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CARBON AND ITS COMPOUNDS (B)Hydrocarbons

CHAPTER-12
CARBON AND ITS COMPOUNDS
(B)Hydrocarbons
Text Book Question and Answers
I. Answer the following
1. Classify the following into saturated and unsaturated hydrocarbons.
Benxene, cyclopropane, alkene, alkane,
Saturated hydrocarbons: Cycloproparne, Alkane
Unsaturated hydrocarbons: Benxene, alkene
2. Classify the compounds containing double bond and triple bond, ethyne, benzene, butyne, pentene.
Double bond: Benzene, Pentene
Triple bond: Ethyne, Butyne

II. Give reasons for the following
1. Alkanes as chemically stable.
Alkanes are chemically stable as they have only single bonds.
2. Alkanes undergo only substitution reactions but alkenes and alkynes undrgo both substitution and addition reactions. Why?
Alkanes undergo only substitution reactions as they are saturated whereas alkenes and alkynes undergo both substitution and addition reaction as they are unsaturated with double and triple bonds.

III. Answer the following
1. What is homologous series? Give an example of such series.
A homologous series is a family of organic compounds with the same general formula, similar chemical properties and successive members differing by –CH2
Eg: Alkanes, Alkenes and Alkynes are homologous series of aliphatic hydrocarbons.
2. Define isomerism. Give examples
The compounds having same molecular formula but different structural formula are called isomers and the phenomenon is called isomerism
Eg:-Butane (C4H10)
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3. Write the functional group present in methanal. Methanol. Methanoic acid and in amino acid.
CompoundFunctional Group
Methanal-CHO
Methanol-OH
Methanoic acid-COOH
Amino acidNH2-COOH

4. Write the structures of following
i. Isobutane C4H10
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ii. Benzene C6H6
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iii. Cyclohexane C6H12
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iv. Ethane C2H4
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v. Propyne C3H4
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vi. Methanol CH3OH
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5. Mention the uses of benzene.
a) As a solvent for oils, fats, resins, rubber, sulphur, iodine etc.
b) In the manufacture of dyes, drugs, perfumes, explosives etc.
c) In the preparation of gammexane, an insecticide,
d) For dry cleaning.
6. What ldoes IUPAC represent?
International Union of Pure and Applied Chemistry
7. Draw the formulae of the first four members of each homologous series beginning with the following compounds.
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IV. Choose the correct answer from the four alternatives given below
1. When three hydrogen atoms of methane molecule are substituted by three chlorine atoms. We get
(a)DDT (b)Chloroform (c)Methyl alcohol (d) CFC (chloroflurocarbons)
Answer:(b) Chloroform
2. The molecular formula of an alkane containing five carbon atoms is
(a)C5H8 (b)C5H10 (c)C5H5 (d)C5H12
Answer:(d) C5H12
3. The following hydrocarbons contain three double bonds.
(a)ethane (b)ethene (c)benzene (d)cyclohexane
Answer:(c) Benzene
4. The number of hydrogen atoms to be added to benzene to make it cyclohexane is
(a)two (b)three (c)four (d)six
Answer:(d) Six
5. In ethane, each carbon is bonded to
(a)six atoms (b)Three atoms (c)two atoms (d)four atoms
Answer:(d) Four atoms
6. General formula for an alkyne is
(a) CnH2n (b)CnH4n (c)CnH2n-2 (d)CnH2n+1
Answer:(c) CnH2n-2

V. Match the following
1. Aromatic hydrocarbons - Toluene
2. Alicyclic hydrocarbons - Cyclopropane
3. Alkenes - Ethene
4. Polyfuctional compound – Amino acid

