(a) What is a homologous series?
(b) What is the difference in the molecular formula of any two adjacent homogues:
(i) in terms of molecular mass,
(ii) in terms of number and kind of atoms per molecule? [3 MARKS]

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Solution

a) 1 Mark
b) 2 Marks

(a) A group of organic compounds having similar structures and similar properties and whose successive members differ by $- C H_{2}$ group is called a homologous series.
Example: All the alkanes have a similar structure with single covalent bonds and show similar chemical properties. Therefore, they form a homologous series of alkanes. The first six members of this homologous series are given below:
$\begin{matrix} N a m e o f t h e a l k a n e & M o l e c u l a r f o r m u l a & N a m e o f t h e a l k a n e & M o l e c u l a r f o r m u l a 1. M e t h a n e & C H_{4} & 4. B u t a n e & C_{4} H_{10} 2. E t h a n e & C_{2} H_{6} & 5. P e t a n e & C_{5} H_{12} 3. P r o p a n e & C_{3} H_{11} & 6. H e x a n e & C_{6} H_{14} \end{matrix}$
General formula of the homologous series of alkanes is $C_{n} H_{2 n + 2}$ .
(b) (i) Molecular formula of any two adjacent homologues differ from each other by 14 units with regard to molecular mass.
(ii) Molecular formulae of any two adjacent homologues differ by $- C H_{2}$ group, i.e., they differ by one carbon and two hydrogen atoms.

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Similar questions

Q. (a) What is homologous series?
(b) What is the difference in molecular formula of any two adjacent homologues in terms of types of atoms and molecular mass?

Q. What is the difference between two consecutive homologues:

(i) in terms of molecular mass?
(ii) in terms of number and kind of atoms per molecule?

(a) Give the molecular formula of one homologue of each of the following :
(i) $C_{3} H_{6}$ (ii) $C_{2} H_{6}$ (iii) $C_{2} H_{2}$
(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?

Q. Fill in the blanks : [5 MARKS]
(i) Members of the alkene series containing ....... to ....... number of carbon atoms are liquids.
(ii) Among isomers, the one with more branched chain has a ...... boiling point.
(iii) The term ....... is used when one carbon atom is attached to four other carbon atoms.
(iv) The molecular mass of any two homologues differs by ....... amu.
(v) The melting point of alkanes increases with ....... in molecular weight.

Q. What is the difference in the molecular mass of two consecutive members of homologous series?

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(a) What is a homologous series? (b) What is the difference in the molecular formula of any two adjacent homogues: (i) in terms of molecular mass, (ii) in terms of number and kind of atoms per molecule? [3 MARKS]

(a) What is a homologous series?
(b) What is the difference in the molecular formula of any two adjacent homogues:
(i) in terms of molecular mass,
(ii) in terms of number and kind of atoms per molecule? [3 MARKS]