Question

(a) Give the molecular formula of one homologue of each of the following:
(i) C₃H₆
(ii) C₂H₆
(iii) C₂H₂
(b) What is the difference in the molecular mass of any two adjacent homologues?
(c) By how many carbon atoms and hydrogen atoms do any two adjacent homologues differ?

Answer 1

(a)
(i) The molecular formula of a homologue of C₃H₆ is C₄H₈.​ It belongs to the homologous series of alkenes having the general formula C_nH_2n.
(ii) The molecular formula of a homologue of C₂H₆ is C₃H₈. It belongs to the homologous series of alkanes having the general formula C_nH_2n+2.
(iii) The molecular formula of a homologue of C₂H₂ is C₃H₄. I​t belongs to the homologous series of alkynes having the general formula C_nH2n-2.

(b) The difference in the molecular masses of any two adjacent homologues is 14u.

(c) Any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.