CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS

Table of Contents

CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS

SEE MORE NOTES:

CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS

CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS. In organic chemistry, a hydrocarbon is an organic compound that consists entirely of hydrogen and carbon. 620 Hydrocarbons are examples of Group 14 hydroxides. Hydrocarbons are generally colorless and hydrophobic with only faint odors. Due to its diverse molecular structures, it is difficult to generalize further. Most anthropocentric hydrocarbon emissions come from the burning of fossil fuels, including the production and combustion of fuels. Natural sources of hydrocarbons such as ethylene, neoprene, and monotones come from emissions from vegetation.CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS.

CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS

CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS
CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS

CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS

The predominant use of hydrocarbons is as a fuel source. Methane is the predominant component of natural gas. to isomeric alkalies, likeness, and anticyclones are the major constituents of gasoline, naphtha, jet fuel, and specialty industrial solvent blends. With the progressive addition of carbon units, structured hydrocarbons without single rings have higher viscosity, lubrication rates, boiling points, solidification temperatures, and a more intense color. CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS.

CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS

3 s2.0 B978012802444700001X f01 10 9780128024447
CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS

CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS

At the opposite extreme from methane are heavy tars that remain the lowest fraction in a crude oil refining retort. They are collected and widely used as roofing compounds, pavement compounding (bitumen), wood preservatives (the creosote series), and as extremely high viscosity shear resistant liquids.CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS.

Chapter No.12

word image 32

Q.1.What is hydrocarbons? Explain with examples.

Ans. Hydrocarbons:

“The compounds of carbon and hydrogen are called hydrocarbons”.

A Classification of hydrocarbons:

Hydrocarbons are classified into two main groups:

i. Saturated hydrocarbons (alkanes)

Ii.Unsaturated hydrocarbons (alkenes and alkynes)

i. Saturated hydrocarbons:

“The hydrocarbons which contain all carbon-carbon single bonds are called saturated hydrocarbons or alkanes.”

General formula:

They have the general formula of CnH2n+2, where n is the number of carbon atoms.

Examples: Methane (CH4), Ethane (C21-16). Propane (C3H8) and butane (C4Hio) etc. are the examples of saturated hydrocarbons.

ii. Unsaturated hydrocarbons:

“The hydrocarbons containing at least one carbon-carbon double or triple bond are called unsaturated hydrocarbons.”

They are further classified to:

a. Alkenes:

The hydrocarbons which-, 3;’ a: n at least one carbon-carbon double bond are called alkenes.’

General formula:

They have the general formula of CnH2n, where n is the number of carbon atoms.

Examples: Ethene (C2H4). Propene (C3H6). Butane (C4H8) and pentene (C8H1o) are the examples’ of alkenes.

b. Alkynes:

“The hydrocarbons which contain at least on carbon-carbon triple bonds are called alkynes.”

General formula:

They have the general formula of CnH2n_2, where n is the number of carbon atoms.

Examples:

Ethyne (C2H2), propane (C3H4), butane (C4H6) and pentane (C5H8) etc. are the examples of alkynes.

Hydrocarbons;

R Saturated –1 (Unsaturated

, Hydrocarbons)

Hydrocarbons)

(Alkanes like CH4, C2H6etc I Alkenes like C2H4, C: H6 etc.)

`Alkanes like C3H4 C4HE etc. C41-16)

Q.2. Write a short note on alkanes?

Ans. Alkanes:

“The saturated hydrocarbons containing all carbon-carbon or carbon to hydrogen single bonds are called alkanes or paraffin’s.”

Reason of calling paraffin’s;

Paraffin is a Latin word meaning “little affinity”. Since alkanes contain C-C and C-H single bonds, therefore they have little affinity towards chemical reactions that is why they are called paraffin’s.

Reason of calling saturated hydrocarbons:

Since in alkanes each carbon atom is bonded with four other atoms therefore no further atom can be added to alkanes. Hence, they are called saturated hydrocarbons.

General formula:

The general formula of alkanes is CnH2n+2 where n is the number of carbon atoms e.g. if n=1 then the formula will be CH4, which is called methane. Similarly if n=2 then the formula will be C2H6 called ethane etc.

Examples:

The name of first ten alkanes along with their physical states, melting point and boiling points are given in the table below:

c- Atoms Name of Formula Physical alkane CH2 i2 Methane CH4 Gas MP

2

Ethane

C2H6 1 Gas

-172

-89

3

Propane

C3H8 Gas

-188

-421

4 Butane C4H1.0 Gas

-138

-0.5

5 Pentane C5112 Liquid -130

36

6 Hexane C6H14 Liquid -95 . 69

7

Heptane

C7H16

Liquid -91

98 i

8

Octane

C8H18

Liquid -57

126

9

Nonane

C9H20

Liquid -51

151

10

Decane

C1oH22

Liquid -30

174

Q.3. Describe the rules for naming alkanes?

Ans. Rules for naming alkanes nomenclature of alkanes:

The general rules for naming alkanes are given below: Rules for naming branched chain alkanes:

i. Selection of longest continuous chain:

Select the longest continuous chain having maximum number of branches (substituent). This chain is called parent chain.

Example:

CH, C

11

H—(111.—C1 H.—CH;

Branch or substituent longest continuous chain

(Methyl) (Hexane)

ii. Numbering the carbon atoms:

Start numbering the carbon atoms so that the branch gets the lowest number.

Example:

; 4 6

H—C H,—C H,—C H3

iii. Naming the longest chain: Name the longest chain e.g. propane for 3, butane for 4 carbons atoms etc.

It is called the base name or parent name of the compound.

Example:

The parent name of above example is hexane.

  1. Naming the branch:

Name each branch (substituent) attached to the longest chain and give its location by the number of carbon atom to which it is attached. A hyphen is used between the number and name of branch, and comma (,) is used between number and number.

Example:

For example, in the above example 3-methyl is the position of Branch.

  1. Writing the full name:

The parent name is written at the end, after mentioning the Position of substituent.

Example:

The name of above compound is 3-methyl hexane.

  1. Naming two or more identical branches:

When two or more identical branches are present then use prefixes di. Tri, tetra etc. A comma is used to separate the position numbers.

Example:

CH3

3

C H, 71—C H,—C —C H3

– I

CH3 CH3

(2, 2, 4-trimethylpentane)

vii. Numbering the branches on same carbon:

When two branches are present on the same carbon use the number of that carbon twice.

Example:

For example, in the above example two methyl groups are present on same carbon therefore their position is mentioned as 2, 2.

viii. Arranging two or more non-identical branches:

When two or more non-identical branches are present then they are arranged alphabetically.

