1.

Give the formation of alkane by Kolbe's electrolysis method with its examples.

Answer»

Solution :* An aqueous solution of sodium or potassium salt of a CARBOXYLIC acid on electrolysis gives alkane containing even NUMBER of carbon atoms
Example : Salt of Na of acetic, ethane is obtained by the electrolysis of sodium acetate is as follows.

In this reaction there is ALWAYS a formation of even carbon product of alkane.
Reaction :
(a) In aqueous solution of sodium salt of acid, `CH_(3)COO^(-)` is anion and `Na^(+)` is cation in a solution.
`2CH_(3)COO^(-)Na^(+) hArr 2CH_(3)COO_((aq))^(-) + 2Na_((aq))^(+)` ...(a)
(b) (i) Oxidation at anode : Anion `CH_(3)COO^(-)` goes to the anode, LOSSES its electon and doesoxidation and `CH_(3)` is formed.

(ii) `H_(3)overset(.)(C)+overset(.)(C)H_(3) rarr underset("Ethane(gas)")(CH_(3)-CH_(3))uarr`
(c) Reduction at cathode : Cation does not reduced at cathode but `H_(2)O` gets reduced and hydrogen `(H_(2))` is being released.
(i) `H_(2)O + e^(-) rarr ""^(-)OH + overset(.)(H)`
(ii) `2overset(.)(H)rarr H_(2) uarr`
`2Na^(+) + 2H_(2)O + 2e^(-) rarr 2NaOH + H_(2(g))` ...(c)
(d) Total reaction = (a) + (b) + (c) are as follows

Limitations : MEthane cannot be prepared by this by this method.


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