Additional Question and Answers
1. What are hydrocarbons? Give examples
Hydrocarbons are the simplest binary organic compounds containing carbon and hydrogen only.
Eg:-Methane and Propane (gases), Hexane and benzene (liquids), Paraffin and Naphthalene (waxes or low melting solids) etc.
2. Which is the simplest hydrocarbon? Write its molecular formula.
The simplest hydrocarbon is called methane, its molecular formula is CH4.
3. Give four examples of hydrocarbons commonly used in our day-to-day life.
Commonly used hydrocarbons in our day-to-day life include camphor, naphthalene, LPG, kerosene, petrol, cooking oils etc.
4. List the general properties of hydrocarbons.
Hydrocarbons are compounds which contain only carbon and hydrogen atoms. Some of the hydrocarbons are solids, a few are liquids and the rest are gases at room temperature. They have low melting and boiling points. Many of the hydrocarbons combine with their own molecules m large numbers to form polymers. Hydrocarbons may have a single bond, a double bond or a triple bond between their carbon atoms.
5. Name the two principal sources of hydrocarbons.
Petroleum and Coal
6. Where do you obtain aliphatic and aromatic hydrocarbons?
Aliphatic hydrocarbons are mainly obtained by petroleum
Aromatic hydrocarbons are mainly obtained from coal.
7. Mention the nature of hydrocarbons.
Hydrocarbons can be gases (e.g. Methane and propane), can be liquids (e.g. Hexane and pentane), Waxes or low melting solids (e.g. paraffin wax and naphthalene). Polymers (e.g. polyethylene and polypropylene)
8. Write the two classification of hydrocarbon
Based on structure, hydrocarbons are classified into two main groups
1. Open chain or acyclic compounds.
2. Closed chain or cyclic (or ring) compound.
Classifications of hydrocarbons
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9. List five hydrocarbons used in our daily life and classify them into solids, liquids and gases bused on their physical state at room temperature.
Hydrocarbons that we use in our daily life include kerosene, petrol, methane, butane, candle wax, polythene, etc.
Hydrocarbons that are solids at room temperature: Candle wax and polythene
Hydrocarbons that are liquids at room temperature. Kerosene and petrol
Hydrocarbons that are gases at room temperature: Methane and butane.
10. What are aliphatic hydrocarbons?
Aliphatic hydrocarbons are also called acyclic or open chain hydrocarbons. These hydrocarbons consist of straight or branched chains of carbon atoms.
11. Differentiate between
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Aliphatic and cyclic hydrocarbons.
Aliphatic hydrocarbonsCyclic hydrocarbons
Open chainClosed chain
No aromatic ringThese are having at least one aromatic ring

12. Write the general formula of alkanes, alkenes and alkynes.
Alkanes CnH2n+2
Alkenes CnH2n
Alkynes CnH2n-2
13. Differentiate between saturated and unsaturated hydrocarbons.
SaturatedUnsaturated
They have single bond between carbon atomsThey have double or triple bond between carbon atoms
The general formula is CnH2n+2The general formula is CnH2n or CnH2n-2
They are less reactive when compare to unsaturated hydrocarbonsThey are more reactive when compared to saturated hydrocarbons
Eg:-AlkanesEg;-Alkenes and Alkynes

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14. What are the general properties of acyclic hydrocarbons?
Acyclic hydrocarbons have open chain structure. The chains may be of either straight or branched structure. The molecules of these compounds may have a single, double or triple bond between their carbons
15. What are Alkanes? Give example with their structural formula
These are saturated hydrocarbons having single bond between carbon atoms. Their general formula is CnH2n+2(n= Number of carbon atoms)
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16. Why are alkanes called paraffins?
Alkanes are saturated hydrocarbons. They have very little affinity for chemical reactions. Hence they are called paraffins. These are hence saturated hydrocarbons
17. What are Alkenes? Give example with structural formula
Alkenes are unsaturated hydrocarbons having double bond between two carbon atoms, their general formula is CnH2n (n= Number of carbon atoms)
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18. What are alkynes? Give examples with their structure.
Alkynes are unsaturated hydrocarbons having triple bond between two carbon atoms, their general formula is CnH2n-2(n= Number of carbon atoms)
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19. Write the indication of prefix in hydrocarbons.
Prefix or word rootNumber of carbon atoms
Meth-1
Eth-2
Prop-3
But-4
Pent-5
Hex-6
Hept-7
Oct-8
Non-9
Dec-10

20. Write the indication of Primary suffixes in hydrocarbons.
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21. Why Methane is called marsh gas?
It is because Methane is formed in the marshy places by the bacterial decomposition of organic matter
22. Explain the preparation of Methane (CH4) in laboratory?
A mixture of sodium acetate and soda lime (NaOH+Cao) is heated in hard glass test tube and methane gas is evolved. It is collected by the downward.
CH3COONa + NaOH -------Cao------- > Na2CO3 + CH4
23. Methane gas is collected by downward displacement of water why?
Because methane gas is lighter than air and it is slightly soluble in water
24. Why is methane chemically inert?
Methane is a saturated hydrocarbon. This is why methane is chemically inert. However, it gives substitution reactions wherein the hydrogen atoms are replaced by atoms of other elements.
25. Write the properties of Methane?
Physical properties: - Methane is colourless, odourless gas, lighter than air. It is slightly soluble in water and fairly soluble in organic solvents
Chemical properties: - Methane is chemically inert. It will not react with by acids, alkalies and oxidizing agents
26. Explain the combustibility of methane?
Complete combustion (blue flame):-
CH4 (g) + 2O2(g) ------ > CO2(g) +2H2O(l)
Incomplete combustion (golden yellow flame) :-
2CH4(g)+3O2(g) -------> 2CO(g)+4H2O(l)
27. Why carbon monoxide is poisonous?
Carbon monoxide acts as a poison by combining with haemoglobin in blood forming carboxy haemoglobin, which prevents the transportation of oxygen to the tissues and finally leads to death of a person by suffocation
28. What is substitution reaction?
Chemical reaction in which an atom or ion in a molecule is replaced by another atom or ion
29. Explain the substitution reaction which occurs in methane
When a mixture of methane and chlorine is exposed to ultraviolet light – typically sunlight – a substitution reaction occurs and the organic product chloromethane is formed.
CH4 + Cl2 ----uv--- > CH3Cl + HCl
However, the reaction doesn’t stop there, and all the hydrogen’s in the methane can in turn be replaced by chlorine atoms to produce substitution products like chloromethane, dichloromethane, trichloromethane(chloroform) and tetrachloromethane (carbon tetrachloride)
CH4 + Cl----uv--- > CH3Cl + HCl
CH3Cl + Cl----uv--- > CH2Cl2 + HCl
CH2Cl2 + Cl2 ----uv--- > CHCl3 + HCl
CHCl3 + Cl2 ----uv--- > CCl4 + HCl
30. Define Homologous Series
A homologous series is a family of organic compounds with the same general formula, similar chemical properties, and successive members differing by –CH2
31. List out the important characteristics of members of a homologous series.
a) They have properties that vary in a regular and predictable manner.
b) They have similar chemical properties
c) They have gradually varying physical properties
d) Their formulae fit the general molecular formula
e) Adjacent members CH4 and C2H6 or C5H12 and C6H14 differ by one carbon and two hydrogen’s.
32. What are cycloalkanes? Give examples.
Cycloalkanes are closed chain saturated hydrocarbon having general formula CnH2n
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33. What are aromatic hydrocarbons? Write the structure of Benzene, Toluene and Naphthalene.
Aromatic hydrocarbons are hydrocarbons that have at least one aromatic ring (benzene type ring)
Eg: Benzene(C6H6), Toluene(C6H5 CH3) and Naphthalene(C10H8)
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34. Write the uses of Benzene, toluene and naphthalene
Benzene:- it is used in the manufacture of dyes, drugs perfumes and it is used as a solvent for fat, oil, resins, rubber, sulphur etc.
Toluene:-It is used in the making of explosive trinitrotoluene(TNT)
Naphthalene:- It is used in making of moth balls and dyes