Example:

For example, ethyl is placed before methyl.

ix. Selecting longest chain from equal no. of C:

When there are two or more chains having equal no, of carbons, then choose the one with greater no. of branches.1

Example:

CH3

8 7 6 I 5 14 3

CH3—CH2—CH2—CH —CH —CH —CH —C

– CH3

CH3

3-Ethyl-2, 4, 5-trimethyl octane

x. Numbering branches occurring at same position from either end:

When first branch occurs at an equal distance from either end of longest chain, start numbering from that end which gives lowest number to next branch.

Example:

CH3

2 3 4 5 6

C H3— C H—C H—CH, —CH—CH3

CH3 CH3

(2, 3, 5-trimethyl hexane)

Q: Differentiate between alkanes and alkenes. Give methods of preparation of alkanes.

Ans. Difference between alkanes and alkenes:

The difference between alkanes and alkenes is given in the table below:

Alkanes

Alkenes

“The saturated

Hydrocarbons containing all C-C single bonds are called alkanes.”

“The unsaturated

Hydrocarbons containing at least one C-C double bond are called alkenes.”

They have the general

formula of CnH2n+2

They have the general

formula of Cn H2n I

3

In alkanes all the carbon • In alkenes all the carbon atoms

atoms are bonded with 4 are not bonded with 4 other atoms

other atoms .i.e. at least two carbon atoms are

bonded with 3 other atoms.

4

Addition reactions cannot

occur in alkanes .i e. only

Substitution reactions occur
in alkanes.

i Addition reactions
alkenes.

occur in

5

Examples: Examples:

  1. Methane (CH4) 1 i. Ethene (C2114)
  2. Ethane (C2H6) 1 ii. Propene (C3H6)

i …

  1. Propane (C3H8) iii. Butane (C4H8)
  • iv. Butane (C4H10) IV. Pentene (C61110)

Preparation of alkanes:

Alkanes can be prepared by the following methods:

I. From hydrogenation of alkenes or alkynes:

Unsaturated hydrocarbons like alkenes and alkynes can be changed to alkanes by reacting them with hydrogen in the presence of nickel as catalyst at 250-300 °C or in the presence of platinum as catalyst at room temperature.

a. Hydrogenation of Alkenes:

NT

CH2 + H2 250-3000C > CH3 – CH3 (Ethane)

By hydrogenation of alkene the oil is converted to ghee

b. Hydrogenation of alkynes:

It occurs in two steps. In first step alkyne is converted to alkene while in second step alkene is converted to alkane.

Step-i_

Ni

–> CH3 –CH3 (Ethane)

250-306° (‘

CH-CH + 2H2 Step-ii

CH2 =CH2+2H2

Ii. from reduction of alkyl halides: Reduction of alkyl halides means addition of hydrogen to alkyl halides. In this reaction nascent hydrogen is added to alkyl halide the corresponding alkanes i.e. methyl halide will form methane; ethyl halide will form ethane etc.

This reaction occurs in the presence of zinc dust and HCI.

General reaction of alkyl halide and nascent hydrogen to form alkane is:

R-X + 2[H] Zn 4- 1-±2_> R-H + HX

Alkyl halide Nascent H alkane halogen acid

For example, methyl iodide forms methane and hydrogen iodide, on reaction with nascent hydrogen.

CH, – I +2[H] Zn+ NC! > CH 4 ± HI

Similarly, ethyl bromide gives ethane and hydrogen bromide. – Br +2[H] Zn+HCI) C, 116 + HBr

Q.5. Give the properties of alkanes?

Ans. Properties of alkanes:

The properties of alkanes are described below:

Physical properties:

i. Physical state:

The first four members (methane, ethane, propane, butane) of alkane series are gases. Next thirteen members (from C5H12 to C17H36) are colorless liquids while higher alkane (above C17H36) is solids.

ii. Solubility:

Since alkanes are non-polar therefore, they are soluble in non-polar solvents like benzene, acetone, ether etc. However, they are insoluble on polar solvents like water.

iii. Meting points and boiling points:

The melting points and boiling points of alkanes increase with the increase in molecular masses because generally higher molecular masses alkanes have stronger intermolecular forces.

iv. Density:

Their densities increase regularly with increase in molecular mass.

v. Viscosity:

They become more viscous as their molecular size increase.

vi. Flammability:

They are flammable; with increase in size and no. of carbons they become less flammable. As carbon atoms of alkanes are directly bonded with 4 other atoms therefore, only substitution reactions can occur in alkanes.

Alkanes are chemically inert at room temperature due to all C-C and C-H single bonds present in them. However, at higher temperature. Absorption of light etc. the following reactions take place in them:

i. Halogenation:

The substitution of hydrogen of an alkane by halogen is called halogenation.

Alkanes react with halogens in presence of ultra violet light and produce alkyl halides and hydrogen halide.

Example:

For example, chlorine reacts with methane in the presence of diffused sunlight to form chloral-methane:

HiC H Cli CI > H, C I-1C,

Chloromethane In excess of chlorine, this reaction does not stop here. The remaining three hydrogen atoms are also replaced by chlorine atoms to form di, tri and tetra chloral-methane respectively:

CI-CH, – H +CI CI I- I light > -CH, -CI+HC1

(Di-chloromethane)

Cl -CH – H + C11- Cl i’gi–>C1 -CH -CI+ HCI

Cl Cl

(Tri-chloromethane or chloroform)

C! T: tog —> (I – (‘ -CI+ HC1

CI (Tetra-chloromethane or carbon tetrachloride)

ii. Combustion:

It is also called burning. It may be complete or incomplete. Complete Combustion: Alkanes burn completely in excess of oxygen or air to form carbon dioxide, water vapours with evolution of large amount of heat. That’s why alkanes are used as fuels.

Example: CH 4, + 02:

(g) -4 0920.0+ H 20 co+ Heat

Incomplete combustion:

In ‘limited supply of air, incomplete combustion occurs. During incomplete combustion water, unburnt carbon and a poisonous gas, carbon monoxide is produced which creates suffocation and cause death.

Example:

3CH4 (g) + 402(g) -÷ 2C0 (gal+ 6H20(g) + C(unburnt) + Heat

iii. Sulphonation:

“The substitution of hydrogen of an alkane by sulphonate group (—SO3H) is called sulphonation.” Alkanes can be converted to alkyl suiphonic acids with fuming sulphuric acid at 50-60 °C.

Example:

CH3CH2CH2CH3 + H2SO4 CH3CH2CH2CH2S03H+H20

IV. Nitration:

“The substitution of hydrogen atom of an alkane by nitro group (-NO2) is called nitration.” Alkanes can be converted to nitro-alkanes by reacting them with concentrated HNO3.

