycloalkenes.

H,C-CH I II H,C CH CH, Cyclopentene (C,Hg) Cyclohexene (CH,o)

(iii)

Cyclic compounds containing triple bond are called cycloalkynes.

HC--C 2 I Ill H,CC CH, Cyclopentyne (C,H<) ch,="" 1,c,2="" i="" ill="" 4,e="" łł="" ch,="" cyclohexyne="" (ch,)="">

Some hydrocarbons contain at least one benzene ring in their molecules. The benzene ring is a specific type of ring structure of six H I C 1-Ł c-H I II H-C\ Ł -H C I Benzene H O Benzene

carbon atoms having carbon-carbon single and carbon-carbon double bonds in alternate positions. Most of these compounds have pleasant smell. They are also known as aromatic compounds. Few other members of this class are O□ OH O o Toluene Phenol Naphthalene

12.6 ALKYL GROUP

An alkyl group is obtained by removing one atom of hydrogen from an alkane molecule.

-H , -CH -n"2n + 1 Alkane Alkyl

Table 12.2 : Alkyl radicals

I Name

Molecular

formula

Abbreviated

formula

'a

Structural

formula

Methyl

-CH,

-CH,

H

I

-C -H

I

H

Ethyl

-CH,

-CH,-CH,

H H

I I

-C-C-H

I I

H H

Propyl

-C,H, new.

-CH, -CH, CH,

H H H

I I I

-C-C-C-H

I I I

H H H

Butyl

-C,H,

-CH,-CH,-CH,-CH,

H H H H

I I I I

-C-C-C-C-H

I I I I

H H H H

Thus general formula of alkyl is -C"H2+1*

-H , Methane Methyl

An alkyl group is named by replacing the suffix ane of the alkane with the suffix -yl. All members of the alkyl group have an unpaired electron, which is indicated by a line with no symbol attached.

Table 12.3 : Some common functional groups R represents the alkyl group (-C" H2n + 1)

Functional group

General formulae

Types of Organic compounds

Suffix

Examples with common names and IUPAC names

Halide-X

(F, Cl, Br, I)

R-X

Haloalkanes

ane

CH,CI

Methyl chloride

Chloromethane

C,H,CI

Ethyl chloride

Chloroethane

Hydroxyl -OH

R-OH

Alcohols

ol

CH,OH

Methyl alcohol

Methanol

CH,OH

Ethyl alcohol

Ethanol

Aldehyde -CHO

2>c=o

R

°

Aldehydes

al

HCHO

Formaldehyde

Methanal

CH,CHO

Acetaldehyde

Ethanal

Carboxyl -COOH

0

II

II

R-COH

0

Carboxylic acids

oic acid

CH,COOH

Acetic acid

Ethanoic acid

CH,CH,COOH

Propionic acid

Propanoic acid

Keto -C-

I I

R-CR*

Ketooes

one

CH,COCH,

Acetone

Propanone

CH,COCH,

Diethyl ketone

Pentanone

Ethers-C-O-C-

I I

R-OR

Ethers

Oxy

CH, O-CH,

Dimethyl ether

Methoxy methane

CH,-O-C,H-

Ethyl methyl ether

Methoxy ethane

12.7 FUNCTIONAL GROUP

A functional group is an atom or a group of atoms that defines the structure ( or the properties of a particular family) of organic compounds.

Alkanes do not contain any functional group. The functional group of alkenes is considered as double bond >C=C < while="" in="" alkynes="" it="" is="" triple="" bond="" c="C-." for="" other="" examples="" refer="" table="" 12.3.="" />

For example : Butane (CHjo) can be represented in the following way

Structural formula

H H H H I I I I HCCCCH I I I I HH H H

A molecule having the bigger structural fonnula is often cumbersome. We represent it by abbreviated formula.

Abbreviated or Condensed formula of butane

12.7.1 Characteristics of functional groups:

(i)

The chemical properties of the compounds containing the same functional group are similar. Therefore, the compounds of the same functional groups are identified using the same type of tests.

(ii)

The physical and chemical properties of the compounds of different functional groups are different.

(iii)

There exists a homologous series of compounds containing a particular type of functional group. For example, the homologous series of alcohols is CHOH, C,HOH and C,H,OH.

12.8. STRUCTURE

Hydrocarbons are usually represented by their structural formula.

CH,-CH, CH, CH, A structure that shows only the linking of carbon atoms in a molecule is called the carbon skeleton.

Carbon skeleton of batane

Cccc

12.9 ISOMERS

Compounds having the same molecular formula but different structural formula are known as ISOMERS and the phenomenon as ISOMERISM (ISO = same, meros = parts).

Isomers differ in physical properties or chemical properties or both.

We can illustrate isomerism by referring to two different compounds, butane and isobutane both of which have the molecular formula C4Hjo-

The fonnula that shows how atoms of different elements are linked together in a molecule is known as structural formula.

H H H I I I H H H H I I I I HCCCH HCCCCH I I I I H H H H Butane (liquefies at 0°C) I I I H H HC-H I H Isobutane (liquefies at -12°C)

The following flow chart shows different types of isomerism

I Chain I I ISOMERISM I I I Structural Isomerism I I I Position Functional Stereo isomerism or space isomerism (Geometrical isomerism) I Metamerism

There are two main causes of isomerism

1.

Difference in the mode of linking of atoms : For example : C4HjoO shows different types of linkages and thus it stands for three different types of ether.

This type of isomerism is structural isomerism.

C,H, O -CH,

CH, -O -C,H,

CH, -O -CH(CH,)2

Diethyl ether

Methyl propyl ether

Methyl iso-propyl ether

(ii)

Position isomerism : When two or more compounds with the same molecular formula differ in the position of substituent atom or functional group on the carbon atom, they are called position isomers and this phenomenon is termed position isomerism.

For example:

(i)

CH, CHC = C-H and CH, C = C-CH, but-1-yne but-2-yne 0 0 II II

(ii)

CH,CH, C-CHCH, and CH, C-CH,CH,CH, pentan-3-one pentan-2-one

*(iii) Functional isomerism : Two or more compounds with the same molecular formula but different functional groups are called functional isomers and this phenomenon is termed as functional isomerism

For example :

2.

Difference in the arrangement of atoms or groups in space

This type of isomerism is stereo isomerism.

For example : l, 2-dichloro ethene

H H H Cl C=c C=cŁ i ci ci H

Different types of structural isomerism are

(i)

Chain Isomerism : When two or more compounds have a similar molecular formula but are different in the arrangement of carbon atoms in straight or branched chains the compounds are referred to as chain isomers and the phenomenon is termed as chain isomerism.

For example : Pentane C

CH, I CH,CH,CH,CH,CH, CH,CHCH,CH, Pentane iso-pentane (2-methyl butane) CH, I CH, C-CH, I CH, neo-peotane (2, 2-dimethyl propane)

CH,CH,OH and CH, OCH, ethanol dimethyl ether

*(iv) Metamerism· : It arises due to unequal distribution of alkyl groups on either side of the functional groups in the molecules.

For example :

CH,OC,H,

and

CH,OC,Hs

methoxy propane

ethoxyethane

methyl propyl ether

Diethyl ether

Note : The number of isomers increases with the number of carbon atoms; butane with 4 carbon atoms has 2 isomers, hexane has 5 isomers. An organic compound having formula CiH4a has about a million isomers and so on.

12.10 HOMOLOGOUS SERIES

A homologous series is a group of organic compounds having a similar structure and similar chemical properties in which the successive compounds differ by a CH group.

By adding CH> group (known as methylene group) in a given hydrocarbon, another hydrocarbon with a higher number of carbon atoms is obtained,

e.g.,

CH, + CH, Ł CH Methane Ethane

* Not in syllabus

Similarly, by removing CH, group from a hydrocarbon, another hydrocarbon with a lesser number of carbon atoms is obtained, e.g.,

C,H,o Ł C,H + CH, Butane Propane

12.10.1 Characteristics of a homologous series

1.

Each member of the series differs from the preceding one by the addition of CH, group and by molecular mass of 14 a.m.u.

2.

All members of a homologous series share the general formula. (Same elements and same functional group).

For example, the general formula for alkane is C alkene is C, Ha, , H2a+2 ,

3.

The physical properties of the members change gradually i.e. show gradation in properties as the number of carbon atoms per molecule increases, i.e., as molecular mass increases.

For example, melting point, boiling point and the density of the successive members of the homologous series increase with the increase in molecular mass.

Examples:

Alkane

Molar mass

Boiling point

Physical state

(i)

Methane

16

-161.4°C

gas

(ii)

Ethane

30

-88.3°C

gas

(iii)

Propane

44

-44.5°C

gas

(iv)

Butane

58

0°C

gas

(v)

Pentane

72

36.2°C

liquid

4.

Members of a homologous series have similar chemical properties. For example : Methane reacts with chlorine to form methyl chloride.

CH, + Cl, Ł CH,CI + HCI.

Similarly, ethane reacts to form ethyl chloride C,H, + CI, > CH,CI + HCI.

5.

All the members of a homologous series can be prepared by using the same general method of preparation.

For example : Alcohols are prepared by alkyl halides.

CH,Br + KOH boil_, CH,OH + KBr. (aqueous)

CH,Br + KOH boil_, CHOH + KBr. (aqueous)

Examples of Homologous Series.

I. ALKANE

Gen. formula [C"H2+2l

Molecular formula

Methane

CH,

Ethane

C,H

Propane

C,Ha

Butane

C,Ho

Pentane

C-H2

Hexane

CH4

Heptane

CH

, is

Octane

CH

Nooaoe

CH2o

Decaoe

€io]2

2.

ALKENE:

Gen. formula [C"H,"]

Molecular formula

Ethene

C,H,

Propene

C,H

Butene

C,Ha

Peotene

CH

, io

Hexene

C

Heptene

C,H,4

iDctene

CH,

Nonene

C"Hs

Decene

Co]2%

3.

ALKYNE:

Gen. formula [C""H2"2l

Molecular formula

Ethyne

C,H,

Propyne

C,H,

Butyne

C,H

Pentyne

C,Ha

Hexyne

CH

Heptyne

C,H,2

Octyne

CH4

4.

ALCOHOLS:

Gen. formula [C"H2",,OH]

Molecular formula

Methanol

CH,OH

Ethanol

C,HOH

Propanol

C,H,OH

Butanol

C,HOH

Pentanol

C,HOH

Hexanol

CH,OH

Heptanol

C,H-OH

Octanol

CH,-OH

12.10.2 Significance of the homologous series

(i)

The nature of any member of that family of compounds can be ascertained, if the properties of the first few members of that series are known.

(ii)

It helps to predict the properties of even those members of the series that are yet to be prepared.

(iii)

Knowledge of homologous series is useful for the systematic study of organic chemistry, since it saves learning time.

Note : In an organic compound the alkyl group determines mainly the physical properties, whereas the functional group is responsible for the chemical properties or reactivity of the compounds.

Ł Intext Questions

1.

(a) What are organic compounds?

(b} What is vital force theory? Why was it discarded?

2.

(a) Name a few sources of organic compounds.

(b} Give the various applications of organic chemistry.

3.

Organic chemistry plays a key role in all walks of life. Discuss.

4.

Carbon shows some unique properties, name them.

5.

Explain the following :

(a)

tetravalency,

(b)

catenation.

6.

Write any four properties of organic compounds that distinguish them from inorganic compounds.

7.

