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Chapter 12

Organic Chemistry

Class 10 - Concise Chemistry Selina



Intext Questions 1

Question 1

(a) What are organic compounds?

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

Answer

(a) Organic compounds are the compounds of carbon excluding oxides of carbon, metallic carbonates and related compounds like metal cyanides, metal carbides, etc.

(b) As organic compounds were obtained straight from nature and there was no known method of preparing them in the laboratory, hence it was believed that they were the products of some vital force of nature. This theory was known as vital force theory.

This theory was soon discarded when in 1828, Friedrich Wohler demonstrated that an organic chemical (urea) could be produced in the laboratory.

Question 2

(a) Name a few sources of organic compounds.

(b) Give the various applications of organic chemistry.

Answer

(a) Sources of organic compounds are:

  1. Plants
  2. Animals
  3. Coal
  4. Petroleum
  5. Fermentation
  6. Wood
  7. Synthetic methods

(b) Organic chemistry is used in the manufacturing of soaps, shampoos, powders, and perfumes. The clothes we wear, the 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 use organic compounds.

Question 3

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

Answer

Organic chemistry is 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 use organic compounds.

Question 4

Carbon shows some unique properties, name them.

Answer

Unique properties of carbon are :

  1. Tetravalency of carbon
  2. Catenation

Question 5

Explain the following:

(a) Tetravalency

(b) Catenation

Answer

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

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

Question 6

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

Answer

CharacteristicsOrganic compoundsInorganic compounds
Presence of carbonCarbon is necessary element in every organic compoundCarbon is not an essential element in inorganic compound
Solubility in waterThey generally do not dissolve in water.They generally dissolve in water.
Solubility in organic solventsThey dissolve in organic solvents like alcohol, benzene and chloroform.All inorganic compounds do not dissolve in organic solvents.
Melting and boiling pointThey 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.

Question 7

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

Answer

The 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 thousand are added every year. Hence, it demands a new field of chemistry i.e., organic chemistry.

Question 8

What are hydrocarbons? Compare saturated and unsaturated hydrocarbons?

Answer

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

Saturated HydrocarbonsUnsaturated Hydrocarbons
All the four valencies of each carbon atom are satisfied by forming single covalent bonds with carbon and with hydrogen atoms.The valencies of at least two carbon atoms are not fully satisfied by the hydrogen atoms.
Carbon atoms are joined only by a single covalent bond.Carbon atoms are joined by double covalent bonds >C=C< or triple covalent bonds -C≡C-
They are less reactive due to the non-availability of electrons in the single covalent bonds, and therefore they undergo substitution reaction.They are more reactive due to the presence of electrons in the double or the triple bond, and therefore undergo addition reaction.

Question 9

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

Answer

Carbon shows unique properties of tetravalency and catenation. Due to this unique nature of carbon atoms, they form single, double and triple covalent bonds with other carbon atoms and a variety of other elements. Carbon atoms have the ability to form stable bonds with other atoms resulting in the formation of long chains, branched structures, and cyclic compounds. These properties of carbon atom gives rise to the formation of a large number of compounds.

Question 10

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

(a) Single bond compound

(b) Double bond compound

(c) Triple bond compound

Answer

(a) Single bond compound : C4H10 has two chain isomers

1. n-butane

Give at least one example in each case to show the structure of isomers of Single bond compound. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

2. Isobutane

Give at least one example in each case to show the structure of isomers of Single bond compound. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(b) Double bond compound : C4H8 has two position isomers

1. But-1-ene

Give at least one example in each case to show the structure of isomers of Double bond compound. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

2. But-2-ene

Give at least one example in each case to show the structure of isomers of Double bond compound. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(c) Triple bond compound : C4H6 has two position isomers

1. But-1-yne

Give at least one example in each case to show the structure of isomers of Triple bond compound. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

2. But-2-yne

Give at least one example in each case to show the structure of isomers of Triple bond compound. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 11

Name a compound of each type and draw the figure,

(a) Cyclic compound with single bond

(b) Cyclic compound with triple bond

Answer

(a) Cyclopropane [C3H6]

Name a compound of each type and draw the figure, (a) Cyclic compound with single bond (b) Cyclic compound with triple bond. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(b) Cyclopentyne [C5H6]

Name a compound of each type and draw the figure, (a) Cyclic compound with single bond (b) Cyclic compound with triple bond. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 12

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

(a) saturated hydrocarbons

(b) unsaturated hydrocarbons

Answer

(a) Methane

(b) Ethene

Question 13

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

Answer

Substitution reactions — 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 + Cl2 ⟶ CH3Cl + HCl

Addition reactions — A reaction involving addition of atoms or molecules to the double or the triple bond of an unsaturated compound so as to yield a saturated product is known as addition reaction.

e.g., C2H4 + Br2 ⟶ C2H4Br2

Intext Questions 2

Question 1

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

(a) Ketone

(b) Alcohols

(c) Aldehydes

Answer

Functional group is defined as an atom or group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compounds.

The structural formula of the functional groups are given below:

(a) -C-O||\overset{\underset{\text{||}}{\text{O}}}{\text{-C-}}

(b) -OH

(c) -CH=O

Question 2

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

(a) Alkyne

(b) Alcohol

Answer

(a) Butyne C4H6

(b) Butanol C4H9OH

Question 3

Which part of an organic compound determines

(i) Physical properties

(ii) Chemical properties

Answer

(i) Alkyl group

(ii) Functional group

Question 4

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

(a) CH3OH

(b) C2H5OH

(c) C3H7CHO

(d) C4H9COOH

(e) CH3COOH

(f) HCHO

Answer

(a) CH3OH

Alkyl radical — Methyl (-CH3)

Functional group — Alcohol (-OH)

(b) C2H5OH

Alkyl radical — Ethyl (-C2H5)

Functional group — Alcohol (-OH)

(c) C3H7CHO

Alkyl radical — Propyl (-C3H7)

Functional group — Aldehyde (-CHO)

(d) C4H9COOH

Alkyl radical — Butyl (-C4H9)

Functional group — carboxyl (-COOH)

(e) CH3COOH

Alkyl radical — Methyl (-CH3)

Functional group — carboxyl (-COOH)

(f) HCHO

Alkyl radical — (-H)

Functional group — Aldehyde (-CHO)

Question 5

(a) What is an alkyl group?

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

Answer

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

(b) Three alkyl radicals are:

  1. Methyl
  2. Ethyl
  3. Propyl

These are formed by losing one hydrogen atom

CH4 ⟶ CH3 + H

C2H6 ⟶ C2H5 + H

C3H8 ⟶ C3H7 + H

Question 6

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

Answer

First three members of the homologous series of alkanes are :

1. Methane (CH4)

Structural formula for Methane. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

2. Ethane(C2H6)

Structural formula for Ethane. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

3. Propane (C3H8)

Structural formula for Propane. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 7

(a) What is a homologous series?

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

  1. in terms of molecular mass.
  2. in terms of number and kind of atoms per molecule?

Answer

(a) 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 CH2 group.

(b) The difference in the molecular formula of two adjacent homologues:

  1. In terms of molecular mass is 14 a.m.u.
  2. In terms of number & kind of atoms per molecule is that each member of the series differs from the preceding one by the addition of CH2 group.

Exercise 12A

Question 1(a)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

2,2-Dimethylpropane

Question 1(b)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

2-Methylbutane

Question 1(c)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

Prop-1-ene

Question 1(d)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

2,2-Dimethylpentane

Question 1(e)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

Pent-2-yne

Question 1(f)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

3-Methylbut-1-yne

Question 1(g)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

2,3-Dichloropentane

Question 1(h)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

3-Methylheptane

Question 1(i)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

But-2-ene

Question 1(j)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

Hept-2-yne

Question 1(k)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

5,5-Dimethylhexanal

Question 1(l)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

Pentan-2-ol

Question 1(m)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

4-Methylpentanoic acid

Question 1(n)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

2-Bromo-2-methylbutane

Question 1(o)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

1-Bromo-3-methylbutane

Question 1(p)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

Prop-1-yne

Question 1(q)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

Methanal

Question 1(r)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

Prop-1-yne

Question 1(s)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

Propan-1-ol

Question 1(t)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

Ethanoic acid

Question 1(u)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

Ethanal

Question 1(v)

Write the IUPAC name of:

Write the IUPAC name of. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

1,2-Dichloroethane

Question 2(a)

Write the structure of Prop-1-ene

Answer

Prop-1-ene

Write the structure of Prop-1-ene. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 2(b)

Write the structure of 2,3-dimethylbutane

Answer

2,3-dimethylbutane

Draw the structural formula for 2, 3 – dimethyl butane. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 2(c)

Write the structure of 2-methylpropane

Answer

2-methylpropane

Write the structure of 2-methylpropane. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 2(d)

Write the structure of 3-hexene

Answer

3-hexene

Write the structure of 3-hexene. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 2(e)

Write the structure of Prop-1-yne

Answer

Prop-1-yne

Write the structure of Prop-1-yne. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 2(f)

Write the structure of 2-methylprop-1-ene.

Answer

2-methylprop-1-ene

Write the structure of 2-methylprop-1-ene. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 2(g)

Write the structure of Alcohol with molecular formula C4H10O

Answer

Alcohol with molecular formula C4H10O

Write the structure of Alcohol with molecular formula C4H10O. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 3(a)

Choose the correct answer:

C5H11 is an

  1. alkane
  2. alkene
  3. alkyne
  4. alkyl group

Answer

(a) Alkyl group

Reason — It follows the formula CnH2n + 1

Question 3(b)

Choose the correct answer:

A hydrocarbon of the general formula CnH2n is

  1. C15H30
  2. C12H26
  3. C8H20
  4. C6H14

Answer

C15H30

Reason — According to the formula CnH2n, hydrogen is double of carbon, hence, C15H30 follows the formula CnH2n

Question 3(c)

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

  1. 5
  2. 4
  3. 3
  4. 2

Answer

2

Reason — The chain structures are shown below:

n-butane

The total number of different carbon chains that four carbon atoms form in alkane is? Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Isobutane

The total number of different carbon chains that four carbon atoms form in alkane is? Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 3(d)

CH3-CH2-OH and CH3-O-CH3 are :

  1. Position isomers
  2. Chain isomers
  3. Homologous
  4. Functional group isomers

Answer

Functional group isomers

Reason — CH3-CH2-OH is ethyl alcohol and contains Hydroxyl (OH) as the functional group.