Example:

CH4 + CH3NO2 + H2O

Q.6. what is alkene? Give examples.

Ans. Alkenes:

“The unsaturated hydrocarbons containing at least one carbon-carbon double bond are called alkenes or olefins.”

Reason of calling olefins:

Olefin is a Latin word meaning “oil forming”. Since alkenes react with halogens to form oily liquids therefore they are called olefins.

General formula:

The general formula of alkenes is CnH2n, where n is the number of carbon atoms. It is clear from the general formula of alkenes that they have two hydrogen atoms less than the corresponding alkane.

Examples:

i. CH2=CH2

ii. CH3—CH=CH2

iii. CH3—CH2—CH=CH2

iv. CH3 —CH2—CH2—CH=CH2

v. CH3 —CH2—CH2—CH2—CH=CH2

Hydrocarbons:

(Ethene or ethylene) (Propene or propylene) (Butane or butylene) (Pentene or 1-pentene) (Hexane) Structural formula of first five Alkenes: Electron crosses and dot formula of first five alkenes:

HH ,

c=C\ H-C-C=C

Ethene Propene

H HHH

H—C—c—c—c=cH

H H H

Pentene

H H H ! .

H—C—C—C=C

H H Butene

H HHHH

H HHH Hexene

H.

H H

Ethene H H

xH

HC • • OD’H H

Propene H H H Hx. C••C••C::C:„H

Butene

HHHH

x X X

‘A A A

Pentene Hx•C-O.6.6.O: c:x1-1 H HHHH

X X X

(=i X H

Q.7.How alkenes are named? OR

Write the rules for naming alkenes?

Ans. Rules for naming Alkenes (Nomenclature):

General rules for naming alkenes are given below:

i. Selection of longest continuous chain:

Select the longest continuous chain containing double bond. This is called the parent chain.

Example:

CH3 CH3

H3 — = C— CH, — C H3

CH.

ii. Naming the parent chain:

The name of the parent chain is derived from corresponding alkane in which the last —ane of alkane is replaced by —end.

Example:

For example, the parent name of the above example is hexane.

iii. Numbering the carbon atoms:

Number the longest continuous chain containing double bonds. Start numbering from that end which gives lower number to double bond. If double bond get same number from either end with same branches, it can be numbered from either end.

Example:

CH3 CH3

1 2 3 4 5 6

CH3 —CH—C=C—CH, —CH3

iv. Showing the position of double bond:

The position of double bond is shown by putting number of first carbon atom of double bond as prefix.

Example:

The position of double bond-of above example is shown as .3-Hexene

v. Indicating the position of branches:

Indicate the position of branches by number of carbon atom to which they are attached. Use prefix di, tri etc. if the same branch occurs more than one time.

If different branches are present then alphabetical order will be used e.g. ethyl before methyl.

Example:

In the above example the branches are shown as: 2, 3, 4-Trimethy1- 3-hexene.

The above rules are given below:

Some more examples explaining

i. H2 = CH2

(1-ethene)

3 2 I

ii. CH3—CH =CH2

(1-propene)

4 3 2 I

iii. C H3—C H,—C H =CH2

(1-butene)

4 3 2 I

iv. CI-1;—CH =CH—CH,

– 2 3 4

(2-butene)

CH3 CH3

\ 3 2/

V. C=C

4 /

CH3 CH3

(2, 3-dimethy1-2-butene)

Q.8. Write down the methods for the preparation of alkenes.

Ans. Preparation of alkenes:

Most methods of preparation of alkenes involve elimination of two atoms or group of atoms from the adjacent carbon atoms of saturated organic compounds. Some methods are given below:

i. Dehydration of alcohols:

“Removal of water molecule from an alcohol is called dehydration of alcohol”

When an alcohol is heated up to 180 °C in the presence of concentrated sulphuric acid as catalyst, a molecule of water is eliminated from the alcohol forming an alkene.

Example:

H H

I I

H C

H OH H H

Ethyl alcohol Ethene

ii. Dehydrohalopenation of alkyl halides:

“The removal of hydrogen along with halogen from adjacent atoms of alkyl halide is called Dehydrohalopenation of alkyl halides.” In this process an alkyl halide is heated with an alcoholic solution of potassium hydroxide. As a result, a molecule of hydrogen halide is removed to form an alkene. In this elimination, a hydrogen atom along with the adjacent halogen, are removed from the alkyl halide molecule,

Bromoethane or Ethyl bromide Ethene

*2) C H3-5 H —C H3 (KOH4-C2H5OH) ► CH2= CH -CH 3+ HBr

Br

2-Bromo propane 1-Propene

Q.9. Give the physical properties of alkenes?

Ans. Physical properties of alkenes:

Some physical properties of alkenes are given below:

i. Physical state:

The first three members of alkenes i.e. Ethene, propane and butane are gases. Linear members from five to sixteen are liquids while higher alkenes are solids.

ii. Solubility:

. As they are non-polar therefore, they are soluble in non-polar solvents like benzene. They are insoluble in water.

iii. Melting points and boiling points:

Their melting points and boiling points increase with increase in molecular mass.

iv. Density:

The first member has less density than air. While, others are denser than air. Their densities increase with increase in molecular mass.

Q.10: Give important reactions of alkenes?

Ans: Reactions of alkenes:

Alkenes are reactive compounds as the electrons of double bonds are easily available for reaction. As alkenes contain double bonds, therefore, this bond can be broken down to add other atoms to alkene molecules. That is, addition reactions occur in alkenes by the breaking of double bonds and they are changed into saturated organic compounds. Some important reactions of alkenes are given below:

  1. Addition of Halogens:

Chlorine and bromine are quickly added to the alkenes, with breaking of double bonds of alkenes, in the presence of an inert solvent like carbon tetrachloride to form dialog compounds. This reaction does not need high energy or sunlight.

Examples:

i. For example, bromine (a red liquid) is reacted with Ethene. It adds to Ethene to form 1, 2-dibromoethane. During this reaction the red colour of bromine disappears. Thus, bromine is used to detect the double bonds of alkenes.

H H

I I

H/C=CH

+ Br2

cci4

• H BCr— CB—r H

I I

H

Ethene 1,2-dibromoethane

Fl

I I

2 C —C — H

H

CI CI

I I

• H

Ethene 1, 2-dichloroethane

2. Addition of Hydrogen Halides:

Addition of hydrogen halides means the addition of hydrogen along with halogen like HCI, HBr, HI to alkenes. When a hydrogen halide is reacted with alkene its molecule is added with alkene to form alkyl halides. The order of reacting alkene with hydrogen halides is HI>HBr>HCI.

