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Hydrocarbons

Question
CBSEENCH11007754
Wired Faculty App

How are alkanes formed from:
(i) unsaturated hydrocarbons
(ii) sodium salt of fatty acids?

Solution

(i) From unsaturated hydrocarbons: It consist of passing hydrogen gas through alkenes or alkynes in the presence of finely divided nickel at 523 - 573 K. Saturated hydrocarbons are produced.
 
stack straight R space minus space CH space equals space CH subscript 2 with Alkene below space plus space straight H subscript 2 space space rightwards arrow from 523 space minus 573 space straight K to Ni of thin space straight R space minus space stack CH subscript 2 space minus space CH subscript 3 with Alkane below stack straight H subscript 2 straight C equals CH subscript 2 with Ethene below space plus space straight H subscript 2 space space rightwards arrow from 523 space minus space 573 space straight K to Ni of space space stack CH subscript 3 space minus space CH subscript 3 with Ethane below CH subscript 3 space minus space stack CH space equals space CH subscript 2 space plus space straight H subscript 2 with Propene below space space rightwards arrow from 523 space minus space 573 straight K to Ni of space stack CH subscript 3 minus space CH subscript 2 space minus space CH subscript 3 with Propane below stack straight R minus straight C space identical to straight C minus straight R with Alkyne below space plus 2 straight H subscript 2 space rightwards arrow from 523 minus 573 space straight K to Ni of space stack straight R minus CH subscript 2 with Alkane below space minus CH subscript 2 minus straight R stack HC identical to CH with Acetylene below space plus space 2 straight H subscript 2 space rightwards arrow from 523 space minus 573 space straight K to Ni of space stack CH subscript 3 space minus space CH subscript 3 with Ethane below
These are known as Sabatier and Senderen's reactions.
Methane can not be prepared by this method. 
(ii) From sodium salt of fatty acids. The sodium salt of carboxylic acids on strong heating with soda lime (NaOH + CaO) yield alkanes. The reaction is termed as decarboxylation reaction since it involves the removal of carbon dioxide.
RCOONa with Sod. space salt space of space carboxylic space acid below space plus space NaOH space space rightwards arrow from CaO to Heat of space space RH with Alkane below space plus space Na subscript 2 CO subscript 3
stack CH subscript 3 COONa with Sodium space acetate below space plus space NaOH space space rightwards arrow from CaO to Heat of space stack CH subscript 4 with Methane below space plus space Na subscript 2 CO subscript 3
CH subscript 3 CH subscript 2 COONa space plus space NaOH space rightwards arrow from CaO to Heat of space stack straight H subscript 3 straight C space minus CH subscript 3 with Ethane below space plus space Na subscript 2 CO subscript 3

Some More Questions From Hydrocarbons Chapter

Out of n-pentane, isopentane and neopentane which has lower boiling point?

During the pyrolysis of alkanes C-C bonds break in preference to C-H bond. Why?

Define cracking. 

What is the function of iodic acid in the iodination of alkanes? Can we use any other substance in its place?

What is alternation effect?

Arrange the following compounds in order of their increasing boiling points:
n-Pentane, n-Hexane, Ethane, 2-2-Dimethylpentane, 2-Methylpentane.

Why is light or heat necessary to initiate chlorination reaction of alkanes?

What are conformation or rotational isomers?

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