CH3-O-CH3 is Dimethyl ether and contains Ether C-O-C as the functional group.

As the two have same molecular formula but different but different functional groups hence, they are called functional isomers.

Question 3(e)

The IUPAC name of the compound is :

The IUPAC name of the compound is. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10
  1. 3-trimethylhexane

  2. 3-methyl hexane

  3. 4-methyl hexane

Answer

3-methylhexane

Reason — As one methyl group is attached at the third carbon and the longest chain is of 6 carbon atoms, hence, the name is 3-methylhexane

Question 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, CH2, CH3)

(d) As the molecular masses of hydrocarbons increase, their boiling points ............... and melting points ............... (increase, decrease)

(e) C25H52 and C50H102 belong to ............... homologous series (the same, different)

(f) CO is an ............... 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)

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

Answer

(a) Propane and ethane are homologous.

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

(c) Succeeding members of homologous series differ by CH2.

(d) As the molecular masses of hydrocarbons increase, their boiling points increase and melting points increase.

(e) C25H52 and C50H102 belong to the same homologous series

(f) CO is an inorganic compound.

(g) The chemical properties of an organic compound are largely decided by the functional group and the physical properties of an organic compound are largely decided by the number of carbon atom.

(h) CHO is the functional group of an aldehyde.

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

(j) But-1-ene and but-2-ene are examples of position isomerism.

Question 5

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

Answer

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 as chain isomers.

Example: Pentane C5H12

Pentane [n-pentane]

Draw the structures of isomers of pentane. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

2-Methyl butane [iso-pentane]

Draw the structures of isomers of pentane. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

2,2 Dimethyl Propane [neo-pentane]

Draw the structures of isomers of pentane. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Position isomers — 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.

Example : But-1-yne and But-2-yne

But-1-yne

Give at least one example in each case to show the structure of isomers of Triple bond compound. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

But-2-yne

Draw the structural formula of But-2-yne. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Question 6(a)

Define the term isomerism. State two main causes of isomerism.

Answer

Isomerism is the phenomenon due to which two or more compounds have the same molecular formula but differ in molecular arrangement or in structural formula.

Two main causes of isomerism are:

  1. Difference is the mode of linking of atoms.
  2. Difference in the arrangement of atoms or groups in space.

Question 6(b)

Draw the chain isomers of hexane (C6H14).

Answer

The chain isomers of hexane are shown below:

n-hexane

Draw the chain isomers of hexane C6H14. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

2 Methylpentane

Draw the chain isomers of hexane C6H14. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

3 Methylpentane

Draw the chain isomers of hexane C6H14. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

2,3 Dimethylbutane

Draw the chain isomers of hexane C6H14. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

2,2 Dimethylbutane

Draw the chain isomers of hexane C6H14. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 6(c)

Draw position isomers of butene (C4H8)

Answer

Position isomers of butene are shown below:

1-butene

Structural formula for 1-butene. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

2-butene

Structural formula for 2-butene. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Question 7

Draw structural formula for each of the following compounds:

(a) isomer of n-butane

(b) Vinegar

(c) 2-Propanol

(d) Ethanal

(e) Acetone

(f) Diethyl ether

What is used to describe these compounds together?

Answer

(a) isomer of n-butane is Isobutane. Its structural formula is shown below:

Isobutane

Give at least one example in each case to show the structure of isomers of Single bond compound. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(b) Vinegar (acetic acid)

Write structural formula of Vinegar. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10.

(c) 2-Propanol

Give the structural formulae for 2-propanol. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10.

(d) Ethanal

Draw the structural formula of Ethanal. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10.

(e) Acetone

Draw the structural formula of Acetone. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10.

(f) Diethyl ether

Draw the structural formula for Diethyl ether. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10.

These compounds together can be called organic compounds.

Question 8

(a) What is the special feature of the structure of:

(i) Ethene

(ii) Ethyne

(b) What type of reaction is common to both of the above compounds? Why methane does not undergo this type of reaction.

(c) What is the IUPAC name of dimethyl ether.

Answer

(i) The special feature of the structure of ethene is that the two carbon atoms are linked by double covalent bond formed by sharing two pairs of electrons between the two carbon atoms.

(ii) The special feature of the structure of ethyne is that the two carbon atoms are linked by triple covalent bond formed by sharing three pairs of electrons between the two carbon atoms.

(b) The above compounds undergo addition reactions. Methane does not undergo this type of reaction as its all 4 valencies are satisfied by hydrogen atoms forming single bond and so they are less reactive and undergo substitution reaction only.

(c) Methoxymethane

Question 9

Which type of reaction will (i) ethane and (ii) ethene undergoe?

Answer

(i) Ethane will undergo Substitution reactions.
Reason — In case of ethane, all of its 4 valencies are satisfied by hydrogen atoms forming single bond and so they are less reactive and undergo substitution reaction only.

(ii) Ethene will undergo Addition reactions.
Reason — In case of ethene, the valencies of atleast 2 carbon atoms are not fully satisfied by hydrogen atoms. The availability of electrons in the double bond makes them more reactive and hence they undergo addition reactions only.

Question 10

Choosing only words from the following list, write down appropriate words to fill in the blanks from (a) to (e) given below.

Addition, carbohydrates, CnH2n-2, CnH2n, CnH2n+2, electrochemical, homologous, hydrocarbon, saturated, substitution, unsaturated.

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

Answer

The alkanes form a (a) homologous series with the general formula (b) CnH2n+2. The alkanes are (c) saturated (d) hydrocarbons which generally undergo (e) substitution reactions.

Question 11

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.

Answer

(a) Ethane : CH3-CH3

Structural formula for Ethane. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(b) Ethanol : C2H5OH

Write structural formula of ethanol. Concise Chemistry Solutions ICSE Class 10.

(c) Ethyne : C2H2

Draw the structural formula of Ethyne. Concise Chemistry Solutions ICSE Class 10

Question 12

Ethane, Ethene, Ethanoic acid, Ethyne, Ethanol.

From the above, name

(a) The compound with -OH as the part of it's structure.

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

(C) Homologue of homologous series with general formula CnH2n.

Answer

(a) Ethanol

(b) Ethanoic acid

(c) Ethene

Question 13

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

Give the correct IUPAC name and the functional group for each of the compounds whose structural formulae are given below. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Answer

(a) IUPAC name: Propanoic acid

Functional group: -COOH

(b) IUPAC name: Propanol

Functional group: -OH

Question 14

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

General FormulaCnH2nCnH2n-2CnH2n+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  

Answer

General FormulaCnH2nCnH2n-2CnH2n+2
IUPAC name of the homologous seriesAlkeneAlkyneAlkane
Characteristic bond typeDouble bondsTriple bondsSingle bonds
IUPAC name of the first member of the seriesEtheneEthyneMethane
Type of reaction with chlorineAdditionAdditionSubstitution

Question 15

Fill in the blanks with the correct words from the brackets:

(a) Alkenes are the (i) ............... (analogous/homologous) series of (ii) ............... (saturated/unsaturated) hydrocarbons. They differ from alkanes due to the presence of (iii) ............... (double/single) bonds. Alkenes mainly undergo (iv) ............... (addition/substitution) reactions.

(b) The organic compound which undergoes substitution reaction is (v) ............... (C2H2, C2H4, C10H18, C2H6)

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

Answer

(a) Alkenes are the (i) homologous series of (ii) unsaturated hydrocarbons. They differ from alkanes due to the presence of (iii) double bonds. Alkenes mainly undergo (iv) addition reactions.

(b) The organic compound which undergoes substitution reaction is (v) C2H6.

(c) The correct IUPAC names of isomers of Butane are Butane and 2-Methyl propane. Their structural formulae are given below:

  1. Butane [n-butane]
Give the structural formulae of n-butane. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10
  1. 2-Methyl propane [iso-butane]
Give the structural formulae of 2-methyl propane. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Question 16

Name:

(a) The saturated hydrocarbon containing two carbon atoms.

(b) An alcohol with three carbon atom.

(c) A triple bond hydrocarbon with two carbon atoms.

Answer

(a) Ethane [C2H6]

(b) Propan-1-ol [C3H7OH]

(c) Ethyne [C2H4]

Exercise 12B

Question 1

State the sources of alkanes.

Answer

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

Question 2

Methane is a greenhouse gas. Comment

Answer

Methane is a primary constituent of natural gas. It absorbs outgoing heat radiations from the earth and thus contributes to the green house effect and so is 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 carbon dioxide.

Question 3

Give the general formula of the alkanes.

Answer

The general formula for alkanes is CnH2n+2, where n is the number of carbon atoms.

Question 4

Draw the structures of isomers of:

(a) butane

(b) pentane

Answer

(a) Isomers of butane [C4H10]:

1. n-butane

Give at least one example in each case to show the structure of isomers of Single bond compound. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

2. Isobutane

Give at least one example in each case to show the structure of isomers of Single bond compound. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(b) Isomers of pentane [C5H12]:

Pentane [n-pentane]

Draw the structures of isomers of pentane. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

2-Methyl butane [iso-pentane]

Draw the structures of isomers of pentane. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

2,2 Dimethyl Propane [neo-pentane]

Draw the structures of isomers of pentane. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Question 5

Write the :

(a) molecular formula.

(b) electron dot formula and

(c) structural formula of methane and ethane.

Answer

(a) Molecular formula

Methane - CH4

Ethane - C2H6

(b) Electron dot formula

Methane

Write the : (a) molecular formula. (b) electron dot formula and (c) structural formula of methane and ethane. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Ethane

Write the : (a) molecular formula. (b) electron dot formula and (c) structural formula of methane and ethane. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(c) Structural formula

Methane (CH4)

Structural formula for Methane. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Ethane(C2H6)

Structural formula for Ethane. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 6

How is:

(a) methane and

(b) ethane prepared in the laboratory?

Answer

(a) Laboratory preparation of methane

A mixture of sodium ethanoate (sodium acetate) and soda lime is taken in a hard glass test tube and heated over a bunsen flame.