Examples:

i. CH2=CH2 + HBr ► CH3-CH2-Br

(Ethene) (Ethyl bromide)

CH2=CH2 + HCI CH3-CH2-CI

(Ethene) (Ethyl chloride)

3. Oxidation of Alkenes

Alkenes react with cold dilute potassium permanganate solution (acidified) to form glycol. Glycols are the alcohols containing two hydroxyl groups (-OH) on two adjacent carbon atoms.

Example:

For example Ethene reacts with acidified solution of potassium permanganate to produce ethylene glycol. Manganese dioxide and potassium hydroxide due to which the purple colour of potassium permanganate solutions disappears. This is a very useful test for the detection of alkenes and is called Bayer’s test.

3CH2=CH2 + 2KMn04+4H20 3CH2-CH2+2MnO2+ 2KOH

OH

(Ethylene glycol)

4. Hydrogenation:

“Addition of hydrogen to alkenes is called hydrogenation”. Hydrogen is added to alkenes in presence of nickel as catalyst and 240°C to form the corresponding alkane. Hydrogenation of alkene is an exothermic process.

Example:

CH2=CH2 + H2 Ni/240°C >CH3-CH3 + Heat

Conclusion:

It is concluded from the above activity that ethane has C-C single bond while Ethene has C-C double bond.

Activity 2:

Distinguish between propane and propene using Baeyer’s test. Procedure:

i. Pass propane gas through cold and dilute solution of potassium permanganate.

ii. No change in the colour of potassium permanganate occurs showing that propane does not react with potassium permanganate due to the presence of C-C single bonds.

iii. Now pass propane gas through cold and dilute solution of potassium permanganate.

Iv.These purple colour of potassium permanganate will disappear showing that propene has reacted with potassium permanganate due to the presence of C-C double bond.

Chemical equations:

CH3-CH2-CH3 + KMnO4 No reaction

3CH3-CH=CH2 + 2KMn04+4H20 3CH3-CH-CH2+2MnO2+ 2KOH

OH (propylene glycol)

Q.11. what are alkynes? Give examples.

Ans. Alkynes:

“The unsaturated hydrocarbons containing at least one carbon-carbon triple bond are called alkynes.”

General formula:

The general formula of alkynes is CnH2n_2, where n is the number of carbon atoms.

Examples:

A few examples are given below:

i. CH=- CH (Acetylene or etherize)

ii. CH3-C,-__CH (1-Propyne)

iii. CH3-CH2-C = CH (1-Butyne)

iv. CH3-CH2-CH2-C CH (1-Pentyne)

Structural formula of first alkynes:

HHH

Ethyne Propene

  • H H H CC C-C=C -H
  • H H

Pentene

Electron cross and dot formula of first fie alkynes:

•Ci:C•.H H 1;1

Ethyne Propene H

, 171 H. •••••••C! C•.H Butane

0 0 0 1; 1 it

Hx•••••••••Cinch..H 0 0

Pentene Hexane

Q.12. How alkynes are named? OR write the rules for naming alkynes?

Ans. Rules for Naming Alwen’s (Nomenclature):

General rules for naming alkynes are given below:

i. Selection of Longest Continuous Chain:

Select the longest continuous chain containing triple bond. This is called the parent chain.

Example:

CH3

IC H3 — C— C C— C H C H3

CH3 CH3

ii. Naming the Parent Chain:

The name of the parent chain is derived from corresponding alkane in which the last —ane of alkane is replaced by —yen.

Example:

For example, the parent name of the above example is hexane.

iii. Numbering the Carbon Atoms:

Number the longest continuous chain containing triple bonds. Start numbering from that end which gives lower number to triple bond. If triple bond gets same number from either end or branches are at different places then start numbering from that end which gives lowest number to branch.

Example:

CH3

3 4 5 6

CH3 -C-C= C-CH-CH3

I

CH3 CH3

iv. Showing the Position of Triple Bond:

The position of triple bond is shown by putting number of first carbon atom of triple bond as prefix.

Example:

The position of triple bond of above example is shown as 3-Hexyne

v. Indicating the Position of Branches:

Indicate the position of branches by number of carbon atom to which they are attached. Use prefix di, tri etc. if the same branch occurs more than one time. If different branches are present then alphabetical order will be used e.g. ethyl before methyl.

Example:

In the above example the branches are shown as: 2, 2, and 5-Trimethy1-3- hexyne

Some More Examples:

Some more examples explaining the above rules are given below:

i. CH-=’.H (1-ethyne)

3 2 I

ii. C11,—C=CH (1-propyne).

4 3 2 I

iii. CH;—CH,—Cm-CH (1-butyne)

4 3 2 I

iv. CH„-LC=C—C1-1,

1 – 2 3 ‘ 4 –

(2-butyne)

13. Write a note on the preparation of alkynes?

Ans. Preparation of Alkynes:

Alkynes can be prepared by the following methods:

1. Dehydrohalopenation of vicinal halides:

“Compounds that contain two halogen atoms first and second carbon atoms are called vicinal halides or 1, 2-dihalides.”

Alkynes are obtained by reacting vicinal halides with alcoholic solution of potassium hydroxide. In this reaction two molecules of hydrogen halides are eliminated to form alkynes.

Example:

Acetylene can be prepared by reacting alcoholic solution of potassium hydroxide with vicinal dibromoethane. This reaction is completed in the following two steps:

Step-i:

In the first step one molecule of hydrogen bromide is eliminated and single bond between C-C atoms is converted into double bond to form Bromoethane and HBr.

H Br

I I

H-C-C-H I H Br

KOH (alcoholic) I I

10. H-C H + HBr

Br H Bromoethane

1, 2-Dibromoethane

Step-ii:

In the second step another molecule of hydrogen bromide is eliminated and the double bond is converted into triple bond to form acetylene and HBr.

KOH (alcoholic)

H—C=C—H

Bromoethane H C =C H + HBr Acetylene or Ethyne

2. Dehalopenation Of Tetra halides:

“Compounds that contain four .halogen atoms at two adjacent carbon atoms are called tetra halides.” When alkyl tetra halides like 1, 1, 2, 2-tetrabromoethane is reacted with an active metal like zinc dust, bromine atoms are removed and acetylene is formed.

Example:

►H— C = C—H + 2ZnBr2

Acetylene or Ethyne

Q.14. Give the physical properties of alkynes?

