Chapter 23, Problem 75A

Interpretation Introduction

Interpretation:

The number of moles of hydrogen gas which are required for the complete hydrogenation of 1 mole of linolenic acid should be calculation. The balanced equation for the hydrogenation of linolenic acid should be written.

Concept introduction:

The chemical reaction in which the number of atoms of each element present in the reaction is same on both left hand side that is reactant side and right hand side that is product side is known as balanced chemical reaction.

A chemical reaction in which addition of hydrogen takes place in alkene or any compound is known as hydrogenation reaction.

Answer to Problem 75A

Three hydrogen molecules are required for hydrogenation of 1 mole of linolenic acid.

The balanced chemical equation is:

${\text{C}}_{\text{18}}{\text{H}}_{\text{30}}{\text{O}}_{\text{2}}{\text{+H}}_{\text{2}}\to {\text{C}}_{\text{18}}{\text{H}}_{\text{36}}{\text{O}}_{\text{2}}$

Explanation of Solution

Molecular formula of linolenic acid = ${\text{C}}_{\text{18}}{\text{H}}_{\text{30}}{\text{O}}_{\text{2}}$

Condensed structural formula of linolenic acid:

${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH=CHCH}}_{\text{2}}{\text{CH=CHCH}}_{\text{2}}{\text{CH=CH(CH}}_{\text{2}}{\text{)}}_{\text{7}}\text{COOH}$

The reaction between linolenic acid and hydrogen molecule is:

Also,

${\text{C}}_{\text{18}}{\text{H}}_{\text{30}}{\text{O}}_{\text{2}}{\text{+H}}_{\text{2}}\to {\text{C}}_{\text{18}}{\text{H}}_{\text{36}}{\text{O}}_{\text{2}}$

Now, to balance the above equation, hydrogen atoms must be equal on both sides of reaction

Thus, coefficient three should be placed before hydrogen molecule.

Hence, the balanced chemical equation is:

${\text{C}}_{\text{18}}{\text{H}}_{\text{30}}{\text{O}}_{\text{2}}{\text{+3H}}_{\text{2}}\to {\text{C}}_{\text{18}}{\text{H}}_{\text{36}}{\text{O}}_{\text{2}}$

According to above reaction, three hydrogen molecules are required for hydrogenation of 1 mole of linolenic acid.