Why are organic compounds studied as a separate branch of chemistry ?

8.

What are hydrocarbons ? Compare saturated and unsaturated hydrocarbons?

9.

Give reason for the existence of the large number of organic compounds.

10.

Give at least one example in each case to show structure of isomers of :

(a)

single bond compound,

(b)

double bond compound,

(c)

triple bond compound.

11.

Name a compound of each type and draw the figure.

(a)

Cyclic compound with single bond.

(b)

Cyclic compound with triple bond.

12.

Give the name of one member of each of the following :

(a)

saturated hydrocarbons,

(b)

unsaturated hydrocarbons.

13.

Define substitution and addition reaction. Give an example for each.

14.

Define or explain chain isomerism and position isomerism with examples in each case.

15.

(a) Define the term isomerism. State two main causes of isomerism.

(b)

Draw the chain isomers of hexane (CH42)­

(c)

Draw position isomers of butene (C"Hg).

16.

Define a functional group and give the structural formula of the following functional groups:

(a)

ketone, (b) alcohols, (c) aldehydes.

17.

Write the name and formula of fourth member of the following homologous series :

(a)

Alkyne

(b)

Alcohol

18.

Which part of an organic compound determines (i) physical properties (ii) chemical properties?

19.

Name the alkyl radical and the functional group of the following organic compounds :

(a)

CH"OH,

(b)

C"HOH,

(c)

CgH,CHO,

(d)

C,HgCOOH,

(e)

CHaCOOH

(f)

HCHO.

20.

(a) What is an alkyl group ?

(b)

Give the names of any three alkyl radicals. How are they formed ?

21.

Give the names and the structural formula of the first three members of the homologous series of alkanes.

22.

(a) What is a homologous series?

(b)

What is the difference in the molecular formula of any two adjacent homologues :

(i)

in terms of molecular mass,

(ii)

in terms of number and kind of atoms per molecule?

12.11 NOMENCLATURE

Nomenclature is the system of assignment of names to organic compounds.

System of nomenclature are Trivial system and IUPAC (International Union of Pure and Applied Chemistry) system.

In the early days, the name of a compound depended on the source from which it was obtained. For example, CH, was named marsh gas, since it was obtained from marshy places. Acetic acid (Latin : acetum = vinegar) was obtained from

Downloaded from https:// www.studiestoday.com vinegar, methyl alcohol (methus = spirit, hule= wood) was obtained from wood, and citric acid from the botanical source citrus. Such names are called common names or trivial names.

Prefix also indicates additional substituent or functional group. Di-, tri-, tetra-, are used for two, three and four groups of the same type respectively.

However, the nomenclature was systematized by the chemists of IUPAC in 1957.

According to this system, the name of an organic compound consists of three parts

(i)

root word,

(ii)

suffix,

(iii)

prefix.

(i)

Root word : It depends upon the number of carbon atoms present in the longest carbon chain selected (Table 12.4).

Table 12.4

Number of carbon atoms

Root Word (Greek name)

One carbon atom

C,

Meth

Two carbon atoms

C

a

Eth

Three carbon atoms

C,

Prop

Four carbon atoms

C,

But

Five carbon atoms

C

Pent

Six carbon atoms

C

Hex

Seven carbon atoms

C,

Hept

Eight carbon atoms

C

s

Oct

Nine carbon atoms

ea

Non

Ten carbon atoms

C

o

Dec

(ii)

Suffix : The root word is followed by an appropriate suffix, which represents the nature of the bond in a carbon -carbon atom i.e.

C-C

[single bond] -ane

C=C [double bond] -ene

C=C [triple bond] -yne

In naming an organic compound, the following simple rules are followed

1.

Selection of carbon chains : The longest continuous chain of 'C' atoms, known as parent chain, is selected. The longest chain need not be straight. For example:

(i) 1 2 3 4 5 C---C---C--C--C

The longest chain is of 5 carbon atoms so root word is 'pent'.

(ii) 1 2 3 C--C---C---C---C I C---C---C---C 4 5 6 7

Here the longest chain is of 7 carbon atoms so root word is 'hept'. The remaining two carbon atoms (unnumbered) are for substituent.

2.

The branch chains are considered to be substituents, and their positions are indicated by the number of carbon atoms to which they are attached. For example

1 2 3 4 5 C---C---C---C---C I CH,

2-Metbyl (because methyl is attached to second C)

Table 12.5

Nature of bond

Suffix

General

name

General formula

Single bond (C-C)

-ane

Alkane

C"H2n+2

Double bond (C=C)

-ene

Alkene

C,"2"

Triple bond (C=C)

-yne

Alkyne

C"2a-2

Group (R-)

-yl

Alkyl

C"H2n+1

3.

The carbon atoms of the longest chain are numbered in such a way that the alkyl groups (substituents) get the smallest possible number. For example

1 2 3 4 5 C--C--C---C---C I CH, 2-Methyl Right 5 4 3 2 1 C--C--C---C--C I CH, 4-Methyl Wrong

(iii)

Prefix : It denotes the substituent, alkyl or functional group and its position in the carbon chain.

1

2 3 4 5 C--C--C-C--C I

CH,

2-Methyl (because methyl is attached to second C)

4.

In case, any functional group is also present in the chain, then the carbon atoms are numbered in such a way that the functional group gets the smallest possible number.

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eŁ For example:

5 4 3 2 1 CH, CH-CH, CH-CH, I I CH, OH 4-methylpentan-2-ol

Example 2 : 4 3 2 I CH,-CH-CH-CH, I I CH, CH, Word Root Suffix Prefix IUPAC name But­-ane 2, 3-dimethyl 2, 3-dimethyl butane

Right

1 2 3 4 5 CH, CH-CH, -CH-CH, I I CH, OH 2-methylpentan-4-ol 1CH,OH I Wrong CH, CH, CH-CH, CH, CH, 2 3 4 5 2-ethylpentan -1-0l

Note: In nomenclature, 'e' of alkane is replaced by suffix of functional group indicating the position.

5.

In case, different types of substituents are attached to the chain, they are arranged and named alphabetically.

1 2 3 4 5 6 CH, CH-CH, CH-CH, CH, I I Br Cl 2-Bromo 4-chloro hexane

Example 3 : Cl Cl I, la Word Root : Eth­Suffix : -ane H-C-CH I I Prefix : 1, 1, 2, 2-tetrachloro IUPAC name : 1, 1, 2, 2-tetrachloro ethane Cl Cl Example 4: H 0 H I I II 2 la H-C-CCH Word Root : Prop Suffix : -ane Prefix : 2-one I H I H IUPAC name : Propan-2-one Common name : Acetone Example 5 : H H '1 2 3 4l H-C-C= c-c-H I I H H Word Root But-Suffix -yne Prefix 2 IUPAC name But-2-yne Example 6: CH, CH, CH-CH, CH, I CH,

6.

The position(s) of alkyl group(s) are indicated by writing the position and name of the alkyl group just before the name of parent hydrocarbon.

I 2 3 CH, CH, CH-CH, CH, I CH, CH, CH, CH, 4 5 6 7 3-ethylheptane

7.

Multiple alkyl groups are labelled with the Greek numerical prefixes such as 'di' for two, 'tri' for three, 'tetra' for four, 'penta' for five.

If two alkyl groups are on the same carbon atom, the numeral is repeated.

CH, I CH, CCH, CH, I CH, 2, 2-dimethyl butane

The longest chain is of 5 carbon atoms so-root word is Pent. The nature of carbon chain is C -C [single bond] -Suffix -ane and the substituent is an (alkyl) methyl -CH, group. Thus name of compound is : 3-methyl pentane.

Example 7:

CH, 6 5 4 3l 2 1 CH, CH, CH, CH-CH, CH, 3-methyl hexane

Examples of IUPAC names

Example 8: CH, CH, 7 6 5 4 31 2l 1 CH, CH, -CH, CH CH-CH-CHa 2, 3-dimethyl heptane Example 9 :

CH, 6 5 4 3l 2 1 CH, CH, CH, C-CH, CH, I

Example 1 :

I 2 3 CH, -CH -CH, I

Word Root : Prop­Suffix : -ane Prefix : 2 methyl IUPAC name : 2-methyl propane

CH,

3, 3-dimethyl hexane

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Example 10 :

4 3 2 1 CH, CH = CH-CH,

But-2-ene

Example 11 : 1 2 3 4 5 CH, CH = CCH, CH, I CH,

3-methylpent-2-ene

Example 12:

H H H O H sl 4l 3l 2ll 1l HCCccCH I I I I Cl H H H 5-chloropentan-2-one

Example 13: Cl 4 3 21 1 CH, CH, C-CH,OH I CH,

2-chloro-2-methyl butan-1-ol.

Example 14:

CH, 3 I 2 1 CH, CH-CH,OH 2-methyl propan-1-ol.

Example 15: CH, CHs 5 4l 3 2l 1 CH, C-CH, CH-CH,OH CH,

Example 16 :

2 1 CH,CHO 3 I 4 5 CH,-CH-CHO Pentan-1, 5-dial

2-ethyl 4, 4-dimethyl pentan-1-ol.

Example 17:

1 2ll 3 4 5 CH, C-CH, CH, CH, pentan-2-one.

Example 18 :

CH5 4 3 l2 1 CH, CHaCH-COOH 2-ethyl butan-1-oic acid

12.12 WRITING STRUCTURAL FORMULA FROM IUPAC NAME

Following steps to be followed

1.

Write the number of carbon atoms according to the word root (carbon skeleton).

2.

Number the carbon atoms from any end.

3.

According to the suffix ane, ene or yne, the position of the bond is specified in the parent chain.

4.

Attach the substituent or functional group at the mentioned carbon atom.

5.

Satisfy the four. valencies of carbon atom by attaching hydrogen atoms.