Ans. Physical Properties of Alkynes:

Some physical properties of alkynes are given below:

i. Physical State:

The first three members of alkynes i.e. Ethyne, propane and butane are gases while members from five to thirteen are liquids while higher alkynes are solids.

ii. Solubility:

As they are non-polar therefore, they are soluble in non-polar solvents like benzene. They are insoluble in water.

iii. Melting Points and Boiling Points:

Their melting points and boiling points increase with increase in molecular mass.

iv. Density:

Their densities increase with increase in molecular mass

Q.15. Give important reactions of alkynes?

Ans. Important reactions of alkynes:

As alkynes are unsaturated therefore, they easily undergo addition reactions. And thus, they are converted to saturated organic compounds. Some important reactions of alkynes are given below:

1. Halogenation:

“Addition of halogens to alkyne is called halogenation. “Chlorine and bromine react readily while iodine reacts slowly with alkynes. Phosphorus dichloride is used as a catalyst. This reaction occurs in two steps:

Step-i:

In first step triple bond is converted into double bond by the addition of two atoms of halogens to form halides:

pci3

H—C +C12 ► H—C =C—H

Step-ii: 1, 2-dichloroethene

In this step double bond is converted to single bond by the addition of two atoms of halogens to form tetra halides.

As a

H –c =C—H + C12

1,2-dichloroethene CI CI

pa3

—C—C—H

I I

CI CI

1, 1, 2, 2-tetrachioroethane

2. Oxidation with KMn04:

When alkynes are oxidized with solution of potassium permanganate, the triple bond of alkynes is broken to form carboxylic acid and carbon dioxide.

00

II II

2H-CEC-H + 8[0] Mon, > HO-C-C-OH + 2CO2

(Ethyne) (Oxalic acid)

3. Hydrogenation:

Hydrogen can be added to alkynes in presence of nickel as catalyst and suitable temperature to form alkanes.

Example:

H —C C —H + 2H2 Mackle /250°C

4. Addition of halogen acids:

Halogen acids are added to alkynes in the presence of FeX3 as catalyst to form 1,1-dihaloalkanes. The reaction completes in two steps. Example:

FeBr3 H Br

H—CMC—H + C—H

F1 Br

I I

H—C=C—H+ HBr FeBr3 H

I I

► H—C —C—H

I I

H Br

1, 1-dibromoethane

EXERCISE

A. Choose the Correct Option.

1. Which one of the following is a substitution reaction?

a. Halogenation of alkynes b. Halogenation of alkenes

b. Halogenation of alkane’s d. Oxidation of alkene

2. When Ethene reacts with HBr, the compound formed is

a. CH3— CH2— Br b. Br—CH2— CH2 —Br

c. CH3— CH2– CH8 d.CHE_–CH

3. Halogenations of methane in the presence of diffused sunlight occurs

a. Quickly, only in one steps b. Slowly, only in one step

c. In a series of four steps d. quickly, in two steps

4. Dehydrohalopenation of alkyl halide is

a. Removal of hydrogen

b. Removal of halogen

c. Removal of hydrogen and halogen

d. Addition of hydrogen and halogen

5. Which one of the following decolourisesBr2 water

a. Ethane b. Ethene c. Propane d. Methane

6. The general formula of alkane

a. CnH2n b. CnH2rix2 C. CnH2n+2 d. C,H2n-2

7. Dehydration of ethyl alcohol with conc. H2SO4 results in the formation of

a. Ethane b. Methane c. Ethyne d. Ethene

8. Substitution reaction is the characteristic of

a. Alkynes b. Alkenes c. Alkanes d. None of these

9. Which one is the least reactive?

a. Ethyne b. Propane c. Ethene d. Ethane

10. The order of reactivity of hydrogen halides with alkenes is

a. HI >HCI>HBr b. HI <HBr<HCI

c. HCI>HBr> HI d. HI > HBr >HCI

word image 33

Q.1. how would you test that alkenes undergo an addition reaction.

Ans. Test for detection of addition reaction by alkene:

Alkene are unsaturated hydrocarbons therefore, they undergo addition reactions during which their double bond is converted into single bond. It can be tested by two ways:

i. Baeyer’s test:

Alkenes react with cold dilute potassium permanganate solution (acidified) to form glycol. Glycols are the alcohols containing two hydroxyl groups(-OH) on two adjacent carbon atoms.

Example:

The reaction of potassium permanganate with Ethene is given below: 3CH2=CH2 2KMn04+4H20 3H2-CH2+2Mn024- 2KOH

OH

(Ethylene glycol)

During this reaction potassium permanganate is changed to manganese dioxide and potassium hydroxide due to which its purple colour disappears. Thus, the change in colour proves that, addition reaction has taken place.

Ii. by the Reaction of Bromine:

Bromine (a red liquid) is reacted with Ethene to form 1,2- dibromoethane. During this reaction the red colour of bromine disappears. Thus, it is proved that addition reaction has taken place.

CcI4 I I H

C Br2 ►H C —C—H

H H I I

Br

Ethene 1, 2-dibromoethane

2. Which one is more reactive between alkane and alkene? Explain.

Ans.: More Reactive Between Alkane and Alkene:

Alkenes contain C-C double bonds and double bonds are weaker and can easily be broken. The electrons of double bonds are easily available for reaction. Therefore, alkenes are more reactive. On the other hand alkanes contain all C-C single bonds which are stronger and cannot be easily broken. That’s why alkenes are more reactive than alkanes.

Conclusion:

Alkenes are more reactive than the corresponding alkanes.

Example:

For example ethane does not react with bromine solution while? Ethane reacts easily with bromine solution, decolorizing its red colour.

3. Justify alkenes and alkynes as unsaturated hydrocarbons.

Ans: Reason for alkenes and alkynes being unsaturated hydrocarbons:

Alkenes and alkynes are unsaturated hydrocarbons because addition reactions occur in alkenes and alkynes. The reason for addition reaction is that two carbon atoms of alkenes and alkynes are directly bonded with less than 4 other atoms. Therefore, more atoms can be added to them by the breaking of double or triple bonds.

Examples:

A CI

H —C FIC—H + Cl2 PCI, I I► H —C =C—H

, 2-dichbroethene

CH2=CH2 + HBr CH3-CH2-Br

(Ethene) (Ethyl bromide)

Q.4: Why alkanes are inert in nature?

Ans. Reason for inertness of alkanes:

Alkanes contain C-C and C-H single bonds and these bonds are strong. The electrons of these are not easily available for reaction. That is \11.y alkanes are inert in nature due to which they are called paraffin’s.

5. What happens when alkyl halide is reduced?

Ans. Reduction of alkyl halides:

When alkyl halides are reduced, alkanes are produced. Reduction of alkyl halides means addition of hydrogen to alkyl halides. In this reaction nascent hydrogen is added to alkyl halides to form the corresponding alkanes i.e. methyl halide will form methane; ethyl halide will form ethane etc. This reaction occurs in the presence of zinc dust and HCI.