How is: (a) methane and (b) ethane prepared in the laboratory? Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

CH3COONa sodium acetate+NaOHsodalime300°CCaOCH4methane+Na2CO3\underset{\text{ sodium acetate}}{\text{CH}_3\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{methane}}{\text{C}\text{H}_4}↑ + \text{Na}_2\text{CO}_3

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

(b) Laboratory preparation of ethane

A mixture of sodium propionate and soda lime is taken in a boiling tube and heated over a bunsen flame.

How is: (a) methane and (b) ethane prepared in the laboratory? Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

C2H5COONasodium propionate+NaOHsodalime300°CCaOC2H6ethane+Na2CO3\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑ + \text{Na}_2\text{CO}_3

The gas evolved is collected by downward displacement of water.

Question 7

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

Answer

Iodomethane (Methyl iodide) and bromoethane (ethyl bromide) are reduced by nascent hydrogen at ordinary room temperature.

CH3I + 2[H] ⟶ CH4 + HI

C2H5Br + 2[H] ⟶ C2H6 + HBr

Nascent hydrogen is produced by the action of Zn powder and dil. HCl or Zn/Cu couple in alcohol.

Question 8

What is a substitution reaction? Give the reaction of chlorine with ethane and name the product formed.

Answer

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 + Cl2 ⟶ CH3Cl + HCl

Reaction of chlorine with ethane is given below:

C2H6 + Cl2 ⟶ C2H5Cl + HCl

The product formed is Monochloroetahne [C2H5Cl]

Question 9

Name the compounds formed when methane burns in:

(a) sufficient air

(b) insufficient air

Give a balanced equation.

Answer

(a) The compounds formed are carbon dioxide and water

CH4 methane+2O2[excess]CO2+2H2O\underset{\text{ methane} }{\text{CH}_4} + 2\text{O}_2\text{[excess]} \longrightarrow \text{CO}_2 + 2\text{H}_2\text{O}

(b) The compounds formed are carbon monoxide and water

2CH4 methane+3O2[insufficient]2CO+4H2O\underset{\text{ methane} }{\text{2CH}_4} + 3\text{O}_2\text{[insufficient]} \longrightarrow \text{2CO} + 4\text{H}_2\text{O}

Question 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.

Answer

(a) Methane

(i) Reaction with chlorine: Chloromethane [CH3Cl] and Hydrochloric acid [HCl] are formed when methane reacts with chlorine.

CH4 + Cl2 or 600Kdiffused sunlight\xrightarrow[\text{or 600K}]{\text{diffused sunlight}} CH3Cl + HCl

(ii) Reaction with Bromine : Bromomethane [CH3Br] and Hydrogen bromide [HBr] are formed when methane reacts with bromine.

CH4 + Br2 ⟶ CH3Br + HBr

(b) Ethane

(i) Reaction with chlorine: Chloroethane [C2H5Cl] and Hydrochloric acid [HCl] are formed when ethane reacts with chlorine.

C2H6 + Cl2 ⟶ C2H5Cl + HCl

(ii) Reaction with Bromine : Bromoethane [C2H5Br] and Hydrogen bromide [HBr] are formed when ethane reacts with bromine.

C2H6 + Br2 ⟶ C2H5Br + HBr

Question 11

Name the compound prepared from:

(a) Sodium propionate

(b) Methyl iodide and

(c) Ethyl bromide.

Write a balanced equation for the same.

Answer

(a) Sodium propionate : compound prepared are ethane and sodium carbonate

C2H5COONasodium propionate+NaOHsodalimeΔCaOC2H6ethane+Na2CO3\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[\Delta]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑ + \text{Na}_2\text{CO}_3

(b) Methyl iodide : compound prepared are methane and hydrogen iodide

CH3Imethyl iodide+2[H]nascent hydrogenalcoholZn/Cu coupleCH4methane+HI\underset{\text{methyl iodide}}{\text{CH}_3\text{I}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{methane}}{\text{CH}_4} ↑ +\text{HI}

(c) Ethyl bromide : compound prepared are ethane and hydrogen bromide

C2H5Brethylbromide+2[H]nascent hydrogenalcoholZn/Cu coupleC2H6ethane+HBr\underset{\text{ethylbromide}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑+\text{HBr}

Question 12

Write the equation for the complete combustion of

(i) Methane

(ii) Ethane

Answer

(i) Methane:

CH4 methane+2O2[excess]CO2+2H2O\underset{\text{ methane} }{\text{CH}_4} + 2\text{O}_2\text{[excess]} \longrightarrow \text{CO}_2 + 2\text{H}_2\text{O}

(ii) Ethane

2C2H6 ethane+7O2[excess]4CO2+6H2O\underset{\text{ ethane} }{2\text{C}_2\text{H}_6} + 7\text{O}_2\text{[excess]} \longrightarrow 4\text{CO}_2 + 6\text{H}_2\text{O}

Question 13

Convert:

(a) Methane into chloroform.

(b) Sodium acetate into methane

(c) Methyl iodide into ethane.

(d) Methane to methyl alcohol

Answer

(a) Methane into chloroform

CH4 methane+Cl2diffused sunlightΔCH3Clmonochloromethane+HCl\underset{\text{ methane} }{\text{CH}_4} + \text{Cl}_2 \underset{\Delta}{\xrightarrow{\text{diffused sunlight}}} \underset{\text{monochloromethane}}{\text{CH}_3\text{Cl}} + \text{HCl}

CH3Clmonochloromethane+Cl2[excess]CH2Cl2dichloromethane+HCl\underset{\text{monochloromethane}}{\text{CH}_3\text{Cl}} + \underset{\text{[excess]}}{\text{Cl}_2} \longrightarrow \underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2} + \text{HCl}

CH2Cl2dichloromethane+Cl2CHCl3trichloromethane or chloroform+HCl\underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2} + \text{Cl}_2 \longrightarrow \underset{\text{trichloromethane or chloroform}}{\text{CHCl}_3}+ \text{HCl}

(b) Sodium acetate into methane

CH3COONasodium acetate+NaOHsodalimeCaOΔCH4methane+Na2CO3\underset{\text{sodium acetate}}{\text{CH}_3\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \underset{\Delta}{\xrightarrow{\text{CaO}}} \underset{\text{methane}}{\text{CH}_4} + \text{Na}_2\text{CO}_3

(c) Methyl iodide into ethane

2CH3Imethyl iodide+2Nadry etherC2H6ethane+2NaI\underset{\text{methyl iodide}}{2\text{CH}_3\text{I}} + 2\text{Na} \xrightarrow{\text{dry ether}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑ + 2\text{NaI}

(d) Methane to methyl alcohol

2CH4 methane+O2120 atm.475 K Cu tube2CH3OHmethyl alcohol\underset{\text{ methane}}{2\text{CH}_4} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{475 K Cu tube}} \underset{\text{methyl alcohol}}{2\text{CH}_3\text{OH}}

Question 14

Give three uses of:

(a) Methane

(b) Ethane

Answer

(a) Methane

  1. Methane is a source of carbon monoxide and hydrogen.
  2. It is used in the preparation of useful compounds like ethyne, methanal, methanol, chloro-methane, and tetrachloro-methane.
  3. It is employed as a domestic fuel.

(b) Ethane

  1. It is used in the preparation of ethene, ethanol, ethanal and ethanoic acid.
  2. It forms ethyl chloride, which is used to make tetraethyllead.
  3. Ethane is also a good fuel.

Question 15

Under what conditions does ethane get converted to:

(a) ethyl alcohol

(b) acetaldehyde

(c) acetic acid

Answer

(a) Ethyl alcohol — is produced when ethane and oxygen react at 120 atm pressure, 475 K temperature and pushed through copper tubes.

2C2H6 ethane+O2120 atm.Cu tube 475 K2C2H5OHethyl alcohol\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}

(b) Acetaldehyde — is produced when ethane and oxygen react by using catalyst MoO

C2H6 ethane+O2MoOCH3CHOacetaldehyde+H2O\underset{\text{ ethane}}{\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow{\text{MoO}} \underset{\text{acetaldehyde} }{\text{CH}_3\text{CHO}} + \text{H}_2\text{O}

(c) Acetic acid

2C2H6 ethane+O2120 atm.Cu tube 475 K2C2H5OHethyl alcohol\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}

C2H5OHethyl alcohol+O2Pt. 300°CCH3COOH+H2Oacetic acid\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{O}_2 \xrightarrow{\text{Pt. 300}\degree\text{C}} \underset{\text{acetic acid}}{\text{CH}_3\text{COOH} + \text{H}_2\text{O}}

Question 16

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

Answer

Alcohol ⟶ Ethyl alcohol [C2H5OH]

Aldehyde ⟶ Acetaldehyde [CH3CHO]

Acid ⟶ Acetic acid [CH3COOH]

Ethane to an alcohol :

2C2H6 ethane+O2120 atm.Cu tube 475 K2C2H5OHethyl alcohol\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}

Ethane to an aldehyde :

C2H6 ethane+O2MoOCH3CHOacetaldehyde+H2O\underset{\text{ ethane}}{\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow{\text{MoO}} \underset{\text{acetaldehyde} }{\text{CH}_3\text{CHO}} + \text{H}_2\text{O}

Ethane to an acid :

2C2H6 ethane+O2120 atm.Cu tube 475 K2C2H5OHethyl alcohol\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}

C2H5OHethyl alcohol+O2Pt. 300°CCH3COOH+H2Oacetic acid\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{O}_2 \xrightarrow{\text{Pt. 300}\degree\text{C}} \underset{\text{acetic acid}}{\text{CH}_3\text{COOH} + \text{H}_2\text{O}}

Excercise 12C

Question 1

Write:

(a) molecular formula

(b) electron dot formula and

(c) structural formula of ethene (ethylene).

Answer

(a) C2H4

(b) Electron dot formula of ethene:

Write: (a) molecular formula (b) electron dot formula and (c) structural formula of ethene (ethylene). Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(c) Structural formula of ethene:

Structural formula of Ethene. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10.

Question 2

The molecules of alkene family are represented by a general formula CnH2n.

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.

Answer

(a) n is the number of carbon atoms in the molecule and 2n is the number of hydrogen atoms.

