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

Answer:

a

i-CnH2n

ii-CnH2n+2

iii-CnH2n-2

b

(CH2) difference is 14

c

one carbon and two hydrogen

Answer 2

Explanation:

(A) The molecular formula of one homologue of each of the following is:

(i) $C_{3} H_{6} \rightarrow C_{4} H_{8}$

(ii) $C_{2} H_{6} \rightarrow C_{3} H_{8}$

(iii) $C_{2} H_{2} \rightarrow C_{3} H_{4}$

(B) The adjacent homologues differ by infusing a unit of $\mathrm{CH}_{2}$ to the chain. Therefore, the difference in the molecular mass of any two adjacent homologues is the molecular mass of the unit of $\mathrm{CH}_{2}$ i.e., 12+1+1= 14 atomic mass unit or 14 u.

(C) Two adjacent homologues differ by 2 Hydrogen atoms and 1 Carbon atom. So, it is basically a $\mathrm{CH}_{2}$ group.