Q7 of 60 Page 1

What are homologous series of carbon compounds? Write the molecular formula of two consecutive members of homologous series of aldehydes. State which part of the compounds determines their (i) physical and (ii) chemical properties.

The series which consists of similar structures and similar chemical properties in which the successive compounds differs by a CH2 group is termed as homologous series.


The two characteristics of homologous series are as follows:


1. The members of the homologous series consists of same general formula such as Alkanes have general formula CnH2n+2


2. The two adjacent homologues have a difference of molecular mass of 14 u.


The molecular formula of two consecutive members of homologous series of aldehydes are :


1. Methanol: H-CHO


2. Ethanal: CH3–CHO


3. Propanal: C2H5 – CHO


(i) The physical properties of the compounds is determined by the carbon chain attached to the aldehyde group.


(ii) The chemical properties of the compound is determined by the functional group attached to the aldehyde group.


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