$C_{n} H_{2 n + 2}$ is the general formula of a homologous series of hydrocarbons.
i) Is this series saturated or unsaturated?
ii) Name the series described above. Give the formula and name of the member with two carbon atoms.
iii) Draw the structural formula of the first member of this series.
iv) Define the homologous series and find the common difference between the successive members of this family.
v) Write the formula of n-butane and n-pentane.

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Solution

(i) $C_{n} H_{2 n + 2}$ corresponds to general formula of alkanes. Since, alkanes are saturated so this series is saturated series.
(ii) Alkanes
$C_{2} H_{2 \times 2 + 2} = C_{2} H_{6}$
$H_{3} C - C H_{3} (E t h a n e)$
(iii) Methane with molecular formula $C H_{4}$ is first member of this series.
(Refer to Image)
(iv) Homologous series is a series of compounds with same functional group. They have similar chemical properties and physical properties. Compounds of same homologous series have same general formula.
Common difference between successive members of family is $- C H_{2}$ group.
(v) n-butane
$C_{4} H_{10}$
$C H_{3} - C H_{2} - C H_{2} - C H_{3}$
n-pentane
$C_{5} H_{12}$
$C H_{3} - C H_{2} - C H_{2} - C H_{2} - C H_{3}$

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