(b) Butene

(c) When n=4 then no. of carbon atoms is n=4 and hydrogen atoms is 2n=8, hence alkene is C4H8

(d) When 2n=10 then no. of carbon atoms is n=5 and hydrogen atoms is 2n=10, hence alkene is C5H10

(e) Third member of the alkene family is Butene. Its structural formula is shown below:

The molecules of alkene family are represented by a general formula CnH2n. What do n and 2n signify? What is the name of alkene when n=4. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(f) Lower homologous: C3H6

Higher homologues : C5H10

Question 3(a)

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

Answer

Structural formula of Ethane [saturated]:

Structural formula of Ethane. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Structural formula of Ethene [unsaturated]:

Structural formula of Ethene. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Question 3(b)

Draw the structures of isomers of butene and write their IUPAC names.

Answer

Butene has three isomers:

But−1−ene — CH3-CH2-CH=CH2

Structural formula for 1-butene. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

But−2−ene — CH3-CH=CH-CH3

Structural formula for 2-butene. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

2-methyl-prop-1-ene — CH2=C(CH3)-CH3

Draw the branched structural formula of 2-methyl-prop-1-ene. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Question 4

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

Answer

C2H5OH ethyl alcohol170°CConc. H2SO4[excess]C2H4ethylene+H2\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethylene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\

The gas is collected by downward displacement of water.

Question 5

How is ethene prepared by:

(a) dehydrohalogenation reaction?

(b) dehydration reaction?

Give equations and name the products formed.

Answer

(a) Dehydrohalogenation involves elimination of hydrogen halide.

C2H5Br Bromo ethane [ethyl bromide]+KOHalcoholic, hot and conc.C2H4ethene [ethylene]+KBr Potassium bromide+H2O\underset{\text{ Bromo ethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{alcoholic, hot and conc.}}{\text{KOH}} \longrightarrow \underset{\text{ethene [ethylene]}}{\text{C}_2\text{H}_4} + \underset{\text{ Potassium bromide}}{\text{KBr}} + \text{H}_2\text{O}

The products formed are ethene, potassium bromide and water.

(b) Dehydration involves elimination of elements of water from alcohol. Conc. sulphuric acid act as dehydrating agent.

C2H5OH ethyl alcohol170°CConc. H2SO4[excess]C2H4ethene+H2\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\

The products formed are ethene and water.

Question 6

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

(b) Give the conditions and the main product formed by hydrogenation of ethene.

Answer

(a)

C2H4 ethene+Cl2[inert solvent]CCl4C2H4Cl21,2, dichloroethane [ethylene chloride]\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Cl}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dichloroethane [ethylene chloride]}}{\text{C}_2\text{H}_4\text{Cl}_2}

Product formed is 1,2, dichloroethane [ethylene chloride]

C2H4 ethene+Br2[inert solvent]CCl4C2H4Br21,2, dibromooethane [ethylene bromide]\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Br}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dibromooethane [ethylene bromide]}}{\text{C}_2\text{H}_4\text{Br}_2}

Product formed is 1,2, dibromooethane [ethylene bromide]

(b) Conditions for hydrogenation of ethene : finely divided catalyst, such as platinum or palladium at ordinary temperature or nickel at 200°C. Main product formed is ethane.

C2H4 ethene+H2200°CNickleC2H6ethane\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow[200\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}

Question 7

Convert ethanol into ethene using:

(a) solid dehydrating agent

(b) hot conc. H2SO4?

Give only balanced equations.

Answer

(a) Using Al2O3 as dehydrating agent.

C2H5OH ethyl alcohol350°CAl2O3C2H4ethene+H2\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[350\degree\text{C}]{\text{Al}_2\text{O}_3} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\

(b) Using hot conc. H2SO4

C2H5OH ethyl alcohol170°CConc. H2SO4[excess]C2H4ethene+H2\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\

Question 8

Write the following properties of ethene:

(a) Physical state

(b) Odour

(c) Density as compared to air

(d) Solubility

Answer

(a) Colourless and inflammable gas.

(b) Faint sweetish odour.

(c) Slightly less dense than air.

(d) Sparingly soluble in water but highly soluble in organic solvents like alcohol, ether and chloroform.

Question 9

How would you convert:

(a) ethyl bromide into ethene

(b) ethene into 1,2-dibromoethane

(c) ethene into ethane

Answer

(a) ethyl bromide into ethene : Dehydrohalogenation

C2H5Br Bromo ethane [ethyl bromide]+KOHalcoholic, hot and conc.C2H4ethene [ethylene]+KBr+H2O\underset{\text{ Bromo ethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{alcoholic, hot and conc.}}{\text{KOH}} \longrightarrow \underset{\text{ethene [ethylene]}}{\text{C}_2\text{H}_4} + \text{KBr} + \text{H}_2\text{O}

(b) ethene into 1,2-dibromoethane : Halogenation

C2H4 ethene+Br2[inert solvent]CCl4C2H4Br21,2, dibromooethane [ethylene bromide]\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Br}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dibromooethane [ethylene bromide]}}{\text{C}_2\text{H}_4\text{Br}_2}

(c) ethene into ethane : Hydrogenation

H2C=CH2 ethene [ethylene]+H2200°CNickleC2H6ethane\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{H}_2 \xrightarrow[200\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}

Question 10

Give balanced equations when:

(a) ethene is burnt in excess of oxygen.

(b) ethene reacts with chlorine gas.

(c) ethene combines with hydrogen chloride.

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

Answer

(a) ethene is burnt in excess of oxygen.

C2H4 + 3O2 ⟶ 2CO2 + 2H2O + heat

(b) ethene reacts with chlorine gas.

C2H4 ethene+Cl2[inert solvent]CCl4C2H4Cl21,2, dichloroethane [ethylene chloride]\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Cl}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dichloroethane [ethylene chloride]}}{\text{C}_2\text{H}_4\text{Cl}_2}

(c) ethene combines with hydrogen chloride.

H2C=CH2 ethene [ethylene]+HCl (aq.)CH3CH2Clchloroethane\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{HCl (aq.)}\longrightarrow \underset{\text{chloroethane}}{\text{CH}_3\text{CH}_2\text{Cl}}

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

H2C=CH2 ethene [ethylene]+H2200°CNickleC2H6ethane\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{H}_2 \xrightarrow[200\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}

Question 11

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

(a)

CH4-HClCl2A-HClCl2B-HClCl2C-HClCl2D\text{CH}_4 \xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{A} \xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{B}\xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{C}\xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{D}

(b)
C2H2H2AH2B-HBrBr2C-HBrBr2D\text{C}_2\text{H}_2 \xrightarrow{\text{H}_2} \text{A} \xrightarrow{\text{H}_2} \text{B}\xrightarrow[\text{-HBr}]{\text{Br}_2} \text{C}\xrightarrow[\text{-HBr}]{\text{Br}_2} \text{D}

(c)
C2H4+BNickle200°CC2H6\text{C}_2\text{H}_4 + \text{B} \xrightarrow[\text{Nickle}]{200\degree\text{C}} \text{C}_2\text{H}_6

Answer

(a) A — CH3Cl (Chloro methane)

B — CH2Cl2 (Di-chloromethane)

C — CHCl3 (Tri-chloro methane)

D — CCl4 (Carbon tetrachloride)

CH4-HClCl2CH3Cl-HClCl2CH2Cl2-HClCl2CHCl3-HClCl2CCl4\text{CH}_4 \xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{CH}_3\text{Cl} \xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{CH}_2\text{Cl}_2\xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{CH}\text{Cl}_3\xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{CCl}_4

(b) A — C2H4 (ethene)

B — C2H6 (ethane)

C — C2H5Br (bromo-ethane)

D — C2H4Br2 (1,2-Di-bromoethane)

C2H2H2C2H4H2C2H6-HBrBr2C2H5Br-HBrBr2C2H4Br2\text{C}_2\text{H}_2 \xrightarrow{\text{H}_2} \text{C}_2\text{H}_4 \xrightarrow{\text{H}_2} \text{C}_2\text{H}_6 \xrightarrow[\text{-HBr}]{\text{Br}_2} \text{C}_2\text{H}_5\text{Br}\xrightarrow[\text{-HBr}]{\text{Br}_2} \text{C}_2\text{H}_4\text{Br}_2

(c) B — H2 (Hydrogen)

C2H4+H2Nickle200°CC2H6\text{C}_2\text{H}_4 + \text{H}_2 \xrightarrow[\text{Nickle}]{200\degree\text{C}} \text{C}_2\text{H}_6

Question 12

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

(a) C2H4 + Cl2 ⟶ ...............

(b) C2H5I + KOH (alc.) Δ\xrightarrow{\Delta} ...............

(c) H2C=CH2 alc. KMnO4\xrightarrow{\text{alc. KMnO}_4} ...............

(d) H2C=CH2 + HBr ⟶...............

Answer

(a) C2H4 + Cl2Cl-CH2-CH2-Cl

Product formed is 1,2-dichloroethane[Cl-CH2-CH2-Cl]

(b) C2H5I + KOH (alc.) Δ\xrightarrow{\Delta} C2H4 + KI + H2O

Product formed is ethene [C2H4], KI and water

(c) H2C=CH2 alk. KMnO4\xrightarrow{\text{alk. KMnO}_4} CH2(OH)-CH2(OH)

Product formed is 1,2-Ethane-diol [CH2(OH)-CH2(OH)]

(d) H2C=CH2 + HBr ⟶ C2H5Br

Product formed is Bromoethane [C2H5Br]

Question 13

What do you observe when ethene is passed through alkaline KMnO4 solution?

Answer

Ethene is oxidised with alkaline KMnO4 at room temperature, the purple colour of KMnO4 decolourises.

H2C=CH2 ethene [ethylene]+H-O-H+[O] cold alkalineOH-CH2CH2OH1,2-Ethane-diol\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \underset{\text{ cold alkaline}}{\text{H-O-H} + \text{[O]}} \longrightarrow \underset{\text{1,2-Ethane-diol}}{\text{OH-CH}_2-\text{CH}_2\text{OH}}

Question 14

Name three compounds formed by ethene and give one use of each compound.

