Question 143 marksShort AnswerSection A

(a) What is a homologous series of compounds ? List any two of its characteristics. (b) What is the next higher homologue of C3H7OHC_3H_7OH ? What is its formula and what is it called ?

Carbon and its Compounds
Homologous Series

Official answer

(a) A homologous series is a series of carbon compounds in which the same functional group substitutes for hydrogen in a carbon chain, resulting in similar chemical properties.


Two characteristics are:

  1. Any two adjacent members of the series differ by a −CH2−-CH_2- unit in their molecular formula.
  2. The difference in molecular mass between two successive members is 14u14u.

(b) The next higher homologue of C3H7OHC_3H_7OH (Propanol) is Butanol. Its formula is C4H9OHC_4H_9OH.

Answer keywords:homologous seriesfunctional group-CH2-14uButanolC4H9OH

Marking scheme

  1. 1.Definition of homologous series: 1 mark
  2. 2.Two characteristics: 1 mark (0.5 each)
  3. 3.Formula and name of next homologue: 1 mark

Hint

Add a −CH2−-CH_2- group to the given formula to find the next member.

Quick oral answer

A homologous series is a family of compounds with the same functional group where each member differs from the next by a -CH2 group. For example, the next member after propanol is butanol.

Common mistakes

  1. 1.Adding only a Carbon atom without adjusting Hydrogen atoms.
  2. 2.Confusing the mass difference (stating 12u instead of 14u).

Analysis and explanation

A homologous series (like the alkanes shown in Table 4.2) shows a regular gradation in physical properties while maintaining similar chemical reactivity due to the same functional group. For alcohols, the series starts with Methanol (CH3OHCH_3OH), Ethane (C2H5OHC_2H_5OH), etc. Adding a −CH2−-CH_2- unit to Propanol (C3H7OHC_3H_7OH) gives Butanol (C4H9OHC_4H_9OH).

Interesting facts

In a homologous series, as the molecular mass increases, the melting and boiling points also increase due to stronger intermolecular forces.

Question details

Q14 of 41 questions

Board
CBSE
Class
Class 10
Subject
Science
Year
2011
Section
Section A
Marks
3
Type
Short Answer
Chapter
Carbon and its Compounds
Topic
Homologous Series
Bloom's level
Understanding
Syllabus topic
Homologous series

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Frequently asked questions

How many marks does this question carry in CBSE Class 10 Science 2011?

This question carries 3 marks in the CBSE Class 10 Science 2011 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Carbon and its Compounds" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Homologous Series" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2011 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2011 paper.