Q. 5

C_nH_2n+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.

Class 10th Tamil Nadu Board - Science 13. Carbon and its Compounds

Answer :

i) The series is saturated.

Explanation: C_nH_2n+2 is the general formula of a homologous series of alkane which is a saturated hydrocarbon.

Note: Saturated hydrocarbons are those organic compounds which contain carbon–carbon single bond. These were earlier named as paraffins.

ii) The given is homologues series of alkane hydrocarbons.

The formula and name of the member with two carbon atoms:

n=2

C₂H_2×2+2 = C₂H₆ (ethane)

Thus, formula is C₂H₆ and name is ethane

iii) The first member of the series is:

n=1

C₁H_2×1+2 = CH₄ (methane)

The structural formula of methane is:

iv) Homologues series: A homologous series is a group or a class of organic compounds having same general molecular formula and similar chemical properties in which the successive members differ by a CH₂ group.

v) In butane, there are four carbon atoms and in pentane there are five carbon atoms.

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