Answer

  1. Polythene — carry bags are made.
  2. Ethanol — cosmetics and toiletries preparation.
  3. Oxy-ethylene torch — used for cutting and welding of metals.

Exercise 12D

Question 1

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

Answer

Natural gas and petroleum are the sources of alkynes. The general formula of alkynes is : CnH2n-2

Question 2

Give an example of isomers shown by triple bond hydrocarbons (alkynes) and write their IUPAC names.

Answer

Isomers of Butyne exhibit position isomerism:

IUPAC name : but-1-yne

but-1-yne isomer of Butyne exhibits position isomerism. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

IUPAC name : but-2-yne

but-2-yne isomer of Butyne exhibits position isomerism. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Question 3

How is ethyne prepared in the laboratory?

(a) Draw a diagram

(b) Give an equation

(c) How is pure dry gas collected?

Answer

(a) Below diagram shows the setup for laboratory preparation of ethyne:

How is ethyne prepared in the laboratory? (a) Draw a diagram (b) Give an equation (c) How is pure dry gas collected? Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(b) Ethyne [C2H2] from Calcium Carbide :

CaC2calcium carbide+2H2OwaterC2H2ethyne+Ca(OH)2calcium hydroxide\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne}}{\text{C}_2\text{H}_2} + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}

(b) As the pure dry gas is insoluble in water, it is collected by downward displacement of water.

Question 4

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

Answer

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

C2H4Br2 ethylene dibromide+2KOHalcoholicboiling200°CC2H2ethyne+2KBr+2H2O\underset{\text{ ethylene dibromide}}{\text{C}_2\text{H}_4\text{Br}_2} + \underset{\text{alcoholic}}{\text{2KOH}} \xrightarrow[\text{boiling}]{\text{200}\degree \text{C}} \underset{\text{ethyne}}{\text{C}_2\text{H}_2} + 2\text{KBr} + 2\text{H}_2\text{O}

Question 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 ethyne (acetylene) gas when treated with water.

Answer

(a) Methane

(b) Ethene

(c) Ethyne

(d) Ethyne

(e) Alkanes

(f) Alkenes

(g) Calcium carbide

Question 6

Classify the following compounds as alkanes, alkenes and alkynes: C3H4, C3H8, C5H8, C3H6

Answer

  • Alkanes — C3H8
  • Alkenes — C3H6
  • Alkynes — C3H4, C5H8

Question 7

Give a chemical test to distinguish between

(a) saturated and unsaturated compounds

(b) ethane and ethene

(c) ethene (ethylene) and ethyne (acetylene)

Answer

(a) On adding few drops of alkaline potassium permanganate (purple colour) to the hydrocarbons, no change is seen in saturated hydrocarbons whereas the purple colour fades in case of unsaturated hydrocarbons.

(b) When bromine is passed through solutions of ethane and ethene in an inert solvent [CCl4] at room temperature, incase of ethene gas, brown colour of bromine is discharged whereas in case of ethane gas no change in the colour is observed.

(c) On adding ammoniacal silver nitrate, no change is seen in ethene whereas white ppt. of silver acetylide is formed in case of ethyne.

Question 8

Compound X is bubbled through bromine dissolved in CCl4;

Compound X is bubbled through bromine dissolved in CCl4. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(a) Draw the structure of X.

(b) State your observation during the reaction.

Answer

(a) Compound 'X' is Ethene (H2C=CH2). Its structural formula is shown below:

Compound X is bubbled through bromine dissolved in CCl<sub>4</sub> and the product formed is CH2Br – CH2Br. Draw the structural formula of X and state what type of reaction X has undergone. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

(b) Brown colour of bromine is discharged.

Question 9

Give balanced equations for the following conversions:

(a) An alkene to an alkane

(b) An alkene to an alcohol

(c) An alkyne to an alkene.

Answer

(a) An alkene to an alkane

C2H4ethene+H2300°CNickleC2H6ethane\underset{\text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow[300\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}

(b) An alkene to an alcohol

C2H4 ethene+H2O300°C, 60 atm.H3PO4C2H5OHethene\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O} \xrightarrow[300\degree\text{C, 60 atm.}]{\text{H}_3\text{PO}_4} \underset{\text{ethene}}{\text{C}_2\text{H}_5\text{OH}}

(c) An alkyne to an alkene.

H2C2 ethyne [acetylene]+H2300°CNickleC2H4ethene\underset{\text{ ethyne [acetylene]}}{\text{H}_2\text{C}_2} + \text{H}_2 \xrightarrow[300\degree\text{C}]{\text{Nickle}} \underset{\text{ethene}}{\text{C}_2\text{H}_4}

Question 10

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.

Answer

1,2-dichloro ethene and 1,1,2,2 -tetrachloro ethane will be formed.

C2H2 + Cl2 ⟶ C2H2Cl2 + Cl2 ⟶ C2H2Cl4

(b) Bromine

1,2-dibromo ethene and 1,1,2,2 -tetrabromo ethane will be formed.

C2H2 + Br2 ⟶ C2H2Br2 + Br2 ⟶ C2H2Br4

(c) Iodine

1,2-di-iodoethene will be formed.

C2H2 + I2 ⟶ ICH=CHI

(d) Hydrogen

Ethene and then ethane will be formed.

C2H2 Ethyne+H2NickleC2H4ethene+H2NickleC2H6ethane\underset{\text{ Ethyne}}{\text{C}_2\text{H}_2} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}

(e) Excess of hydrochloric acid.

Chloro ethene and then 1,1-dichloro ethane will be formed.

C2H2 Ethyne+ HClC2H3Clchloro ethene+ HClC2H4Cl21,1-dichloro ethane\underset{\text{ Ethyne}}{\text{C}_2\text{H}_2} \xrightarrow{\text{+ HCl}} \underset{\text{chloro ethene}}{\text{C}_2\text{H}_3\text{Cl}} \xrightarrow{\text{+ HCl}} \underset{\text{1,1-dichloro ethane}}{\text{C}_2\text{H}_4\text{Cl}_2}

Question 11

Substitution reactions are characteristic reactions of ............... (alkynes/alkenes/alkanes).

Answer

Substitution reactions are characteristic reactions of alkanes.

Question 12

(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 ethyne is bubbled through a solution of bromine in carbon tetrachloride?

(c) Name the addition product formed between ethene and water.

Answer

(a) (i) Ethyne [C2H2] from Calcium Carbide :

CaC2calcium carbide+2H2OwaterC2H2ethyne+Ca(OH)2calcium hydroxide\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne}}{\text{C}_2\text{H}_2} ↑ + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}

(ii) An alcohol from ethyl bromide.

C2H5-Br Bromoethane [ethyl bromide]+KOH [aq.]boilC2H5OH ethyl alcohol+KBr\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \text{KOH [aq.]} \xrightarrow{\text{boil}} \underset{ \text{ ethyl alcohol}} {\text{C}_2\text{H}_5\text{OH}} + \text{KBr}

(b) Brown colour of bromine disappears when ethyne is bubbled through a solution of bromine in carbon tetrachloride.

C2H2 + Br2 ⟶ C2H2Br2 + Br2 ⟶ C2H2Br4

(c) Ethanol (C2H5OH)

C2H4 + H2O ⟶ C2H5OH

Question 13

Give reasons:

(a) Ethyne is more reactive than ethene.

(b) Ethene is more reactive than ethane.

(c) Hydrocarbons are excellent fuels.

Answer

(a) The two carbon atoms of ethyne form a triple covalent bond whereas that of ethene form a double covalent bond. Hence, there are more electrons available in case of ethyne making it more reactive than ethene.

(b) Ethene is an unsaturated hydrocarbon having two carbon atoms forming a double covalent bond as their valencies are not fully satisfied by hydrogen atoms whereas ethane is a saturated hydrocarbon as all the four valencies of its two carbon atoms are satisfied by the hydrogen atoms. The availability of electrons in the double bond in case of ethene makes it more reactive than ethane which has does not have electrons available in the single covalent bond.

(c) Hydrocarbons have high calorific value. They are easily combustible and the reaction is exothermic releasing heat energy. Hence, they are excellent fuels.

Question 14

(a) Write the 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 ethyne to ethane.

Answer

(i) C4H10 + 6O2 ⟶ 4CO2 + 5H2O

(ii)

C2H5OH ethyl alcohol170°CConc. H2SO4[excess]C2H4ethylene+H2\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethylene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\

(b) (i) Convert ethane to acetic acid

2C2H6 ethane+O2120 atm.Cu tube 475 K2C2H5OHethyl alcohol\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}

C2H5OHethyl alcohol+O2Pt. 300°CCH3COOH+H2Oacetic acid\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{O}_2 \xrightarrow{\text{Pt. 300}\degree\text{C}} \underset{\text{acetic acid}}{\text{CH}_3\text{COOH} + \text{H}_2\text{O}}

(ii) Convert ethyne to ethane.

C2H2 Ethyne+H2NickleC2H4ethene+H2NickleC2H6ethane\underset{\text{ Ethyne}}{\text{C}_2\text{H}_2} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}

Question 15

(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?

Answer

(a) Carbon tetrachloride from methane

CH4 methane+Cl2or 600Kdiffused sunlightCH3Cl+HCl\underset{\text{ methane} }{\text{CH}_4} + \text{Cl}_2 \xrightarrow[\text{or 600K}]{\text{diffused sunlight}} \text{CH}_3\text{Cl} + \text{HCl}

CH3Cl chloromethane+Cl2CH2Cl2dichloromethane+HCl\underset{\text{ chloromethane} }{\text{CH}_3\text{Cl}} + \text{Cl}_2 \longrightarrow \underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2}+ \text{HCl}

CH2Cl2dichloromethane+Cl2CHCl3trichloromethane+HCl\underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2} + \text{Cl}_2 \longrightarrow \underset{\text{trichloromethane}}{\text{CH}\text{Cl}_3}+ \text{HCl}

CHCl3trichloromethane+Cl2CCl4tetrachloromethane+HCl\underset{\text{trichloromethane}}{\text{CHCl}_3} + \text{Cl}_2 \longrightarrow \underset{\text{tetrachloromethane}}{\text{CCl}_4}+ \text{HCl}

(b) Structural formula of ethyne is shown below:

(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? Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(c) Alkynes contain triple bonds while alkenes contain double bonds.

Exercise 12E

Question 1

(a) What are alcohols? State their sources.

(b) Give general formulae of monohydric alcohol.

Answer

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

Alcohols are not found naturally in the earth's atmosphere, they are obtained by artificial synthesis in the laboratory.

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

(b) CnH2n+1OH

Question 2

Give the:

(a) dot diagram of first member of alcohol.

(b) abbreviated formula of third member of alcohol.

(c) structure of second member of the alcohol group.

(d) structure of alcohol with 4 carbon atoms.

Answer

(a) Methyl alcohol (CH3OH) is the first member of alcohol. Its electron dot structure is shown below:

Give the: (a) dot diagram of first member of alcohol. (b) abbreviated formula of third member of alcohol. (c) structure of second member of the alcohol group. (d) structure of alcohol with 4 carbon atoms. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(b) Propyl alcohol : CH3-CH2-CH2-OH

(c) Ethyl alcohol : CH3-CH2-OH

Give the: (a) dot diagram of first member of alcohol. (b) abbreviated formula of third member of alcohol. (c) structure of second member of the alcohol group. (d) structure of alcohol with 4 carbon atoms. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

(d) Butyl alcohol : CH3-CH2-CH2-CH2-OH

Give the: (a) dot diagram of first member of alcohol. (b) abbreviated formula of third member of alcohol. (c) structure of second member of the alcohol group. (d) structure of alcohol with 4 carbon atoms. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Question 3

State the method of preparation of ethanol:

(a) by hydrolysis of ethene.

(b) by hydrolysis of ethyl bromide.

Answer

(a) Hydrolysis of ethene — Ethanol is produced when ethene is heated with water at 300°C and 60 atmosphere pressure in presence of phosphoric acid (catalyst).

C2H4 ethene+H2O300°C, 60 atm.H3PO4C2H5OHethanol\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O} \xrightarrow[300\degree\text{C, 60 atm.}]{\text{H}_3\text{PO}_4} \underset{\text{ethanol}}{\text{C}_2\text{H}_5\text{OH}}

(b) Hydrolysis of ethyl bromide — Ethanol can be prepared by boiling aq. NaOH with ethyl bromide.

C2H5-Br Bromoethane [ethyl bromide]+NaOH aqueousboilC2H5OHethanol+NaBr\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \underset{\text{ aqueous}}{\text{NaOH}} \xrightarrow{\text{boil}} \underset{ \text{ethanol}} {\text{C}_2\text{H}_5\text{OH}} + \text{NaBr}

Question 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.

Answer

Ethyl alcohol can be prepared by hydrolysis of haloalkane on reaction with hot and dilute alkali or when an alkyl halide is boiled with aqueous alkalis.

C2H5-Br Bromoethane [ethyl bromide]+NaOHaqueousboilC2H5OH ethyl alcohol+NaBr\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \underset{\text{aqueous}}{\text{NaOH}} \xrightarrow{\text{boil}} \underset{ \text{ ethyl alcohol}} {\text{C}_2\text{H}_5\text{OH}} + \text{NaBr}

Question 5

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

(b) Name the product formed when ethanol reacts with acetic acid. Give an equation.

(c) What is the name given to this type of reaction?

Answer

(a) The boiling point and melting point increase with increasing molecular weight in the homologous series of alcohols.

(b) Ethyl acetate is generated when ethanol combines with acetic acid.

C2H5OHethanol+CH3COOHacetic acidΔConc. H2SO4CH3COOC2H5ethyl acetate+H2O\underset{\text{ethanol}}{\text{C}_2\text{H}_5\text{OH}} + \underset{\text{acetic acid}}{\text{CH}_3\text{COOH}} \xrightarrow[\Delta]{\text{Conc. H}_2\text{SO}_4} \underset{\text{ethyl acetate}}{\text{CH}_3-\text{COO}-\text{C}_2\text{H}_5} + \text{H}_2\text{O}

(c) Esterification.

Question 6

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

(a) H-C≡C-H + H2 ⟶ ............... + H2 ⟶ ...............

(b) C2H4 + Br2 ⟶ ...............

(c) C2H4 + HCl ⟶ ...............

(d) CaC2+ H2O ⟶ ...............

(e) C2H2 + Br2 ⟶ ...............

(f) C2H5OH K2Cr2O7[O]\xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} ...............

Answer

(a) H-C≡C-H + H2H2C=CH2 + H2H3C-CH3

(b) C2H4 + Br2Br-CH2-CH2-Br

(c) C2H4 + HCl ⟶ CH3CH2Cl

(d) CaC2 + 2H2O ⟶ C2H2 + Ca(OH)2

(e) C2H2 + Br2 ⟶ C2H2Br2

(f) C2H5OH K2Cr2O7[O]\xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} CH3CHO

Question 7

What is the effect of ethanol on human body?

Answer

Ethanol affects the part of the brain which controls our muscular movements. It gives temporary relief from tiredness, but it damages the liver and kidney too in excess quantities.

Question 8

How are the following obtained:

(a) absolute alcohol

(b) spurious alcohol

(c) methylated spirit

Answer

(a) Absolute alcohol — By distilling wet alcohol with benzene, absolute alcohol can be obtained. The mixture of water and benzene distils off, leaving behind anhydrous alcohol.

(b) Spurious alcohol — It is illicit liquor made by improper distillation. It contains large proportions of methanol in a mixture of alcohols.

It's a blend of alcohol with a lot of methanol in it. It is fatal for human consumption.

(c) Methylated spirit — Ethyl alcohol is mixed 5% methyl alcohol, a coloured dye, and some pyridine to obtain methylated spirit.

Question 9

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

(a) Sodium reacting with ethyl alcohol.

(b) Ethanol oxidised by acidified potassium dichromate.

Answer

(a) When sodium reacts with ethyl alcohol, hydrogen is produced, and sodium ethoxide is formed.

C2H5OH + 2Na ⟶ 2C2H5ONa + H2

(b) Ethanol is oxidised and transformed to ethanal, which is then turned to acetic acid.

C2H5OHethanolK2Cr2O7[O]CH3CHOethanalK2Cr2O7[O]CH3COOHethanoic acid\underset{ \text{ethanol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal}}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanoic acid}}{\text{CH}_3\text{COOH}}

Question 10

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

(a) C3H6

(b) C2H4

(c) C2H2

(d) CH3OH

(e) C2H5OH

Answer

S. No.FormulaCommon nameIUPAC name
a)C3H6PropylenePropene
b)C2H4EthyleneEthene
c)C2H2AcetyleneEthyne
d)CH3OHMethyl alcoholMethanol
e)C2H5OHEthyl alcoholEthanol

Question 11

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

Answer

Ethanol under high pressure and low temperature when treated with oxidising agent like acidified potassium dichromate produces ethanoic acid

C2H5OH ethanol[ethyl alcohol]K2Cr2O7[O]CH3CHOethanal [acetaldehyde] K2Cr2O7[O]CH3COOHethanoic acid[acetic acid]\underset{ \text{ ethanol[ethyl alcohol]}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{ \text{ethanoic acid[acetic acid]} }{\text{CH}_3\text{COOH}}

Question 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 gums and resins.

(h) dehydrated to produced ethene.

Answer

(a) Ethyne

(b) Ethyne

(c) Methanol

(d) Methanol

(e) Ethanol

(f) Methanol

(g) Ethanol

(h) Ethanol

Question 13

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 ............... (conc. HCl, conc. HNO3, conc. H2SO4).

(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).

Answer

(a) The conversion of ethanol into ethene is an example of dehydration

(b) Converting ethanol into ethene requires the use of conc. H2SO4

(c) The conversion of ethene into ethane is an example of hydrogenation

(d) The catalyst used in the conversion of ethene into ethane is commonly nickel

Question 14

Write the equations for the following lab. preparations:

(a) Ethane from sodium propionate.

(b) Ethene from iodoethane.

(c) Ethyne from calcium carbide.

(d) Methanol from iodomethane.

Answer

(a) Ethane [C2H6] from sodium propionate:

C2H5COONasodium propionate+NaOHsodalime300°CCaOC2H6ethane+Na2CO3\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} + \text{Na}_2\text{CO}_3

(b) Ethene from iodoethane:

C2H5I iodoethane+KOHalcoholicboilH2C=CH2ethene [ethylene]+KI+H2O\underset{\text{ iodoethane}}{\text{C}_2\text{H}_5\text{I}} + \underset{\text{alcoholic}}{\text{KOH}} \xrightarrow{\text{boil}} \underset{\text{ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{KI} + \text{H}_2\text{O}

(c) Ethyne from calcium carbide:

CaC2calcium carbide+2H2OwaterC2H2ethyne [acetylene]+Ca(OH)2\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \text{Ca(OH)}_2

(d) Methanol from idomethane.

CH3I+NaOHCH3OH+NaI\text{CH}_3\text{I} + \text{NaOH} \longrightarrow \text{CH}_3\text{OH} + \text{NaI}

Question 15

Name the compound prepared by each of the following reactions:

(i) C2H5COONa + NaOH ⟶

(ii) CH3I + 2H ⟶

(iii) C2H5Br + KOH (alcoholic solution)⟶

(iv) CO + 2H2 (Zinc oxide catalyst) ⟶

(v) CaC2 + 2H2O ⟶

Answer

(i) Ethane

C2H5COONasodium propionate+NaOHsodalime300°CCaOC2H6ethane+Na2CO3\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} + \text{Na}_2\text{CO}_3

(ii) Methane

CH3Imethyl iodide+2[H]nascent hydrogenalcoholZn/Cu coupleCH4methane+HI\underset{\text{methyl iodide}}{\text{CH}_3\text{I}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{methane}}{\text{CH}_4} +\text{HI}

(iii) Ethene [ethylene]

C2H5Br Bromo ethane [ethyl bromide]+KOHalcoholicboilH2C=CH2ethene [ethylene]+KBr+H2O\underset{\text{ Bromo ethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{alcoholic}}{\text{KOH}} \xrightarrow{\text{boil}} \underset{\text{ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{KBr} + \text{H}_2\text{O}

(iv) Methanol

CO+2H2catalystZinc oxideCH3OH\text{CO} + 2\text{H}_2 \xrightarrow[\text{catalyst}]{\text{Zinc oxide}} \text{CH}_3\text{OH}

(v) Ethyne [Acetylene]

CaC2calcium carbide+2H2OwaterC2H2ethyne [acetylene]+Ca(OH)2calcium hydroxide\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}

Question 16

Write the equations for the following reactions:

(a) Calcium carbide and water.

(b) Ethene and water (steam).

(c) Bromoethane and an aqueous solution of sodium hydroxide.

Answer

(a) Water is added to calcium carbide:

CaC2calcium carbide+2H2OwaterC2H2ethyne [acetylene]+Ca(OH)2calcium hydroxide\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}

(b) Ethene and water (steam).

C2H4 ethene+H2O300°C, 60 atm.H3PO4C2H5OHethene\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O} \xrightarrow[300\degree\text{C, 60 atm.}]{\text{H}_3\text{PO}_4} \underset{\text{ethene}}{\text{C}_2\text{H}_5\text{OH}}

(c) Bromoethane and an aqueous solution of sodium hydroxide.

C2H5-Br Bromoethane [ethyl bromide]+NaOH aqueousboilC2H5OHethanol+NaBr\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \underset{\text{ aqueous}}{\text{NaOH}} \xrightarrow{\text{boil}} \underset{ \text{ethanol}} {\text{C}_2\text{H}_5\text{OH}} + \text{NaBr}

Exercise 12F

Question 1

What are carboxylic acids? Give their general formula

Answer

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

General formula : CnH2n+1COOH (or RCOOH)

Question 2

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.

Answer

(a) First three members of carboxylic acid series are:

  1. Methanoic acid (formic acid)
  2. Ethanoic acid (acetic acid)
  3. propanoic acid (propionic acid)

(b) Three compounds which can be oxidised directly, or in stages to produce acetic acid are:

  1. Ethanol
  2. Acetylene
  3. Ethanal

Question 3

(a) Give the structural formulae of acetic acid.

(b) IUPAC name of acetic acid.

(c) What is glacial acetic acid?

Answer

(a) Structural formula of acetic acid is shown below:

Write structural formula of acetic acid. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10.

(b) Ethanoic acid

(c) Acetic acid that contains a very low amount of water (less than 1%) is called anhydrous (water-free) acetic acid or glacial acetic acid. Its melting point is around 17°C. On cooling it forms a crystalline mass resembling ice and for this reason it is called glacial acetic acid.

Question 4

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

Answer

Dilute (4-5 percent) solution of ethanoic acid is also called vinegar. The presence of a colouring matter gives vinegar a greyish colour while the presence of other organic compounds imparts it the usual taste and flavour.

Question 5

Complete:

(a) Vinegar is prepared by the bacterial oxidation of ...............

(b) The organic acid present in vinegar is ...............

(c) The next higher homologue of ethanoic acid is ...............

Answer

(a) Vinegar is prepared by the bacterial oxidation of ethanol

(b) The organic acid present in vinegar is acetic acid

(c) The next higher homologue of ethanoic acid is propanoic acid

Question 6

How is acetic acid prepared from

(a) Ethanol

(b) Acetylene

Answer

(a) Ethanol under high pressure and low temperature when treated with oxidising agent like acidified potassium dichromate produces ethanoic acid (acetic acid).

C2H5OH ethanol[ethyl alcohol]K2Cr2O7[O]CH3CHOethanal [acetaldehyde] K2Cr2O7[O]CH3COOHethanoic acid[acetic acid]\underset{ \text{ ethanol[ethyl alcohol]}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{ \text{ethanoic acid[acetic acid]} }{\text{CH}_3\text{COOH}}

(b) Acetylene is first converted to acetaldehyde by passing it through a 40 percent H2SO4 solution at 60°C in the presence of 1% Mercury(II) Sulphate [HgSO4].

C2H2acetylene+H2OH2SO4(dil) , HgSO4CH3CHOethanal [acetaldehyde] \underset{\text{acetylene}}{\text{C}_2\text{H}_2} + \text{H}_2\text{O} \xrightarrow{\text{H}_2\text{SO}_4\text{(dil) , HgSO}_4}\underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}}

The acetaldehyde is oxidised to acetic acid by passsing a mixture of acetaldehyde vapous and air over manganese acetate at 70°C

2CH3CHOethanal [acetaldehyde] +O2CatalystΔ2CH3COOHethanoic acid[acetic acid]\underset{\text{ethanal [acetaldehyde] }}{2\text{CH}_3\text{CHO}} + \text{O}_2 \xrightarrow[\text{Catalyst}]{\Delta} \underset{ \text{ethanoic acid[acetic acid]} }{2\text{CH}_3\text{COOH}}

Question 7

What do you notice when acetic acid reacts with

(a) litmus

(b) metals

(c) alkalies

(d) alcohol

Answer

(a) Acetic acid turns moist blue litmus red.

(b) Hydrogen gas with a pop sound is evolved.

2CH3COOH + Zn ⟶ (CH3COO)2Zn + H2

(c) Reacts with alkalis to form salt and water.

CH3COOH + NaOH ⟶ CH3COONa + H2O

(d) Forms an ester (pleasant fruity smelling compound) on reacting with alcohol in the presence of dehydrating agents like concentrated sulphuric acid.

C2H5OHethyl alcohol+CH3COOHconc. H2SO4CH3COOC2H5ethyl acetate+H2O\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{CH}_3\text{COOH} \xrightarrow{\text{conc. H}_2\text{SO}_4} \underset{\text{ethyl acetate}}{{\text{CH}_3\text{COOC}_2\text{H}_5}} + \text{H}_2\text{O}

Question 8

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

(a) a metal

(b) a base/alkali

(c) a carbonate

(d) a bicarbonate

Answer

(a) a metal

2CH3COOH + Zn ⟶ (CH3COO)2Zn + H2

(b) a base/alkali

CH3COOH + NaOH ⟶ CH3COONa + H2O

(c) a carbonate

2CH3COOH + Na2CO3 ⟶ 2CH3COONa + H2O + CO2

(d) a bicarbonate

CH3COOH + NaHCO3 ⟶ CH3COONa + H2O + CO2

Question 9

What do you observe when acetic acid is added to

(a) sodium bicarbonate

(b) ethyl alcohol in the presence of sulphuric acid.

(c) neutral FeCl3 solution?

Answer

(a) Carbon dioxide is produced when acetic acid is added to sodium bicarbonate.

(b) When warmed with ethyl alcohol in the presence of sulphuric acid, a pleasant fruity smell of ethyl acetate is produced.

(c) On adding acetic acid to neutral FeCl3 solution, wine red colour is produced.

Question 10

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.

Answer

(a) Ethyl acetate

(b) Lithium aluminium hydride (LiAlH4)

(c) Phosphorus pentoxide (P2O5)

Miscellaneous

Question 1(a)

(a) Which of the following statements is wrong about alkanes?

  1. They are all saturated hydrocarbon.
  2. They can undergo addition as well as substitution reaction.
  3. They are almost non polar in nature.
  4. On complete combustion give out carbon dioxide and water.

Answer

They can undergo addition as well as substitution reaction.

Reason — The non-availability of electrons in the single covalent bond makes them less reactive and therefore undergo characteristic substitution reaction only.

Question 1(b)

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

  1. Methanol
  2. Ethanol
  3. Ethane
  4. Methanoic acid

Answer

Ethanol

Reason

C12H22O11cane sugar [molasses]+H2O[yeast]invertase C6H12O6glucose+C6H12O6fructose\underset{\text{cane sugar [molasses]}}{\text{C}_{12}\text{H}_{22}\text{O}_{11}} + \text{H}_2\text{O} \xrightarrow[\text{[yeast]}]{\text{invertase }} \underset{\text{glucose}}{{\text{C}_6\text{H}_{12}\text{O}_6}} + \underset{\text{fructose}}{{\text{C}_6\text{H}_{12}\text{O}_6}}

C6H12O6glucosefermentationzymase [yeast]2C2H5OHethanol+2CO2\underset{\text{glucose}}{{\text{C}_6\text{H}_{12}\text{O}_6}} \xrightarrow[\text{fermentation}]{\text{zymase [yeast]}} \underset{\text{ethanol}}{{2\text{C}_2\text{H}_{5}\text{OH}}} + 2\text{CO}_2

Question 1(c)

Find the odd one out and explain:

C3H8, C5H10, C2H6, CH4

Answer

C5H10

Reason — As it is not following the general alkane formula (CnH2n+2). It is an alkene with general formula CnH2n.

Question 2

Give chemical equation for:

(a) The laboratory preparation of methane from sodium acetate.

(b) The reaction of one mole of ethene with one mole of chlorine gas.

(c) The preparation of ethyne from 1,2-dibromoethane.

Answer

(a) Methane from sodium acetate :

CH3COONasodium acetate+NaOHsodalimeCaOΔCH4methane+Na2CO3\underset{\text{sodium acetate}}{\text{CH}_3\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \underset{\Delta}{\xrightarrow{\text{CaO}}} \underset{\text{methane}}{\text{CH}_4} + \text{Na}_2\text{CO}_3

(b) one mole of ethene with one mole of chlorine gas:

Give chemical equation for the reaction of one mole of ethene with one mole of chlorine gas. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

(c) ethyne from 1, 2 – dibromoethane.

Give chemical equation for the preparation of ethyne from 1, 2 – dibromoethane. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Question 3

State how the following conversions can be carried out:

(a) Ethyl chloride to ethyl alcohol

(b) Ethyl chloride to ethene

(c) Ethene to ethyl alcohol

(d) Ethyl alcohol to ethene

Answer

(a) By boiling ethyl chloride with aqueous NaOH.

C2H5-Cl Chloroethane [ethyl chloride]+NaOH [aq.]boilC2H5OH Ethanol [ethyl alcohol]+NaCl\underset{\text{ Chloroethane [ethyl chloride]}}{\text{C}_2\text{H}_5\text{-Cl}} + \text{NaOH [aq.]} \xrightarrow{\text{boil}} \underset{\text{ Ethanol [ethyl alcohol]}}{\text{C}_2\text{H}_5\text{OH}} + \text{NaCl}

(b) By boiling ethyl chloride with alcoholic KOH.

C2H5-Cl Chloroethane [ethyl chloride]+KOH [aq.] alcoholic KOHboilC2H4 Ethene [ethylene]+KCl+H2O\underset{\text{ Chloroethane [ethyl chloride]}}{\text{C}_2\text{H}_5\text{-Cl}} + \underset{\text{ alcoholic KOH}}{\text{KOH [aq.]}} \xrightarrow{\text{boil}} \underset{\text{ Ethene [ethylene]} }{\text{C}_2\text{H}_4} + \text{KCl} +\text{H}_2\text{O}

(c) Ethene is absorbed in conc. sulphuric acid at 80 °C under 30 atmos. to give ethyl hydrogen sulphate, which on hydrolysis with steam gives ethanol.

C2H4 Ethene+H2SO4conc.80°C30 atmos.C2H5-HSO4 Ethyl hydrogen sulphate\underset{\text{ Ethene} }{\text{C}_2\text{H}_4} + \underset{\text{conc.}}{\text{H}_2\text{SO}_4} \underset{30 \text{ atmos.}}{\xrightarrow{80 \degree \text{C}}} \underset{\text{ Ethyl hydrogen sulphate} }{\text{C}_2\text{H}_5\text{-HSO}_4}

C2H5-HSO4 Ethyl hydrogen sulphate +H2OsteamC2H5-OH Ethanol [ethyl alcohol]+H2SO4\underset{\text{ Ethyl hydrogen sulphate }}{\text{C}_2\text{H}_5\text{-HSO}_4} + \underset{\text{steam}}{\text{H}_2\text{O}} \longrightarrow \underset{ \text{ Ethanol [ethyl alcohol]} }{\text{C}_2\text{H}_5\text{-OH}} + \text{H}_2\text{SO}_4

(d) By heating ethyl alcohol with concentrated H2SO4 at 170°C.

C2H5OH ethyl alcohol170°CConc. H2SO4[excess]C2H4ethene+H2\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\

Question 4

(a) Define isomerism

(b) Give the IUPAC name of the isomer C4H10 which has a branched chain.

Answer

(a) Isomerism is the phenomenon due to which two or more compounds have the same molecular formula but differ in molecular arrangement or in structural formula.

Example : Isomers of pentane are (i) n pentane, (ii) isopentane and (iii) neo-pentane

(b) IUPAC name of C4H10 is Butane.

Question 5

A compound X when treated with an organic acid Y (having vinegar like smell) in the presence of the acid Z, forms a compound P which has a fruity smell.

(a) Identify X, Y and Z.

(b) Write structural formula of X and Y.

(c) What type of compound is P?

(d) Name the above reaction.

(e) If compound X and Y both have 2 carbon atoms. Write the reaction.

Answer

(a) X, Y and Z are:

   X → Ethyl alcohol
   Y → Acetic acid
   Z → Conc. Sulphuric acid

(b) The structural formulae are shown below:

Ethyl alcohol (X)

A compound X when treated with an organic acid Y (having vinegar like smell) in the presence of the acid Z, forms a compound P which has a fruity smell. (a) Identify X, Y and Z. (b) Write structural formula of X and Y. (c) What type of compound is P? (d) Name the above reaction.(e) If compound X and Y both have 2 carbon atoms. Write the reaction. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10

Acetic acid (Y)

A compound X when treated with an organic acid Y (having vinegar like smell) in the presence of the acid Z, forms a compound P which has a fruity smell. Identify X, Y and Z. Write structural formula of X and Y. What type of compound is P? Name the above reaction. If compound X and Y both have 2 carbon atoms. Write the reaction. Organic Chemistry, Concise Chemistry Solutions ICSE Class 10.

(c) Ester

(d) Esterification

(e) The reaction is given below:

C2H5OHethyl alcohol+CH3COOHacetic acidConc. H2SO4CH3COOC2H5ethyl ethanoate+H2O\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \underset{\text{acetic acid}}{\text{CH}_3\text{COOH}} \xrightarrow{\text{Conc. H}_2\text{SO}_4} \underset{\text{ethyl ethanoate}}{\text{CH}_3-\text{COO}-\text{C}_2\text{H}_5} + \text{H}_2\text{O}

Question 1a(2010)

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

  1. Ethane
  2. Ethene
  3. Ethyne
  4. Ethanol

Answer

Ethyne

Question 1b(2010)

An organic weak acid is :

  1. Formic acid
  2. Sulphuric acid
  3. Nitric acid
  4. Hydrochloric acid

Answer

Formic acid

Question 1c(2010)

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

  1. Methanol
  2. Methanoic acid
  3. Methanal
  4. Ethanoic acid

Answer

Methanol

Question 1d(2010)

Draw the structural formula for each of the following—

(i) Ethanoic acid

(ii) But-2-yne

Answer

(i) Structural formula of Ethanoic acid is shown below:

Draw the structural formula of Ethanoic acid. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

(ii) Structural formula of But-2-yne is shown below:

Draw the structural formula of But-2-yne. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Question 1e(2010)

Compound A is bubbled through bromine dissolved in carbon tetrachloride and the product formed is CH2Br–CH2Br.

(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 ?

Answer

(i) Compound A is Ethene (H2C=CH2). It's structural formula is shown below:

Compound X is bubbled through bromine dissolved in CCl<sub>4</sub> and the product formed is CH2Br – CH2Br. Draw the structural formula of X and state what type of reaction X has undergone. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

(ii) Ethene [CH2=CH2] has undergone addition reaction.

(iii) Brown colour of bromine is discharged.

(iv) Ethanol

C2H4Ethene+H2O waterH+acidC2H5OH ethanol\underset{\text{Ethene}}{\text{C}_2\text{H}_4} + \underset{\text{ water} }{\text{H}_2\text{O}} \underset{\text{acid}}{\xrightarrow{\text{H}}^+} \underset{\text{ ethanol} }{\text{C}_2\text{H}_5\text{OH}}

(v) Ethanol can be converted into ethene, by dehydrating it with concentrated H2SO4 at 170°C.

C2H5OH ethyl alcohol170°CConc. H2SO4[excess]C2H4ethene+H2\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\

Question 1a(2011)

The functional group present in acetic acid is:

  1. Ketonic >C=O
  2. Hydroxyl -OH
  3. Aldehydic -CHO
  4. Carboxyl -COOH

Answer

Carboxyl -COOH

Reason — Formula of acetic acid is CH3-COOH. Hence, we can see that Carboxyl -COOH is present.

Question 1b(2011)

The unsaturated hydrocarbons undergo:

  1. a substitution reaction
  2. an oxidation reaction
  3. an addition reaction
  4. none of the above

Answer

Addition reaction

Reason — The availability of electrons in the double or triple bond makes them more reactive and therefore they undergo characteristic addition reactions only.

Question 1c(2011)

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

  1. Four
  2. Six
  3. Eight
  4. Ten

Answer

Six

Reason — Below is the structural formula of Ethane:

The number of C – H bonds in ethane molecule are? Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

Question 1d(2011)

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

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

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

(iii) Ethanoic acid reacts with ethanol in the presence of concentrated H2SO4, so as to form a compound and water. The chemical reaction which takes place is called ............... (dehydration/hydrogenation/esterification)

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

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

Answer

(i) The catalyst used for conversion of ethene to ethane is commonly nickel.

(ii) When acetaldehyde is oxidized with acidified potassium dichromate, it forms acetic acid.

(iii) Ethanoic acid reacts with ethanol in the presence of concentrated H2SO4, so as to form a compound and water. The chemical reaction which takes place is called esterification

(iv) Reaction between 1, 2 – dibromoethane and alcoholic potassium hydroxide:

Write balanced chemical equation for the reaction between 1, 2 – dibromoethane and alcoholic potassium hydroxide. Organic Chemistry, Simplified Chemistry Dalal Solutions ICSE Class 10

(v) The product formed when ethene gas reacts with water in the presence of sulphuric acid is ethanol.

Question 1e(2011)

Write balanced chemical equations for the following:

(i) Monochloro ethane is hydrolysed with aqueous KOH.

(ii) A mixture of sodalime and sodium acetate is heated.

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

(iv) Water is added to calcium carbide.

(v) Ethanol reacts with sodium at room temperature.

Answer

(i) Monochloro ethane is hydrolysed with aqueous KOH:

C2H5-Cl Chloroethane [ethyl chloride]+KOH [aq.]boilC2H5-OH Ethanol [ethyl alcohol]+KCl\underset{\text{ Chloroethane [ethyl chloride]}}{\text{C}_2\text{H}_5\text{-Cl}} + \text{KOH [aq.]} \xrightarrow{\text{boil}} \underset{\text{ Ethanol [ethyl alcohol]} }{\text{C}_2\text{H}_5\text{-OH}} + \text{KCl}

(ii) A mixture of sodalime and sodium acetate is heated:

CH3COONasodium acetate+NaOHsodalimeCaOΔCH4methane+Na2CO3\underset{\text{sodium acetate}}{\text{CH}_3\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \underset{\Delta}{\xrightarrow{\text{CaO}}} \underset{\text{methane}}{\text{CH}_4} + \text{Na}_2\text{CO}_3

(iii) Ethanol under high pressure and low temperature is treated with acidified potassium dichromate:

C2H5OH ethanol[ethyl alcohol]K2Cr2O7[O]CH3CHOethanal [acetaldehyde] K2Cr2O7[O]CH3COOHethanoic acid[acetic acid]\underset{ \text{ ethanol[ethyl alcohol]}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{ \text{ethanoic acid[acetic acid]} }{\text{CH}_3\text{COOH}}

(iv) Water is added to calcium carbide:

CaC2calcium carbide+2H2OwaterC2H2ethyne [acetylene]+Ca(OH)2\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \text{Ca(OH)}_2

(v) Ethanol reacts with sodium at room temperature:

2C2H5OH ethanol+2Na2C2H5ONa sodium ethoxide+H2\underset{\text{ ethanol} }{2\text{C}_2\text{H}_5\text{OH}} + 2\text{Na} \longrightarrow \underset{\text{ sodium ethoxide} }{2\text{C}_2\text{H}_5\text{ONa}} + \text{H}_2

Question 1a(2012)

(a) Give the structural formu