Example:

For example, methyl iodide forms methane and hydrogen iodide, on reaction with nascent hydrogen.

VQ Zn+ HCI).y c 1 4 + Hi

CH, – I +2[11]

6. Can you predict the product if KMnO4 solution reacts with alkene?

Ans. Yes, the detail is given below:

Reaction of alkene with kmno4 solution:

Alkenes react with cold dilute potassium permanganate solution

(Acidified) to form glycol. Glycols are the alcohols containing two hydroxyl groups (-OH) on two adjacent carbon atoms.

Example:

For example Ethene reacts with acidified solution of potassium permanganate to produce ethylene glycol, manganese dioxide and potassium hydroxide due to which the purple colour of potassium permanganate solutions disappears. This is a very useful test for the detection of alkenes and is called Bayer’s test.

3CH2=CH2 + 2KMn04+4H20 —• 3CH2-CH2+2MnO2+ 2KOH

OH

Q7. Why the colour of bromine water discharges on addition to ethane?

Ans. reason for discharge of colour of bromine:

The colour of bromine water discharges on addition to ethane because it chemically reacts with ethane.

The detail is given below:

Bromine (a red liquid) is reacted with ethane it adds to ethane to form 1,2-dibromoethane. During this reaction the red colour of bromine disappears due to its addition to ethane.

HH H

co.: I

\ /

►H C—C—H

I I

Br

1, 2-dibromoethane

Q.8 .Compare the reactivity of alkane and alkene.

Ans. Comparison between the reactivity of alkane and alkene:

The comparison between the reactivity of alkanes and alkenes is given below:

1

Alkanes are saturated hydrocarbons having carbon- carbon single bonds. These single bonds are strong; therefore they are less reactive than alkenes.

Alkanes are un-saturated hydrocarbons having carbon-

‘Carbon double bonds. The double bonds are weak; therefore they are more reactive than alkanes.

2

Substitution reactions occur in alkanes.

Addition reactions occur in alkenes.

3

Example:

Example:

They do not react with bromine.

They react with bromine, decolorizing its colour.

Q.9. Why addition reactions take place in ethane and Ethyne but not then.

Ans. Reason for addition reaction, occurring in ethane and Ethyne:

Carbon atom has four electrons in its valance shell and it can directly form bond with maximum of four atoms. Ethene and Ethyne are unsaturated hydrocarbons containing carbon-carbon double and triple bonds respectively. Therefore, the two carbon atoms of ethane and ethane are directly bonded with less than 4 other atoms. Therefore, more atoms can be added to them by the breaking of double or triple bonds. That is why addition reactions occur in ethane and Ethyne. Reason for addition reaction not occurs in ethane: Ethane is saturated hydrocarbon containing C-C and C-H single bonds. Carbon is directly bonded to 4 other atoms therefore, no further atom can be added to it i.e. addition reaction does not occur. Only substitution reactions occur in ethane by the replacement of H-atoms

Write equations for the preparation of Ethene from ethyl alcohol d ethyl chloride.

Ans: The answer of the given question is explained under the following headings:

1. Preparation of Ethene from ethyl alcohol:

When ethyl alcohol is heated up to 180 °C in the presence of concentrated sulphuric acid as catalyst, a molecule of water is eliminated from ethyl alcohol, forming ethane.

Chemical Equation:

H

I I

H2SO,/180°C

H CC H ► C =C +H20

I I /

j H OH

Ethyl alcohol Ethene

2. from Ethyl Chloride:

When ethyl chloride is heated with an alcoholic solution of potassium hydroxide, a molecule of hydrogen chloride is removed to form ethane.

Chemical Equation:

H

I I

H 5—H (KOH+C2H5OH) ► C =c + HCI

H H

Ethene

H Cl

Ethyl Chloride

word image 34

1. (A Write down the equations for the preparation of alkanes, alkenes and alkynes.

Ans. For answer see Question no 4+8+13

(b)Draw the molecular, dot and cross, condensed and structural formula of each of the following

(a)Propene (b) Butane (c) Pentane (d) Heptane (e) Butane

Ans: First we write molecular and condensed formulas and then dot and cross, structural formulas for the given compounds.

Compound i Molecular Name Formula

Condensed
Formula

Propene C H6

CH2=CH-CH3

Butane

C4H6

CH-r-C-CH3

Pentane

C5H12

CH3(CH2)3CH3

Heptane

C7H12

CH.1-C-(CH2)4CH3

Butane

C4H10

CH3(CH2)2CH3

(a) Propene:

Structural Formula:

H

H-C-C=C’H

H Propene

Dot and Cross Formula:

1 (b) Butane: Structural Formula: H H

H

X1-1

H

Propene

H

H-C=C- 9–y-H

H Butane

Dot and Cross Formula:

X 1; 1

H)-C—C.

1)

Butane

(c)Pentane Structural Formula:

H HHHH

H—C—C—C—C—C—H

11111

11111

H HHHH

Pentane

Dot and Cross Formula:

HHHHH

, 6.-C•xH

I ( I I LI I I(

Pentane

(d) Heptane Structural Formula:

H HHHH HCCCCCC=”C—H

H HHHH

Heptane

Dot and Cross Formula:

It 1; 1 tl 171, Fi

An A

Heptane

(e)ButeneStructural Formula:

H

H H Butane

Dot and Cross Formula:

H

1-<1

Butane

Q.2. (LiThe general formula of alkanes is Cnii2„2• Determine the general formula of cycloalkanes.

Ans. General Formula of Cyclo-alkanes:

Cyclo-alkanes are formed by removing two hydrogen atoms from the corresponding alkanes. Thus the general formula of Cyclo-alkanes is C2H2n•

Examples:

  1. The formula of cyclo-hexane is C61-112.
  2. The formula of cyclo-heptane is C7H14.

Write a balanced equation for the complete combustion of each of the following.

(A) Methane (b) Ethene (c) Ethyne

Ans. Complete combustion of methane, ethane andethyne:

All the given compounds react with excess oxygen to form carbon dioxide, water and heat. This is called complete combustion.

The chemical equation for each of them is given below:

a. Methane:

CH4 (g) + 02(g) —>CO2 (g) + H2O (g) + Heat

b. Ethene: C2H4 (g) +302(g) 2CO2 (g) + 2H2O (g) + Heat

c. Ethyne: 2C2H2 (g) +502(g) –> 4CO2 (g) + 2H2O (g) + Heat

(c) Explain briefly that why ethylene (acetylene) undergoes addition reaction in two steps.

