Question

On the basis of \[{E^o}\] values, ${O_2}$ gas should be liberated at anode but it is $C{l_2}$ gas which is liberated in the electrolysis of aqueous $NaCl$.

Answer 1

Hint: The oxidation results in the formation of oxygen in the electrolysis process. But here the concept of excess voltage or overvoltage is the reason behind this condition. Hence a chain is observed in the reaction at the anode.

Complete step by step answer:
According to the character of ${E^o}$values, the oxygen gas should be liberated when aqueous $NaCl$ is subjected to electrolysis. The anode is the positive electrode in the electrolysis process and hence the anions or the negative ions move towards the anode. Hence in the specific electrolysis process $O{H^ - }$ ions and $C{l^ - }$ ions move towards the anode.
In the process the oxidation of ${H_2}O$ is necessary which is then converted to ${O_2}$. In this process, the water gets converted so that the oxygen can be liberated at the anode, but that requires a higher voltage. The concept of requirement of higher voltage is because of the presence of hydrogen bonds between the water molecules. Thus, for oxygen to be liberated after the removal of the bonds, a very high voltage is very important.
$NaCl \rightleftharpoons N{a^ + } + C{l^ - }$
${H_2}O \rightleftharpoons {H^ + } + O{H^ - }$
At anode we have $2C{l^ - } + 2e \rightleftharpoons C{l_{}}$
 This is why at a low level of voltage in the electrolysis apparatus the $C{l^ - }$ is converted to the $C{l_2}$ gas at the anode region. Therefore the $C{l_2}$ gas is liberated under the level of normal voltage and the ${O_2}$ is liberated when there is higher voltage which is a condition known as over voltage. This is why even due to \[{E^o}\] value shows the liberation of ${O_2}$ to be favourable, the removal of $C{l_2}$ takes place as that difference in voltage is responsible for easy liberation of chlorine at the anode.

Note: A specific level of voltage is important and in the process of electrolysis the oxidation takes place at the anode. Therefore, the oxidation resulting in the liberation of specific components take place at the anode. The interactions of the molecules involved in electrolysis is equally important.