Define homologous series

Answer: Homologous series are organic compound series with the same functional group and share similar chemical properties. They differ only in Carbon chain length. The members of homologous series are called homologue.

Examples of homologous series:

Alkane-

CH₄ – methane
C₂H₆ – ethane
C₃H₈ – propane

Alcohol-

CH₃OH - Methanol
CH₃CH₂OH - Ethanol
CH₃(CH₂)₂OH - Propanol
CH₃(CH₂)₃OH - Butanol
CH₃(CH₂)₄OH - Pentanol

General Formula

Alkane series having general formula C_nH_2n+2 : CH₄, C₂H₆, C₃H₈, ...
Alkene series having general formula C_nH_2n : C₂H₄, C₃H₆, C₄H₈, …

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Listed below are the characteristics of homologous series:

Homologous series have the same functional group.
They share the same general formula.
All the members of the series have almost the same chemical properties due to the same functional group.
They have different physical properties
They have a common general method of preparation.
They have difference of – CH₂– between two successive members and the difference between their masses is 14 amu.
They show gradation in physical properties like melting and boiling point increase with the increase in molecular weight.
Solubility in particular solvents shows gradation with increase in the molecular weight.

Check Carbon and its Compounds

CBSE CLASS XII Related Questions

1.
Match Column I with Column II and choose the correct option :
Column I Column II
a. Osmotic pressure i. \( \Delta \mathrm{T_f} = \mathrm{K_f}\,m \)
b. Elevation of boiling point ii. \( \pi = CRT \)
c. Depression of freezing point iii. \( \frac{\mathrm{P_1^0 - P_1}}{\mathrm{P_1^0}} = \frac{\mathrm{W_2 \times M_1}}{\mathrm{M_2 \times W_1}} \)
d. Relative lowering of vapour pressure iv. \( \Delta \mathrm{T_b} = \mathrm{K_b}\,m \)

Column I	Column II
a. Osmotic pressure	i. \( \Delta \mathrm{T_f} = \mathrm{K_f}\,m \)
b. Elevation of boiling point	ii. \( \pi = CRT \)
c. Depression of freezing point	iii. \( \frac{\mathrm{P_1^0 - P_1}}{\mathrm{P_1^0}} = \frac{\mathrm{W_2 \times M_1}}{\mathrm{M_2 \times W_1}} \)
d. Relative lowering of vapour pressure	iv. \( \Delta \mathrm{T_b} = \mathrm{K_b}\,m \)

a-i, b-ii, c-iii, d-iv
a-ii, b-i, c-iii, d-iv
a-iv, b-iii, c-ii, d-i
a-ii, b-iv, c-i, d-iii

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2.
Write the reactions taking place at anode and cathode in a lead storage battery, when it is in use.
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3.
Explain the Finkelstein reaction.
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4.
(i) (I) The \(\mathrm{pK_b}\) value of aniline is higher than that of methylamine. Explain why.
(II) Arrange the following compounds in decreasing order of their basic strength in the gaseous phase :
\(\mathrm{NH_3}\), \(\mathrm{(C_2H_5)_2NH}\), \(\mathrm{(C_2H_5)_3N}\), \(\mathrm{C_2H_5NH_2}\)
(III) What is Hinsberg's reagent ? Mention its one use.
(ii) How will you convert the following :
(I) Nitrobenzene to Benzenediazonium chloride ?
(II) Iodomethane to Ethanamine ?
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5.
(i) Give a chemical test to distinguish between Propanal and Propanone.
(ii) Which of the given acids is stronger and why ? \( \mathrm{F_3C{-}C_6H_4{-}COOH} \) or \( \mathrm{H_3C{-}C_6H_4{-}COOH} \)
(iii) Complete the given reaction sequence :
\[ \mathrm{CH_3CH_2CH_2COOC_2H_5} \xrightarrow{\mathrm{NaOH}} \mathrm{A + C_2H_5OH} \]
\[ \mathrm{A} \xrightarrow{\mathrm{H_3O^+}} \mathrm{B} \]
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6.
(a) Define 'Denatured Protein' with an example.
(b) What happens when glucose reacts with HCN ? Write the reaction involved.
(c) Name the disease caused by the deficiency of Vitamin C.
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