Ans. Reason for ethane, undergoing addition reaction in two steps:

Ethyne contains carbon-carbon triple bond. It undergoes addition reaction in two steps because in first step the carbon-carbon triple bond is broken down and two atoms are added. Thus, the triple bond is converted to double bond. While in second step the double bond is broken down and two more atoms are added. Thus, double bond is converted to single bond.

Example:

Chlorination Ethene:

It occurs in two steps which are given below:

Step-i:

In first step triple bond is converted into double bond by the addition of two atoms of chlorine to form dichloromethane.

H—C-_=-C—H +C12 ► H—C=C—H

PCI3

1, 2-dichloroethene

In this step double bond is converted to single bond by the addition of two atoms of chlorine to form tetrachloroethane.

CI CI

I I

H—C=C—H +C12

1, 2-dichloroethene PCI3 CI CI

I I

♦H C—C—H

I I

CI

1, 1, 2, 2-tetrachloroethane

Q 3. (i) Give an example reaction that would yield the following products? Name the organic reactant and product in each reaction.

(a) Alkane (b) Mon halogenated alkane

(c) Halogenated alkane (d) Tetra halogenated alkane

Ans. (a) Reaction yielding alkane:

Unsaturated hydrocarbons like alkenes and alkynes yield alkanes by reacting them with hydrogen in the presence of nickel as catalyst at 250-300 °C or in the presence of platinum as catalyst at room temperature.

i.CH2=CH2 + H2 Ni

250-300°C >CH3e-H3

(Ethene) (Ethane)

ii. CH2= C= CH2 +2H2 NJ

>CH3eH2 eH3

250-300°C

(Propene) (Propane)

(b)Reaction yielding monohalogenated alkane:

In the presence of ultra violet rays methane reacts with chlorine to form monochlormethane which is a monohalogenated alkane.

H2C H+CI Cl 11″ light > H3C — Cl + HCI chloromethane Cl

Cl U`”’81” > CI —C — HC1

CII

CI

CI_C_ H+CI

CI

Halogenated alkane:

In the presence of ultra violet rays monochlormethane reacts with chlorine to form dichloromethane which is a halogenated alkane.

C/ —CH, —1H 1-` light >CI—C: 112 – + HCI

(Monochlormethane) (Di-chloromethane)

(d) Reaction yielding tetra halogenated alkane:

In the presence of ultra violet rays trichlormethane reacts with chlorine to form tetrachlormethar,e, e, e, e, e which is a tetra halogenated alkane.

CI CI

CI__C H+CI light > CI__CI + HCI

(Trichlormethane) (Tetrachloroethane)

ii. (A) Alkenes are unsaturated hydrocarbons. Explain the word unsaturated?

Ans. Explanation of word unsaturated for alkenes:

The word unsaturated for alkenes means that further atoms can be added to them. As they contain carbon-carbon double bonds therefore, more atoms can be added to them by the breaking of double bonds. Hence they are unsaturated hydrocarbons.

Examples:

i. CH2=CH2 + H2 Ni

250-3 00-C >CH3CH

(Ethene) (Ethane)

ii. CH2= C= CH2+2H2 •\,

“c CH3— CH2— CH3

250-30(1

(Propene) (Propane)

b). Describe the bonding between the two carbon atoms in Ethene

Ans. Bonding between two carbon atoms in ethane:

In ethane the two carbon atoms have double covalent bonds i.e. one sigma and one pi bond. Each carbon atom is then bonded to two hydrogen atoms through single covalent bonds.

Structure:

H H

C=C

/

H H

Ethene

(c). which functional group is present in alkenes?

Ans. Functional group in alkene:

The functional group is the active part of an organic compound. The functional group of alkene is the carbon-carbon double bond. .

(d). Describe a simple chemical test to determine whether an unknown hydrocarbon is unsaturated. Describe the result if the test is positive?

Ans. Simple test to determine saturated and unsaturated hydrocarbons:

The simple test for the determination of unsaturated and saturated hydrocarbons is reacting them with bromine water.

The colour of bromine water discharges on addition to alkene because it chemically reacts with alkene. On the other hand, alkanes do not discharge its colour because they do not react with bromine water. Example: Bromine (a red liquid). is reacted with ethane it adds to ethane to form 1,2-dibromoethane. During this reaction the red colour of bromine disappears due to its addition to ethane.

H H H Fl

\ / cci4 1 I

C =C + Br2 •H C H

/ 1 1

H H. Br

Ethene 1, 2-dibromoethane

Positive Result:

If the result is positive i.e. bromine water is decolorized. Then, the co-pound will be an alkene.

Q 4 Using structural formula. Give balanced equations for the following reactions.

(a) Ethene with chlorine

(b) Ethene with hydrogen. Name the catalyst used. Which industrial process uses a similar reaction?

(c) Ethene with hydrogen bromide

(d) Ethene with KMn04

Ans.(a)Reaction of ethane with chlorine:

Ethene reacts with chlorine in the presence of CCI4 as catalyst to form 1,2-dichloroethane.

H\H1 1

C =C + Cl2 1•H H H

C —C—H

H H 1 1

CI a

Fthenp 1, 2-dichloroethane

Reaction of Ethene with hydrogen:

Hydrogen is added to ethane in presence of nickel as catalyst and 240°C to form ethane.

HH

(Ft

C +H N /24

2 P H C —C—H

I I

H

Ethane Industry which uses similar reaction:

Hydrogenation of alkenes is used by Ghee industry to convert vegetable oil to ghee.

(c)Reaction of ethane with hydrogen bromide:

Ethenereacts with hydrogen bromide to from ethyl bromide or broom-ethane.

H H1 Br

C =C + HBr • H C —C— H

H H I I

H

Ethene Ethyl Bromide

(d)Reaction with KMn04:

Ethene reacts with acidified solution of potassium permanganate to produce ethylene glycol, manganese dioxide and potassium hydroxide due to which the purple colour of potassium permanganate solutions disappears. This is a very useful test for the detection of alkenes and is called Bayer’s test.

H

C + 2KMn04+4H20 +2MnO2+ 2KOH

H H OH

Ethene Ethylene Glycol

Q 5. Iustrate the following accordingly has been instructed

(a) Alkane from alkyl halide

Ans: Preparation of alkane from alkyl halide:

For answer see question no.4

B) Bromoethane from ethane

Ans: Preparation of Bromoethane from ethane:

Ethene reacts with bromine water in presence of 0014 as catalyst to form 1,2-dibromoethane. During this reaction the red colour of bromine disappears. Thus, bromine is used to detect the double bonds of alkenes.

