Hydrocarbons Easy Notes For Class 10, First & Second Year

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UNIT. NO 12 HYDROCARBONS
Hydrocarbons:
Those organic compounds which contain only two elements carbon and hydrogen
are called hydrocarbons. There are three basic types of hydrocarbons.
i) Alkanes (C – C) ii) Alkenes (C = C) iii) Alkynes
(𝐶 ≡ 𝐶)
1. Alkanes (C – C):-
Those hydrocarbons that contain carbon-carbon single bond are called alkanes. They are also
called saturated hydrocarbons. Their general formula is “CnH2n+2 , where “n” is number of
carbon atoms.
Example: H

i) 𝑴𝒆𝒕𝒉𝒂𝒏𝒆: 𝐶𝐻4 𝐻−𝐶−𝐻 ii)
𝑬𝒕𝒉𝒂𝒏𝒆: 𝐶 6 𝐻6 𝐶𝐻3 − 𝐶𝐻3
2. Alkenes (C = C):- H
Those hydrocarbons that contain carbon-carbon double bond (=) are called
alkenes. They are also called un-saturated hydrocarbons. Their general formula is “CnH2n, where
“n” is number of carbon atoms.
Example:
i) C2H4 CH2 = CH2 (Ethene) ii) C3H7 CH3 – CH3 = CH2
(Propene)
3. Alkynes (C ≡ C):-
Those hydrocarbons that contain carbon-carbon triple bond (≡) are called
alkynes. They are also called un-saturated hydrocarbons. Their general formula is “CnH2n-2
,where “n” is number of carbon atoms.
Example:
i) Ethyne: CH ≡ CH (C2H2) ii) Propyne: CH3 – C ≡ CH
(C3H4)
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GENERAL METHODS OF PREPARATION OF ALKANES

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First Method:
1. By Hydrogenation of Alkenes and Alkynes:
The process in which hydrogen molecule is
added
in an alkene or alkyne is called hydrogenation. This process takes place in the presence of finally
divided nickel at 200 – 300oC and under high presence. By the hydrogenation of alkene or
alkyne
alkanes are produced.
Ni
CH ≡ CH + H2 CH2 = CH2
200-300 C
Ethyne Ethene
Ni
CH2 = CH2 + H2 CH3 – CH3
200-300 C
Ethene Ethane




SECOND METHOD
By the Reduction of Alkyl Halides:
Alkyl halides are those organic compounds in which one
hydrogen atom of an alkane is replaced by one halogen atom.
When an alkyl halide is treated with Zinc (Zn) in the presence of an aqueous acid then an alkane
is
produced. In this reaction Zinc (Zn) react with aqueous acid (HCl) and as a result atomic
hydrogen is produced. This atomic hydrogen is called nascent hydrogen and this nascent
hydrogen reduces alkyl halide.
𝒁𝒏/𝑯𝑪𝒍
CH3 – Cl + 2[H]
−−−−→ CH4 + HCl
Alkane
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Page : No.76: Self Assessment Exercise No -12.3
Complete the following reactions.

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i) Ni
CH3 – CH = CH2 + H2
200-300 C



Ni
CH3 – CH = CH2 + H2 CH3 – CH2 – CH3
200-300 C



ii) Ni
CH3 – C ≡ CH + H2
200-300 C



Ni
CH3 – C ≡ CH + H2 CH3 – CH = CH2
200-300 C

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Self Assessment Exercise No -12.4
Complete the following reactions.
i) Zn
CH3 - CH2 + [H] HCL(aq)

Cl
Zn
CH3 - CH2 + [H] HCL(aq) CH3 – CH2 + HCl
Cl
ii) Zn
CH3 – CH – CH3 + 2[H] H2SO4(aq)

Cl
Zn
CH3 – CH – CH3 + 2[H] H2SO4(aq) CH3 – CH2 – CH3 + HCl
Cl

Properties of Alkanes:-
1. Alkane molecules are non-polar in nature.
2. Alkane molecules are less dense than water and they are soluble in water.
3. Chemically alkanes are un-reactive towards most of the ionic compounds.