For example

2-Bromo-4-methyl pent-2-ene

Step 1 : Write the carbon atoms of the parent chain, C-C-C-C-C

Step 2 : Number it,

1 2 3 4 5 C-C-C-C-C

Step 3 : Locate the suffix,

1 2 3 4 5 C-C=C-C-C

Step 4 : Attach substituents,

1 2 3 4 5 C-C=C-c-C I I Br CH,

Step 5 : Satisfy valencies by adding hydrogen atoms,

CH, -C = CH -CH -CH, I I Br CH,

1. Write the IUPAC name of the following: CH, I (a) CH, Ł C -CH, I CH, (b) CH, Ł CH -CH, -CH, I CH, H H H I I I (c) H _ C -C C -I H CH, (d) H,C Ł C Ł CH, CH, CH, I CH, (e) CH, -C = C -CH,CH, CH, I (fr) H Ł C -C Ł C Ł I CH, (g) Cl I CH, Ł CH CH, CH, I I CH I Cl (h) CH, -CH -CH, I Ł CH, CH, CH, CH, CH, CH, (i) I CH, -CH -CH, CH, (j) CH, -C = C -CH, CH,CH,CH, CH, I (k) CH, -C -CH, CH,CH,CHO CH, (I) CH, -CH -CH, CH, CH, I OH (m) CH, CH CH, CH, COOH I CH, H H EXERCISE 12A eŁŁŁŁŁ• • • Ł Ł <53ao* sh="" sesose="" ł="" ake.e="" ł="" ł="" ch,="" i="" (n)="" ch,="" -c="" -ch,="" ch,="" i="" br="" ch,="" i="" (0)="" ch,="" -ch="" -ch,="" -ch,br="" h="" i="" (p)="" h-c-c="C-H" h="" h="" h="" h="" h="" h="" i="" i="" i="" (q)="" h-c-c-c-c-c-h="" i="" i="" i="" i="" h="" h="" h="" h="" h="" h="" h="" h="" (r)="" h-c-c-c-h="" ł="" i="" ł="" h-c-h="" i="" h="" h="" 0="" ii="" (s)="" h-c-c="" h="" oh="" h="" h="" i="" (t)="" h-c-c-h="" i="" cl="" cl="" 2.="" write="" the="" structures="" of="" the="" following="" compounds:="" (a)="" prop-l-ene,="" (b)="" 2,="" 3-dimethylbutane,="" (c)="" 2-methylpropane,="" (d)="" 3-hexene,="" (e)="" prop-l-yne,="" (f)="" 2-methylprop-l-ene,="" (g)="" alcohol="" with="" molecular="" formula="" c,h,o.="" 3.="" choose="" the="" correct="" answer:="" (a)="" ch,="" is="" an="" (i)="" alkane="" (ii)="" alkene="" (iii)="" alkyne="" (iv)="" alkyl="" group="">

e

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(b)

A hydrocarbon of the general C"H,, is

(i)

C, sHso

(iii)

CH2o

(

ii)

C_H2s

(iv)

CH,4

(c)

A hydrocarbon with molecular mass 72 is

(i)

an alkane (ii) an alkene

(iii)

an alkyne

(d)

The total number of different carbon chains that four carbon atoms form in alkane is

(i)

5 (ii) 4 (iii) 3

(iv)

2

(e)

CH, CH, OH and CH, OCH, are

(i)

position isomers

(iii)

homologous

(ii)

chain isomers

(iv)

functional-group isomers

(f)

The IUPAC name of the compound is

CH, I CH, CH, CH, CH-CH, CH,

(i)

3-trimethylhexane (ii) 3-methyl hexane

(iii)

4-methyl hexane

4.

Fill in the blanks.

(a)

Propane and ethane are .

(homologous, isomers)

(b)

A saturated hydrocarbon does not participate in a/an .............. reaction (substitution, addition)

(c)

Succeeding members of a homologous series differ by . (CH, CH, CH,)

(d)

As the molecular masses of hydrocarbons increase, their boiling points and melting point .

(increase, decrease)

(e)

C"Hs_ and C<"ho, belong="" to="" .....="" homologous="" series="" (the="" same,="" different)="">

(f)

CO is an ŁŁŁ Ł ŁŁŁŁŁŁ Ł compound. (organic, inorganic)

(g)

The chemical properties of an organic compound are largely decided by the .. . and the physical properties of an organic compound are largely decided by the .

(functional group, number of carbon atoms)

(h)

CHO is the functional group of an .

(alcohol, aldehyde)

(i)

The root in the IUPAC name of an organic compound depends upon the number of carbon atoms in . (any chain, principal chain)

(c)

2-propanol

(e)

acetone

(d)

ethanal,

(f)

diethyl ether

What is used to describe these compounds taken together ?

6.

(a) What is the special feature of the structure of : (i) CH,, (ii) C,H, ?

(b)

What type of reaction is common to both these compounds ? Why methane does not undergo this type of reaction.

7.

Give the names and structural formula of:

(a)

saturated hydrocarbon,

(b)

unsaturated hydrocarbon.

Which type of reaction will they undergo ?

8.

Choosing only words from the following list, write down appropriate words to fill in the blanks from (a) to (e) given below. Addition, carbohydrates, C,"H2"2 C"H2m* C"H2"+2, electrochemical homologous, hydrocarbon, saturated, substitution, unsaturated.

The alkanes form an (a) series with the general formula (b) Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł .. . The alkanes are (c) .. (d) which generally undergo (e) . reactions.

9.

Draw the structural formula of a compound with two carbon atoms in each of the following cases .

(a)

An alkane with a carbon to carbon single bond,

(b)

An alcohol containing two carbon atoms,

(c)

An unsaturated hydrocarbon with a carbon to carbon triple bond.

10.

Ethane, Ethene, Ethanoic acid, Ethyne, Ethanol From the above, name

(a)

The compound with -OH as the part of its structure.

(b)

The compound with -COOH as the part of its structure.

(c)

Homologue of Homologous series with general formula C"H2" Ł

11.

Give the correct IUPAC name and the functional group for each of the compounds whose . structural formulae are given below

(a)

H H 0

I I II H-C-C-C-H I I H H

G)

But-1-ene and but-2-ene are examples of . isomerism. (chain, position, functional)

(b) H H H I I I

5.

Draw structural formula for each of the following compounds:

(a)

isomer of n-butane,

(b)

vinegar,

H-C-C-C-OH I

I '

H

H

H

Downloaded from https:/ www.studiestoday.com 12B HYDROCARBONS : ALKANES

12.13 ALKANES

Alkanes are hydrocarbons in which all the linkages between the carbon atoms are single covalent bonds.

These compounds are known as saturated hydrocarbons since all the four valencies of carbon are fully satisfied in the formula C"H2n+2 by a single bond (saturated by C -C and C -H single bonds) (refer to Table 12.6).

The simple alkanes share many properties in common. All enter into combustion reactions with

oxygen to produce carbon dioxide and water vapour. In other words, many alkanes are flammable. This makes them good fuels. For example, methane is the principle component of natural gas, and butane is common lighter fluid.

CH, + 20, Ł CO, + 2H,O

The combustion of methane

These hydrocarbons are relatively unreactive under ordinary conditions and so, they are also known as paraffins (parum-little, affinis-affinity).

Table 12.6 Homologous series of alkanes (General formula C"H2n+2)

Name

Molecular

formula

Structural formula

Abbreviated formula

(Condensed formula)

Methane

CH,

H

I

a

H C -H

I

'

H

CH,

Ethane

CH@

H H

I I

Ł □

H C C -H

I I

H H

CH, CH,

Propane

C±Hg

H H H

• I I I

e Ł

H C C C -H

I I I

H H H

CH, CHa CH,

Juana

Nonnal butane

C4Hjo

H H H H

I I I

Ł Ł ..2 - A

H C C C C H

I I I I

H H H H

CH, CH, CHA CH,

'. r.

L I

•

Isobutane

(common name) or

2-methyl propane

(IUPAC name)

C4 H1o

H H H

I I I

Ł . Ł Ł

H C C C H

I I I

e

H H

□

H

. C H

I

H

CH, CH CH,

I

CH,

Note : Since a number of organic compounds have the same molecular formula but different properties, it is appropriate to represent them by structural formula or by condensed (abbreviated) formula.

12.13.1 Sources of alkanes

The principal sources of alkanes are natural gas methane, with smaller amounts of ethane, propane and petroleum. Natural gas contains mainly and butane.

12.13.2 Isomerism in alkanes, i.e., single bond hydrocarbons

Alkanes with more than three carbon atoms form isomers. The various isomers differ in the framework of the carbon chains. Therefore, they show chain isomerism.

Examples:

Isomers of butane (C,Ho)

Butane has four carbon atoms. These four carbon atoms can be arranged in two distinct ways. Therefore, there are two isomers of butane.

H H H H I I I I H-C-C-C-C-H I I I I H H H H

n-butane (C,Ho), where 'n' stands for normal

IUPAC Name : Butane H H H I I I H-C-C-C-H 4 I 4 H -C-H I H Iso-butane (C,H,o) IUPAC Name : 2 Methyl propane

['iso', i.e., at least one carbon atom is attached to three other carbon atoms].

Isomers of pentane (CH,>)

Pentane has five carbon atoms, which can be arranged in three different ways. Therefore, pentane can form three isomers.

H H H H H I I I I I H -C-C-C-C-C-H I I I I I H H H H H

IUPAC Name : Pentane

Common name : n-pentane

['n', means normal i.e. carbon atom is attached to maximum two carbon atoms].

CH, I CH, -CH -CH, -CH, IUPAC Name : 2-methyl butane Common name : iso-pentane

CH, CH, -C-CH, I CH,

IUPAC Name : 2, 2-dimethyl propane Common name : neo-pentane

' ['neo', i.e., at least one carbon atom is attached to 'four' other carbon atoms].

12.14 METHANE AND ETHANE

12.14.1 Occurrence of methane and ethane Methane (Marsh gas)

(i)

Marsh gas is formed at the bottom of marshes due to the fermentation of cellulose by a special type of bacteria.

(ii)

It is also present in the air exhaled by animals whose food contains cellulose.

(iii)

It is contained in intestinal gases and in the blood of animals and human beings.

(iv)

Cavities in coal contain 90% methane. It is called 'fire-damp'.

(v)

Methane is produced also by dry distillation of wood, peat (coal).

Ethane : It occurs to the extent of 10-20 percent alongwith methane.

Methane (Green house gas)

Methane is a primary constituent of natural gas. It absorb outgoing heat radiation from the earth, and thus contribute to the green house effect and so considered as a green house gas. Methane remains in the atmosphere for approximately 10 years. It is twenty times more effective in trapping heat in comparison to carbondioxide.

Methane is emitted from variety of natural and human influenced sources like landfills, natural gas and petroleum systems, agricultural activities, coal mining, stationary and mobile combustion, waste water treatment and certain industrial process.

Methane is an important energy source so efforts to prevent or utilize methane emissions can provide significant economical and environmental benefits.

12.14.2 Structure of methane

Reaction :*

The methane molecule is three-dimensional. The four outer electrons in the carbon atom move as far apart from each other as possible, because electrons repel each other (remember that particles with similar charge always repel each other). It is a fact that the electrons will have the greatest distance between themselves when the carbon-hydrogen bonds are in the shape of a tetrahedron. A tetrahedron ('tetra' is a Greek word meaning "four") is pyramid-shaped.

H X o H Cs H ox H Electron dot formula or H I H-C-H H Structural formula

METHANE H

Fig. 12.1 The tetrahedral arrangement of four atoms of hydrogen around a carbon atom in a molecule of methane

12.14.3 Laboratory preparation of methane

Reactants: Sodium ethanoate (sodium acetate) and soda lime.

(Soda lime is in the form of a white porous mass or granules. It is a mixture of sodium hydroxide and calcium oxide).

Procedure : A mixture of sodium ethanoate (sodium acetate) and soda lime is taken in a hard glass test tube (as shown in Fig. 12.2), and heated with a bunsen flame.

BOILING TUBE METHANE

Fig. 12.2 Preparation of methane

CHCOONa + NaOH Ł CaO Ł 300 Na,CO, + CH,I

Collection : The gas evolved is collected by downward displacement of water since it is slightly soluble in water and is lighter than air.

12.14.4 Laboratory preparation of ethane

Reactants : Sodium propionate and soda lime.

Procedure : A mixture of sodium propionate and soda lime is taken in a boiling tube and heated with a bunsen flame (apparatus similar to Fig. 12.2).

Reaction :*

CaO C"HCOONa + NaOH 300°c Na,CO, + C"HI*

Collection : The gas evolved is collected by downward displacement of water.

12.15 OTHER METHODS OF PREPARATION OF METHANE AND ETHANE

I.

Iodomethane (methyl iodide) or bromoethane (ethyl bromide) is reduced by nascent hydrogen at ordinary room temperature.

CH,I + 2[H] Ł CH, + HI lodomethane

CHsBr + 2[H] Ł CH + HBr Bromoethane Ethane

Nascent hydrogen is produced by the action of Zn powder and dil. HCl.