H H H H

Cci4 I

-=C + Br2 • H C —C—H

I I

H H Br

Ethene 1, 2-dibromoethane

(c) Ethylene glycol (1, 2-ethanediol) from Ethene

Ans. Preparation of ethylene glycol from ethane:

For answer see above question no.4

Preparation of ethane from tetra halides:

When alkyl tetrahalides like 1, 1, 2, 2-tetrabromoethane is reacted with an active metal like zinc dust, bromine atoms are removed and

Ethyne (acetylene) is formed.

Br I

H —C —c—H + 2Zn I

Br 14, 2, 2-tetrabromoethine H —C + 2ZnBr2

Acetylene or Ethyne Oxalic_acidirom_Ltoetylene

Preparation of oxalic acid from acetylene:

When acetylene (ethane) is oxidized with solution of potassium Permanganate, the triple bond of acetylene is broken to form oxalic acid and carbon dioxide.

2H-C -C-H + 8[O] KAM!), > HO-C-C-OH + 2002

(Acetylene) (Oxalic acid)

Hydrocarbons

Q. Why alkane is inert in nature?

Ans. Alkanes are chemically inert in nature due to the following reason:

Reason:

Alkanes are chemically inert in nature because they contain carbon-carbon single bonds. The single bonds are very strong and stable and high energy is required to break them, therefore, alkanes are chemically inert as compared to alkynes and alkenes because they contain double or triple bonds which can easily are broken.

What is Baeyer’s test?

Ans: Baeyer’s test:

This test was introduced by German organic chemist Adolf Von Baeyer, therefore, it is called Baeyer test. Purpose of Baeyer’s test: This test is used for the detection of alkenes.

Baeyer’s reagent:

The chemical used in Baeyer’s test are called Baeyer’s reagent. Baeyer’s reagent consists of, alkaline dilute solution of potassium permanganate which is a strong oxidizing agent.

Reaction:

Alkenes react with cold dilute potassium permanganate solution (alkaline) to form glycol. Glycols are the alcohols containing two hydroxyl groups (-OH) on two adjacent carbon atoms:

The reaction of potassium permanganate with ethane is given below:

3CH2=CH2 + 2KMnO4+4H20 3CH2-CH2+2Mn02+ 2KOH

OH OH

(Ethylene glycol)

During this reaction potassium permanganate is changed to manganese dioxide and potassium hydroxide due to which its purple colour disappears.

Q.What is addition reactions?

Ans. Addition reactions;

Generally addition reactions are defined as:

“The reactions in which two or more substances react to form only one substance are called addition reactions.” With regard to organic compounds addition reactions can be defined as:

“The reaction in which molecules like H2, Cl2, and HCI etc. are added to alkenes or alkyne is called addition reaction.”

Addition reactions occur only in unsaturated hydrocarbons i.e. alkenes and alkynes. During addition reactions unsaturated hydrocarbons are changed to saturated hydrocarbons.

Examples:

H H

i. C=C + Br2 CC 14 H H

I

• H —C—C—H

I I

Br Br

ickel 1 250°C

H —C H + 2H2

word image 35

1. Are called saturated hydrocarbons.

(a) Alkane (b) alkyne (c) alkene (d) aromatic compounds

2. Chemically inert hydrocarbons are called

(a) Alkane (b) alkyne (c) alkene (d) aromatic compounds.

3. Hydrocarbons are referred to as:

(a) Paraffin (b) paramagnetic (c) diamagnetic (d) both a & d.

4. Hydrogenation of alkenes ad alkynes is done through the catalyst—-at 200-300°c to form alkane.

(a) Ni (b) Pt. (c) Mn (d) Fe.

5. Alkenes contain at least double bonds.

(a) One (b) two (c) three (d) four.

6. Hydrogenation of alkenes is industrially used for the conversion of

Oils into ghee.

(a) Animals fats (b) cod liver

(c) Vegetables (d) both a & b.

7. Alkynes are hydrocarbons which contains at least bond.

(a) Single (b) double (c) triple (d) one hydrogen bonding.

8. Addition of halogen in double and triple bonds of hydrocarbon are called

(a) Halogenations (b) hydrogenation

(c) Halo hydrogenation. (d) Both a & d.

9. Dehydration of ethyl alcohol with conc.H2SO4results in the formation of:

(a) Ethane (b) methane (c) acetylene (d) ethane.

10. Which one of the following reagents distinguishes ethane from acetylene?

(a) Alkaline solution of KMnO4. (b) Bromine solution.

(c) Carbon tetrachloride solution (d) Alcoholic KOH.

11. Which one of the. Following decolorizes Br2water:

(a) Propane (b) ethane (c) ethane (d) methane.

12. Ethene reacts with HBr, the compound formed is:

(a) CH3—CH2—Br. (b) Br—CH2—CH2—Br.

(c) CH3—CH2—C H3. (d) Acetylene.

13. Which of the following statements is not true for alkynes?

(a) They contain a triple bond. (b) They burn to form CO2.

(c)They perform Baeyer’s test. (d) They undergo addition reaction.

14. General formula for alkenes is:

(A) CnH2nOn (b) (C) OnH2n-2 (d) CnH2n.

15. All the members of alkane series have:

(a) All single bonds (b) at least one double bon

(c) At least one triple bonds (d) all types of bonds.

16. Baeyer’s reagent is:

(a) conc. KMnO4 (b) alkaline KMnO4

(c) Acidic KMnO4 (d) hot KMnO4.

17. Which one gives carboxylic acid with alkaline KMn0,4:

(a) Ethane (b) ethane (c) acetylene (d) methane.

18. Baeyer’s test shows the presence of:

(a) A single bond (b) a double bond (c) a triple bond (d) no bond.

19. Which one is the least reactive?

(a)Ethyne (b) propene (c) ethane (d) ethane.

20. Ethane reacts with chlorine in the presence of:

(a) Carbon tetra chloride (b) ether (c) sunlight (d) water.

21. Chlorination of methane is catalyzed by.

(a) Water (b) Heat (c) sunlight (d) HCI.

22. Which one of the following corresponds to Cr, H21-1, 2.

(a) C2H6 (b) C2H4 (c) C2H2 (d) C2H5

2 thoughts on “CLASS 10th CHEMISTRY NOTES CHAPTER 12 HYDROCARBONS”

  1. Pingback: CLASS 10th CHEMISTRY NOTES CHAPTER 13 BIOCHEMISTRY - Daraz 24

  2. Pingback: Federal Board of Intermediate and Secondary Education 2021 Result - Daraz 24

Leave a Reply

Scroll to Top
%d bloggers like this: