Identify the homologous series to which the following carbon compounds belong
to and name these compounds:
C3H4, C3H6, C2H6
Answers
Questions :(a) What is a homologous series? Explain with an example.
(b) State two characteristics of a homologous series.
(c) The molecular formula of an organic compound is C
18
H
36
. Name its homologous series.
(d) Select the hydrocarbons which belong to the same homologous series. Give the name of each series.
CH
4
,C
2
H
2
,C
3
H
4
,C
2
H
6
,C
4
H
10
,C
3
H
4
,C
3
H
6
.
(e) What is meant by 'heteroatom'? Give examples. Write the names and formulae of two organic compounds containing different heteroatoms.
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ANSWER
(a) A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH
2
group.
Example of Homologous series : All the alkanes have similar structures with single covalent bonds and show similar chemical properties, so they can be grouped together in the form of a homologous series.
Homologous series of alkanes : Methane, CH
4
; Ethane, C
2
H
6
; Propane, C
3
H
8
; Butane, C
4
H
10
; Pentane, C
5
H
12
(b) (i) All the members of the homologous series can be represented by the same general formula.
(ii) Any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.
(c) Alkene, C
n
H
2n
(d) Alkanes : CH
4
,C
2
H
6
,C
4
H
10
Alkenes : C
2
H
4
,C
3
H
6
Alkynes : C
2
H
2
,C
3
H
4
(e) In an organic compound, any atom other than carbon and hydrogen is called a heteroatom.
Example: Chlorine (Cl), Bromine (Br), Oxygen (O)
Chloromethane - CH
3
Cl and methanol - CH
3
OH.
Answer:
Explanation:
(a) A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH2group.
Example of Homologous series : All the alkanes have similar structures with single covalent bonds and show similar chemical properties, so they can be grouped together in the form of a homologous series.
Homologous series of alkanes : Methane, CH4
; Ethane, C2H6
; Propane, C3H8
; Butane, C4H10
; Pentane, C5H12
(b) (i) All the members of the homologous series can be represented by the same general formula.
(ii) Any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.
(c) Alkene, CnH2n
(d) Alkanes : CH4,C2H6,C4H10
Alkenes : C2H 4,C3H6
Alkynes : C2H2,C3H4
(e) In an organic compound, any atom other than carbon and hydrogen is called a heteroatom.
Example: Chlorine (Cl), Bromine (Br), Oxygen (O)
Chloromethane - CH3
Cl and methanol - CH3OH.
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