II.

When water is added at room temperature to aluminium carbide, methane is prepared.

AL,C, + 12H,0 3CH,I + 4A1(OH),U

III. Ethane from alkyl halides :

When methyl iodide or methyl bromide is warmed with sodium metal in the presence of dry ether, ethane is produced.

2cH,I + 2Na ŁŁ H,C -CH, + 2NaI

This reaction is referred to as Wurtz reaction.

Note : Methane cannot be prepared by this method. This method is not suitable for the preparation of alkanes with odd number of carbon atoms.

* This reaction is known as decorboxylation reaction as carbon dioxide molecule is eleminated from a carboxylic acid. CO, is Ł eleminated as carbonate.

Methane

(i)

It is a colourless and an odourless gas.

(ii)

Its melting point is -183 °C and its boiling point is -162 °C.

(iii)

It is negligibly soluble in water and soluble in organic solvents.

Ethane

by a chlorine atom.'This type of reaction is known as substitution reaction and the product formed is known as substitution product.

The product formed (chloromethane) further reacts with chlorine, substituting one more hydrogen atom and producing dichloromethane. This further produces trichloromethane and finally, tetrachloro­methane.

(i)

It is a colourless, odourless, tasteless and non­poisonous gas.

(ii)

Its b.p. is -89 °C and its m.p. is -172 °C.

(iii)

It is sparingly soluble in water but wholly soluble in organic solvents like alcohols, acetone and ether.

CH,CI + Cla Ł Chloromethane CH2CI2 + Cl2 Ł Dichloromethane CHC, Trichloromethane CH,CI2 + HCl Dichloromethane CHCIa + HCI Trichloromethane (Chloroform) + HCl Tetrachloromethane (Carbon tetrachloride)

12.15.2 Chemical properties

Methane and ethane are saturated hydrocarbons. They do not react with bases such as sodium hydroxide, or with oxidising agents such as potassium pennanganate, or with reducing agents such as sodium metal.

They undergo substitution reactions as well as combustion reaction.

The substitution products can be separated by fractional distillation because of the appreciable differences in their respective boiling points.

Ethane also. reacts with chlorine in the same way, producing successively chloroethane, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane and hexachloroethane.

1. Substitution reaction

(i) Reaction with halogens

Alkanes react with chlorine, bromine or iodine in the presence of sunlight or ultraviolet light to give halogen substituted products that are known as alkyl halides.

Alkyl halides contain one or more halogen atoms.

Methane reacts with chlorine in diffused sunlight, or when heated to 600 K, to give chloromethane.

diffused sunlight or600K OR H H I Ł I H-C-H + CI -CI > H -C -Cl + H -Cl I Ł I H Methane H Chloromethane

In this reaction, CH,CI is formed by the substitution of hydrogen atom of a methane

Alkane +

Ł 2

Halogen

Substituted product

+

Acid

CH +

(ethane)

-

Cl,

CH,CI

(monochloroethane)

+

HCl

CH,CI +

(chloroethane)

Cla ➔

CH,CI,

(dichloroethane)

+

HCl

CH,CI, +

(dichloroethane)

Cla ➔

C,H,CI,

(trichloroethane)

+

HCl

CH,CI, +

(trichloroethane)

➔

Cla

CH,CI,

(tetrachloroethane)

+

'HCI

CH,CI, +

(tetrachloroethane)

Cla Ł

C,HCI

(pentachloroethane)

+

HCl

C,HCI, +

(pentachloroethane)

-

Cl,

C,CI

(hexachloroethane)

Ł

HCl

Note : All alkanes react with chlorine, bromine and iodine in a similar manner, producing the corresponding substituted products.

(ii) Reaction with oxygen

Methane and ethane burn in air with a bluish non-sooty flame to form carbon dioxide and

Downloaded from https:// www.studiestoday.com water vapour. A large amount of heat is also given out, so alkanes are good gaseous fuels.

Methane:

CH,

+

20,

Ł

CO,

+

2H,O

Ethane . .

2C,H

+

70,

Ł

4CO,

+

6H,O

(i)

When a mixture of methane and oxygen in the ratio 9:1 by volume is compressed to about 120 atm pressure and passed over copper tubes at 475 K, methyl alcohol is formed.

475 K Cu tube_ 120am. 2CH,OH

During combustion, due to the low carbon content in methane and ethane, they get fully oxidised to carbon dioxide, and bum with a non­sooty flame.

Insufficient supply of air

When alkanes burn in an insufficient supply of air (oxygen), they form carbon monoxide and water.

2CH, + 30, Ł 2CO + 4H,O

2C,H« + 50, Ł 4CO + 6HO

CH, + O, Ł C + 2H,O (with still less oxygen). (soot)

Soot is used in the manufacture of printing inks and tyres.

2. Decomposition of alkanes (Cracking or pyrolysis)

The decomposition of a compound by heat in the absence of air is called Pyrolysis. When pyrolysis occurs in alkanes, the process is termed cracking.

The alkanes, on heating under high temperature or in the presence of a catalyst in absence of air are broken down into lower alkanes, alkenes and hydrogen.

2CH, 1500°C Methane H,C -CH, 500°C A12O, Ethane C,H,2 400-600°C pentane Alumina or silica C,His 400-600°C heptane Alumina or silica HC = CH + 3H, Ethyne H,C = CH, + H, Ethene C,Hs + CH, propane ethene C,Ho + C,H butane propene

(ii)

When a mixture of methane and oxygen is passed through heated molybdenum oxide (M0O), the mixture is oxidised to formaldehyde.

Mo0 CH, + O, ,HCHO + H,O

(iii)

When a manganese based catalyst is used at 100°C, methane can be oxidised to formic acid.

2CH, + 30, Macompomd 2HCOOH + 2H,O

Similarly, ethane oxidises to either ethyl alcohol or acetaldehyde or acetic acid.

120atm 2C,H + 02 owns 47sg 2CH,OH Ethyl alcohol C,H + O, Mo0 ) CH,CHO+ Acetaldehyde CH,OH + O, Pt CH,COOH+ 300°C Acetic acid ° H,O H,O

4. Slow combustion

Methane or ethane can be treated with oxidising agents like acidified K,Cr,O, or acidified KMnO, at high pressure and at comparatively low temperature.

Alkane IO) , Alcohol [O] , Aldehyde [O] , Carboxylic Carbon dioxide and or K,Cr,0, KCrO, K,Cr,O, acid water vapour CH, I01, CH,OH IO1, HCH0 [O), HCOOH [01, CO, + H,0 Methane Methyl Formal-Formic acid alcohol dehyde ([0] represents contribution of the oxidising agent)

Other alkanes also form similar products when reacts with oxidising agent.

12.15.3 Uses

Methane

3. Catalytic oxidation of alkanes

On controlled oxidation or catalytic oxidation, alkanes give alcohols or aldehydes or carboxylic acids, depending upon the reaction conditions.

(i)

Methane is a source of carbon monoxide and hydrogen.

(ii)

It is used in the preparation of useful compounds like ethyne (acetylene), methanal

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(formal-dehyde), methanol, chloro-methane and tetrachloro-methane (carbon tetrachloride).

Earlier chloroform was used for anaesthesia. Since its higher dose can kill a person therefore, now-a-days HALOTHANE (CF,CHBrCI) is used for anaesthetic purposes.

(iii)

It is employed as a domestic fuel.

Ethane

(i)

Ethane is used in the preparation of ethene, ethanol, ethanal (acetaldehyde) and ethanoic acid (acetic acid).

(ii)

It forms ethyl chloride, which is used to make tetraethyllead. 1, 1, I-trichloroethane is one solvent that is used a lot, in dry cleaning.

(iii)

Ethane is also a good fuel.

EXERCISE 12B

1.

State the sources of Alkanes.

2.

Methane is a green house gas. Comment.

3.

Give the general formula of alkanes.

4.

Draw the structures of isomers of :

(a)

butane,

(b)

pentane.

Write the IUPAC and common names of these isomers.

5.

Write the :

(a)

molecular formula,

(b)

electron dot formula and

(c)

structural fonnula of methane and ethane.

6.

How is:

(a)

methane and

(b)

ethane prepared in the laboratory ?

7.

How are methane and ethane prepared from methyl iodide and ethyl bromide ?

8.

What is a substitution reaction ?

Give the reaction of chlorine with ethane and name the product formed.

9.

Name the compounds formed when methane bums in :

(a)

sufficient air,

(b)

insufficient air.

Give a balanced equation.

10.

Write the names and the formula of the products formed when:

(a)

methane, (b) ethane, reacts with : (i) chlorine (ii) bromine

Write the chemical equations.

11.

Name the compound prepared from:

(a)

sodium propionate, (b) methyl iodide and

(c)

ethyl bromide.

Write a balanced 'equation for the same.

12.

What is pyrolysis or cracking ? Explain with example.

13.

Convert :

(a)

Methane into chloroform,

(b)

Sodium acetate into methane,

(c)

Methyl iodide into ethane,

(d)

Aluminium carbide into methane.

14.

Give three uses of :

(a)

methane,

(b)

ethane.

15.

Under what conditions does ethane get converted to :

(a)

ethyl alcohol,

(c)

acetic acid.

(b)

acetaldehyde,

16.

Give the inter-relationship of methane, methyl alcohol, formaldehyde and formic acid with conditions.

12C HYDROCARBONS : ALKENES

12.16 ALKENES

Alkenes are also called olefins (oil-forming) because the lower members of alkenes form oily products when they are treated with chlorine or bromine. Alkenes form a homologous series having the general formula C"Ha, (refer to Table 12.7).

Table 12.7 : Homologous series of alkenes, general formula C"H2,

Molecular

formula

Condensed

formula

Structural

formula

Trivial name

(Common name)

IUPAC name

CH,

CH, = CHa

Ł

H H

Ju■

I

HC=CH

Ethylene

Etbene

C,H

Ł

CH, -CH = CH,

1

HH H

lei I I I

HCC=CH

I

H

Propylene

Propene

C4Hs

CH, CH, CH = CHa

H H H H

I I I I

HCCC=CH

I I

H H

Butylene

Butene

Alkenes are unsaturated aliphatic hydro­carbons that contain one double bond.

Occurrence : Since alkenes are reactive, they seldom occur free in nature. Lower alkenes occur in minute quantities in coal gas. They are produced on a large· scale by the cracking of petroleum.

Isomers in alkenes

Alkenes with 4 or more than 4 carbon atoms can form isomers.

For example : Butene has three isomers

(i)

CH,CH,CH = CHa But-1-ene

(ii)

CH,CH = CHCHa

But-2-ene

(iii)

CH, = C -CH, I CH,

2-methyl propene

(ii)

Position isomerism :

Example

CH,CH,CH = CHa

CH,CH = CHCH,

1-butene

2-butene

12.16.1 Ethene (Ethylene) C"Ha

It is the first member of the alkene series. It is present in natural gas. In small amounts, it occurs as a plant hormone and is responsible for the ripening of fruits.

12.16.2 Structure of ethene

Each carbon atom of ethene is attached to two hydrogen atoms by single covalent bonds and to another carbon atom by a double covalent bond. There are four C-H -single covalent bonds and one C=C double covalent bond. It is a planar (flat) molecule. All bond angles (H-C-H and H-C=C) are of 120°, as shown in Fig. 13.3.

Types of isomerism shown by Alkenes

(i)

Chain Isomerism :

CH,

Example

I

CH,CH,CH = CH2

CH, -C = CHa

I-butene

2-methyl propene

Fig. 12.3 Structure of ethylene

12.16.3 Preparation of ethene (ethylene)

(iii)

Dehydrohalogenation :

(i) Dehydration of ethyl alcohol

Reactants : Ethanol and cone. sulphuric acid.

Procedure : Arrange the apparatus as shown in Fig. 12.4. Take one part of ethyl alcohol in a flask. Add two parts of concentrated sulphuric acid and heat gradually to about l 70°C. Ethylene is evolved. The gas is passed through NaOH solution which removes CO, and SO> (impurities formed by oxidation of the acid). Ethylene is collected by downward displacement of water (add some aluminium sulphate to the water in order to avoid frothing).

cone. Sulphuric acid Ethene gas 3i: Ł : : Water

Fig. 12.4 Preparation of ethene from ethyl alcohol

Reaction : CH,CH,OH + H,SO, CH,CH,HSO, + H,O (Ethanol) (Ethyl hydrogen sulphate) 170°C CH, = CH, + H,SO, Etbene Or

Collection : The gas is collected by downward displacement of water because

(i)

it is an inflammable gas.

(ii)

it is insoluble in water.

(ii) By dehydration : Industrial preparation

By passing ethanol vapours through a tube containing alumina (A1,O,) at 300°C.

C,H,CI + KOH >C,H, + KCI + H,O (ale. hot and cone.) CH, Br + KOH Ł CH, + KBr + H,O (alcoholic) (hot and cone.) C,H,I + KOH Ł CH, + KI + H,O (alcoholic) (hot and cone.)

12.16.4 Properties of Alkenes

A. Physical properties

(i)

Ethene is a colourless and inflammable gas with a peculiar odour (faint sweetish smell).

(ii)

Its boiling point is -102°C and melting point is -169°C.

(iii)

It is sparingly soluble in water but highly soluble in organic solvents like alcohol, ether and chloroform.

(iv)

It produces an anaesthetic effect upon inhalation.

B. Chemical properties

1. Addition Reactions

(i)

Addition of hydrogen (hydrogenation)

When ethene and hydrogen are passed over finely divided catalysts such as platinum or palladium at ordinary temperature or nickel at 200°C, the two atoms of hydrogen molecule are added to the unsaturated molecule, which thus becomes a saturated one.

200°C Ł Ł C,H. Ethane

(ii)

Addition of halogens (halogenation)

Reaction with fluorine is explosive, hence the compound formed is not stable.

Chlorine, bromine and iodine are added to the double bond of ethene (ethylene) at room temperature to form saturated ethylene chloride, ethylene bromide and ethylene iodide.

CH, = CH, + CI, Ł CH, -CH, Ethene I I Cl Cl 1, 2-dichloro ethane (ethylene chloride)

CH, = CH, + Br, Ł CH, -CH, Ethene I I Br Br 1, 2-dibromo ethane (ethylene bromide)

3.

Polymerization : When two or more molecules of the same compound associate to form a bigger molecule, the reaction is called polymerisation.

Ethene polymerises to produce polyethene

Bromine solution in CCl, has an orange colour. When added dropwise to ethene, the orange colour of bromine disappears due to the formation of the colourless ethylene bromide.

C, H,+L, Ł CH,I, 1, 2-di-iodoethane (ethylene iodide)

Reaction with iodine is very slow and ethylene iodide formed is unstable. It eliminates the iodine readily and regenerates the ethene.

(iii) Addition of water (hydration)

A water molecule gets added to alkenes in the presence of acids (e.g., sulphuric acid) to form alcohols.

CH = CH + HOH*_, CH±OH.

(iv) Addition of HCl

When ethene gas is treated with HCI, chloroethane is formed.

CH, = CH, + HCI (aq) CH, -CH,CI. Ethene Ethyl chloride (chloroethane)

If chloroethane is treated with aqueous potassium hydroxide, ethanol is formed.

CH,CH,CI + KOH > CH,CH,OH + KCI.

2.

Reaction with ozone (ozonolysis) : When a stream of ozone is passed through a solution of ethene in ether, ethene ozonide is formed.

H,C = CH, + 0, HC -O -CH,. Ethene Ozone I I 0-0 Ethene ozonide

high temperature n HC = CH, high pressure catalyst' [HC -CH_], (ethene) (Polyethene)

4.

Oxidation : Ethene is oxidised with alkaline KMnO4 at room temperature.

H,C= CH, + H-O-H+[0] HC -CHa. Ethene Cold alkaline I I KMnO, solution OH OH [oxidising agent] 1, 2-Ethanediol (Ethylene glycol)

The purple colour of KMnO, decolourises.

5.

Combustion of ethene : Ethene bums in air with a sooty flame producing a large amount of heat. However, if the supply of air is in excess, it burns with a pale blue flame to produce carbon dioxide, water and a large amount of heat.

CH, + 30, Ł 2CO, + 2H,O + Heat.

12.16.5 Uses of ethene

(i)

Ethene is used in making polythene.

(ii)

It is converted into ethanol which is used as a starting material for other products, mainly cosmetics and toiletry preparations.

(iii)

It is used for ripening of fruits.

(iv)

It is used in making epoxyethane (used in the manufacture of detergents).

(v)

It is used for producing oxy-ethylene flame, which is used for cutting and welding of metals.

(vi)

It is used in the manufacture of synthetic chemicals.

Ł

1.

Write : (a) molecular formula, (b) electron dot formula and (c) structural formula of ethene (ethylene).

2.

The molecules of alkene family are represented by a general formula C"Ha,,-Answer the following:

(a)

What do n and 2n signify ?

(b)

What is the name of alkene when n = 4 ?

(c)

What is the molecular formula of alkene when n = 4 ?

(d)

What is the molecular formula of the alkene if there are ten H atoms in it ?

(e)

What is the structural formula of the third member of the alkene family ?

(f)

Write the molecular formula of lower and higher homologous of an alkene which contains four carbon atoms.

10.

Give balanced equations when :

(a)

ethene is burnt in excess of oxygen.

(b)

ethene reacts with chlorine.

3.

Draw the structures of butene and write IUPAC names.

(c)

ethene combines with hydrogen chloride.

(d)

a mixture of ethene and hydrogen is passed over nickel at 200°C.

4.

Give a balanced equation for the lab. preparation of ethylene. How is the gas collected ?

5.

How is ethene prepared by :

11.

Give the formula and names of A, B, C and D in the following equations

(a)

dehydrohalogenation reaction ?

(a)

CH, "@ Cl» , A "2 Cl, , B "2 Cl, , C " CI , D 4 _HCI -HCI -HCI -HCI

(b)

dehydration reaction ? Give equations and name the products formed.

(b)

C"H, 2 "2H-H» Br. Br, ,A"2,B "2,C '2, D -HBr -HBr

6.

(a) Ethylene when reacts with halogens (chlorine and bromine) form saturated products. Name them and write balanced equations.

(c)

CH, + CI, Ł A

d)

C,H, + B ŁŁ Ł C,H,

(b)

Give the conditions and the main product formed by hydrogenation of ethylene.

12.

Write the name and formula of the product formed in each case below

7.

How is ethanol converted into ethene using

(a)

C,H, + CI, Ł Ł ŁŁŁŁŁŁŁŁŁŁ ..

(a)

solid dehydrating agent

(b)

C,H,Br + KOH (alc.)ŁA ..................

(b)

hot conc. H,SO ? Give only balanced equations.

(c)

HSC = CH, alk.KMnO4 Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł .

8.

Write the following properties of ethene :

(a)

Physical state,

(b)

Odour,

(d)

H,C = CH, + HBr -..................

(e)

HC = CH, + O, -..................

(c)

Density as compared to air,

(d)

Solubility.

9.

How would you convert :

13.

What do you observe when ethylene is passed through alkaline KMnO, solution ?

(a)

ethene into 1, 2-dibromoethane ?

(b)

ethene into ethyl bromide?

14.

Name three compounds formed by ethylene and give the use of these compounds.

12D HYDROCARBONS : ALKYNES

12.17 ALKYNES

The aliphatic hydrocarbons that contain a triple bond (-C= C-), i.e., acetylenic bond, between two carbon atoms are known as alkynes. They are unsaturated compounds, due to the triple bond between two carbon atoms. They form a homologous series, with the general formula C"H2n -2 (Refer to Table 12.8).

Table 12.8 : Homologous series of alkynes (General formula : C"H2"2)

Molecular

formula

Condensed

formula

I Structural formula

Trivial name

IUPAC name of

the compound

CH2

CH = CH

H-C=CH

Acetylene

Ethyne

C,H,

I I

CH, -C = CH

Ł

j

H

Ji I

-CC=CH

I

H

Allylene

Propyne

C4Hs

CH, -CH, C = CH

H H

I I

H-CCC=cH

I I

H H

Crotonylene

Butyne

Sources of alkynes : Natural gas and petroleum.

Isomers in alkynes

Alkynes with four or more than four carbon atoms can form isomers. Alkynes show position isomerism as well as chain isomerism. For example,

Butyne

It shows position isomerism.

(i)

CH, -CH, -C = CH IUPAC Name : But-1-yne

(ii)

CH, -C = C -CH, IUPAC Name : But-2-yne

12.17.1 Ethyne

( Common name : acetylene)

Molecular formula : CH2.

Ethyne (Acetylene) is the first member of the alkyne series. Ethyne being an unsaturated hydrocarbon, is not found in free state.

Sources : Traces of ethyne are present in coal gas and in gases obtained by the decomposition of certain complex organic compounds. It is obtained by cracking of alkanes from various fractions of petroleum.

12.17.2 Structure of ethyne (acetylene)

Each carbon atom in acetylene is attached to one hydrogen atom by single covalent bond and to another carbon atom by a triple covalent bond.

o 00 0 HxCg3CxH

Electron dot formula

H-C=C-H

Structural fonnula

The shape of ethyne molecule is linear.

12.17.3 Laboratory preparation of ethyne (acetylene)

Reactants : Water and calcium carbide.

Procedure : Arrange the apparatus as shown in Fig. 12.5. Take a few pieces of calcium carbide in a conical flask. Add a few drops of water through the thistle funnel. Calcium carbide reacts with water to produce colourless gas with ether like odour (acetylene gas). The reaction is exothermic.

WATER THISTLE FUNNEL PINCH COCK ACETYLENE CALCIUM L...I...I4.l CARBIDE ............... Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Fig. 12.5 Lab. preparation of (acetylene) ethyne.

Reaction:

CaC, + 2H,O Ł Ca(OH), + C"HAT Calcium Calcium acetylene carbide hydroxide

Collection : The gas is collected by downward displacement of water, since it is insoluble in water.

Purification : Impurities like phosphine, hydtogen sulphide, ammonia and arsenic are formed along with acetylene due to the contamination of calcium sulphide and calcium phosphide in calcium carbide. On passing through water, all impurities except phosphine are absorbed. Phosphine is absorbed by passing through acidified copper sulphate solution or acidified potassium dichromate.

Note : Flask should not contain air as acetylene forms explosive mixture with air. The air of the flask is displaced with oil gas.

Preparation from 1, 2-dibromoethane (ethylene dibromide).

When 1, 2-dibromoethane (ethylene dibromide) is boiled with alcoholic potassium hydroxide, ethyne is formed.

CH,Br + 2KOH 1 (alcoholic) CH,Br 200°C boiling CH + 2KBr + 2H,O Ill CH (Ethyne)

12.17.4 Properties of acetylene (ethyne)

A. Physical properties

(i)

Acetylene is a colourless gas with an ether­like odour when it is pure ( the one prepared from calcium carbide has garlic odour due to the presence of traces of phosphine and hydrogen sulphide).

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(ii)

It is negligibly soluble in water but highly soluble in organic solvents like acetone and alcohol.

(iii)

It is lighter than air (V.D. = 13).

(iv)

It liquefies at -84 °C.

(v)

Its boiling point is -75 °C.

B. Chemical properties

Ethyne is a highly reactive compound due to the presence of triple bond between its two carbon atoms.

1. Oxidation of ethyne (combustion)

Ethyne contains a greater proportion of carbon content than does alkanes (ethane) and alkenes (ethene). Since all the carbon particles do not get oxidised completely, it burns with a sooty flame.

Ethyne bums in excess air with a brilliant white flame to produce carbon dioxide, water vapours and a large amount of heat.

2CH = CH + 50, Ł 4C0, + 2H,0 + Heat

2. Addition reactions

Alkynes are unsaturated compounds, so they are associated with addition reactions, since triple bonds break up easily. The breaking up of a triple bond gives a product that is still unsaturated (double bond). Further breaking up of the double bond gives a saturated product.

(i) Addition of hydrogen (catalytic hydrogenation)

In the presence of nickel, platinum or pal1adium, ethyne first takes up two atoms of hydrogen to change to ethene, which further takes up two atoms of hydrogen to give ethane.

First stage of reaction

CH, + H, M , CH, Ethyne Ethene

Second stage

CH, + H, N,CH Ethene Ethane

Therefore,

Hc=cu Ł , cu, = cu, Ł , CH, -CH, Ethyne Ethene Ethane

(ii) Addition of halogen

Reaction with chlorine : Ethyne in an inert solvent of carbon tetra chloride [CCI,] adds chlorine to change into an ethene derivative with carbon­carbon double bond, and then to an ethane derivative with carbon-carbon single bond.

CH CHCI CHCI, Ł Ł Ł ©2 II 2 I Acetylene ethyne CH CHCI Acetylene dichloride 1, 2-dichloro ethene CHCIa Acetylene tetrachloride 1, 1, 2, 2 Ł tetrachloro ethane

Acetylene reacts vigorously with chlorine gas in the presence of sunlight to give out flames.

CH, + Cl2 Ł 2C + 2HCI.

Reaction with bromine· : When bromine, in carbon tetrachloride, is added to ethyne, its brown colour disappears due to the formation of addition products. The reaction is similar to the addition of chlorine.

C,H, Ł 2 Ethyne (Acetylene) "C,HBr, *2CH_Br,. Acetylene Acetylene dibromide tetrabromide

Reaction with iodine : Iodine reacts slowly in the presence of alcohol to form di-iodo derivative.

CH = CH + 12 Ł 1CH = CHI.

(1, 2,-di-iodoethene)

(iii) Reaction with HCl

Ethyne reacts with hydrochloric acid to first form chloroethene and finally 1, 1-dichloro ethane.

CH Ill CH Acetylene +HCL , CHA II CHCl Chloro ethene +HCI , CH, I CHCIa 1,1-dichloro ethane

(iv) Reaction with ozone

Ethyne reacts with ozone at room temperature to produce acetylene ozonide.

0 I \ HC=CH+0, Ł H-C-C-H Etbyne I I 0-0 (Acetylene ozonide)

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12.17.5 Uses of ethyne (acetylene)

It is used

(i)

for oxy-acetylene welding at very high temperatures. These temperatures are obtained when ethyne burns in oxygen.

(ii)

as an illuminant in oxy-acetylene lamp.

(iii)

for artificial ripening and preservation of fruits.

(iv)

also for the manufacture of synthetic products like polymers, artificial rubber and oxalic acid, etc.

(v)

for the manufacture of important organic compounds like acetaldehyde, acetic acid, plastic and rubber, etc.

12.17.6 Chemical Tests to distinguish between Alkanes, Alkenes and Alkynes

No.

Test

Alkanes

(Methane and ethane

Saturated

compound

Alkenes

(Ethylene)

Unsaturated compound

Alkynes

(Acetylene) unsaturated

compound

Ł

1

On adding a few drops of bromine solution in carbon

tetrachloride to the hydrocarbon.

No change is observed.

The reddish brown colour

of bromine solution gets decolorised.

The reddish

brown colour gets decolorised.

Ł

2

* On adding a few drops of alkaline

potassium permanganate (purple colour) to the hydrocarbon.

No change is observed.

The purple colour fades.

Ł

The purple colour fades.

(Baeyer's test)

CH = CH + 4[0]

COOH

5522

) I

potassium

COOH

permanganate

oxalic acid

id

Ł

3

On adding a few drops of ammonical cuprous chloride to the hydrocarbon.

No change is observed.

No change is observed. -

Red precipitate of copper acetylide is formed.

rr

On adding ammonical

Silver nitrate

No observation

No observation

White precipitate of silver acetylide is formed.

ŁŁŁŁŁŁ ŁŁŁ

1.

What are the sources for alkynes ? Give the general formula of alkynes.

2.

Give an example of isomers shown by triple bond hydrocarbon (alkynes) and write its IUPAC name.

3.

How is acetylene prepared in the laboratory ?

(a)

Draw a diagram.

(b)

Give an equation.

(c)

How is pure dry gas collected?

4.

Give the method of preparation of ethyne by 1, 2-dibromoethene.

5.

Name the hydrocarbon which :

(a)

is a tetrahedral molecule,

(b)

is a planar molecule,

(c)

is a linear molecule,

(d)

forms a red precipitate with ammoniacal solution of copper (I) chloride,

(e)

is known as paraffin,

(f)

is known as olefin.

(g)

a compound which will give acetylene (Ethene) gas when treated with water.

6.

Classify the following compounds as alkanes, alkenes and alkynes. C,H,, C,H, CH,, C,H

7.

Give a chemical test to distinguish between

(a)

saturated and unsaturated compounds.

(b)

ethane and ethene,

(c)

ethene (ethylene) and ethyne (acetylene).

8.

Name the products formed and write an equation when ethyne is added to the following in an inert solvent

(a)

chlorine,

(b)

bromine,

(c)

iodine,

(d)

hydrogen.

(e)

excess of hydrochloric acid.

12E ALCOHOLS

12.18 ALCOHOLS

Alcohols are the hydroxyl derivatives of alkanes. They are formed by replacing one or more hydrogen atoms of the alkane with OH group.

Homologous series of alcohols and structural formula are given in Table 12.9.

TABLE 12.9 : HOMOLOGOUS SERIES OF ALCOHOLS (General formula : C"Ha",OH)

Common

Name

Molec ,

Ł_

formu

Abbreviated formula

7

.

Structural formula

IUPAC Name

a

Ł

Methyl alcohol

CH,OH

CH,-OH

H

I

H-C-0-H

I

H

Methanol

Ethyl alcohol

C,HOH

CH, -CH, -OH

H H

I I

H-C-C-O-H

I I

H H

Ethanol a

Propyl alcohol

C,H,OH

-

CH, -CH, -CH, -OH

Ł

Ł Ł

H H H

I I I

H-C-C-C-O-H

I I I

H H H

.

Propanol

Butyl alcohol

C,H,0H

CH,-CH,-CH, -CH, -OH

H H H H

I I I I

• H-C-C-C-C-0-H

I I I I

H H H H

Butanol

Alcohols can be monohydric, i.e., with one OH group attached to the carbon atom.

Example:

Methyl alcohol (CH,OH) and ethyl alcohol (CH,OH).

They can be dihydric, i.e., with two OH groups attached to the carbon atom.

Example : Glycol CH4(OH)z.

They can be trihydric, i.e., with three OH groups attached to the carbon atom.

12.19 ETHANOL

12.19.1 Occurrence

Since alcohols are not found naturally in the earth's atmosphere, so they are obtained by synthesis.

For example, methanol (wood spirit) is obtained from destructive distillation of wood, while ethanol is obtained from fermentation* of sugar.

enzymes 37°c Ł 2CH,OH + 2CO,

Example : Glycerol

CH, -CH -CH,

Cracking of petroleum is a source of ethane, which is used for preparing ethanol.

I I I OH OH OH

IUPAC name : 1, 2, 3-propane triol.

* Fermentation is an anaerobic process. It takes place under conditions where there is no air or oxygen available.

Ethyl alcohol Qyvl@@lAl,EKRR}NUzR6wines and is called SPIRIT OF WINE. It is obtained from starchy grain and is also known as GRAIN ALCOHOL.

12.19.2 Laboratory preparation

Alcohol can be prepared by the hydrolysis of alkyl halides (haloalkanes) on reaction with a hot dilute alkali. [R stands for alkyl group]

Alkyl halide + Alkali

➔

Alcohol

+

Alkali halide

RX

+

KOH

(aqueous)

boil

3

ROH

+

KX

CH,Br

+

KOH

(aqueous)

Ł

boil

CH,OH

+

KBr

CH-CI

+

KOH

(aqueous)

Ł

boil

CH,OH

+

KCl

CH,Br

+

NaOH

(aqueous)

Ł

boil

CH,OH

+

NaBr

12.19.3 Industrial method (large scale method)

"Hydration of ethene : When concentrated sulphuric acid is added to ethene (obtained from cracking of petroleum) at a temperature of 80°C and pressure of 30 atm, ethyl hydrogen sulphate is produced. Ethyl hydrogen sulphate, on hydrolysis with boiling water, gives ethanol.

CH, + HSO, Ethene 80°C 30am, CH,HSO,

CH,HSO, + HO Ł CH,OH + HSO, Ethyl hydrogen (Boiling) Ethanol sulphate

Alternatively, ethanol is produced when ethene is heated with water at 300°C and 60 atmosphere pressure in presence of phosphoric acid catalyst.

12.19.4 Properties of alcohols

A.

Physical properties :

(i)

Nature : They are inflammable volatile liquids.

(ii)

Boiling point : Their boiling point increases with an increase in molecular weight.

Examples : CH,OH = 64.5°C

CHCH,OH = 78-3°C

:// wwNy.stulimstql@xGGWiObie in water as we! as in organic solvents.

(iv)

Density : Ethanol is lighter than water its specific gravity is 0·79 at 293 K.

(v)

They are colourless and have a faint odour and a burning taste.

(vi)

They are toxic.

For example : methyl alcohol, if consumed, causes blindness and even death.

Ethyl alcohol affects that part of the brain which controls our muscular movements and then gives temporary relief from tiredness. But it damages the liver and kidney too.

B.

Chemical properties :

Alcohols are a reactive class of compounds.

1. Combustion (burning)

Alcohol burns readily in air to produce carbon dioxide and water vapours. A lot of heat is produced during the combustion of alcohols.

CHsOH +302 Ł 2C02 + 3H,O

Ethanol bums with a pale blue flame.

2. Oxidation with acidified potassium dichromate (oxidising agents)

Alcohols react with oxidising agents like acidified potassium dichromate and acidified potassium manganate.

These oxidising agent supply nascent oxygen [O] for oxidation and thus alcohols first get converted into aldehydes and later change into their respective. acids.

Alcohol

Oxidising agent

Aldehyde

Oxidising agent

o

Carboxylic acid

CH,OH

Methyl alcohol

01 ,

KaC2°7

HCHO + H,O

Formaldehyde

(methanal)

01 ,

Ka%°7

HCOOH

Formic acid

(methanoic acid)

C,HOH

2

*s

Ethyl alcohol

O1 ,

K,C1A0,

2 7

CH"3,CHO " + H,O

**2

Acetaldehyde

(ethanal)

O1 ,

K,Cr,o

2 2 7

CH,COOH

Acetic acid

(ethanoic acid)

If wine or beer is left open in Ł the air, ethanol is oxidised to ethanoic acid. This is why wine tastes like vinegar after it's been left open for a couple of days. Ł

3. Action wiu@RK}Joaded from https:// www.,ilMIcal@laXi9Rive chtoroatkane and

When sodium reacts with methyl alcohol and ethyl alcohol at room temperature, hydrogen is evolved with the formation of sodium methoxide and sodium ethoxide respectively.

2CH, OH + 2Na Ł 2CH,ONa + Ha Sodium methoxide 2C,H, OH + 2Na Ł 2C,HzONa + Ha Sodium ethoxide

Effervescence of Hydrogen serves as a test for alcohols.

4. Reactions with acetic acid

When alcohols react with acetic acid in the presence of conc. HSO, at high temperature, the respective esters are produced and the process is known as esterification.

CH,OH + CH,COOHoe. H,sO , CH,COOCH, + HO (Methyl acetate) CH,OH + CH,COOH one.H,so, , CH,COOCH± + H,O (Ethyl acetate) Esters can be detected by their fruity smell.

5.

Dehydration with cone. sulphuric acid When concentrated sulphuric acid is added to ethyl alcohol and the mixture is heated upto 170°C, it causes dehydration of ethyl alcohol to give ethene.

C"H,OH one. H2S94 , CH, = CH, + H,O 170°C Ethyl alcohol Ethene

Ethanol can also be dehydrated by aluminium oxide at 350°C.

At 140°C conc. HSO, dehydrates alcohol to give the respective ethers.

2CH,OH conc. HaSO, CH, -O -CH, + HO 140 °C Methyl alcohol Dimethyl ether 2CH,OH conc. HaSO4 CH, -O -CH, + H,O 140°C Ethyl alcohol Diethyl ether

6. Reaction with phosphorus halide

Alcohols react with phosphorus trichloride

phosphorus acid.

3CH,OH + PCIs Ł 3CH,CI + H,PO, Chloromethane 3CH,OH + PCIs Ł 3C,H,CI + H,POa Chloroethane Phosphorus acid

12.19.5 Uses of ethyl alcohol

(i)

It is a good solvent for gums and resins.

(ii)

It is used in thermometers and as preservative for biological specimens, due to its low freezing point.

(iii)

It is used in the manufacture of chemicals such as chloroform, iodoform, ether, acetic acid and synthetic products like dyes, esters (perfumes), antiseptics, preservatives, etc.

(iv)

Ethyl alcohol is used in alcoholic drinks (beverages) like whisky, wine and beer. Beers contain about 4% ethanol, wines about 11% and spirits (rum, brandy and whisky) 40% or more.

(v)

As a fuel in form of power alcohol and as an antifreeze for automobile radiators.

Different commerical forms of ethanol

The alcohol obtained by distillation is 95% pure. It forms a constant boiling mixture of 5% water and 95% ethanol. Absolute alcohol may be obtained by distilling moist alcohol with benzene (an organic solvent). The mixture of water and benzene distills off and anhydrous alcohol is left behind.

1. Denatured alcohol or methylated spirit

Ethyl alcohol is a part of drinking beverages and is also a widely used solvent in industries. In order to make it undrinkable, certain poisonous substances like pyridine, methyl alcohol and copper sulphate are added to it. Methylated spirit or denatured alcohol is ethyl alcohol with 5% methyl alcohol, a coloured dye and some pyridine. It is used for industrial applications.

2. Spurious alcohol

This is illicit liquor made by improper distillation. It contains large proportions of methanol in a mixture of alcohols. It is fatal for human consumption.

Spurious alcohol, though impure, can be used as a solvent for paints and varnishes.

1.

(a) What are alcohols ? State their sources.

(b)

Give general formulae of monohydric alcohol.

2.

Give the:

(a)

dot diagram,

(b)

abbreviated formula,

(c)

structure of second member of the alcohol group.

(d)

structure of alcohol with 4 carbon atoms.

3.

State the method of preparation of ethanol :

(a)

by hydrolysis of ethene,

(b)

by hydrolysis of ethyl bromide.

4.

Halo alkanes reacts with alkalies to produce alcohol. Give the equation for the preparation of second member of homologous series of alcohol. State under what condition the reaction occur.

5.

(a) How do the boiling point and melting point change in the homologous series of alcohols ?

(b)

Name the product fonned when ethanol reacts with acetic acid. Give an equation.

(c)

What is the name given to this type of reaction ?

6.

Complete and balance the following equations. State the conditions wherever necessary.

(a) CH Ill + H, +H, CH

(b) CH, + CI, Ł

(c)

C,H, + HCI Ł

(d)

CaC, + H,O Ł

(e)

C,H, + Bra Ł

() C"H,OH I0 Ka2°7

7.

What is the effect of ethanol on human body ?

8.

How are the following obtained :

(a)

absolute alcohol,

(c)

methylated spirit ?

(b)

spurious alcohol,

9.

Name the products formed and give appropriate chemical equations for the following Ł

(a)

Sodium reacting with ethyl alcohol.

(b)

Ethanol oxidised by acidified potassium dichromate.

10.

Give the trivial (common) names and the IUPAC names of the following

(a)

C,H,

(c)

C,Ha,

(e)

C,H, OH.

(b)

CH,,

(d)

CH,OH,

11.

Ethanol can be oxidised to ethanoic acid. Write the equation and name the oxidising agent.

12.

Name an organic compound which is :

(a)

used for illuminating country houses,

(b)

used for making a household plastic material,

(c)

called 'wood spirit',

(d)

poisonous and contain OH group,

(e)

consumed as a drink,

(f)

made from water gas,

(g)

solvent for ethanol.

12F. CARBOXYLIC ACIDS

12.20 CARBOXYLIC ACIDS

An organic compound containing the carboxyl group (-COOH) is known as carboxylic acid. These compounds possess acidic properties.

General formula C"H2a+1COOH (or RCOOH)

0

II Functional group -C -OH

An organic compound may contain one or more of these groups. Those which contain one -COOH

group are called monocarboxylic acid.

For example:

HCOOH

CH,COOH

Formic acid

Acetic acid

Those which contain two COOH groups are called dicarboxylic acid.

For example : COOH

I OR (COOH)z

COOH

Oxalic acid

IUPAC Name : Ethane-di-oic acid

monocarboxylic acid

(i) From acetylene

Formula

Comnon name

'

llJPAC name

0

I

II

I

H-C-OH

Formic acid

Methanoic acid

0

II

CH, C-OH

Acetic acid

Ethanoic acid

0

II

CH,CH, C-OH

Propionic acid

Propanoic acid

0

II

Butanoic acid

CH,CH,CH,-C-OH

Butyric acid

Acetylene is first converted into acetaldehyde by passing through 40% HSO, at 60°C in the presence of 1% HgSO4 (catalyst).

The acetaldehyde is oxidised to acetic acid by passing a mixture of acetaldehyde vapours and air over manganous acetate at 70°C.

A 2CH,COOH. Catalyst

(ii) From ethanol

IUPAC name : IUPAC name is given by replacing 'e' of the corresponding alkane by 'oic acid', because they are derived from alkanes by replacing one hydrogen atom with the carboxyl (-COOH) group. Thus they are also known as Alkanoic acid.

Acetic acid can also be prepared by passing alcohol vapours over platinum black as catalyst at 300°C in the presence of oxygen.

C,H,OH + O, 300°C _, CH,COOH + H,O Platinum

12.21.3 Physical properties

12.21 ACETIC ACID CHaCOOH

Structural formula :

1.

Physical state : Pure acetic acid is a colourless liquid.

2.

Odour : Characteristic pungent smell.

H I 0 H-C-C I OH H

3.

Boiling point : It boils at 118°C.

The name acetic acid comes from latin word 'ACETUM'. Acetic acid (IUPAC name ethanoic acid) occurs in free state in many fruits and as esters in a number of essential oils.

Dilute (4-5 percent) solution of acetic acid is also called vineger. The presence of a colouring matter gives vinegar a greyish colour while the presence of some other organic compound imparts it the usual taste and flavour. Vinegar is used for flavouring and preserving foods.

12.21 . 1 Lob preparation

Acetic acid can be prepared in the lab by oxidation of ethyl alcohol or acetaldehyde with acidified potassium dichromate or acidified sodium dichromate

Melting point :

4.

The anhydrous acid on cooling forms crystalline mass resembling ice; melting point l7°C and for this reason, it is called glacial acetic acid.

5. Nature:

It is hygroscopic liquid, sp. gr. at 0°C is 1-08.

6.

Solubility : It is miscible with water, alcohol and ether in all proportions.

12.21.4 Chemical properties

1.

It is a weak acid, hence

(i)

turns blue litmus red.

(ii)

reacts with active metals (i.e., Zn and Mg) evolving hydrogen.

CH,CH,OH I01 , CH,CHO IO1_, CH,COOH. (ethanol) (ethanal) ethanoic acid

2CH,COOH + Zn Ł (CH4COO),Zn + Ha1I Zinc acetate 2CH,COOH + Mg Ł (CH,COO)»Mg + H,1 Accetic acid Magnesium acetate

(iii)

forms salt and water with bases

phosphorus pentoxide as, it loses water molecule.

Acid + Base Ł Salt + Water CH,COOH + NaOH Ł CH,COONa + H,0 Acetic acid Sod. acetate

(iv)

liberates carbon dioxide with carbonates or hydrogen carbonates.

2CH,COOH + Na_CO, Ł 2CH,C0ONa + HO + COa1 CH,COOH + NaHC0, Ł CH,COONa + H,0 + COa1

2.

Acetic acid forms ester (pleasant fruity smelling compound) on reacting with alcohol in the presence of conc. HSO4.

CH,C0 0H + HOC,H, H2S04 CH,COOCHs +H,0 Acetic acid Ethanol Ethyl acetate

The reaction is known as reaction of esterification. Structure of Ethyl acetate (ethyl ethanoate)

H H I I H HCC-O ] I I C--C-H H H Ł j ethyl 0 H ethanoate

3.

Acetic Acid reacts with Phosphorus penta chloride and get converted to acetylchloride.

CH,COOH + PCIs Ł CH,COCI + POCI, + HCI

4.

It forms acetic anhydride on heating with

2cH,coou o? (CH,C0)»0 + HO

5.

Reduction : A strong reducing agent such as lithum aluminium hydride (LiAlH,) will reduce acetic acid to ethanol.

CH,C00H + 4[H] > CH±OH + HO

12.21.5 Test

1.

On adding acetic acid to carbonates and bicarbonates, carbon dioxide is evolved.

2.

When warmed with ethyl alcohol and cone. sulphuric acid, a pleasant fruity smell of ethyl acetate is produced.

3.

On adding neutral iron (III) chloride, wine red colour is produced.

12.21.6 Acetic acid is used

1.

as a solvent for resins, cellulose, etc.

2.

as a laboratory reagent:

3.

as vinegar.

4.

in medicines.

5.

in the production of dyes, perfumes, esters, etc.

6.

For coagulating rubber from latex.

7.

For the manufacture of cellulose acetate which is used for making packaging materials, varnishes, rayons, etc.

ŁŁŁŁŁŁŁ ŁŁŁ

1.

What are carboxylic acids ? Give their general formula.

2.

Write the common name, IUPAC name and formula of one monocarboxylic acid and one dicarboxylic acid.

(b)

The organic acid present in vinegar is .

(c)

The next higher homologue of ethanoic acid is

3.

Write the names of :

(a)

first three members of carboxylic acid series.

(b)

three compounds which can be oxidised directly, or in stages to produce acetic acid.

4.

Vinegar is greyish in colour with a particular taste. Explain.

5.

Give the structural formulae and IUPAC name of acetic acid. What is glacial acetic acid?

6.

Complete :

(a)

Vinegar is prepared by the bacterial oxidation of

7.

How is acetic acid prepared from

(a)

ethanol

(b)

acetylene ?

8.

What do you notice when acetic acid reacts with

(a)

litmus,

(b)

metals,

(c)

alkalies,

(d)

alcohol?

9.

Acetic acid is a typical acid. Write one equation in each case for its reaction with

(a)

a metal,

(c)

a carbonate,

(b)

a base/alkali,

(d)

a bicarbonate.

Downloaded from https:// 10. Give two tests to show that CH,COOH is acidic in nature.

11.

What do you observe when acetic acid is added to :

(a)

sodium bicarbonate,

(b)

ethyl alcohol in the presence of sulphuric acid,

(c)

neutral FeCI, solution ?

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12.

Name :

(a)

compound formed when acetic acid and ethanol react together.

(b)

reducing agent used to convert acetic acid into ethanol.

(c)

substance used to change acetic acid to acetic anhydride.

ŁŁŁŁŁ ŁŁŁŁŁŁ

1.

(a) Write an equation for the laboratory preparation of (i) an unsaturated hydrocarbon from calcium carbide. (ii) an alcohol from ethyl bromide.

(b)

What would you see, when etbyne is bubbled through a solution of bromine in carbon tetrachloride ?

(c)

Name the addition product formed between ethene and water.

2.

Ethanol can be converted into ethene which can be changed into ethane. Choose the correct word or phrase from the brackets to complete the following sentences.

(a)

The conversion of ethanol into ethene is an example of (dehydration, dehydrogenation).

(b)

Converting ethanol into ethene requires the use of Ł (conc. HCI, conc. HNO,, conc. H,SO,).

(c)

The conversion of ethene into ethane is an example of (hydration, hydrogenation).

(d)

The catalyst used in the conversion of ethene into ethane is commonly (iron, nickel, cobalt).

3.

Give reasons :

(a)

Ethyne is more reactive than ethene.

(b)

Ethene is more reactive than ethane.

(c)

Hydrocarbons are excellent fuels.

4.

(a) Write balanced equations

(i)

when butane is burnt in oxygen

(ii)

preparation of ethylene from ethyl alcohol.

(b)

(i) Convert ethane to acetic acid

(ii)

Convert acetylene to ethane

(iii)

Convert acetic acid to ethyl alcohol

(iv)

Convert acetic acid to ethyl acetate.

5.

Write the equations for the following lab. preparations:

(a)

Ethane from sodium propionate,

(b)

Ethene from lodoethane,

(c)

Ethyne from calcium carbide,

(d)

Methanol from Iodomethane.

6.

(a) Write the equation for the preparation of carbon tetrachloride from methane.

(b)

Draw the structural formula of ethyne.

(c)

How is the structure of alkynes different from that of alkenes?

7.

Fill in the blanks with the correct words from the brackets

Alkenes are the (a) Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł (analogous/homologous) series of (b) Ł Ł Ł . . . . ... Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł (saturated/unsaturated) hydrocarbons. They differ from alkanes due to the presence of (c) Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł Ł (double/single) bonds. Alkenes mainly undergo (d) ŁŁŁŁŁ Ł ŁŁŁ ŁŁŁ (addition/ substitution) reactions.

8.

(a) Draw the structural formulae of the two isomers of Butane. Give the correct IUPAC name of each isomer.

(b)

State one use of acetylene.

9.

Copy and complete the following table which relates to three homologous series of hydrocarbons:

General Formula

C"H2"

C"H2n-2

C"H2m+2

IUPAC name of the homologous series

Characteristic bond type

Single bonds

IUPAC name of the first member of

the series

Type of reaction with chlorine.

Addition

Downloaded from https:// www.studiestoday.com

2008

(a)

Name the organic compound prepared by each of the following reactions

(i)

CH,COONa + NaOH Ł

(ii)

CH,I + 2H Ł

(iii)

CH

(iv)

CO + 2H, (Zinc oxide catalyst) Ł

(v)

CaC, + 2H,O Ł

(b)

Write the equations for the following reactions :

(i)

Calcium carbide and water.

(ii)

Ethene and water (steam).

(iii)

Bromoethane and an aqueous solution of sodium hydroxide.

(c)

Distinguish between the saturated hydrocarbon ethane and the unsaturated hydrocarbon ethene by drawing their structural formulae.

(d)

Addition reactions and substitution reactions are types of organic reactions. Which type of reaction is shown by:

(i)

ethane

(ii)

ethene ?

(e)

(i) Write the equation for the complete combustion of ethane.

(ii)

Using appropriate catalysts, ethane can be oxidized to an alcohol, an aldehyde and an acid. Name the alcohol, aldehyde and acid formed when ethane is oxidized.

(f)

(i) Why is pure acetic acid known as glacial acetic acid?

(ii)

What type of compound is formed by the reaction between acetic acid and an alcohol ?

2009

(a)

Which of the following statements is wrong about alkanes?

(i)

They are all saturated hydrocarbon.

(ii)

They can undergo addition as well as substitution reaction.

(iii)

They are almost non polar in nature.

(iv)

On complete combustion give out carbon dioxide and water.

(b)

The organic compound obtained as the end product of the fermentation of sugar solution is

(i)

Methanol

(ii)

Ethanol

(iii)

Ethane

(iv)

Methanoic acid

(c)

Find the odd one out and explain :

C,H, C,Ho» CH, CH,

(d)

Give chemical equation for :

(i)

The laboratory preparation of methane from sodium acetate.

(ii)

The industrial preparation fo methanol from water gas.

(iii)

The reaction of one mole of ethene with one mole of chlorine gas.

(iv)

The preparation of ethyne from 1, 2-dibromoethane.

(e)

State how the following conversions can be carried out:

(i)

Ethyl chloride to Ethyl alcohol

(ii)

Ethyl chloride to Ethene

(iii)

Ethene to Ethyl alcohol

(iv)

Ethyl alcohol to Ethene

(f)

(i) Define isomerism

(ii)

Give the IUPAC name of the isomer C"Ho which has a branched chain.

2010

(a)

An organic compound undergoes addition reactions and gives a red colour precipitate with ammoniacal cuprous chloride. Therefore, the organic compound could be

(i)

Ethane

(ii)

Ethene

(iii)

Ethyne

(iv)

Ethanol

(b)

An organic weak acid is :

(i)

Formic acid

(iii)

Nitric acid

(ii)

Sulphuric acid

(iv)

Hydrochloric acid

(c)

The organic compound mixed with ethanol to make it spurious is :

(i)

Methanol

(ii)

Methanoic acid

(iii)

Methanal

(iv)

Ethanoic acid

(d)

Draw the structural formula for each of the following:

(i)

Ethanoic acid

(ii)

But-2-yne

(e)

Compound A is bubbled through bromine dissolved in carbon tetrachloride and the product is CH,Br -CH,Br.

(i)

Draw the structural formula of A.

(ii)

What type of reaction has A undergone ?

(iii)

What is your observation ?

(iv)

Name (not formula) the compound formed when steam reacts with A in the presence of phosphoric acid.

(v)

What is the procedure for converting the product of (e) (iv) back to A ?

2011

(a)

The functional group present in acetic acid is :

(i)

Ketonic C = O

(ii)

Hydroxyl -OH

(iii)

Aldehydic -CHO

(iv)

Carboxyl -COOH

. (b) The unsaturated hydrocarbons undergo :

(i)

a substitution reaction

(i)

An unsaturated hydrocarbon used for welding purposes.

(ii)

an oxidation reaction

(iii)

an addition reaction

(ii)

An organic compound whose functional group is carboxyl.

(iv)

none of the above

(iii)

A hydrocarbon which on catalytic hydrogenation gives a saturated hydrocarbon.

(c)

The number of C-H bonds in ethane molecule are:

(iv)

An organic compound used as a thermometric liquid.

(i)

Four

(ii)

Six

(iii)

Eight

(iv)

Ten

(c)

(i) Why is pure acetic acid known as glacial acetic acid ?

(d)

Choose the correct word/phrase from within the brackets to complete the following sentences

(ii)

Give a chemical equation for the reaction between ethyl alcohol and acetic acid.

(i)

The catalyst used for conversion of ethene to ethane is commonly (nickel/ iron/ cobalt)

2013

(ii)

When acetaldehyde is oxidized with acidified potassium dichromate, it forms (ester / ethanol / acetic acid)

(a)

(i) Give a chemical test to distinguish ethene gas and ethane gas.

(ii)

Identify the statement that is incorrect about alkanes

(iii)

Ethanoic acid reacts with ethanol in presence of concentrated HSO,, so as to form a compound and water. The chemical reaction which takes place is called (dehydration / hydrogenation / esterification)

(A)

They are hydrocarbons.

(B)

There is a single covalent bond between carbon and hydrogen.

(iv)

Write the equation for the reaction taking place between 1, 2-dibromoethane and alcoholic potassium hydroxide.

(C)

They can undergo both substitution as well as addition reactions.

(D)

On complete combustion they produce carbon dioxide and water.

(v)

The product formed when ethene gas reacts with water in the presence of sulphuric acid (ethanol /ethanal / ethanoic acid)

(b)

Give the structural formulae for the following :

(i)

An isomer of n-butane.

(e)

Write balanced chemical equations for the following :

(ii)

2-propanol.

(i)

Monochloro ethane is hydrolysed with aqueous KOH.

2014

(ii)

A mixture of sodalime and sodium acetate is heated.

(a)

The I.U.P.A.C. name of acetylene is :

(iii)

Ethanol under high pressure and low temperature is treated with acidified potassium dichromate.

(i)

propane

(ii)

propyne

(iii)

ethene

(iv)

ethyne

(iv)

Water is added to calcium carbide.

(v)

Ethanol reacts with sodium at room temperature.

2012

(a)

Give the structural formula for the following :

(i)

Methanoic acid

(ii)

Ethanal

(iii)

Ethyne

(iv)

2-methyl propane.

(iv)

Acetone

(b)

From the following organic compounds given below, choose one compound in each case which relates to the description [i] to [iv]

[Ethyne, ethanol, acetic acid, ethene, methane].

0

(b)

Name hydrocarbons containing a -C-functional group.

(c)

Give preparation of ethane from sodium propionate.

(d)

Distinguish ethane and ethene (using alkaline potassium permanganate solution).

(e)

Give the structural formula of the following :

(i)

ethanol

(iii)

ethanoic acid

(ii)

1-propanal

(iv)

1, 2, dichloroethane.

(f)

Give preparation of ethanol from monochloroethane and aq. sodium hydroxide.