On the basis of \( E^\circ \) values, O\(_2\) gas should be liberated at the anode, but it is Cl\(_2\) gas that is liberated in the electrolysis of aqueous NaCl.
Show Hint
Solution and Explanation
Electrolysis of Aqueous NaCl
1. Standard Electrode Potentials:
The standard electrode potential for the reduction of oxygen to water is: \[ E^\circ_{\text{O}_2/\text{H}_2\text{O}} = +1.23 \, \text{V} \] While for the reduction of chloride ions to chlorine gas: \[ E^\circ_{\text{Cl}^-/\text{Cl}_2} = +1.36 \, \text{V} \]
2. Why Chlorine is Liberated at the Anode:
Although the standard electrode potential for chloride ions is slightly more positive than that for oxygen, this does not automatically mean that oxygen will be reduced to water at the anode in the electrolysis of aqueous NaCl.
The reason why chlorine gas (\( \text{Cl}_2 \)) is liberated at the anode during electrolysis is due to the **concentration of ions** in the solution. Chloride ions (\( \text{Cl}^- \)) are present in **much higher concentrations** compared to oxygen in the solution.
The **concentration effect** plays a significant role in determining which ion is more readily oxidized. Even though oxygen has a more positive reduction potential, the abundance of chloride ions ensures that they are more readily oxidized to form chlorine gas at the anode.
3. Explanation of the Process:
During the electrolysis of aqueous NaCl, the **anode** is the site of oxidation, where electrons are released. At the anode, chloride ions (\( \text{Cl}^- \)) are oxidized to chlorine gas (\( \text{Cl}_2 \)): \[ 2\text{Cl}^- (aq) \rightarrow \text{Cl}_2 (g) + 2e^- \] At the **cathode**, water is reduced to form hydroxide ions (\( \text{OH}^- \)) and hydrogen gas (\( \text{H}_2 \)): \[ 2\text{H}_2\text{O} (l) + 2e^- \rightarrow \text{H}_2 (g) + 2\text{OH}^- \]
4. Conclusion:
Despite the standard electrode potential being more positive for oxygen reduction than for chloride ion reduction, chlorine is preferentially liberated at the anode during the electrolysis of aqueous NaCl. This is because the concentration of chloride ions in the solution is much higher, making them more readily available for oxidation.
Top CBSE CLASS XII Chemistry Questions
- ${AgNO_3}$ does not decompose where :
- Azeotropic mixture of water and HCl boils at 381.5 K. By distilling the mixture it is possible to obtain
Write IUPAC names of the following compounds and classify them into primary, secondary and tertiary amines.
(i) (CH3 )2CHNH2 (ii) CH3 (CH2 )2NH2 (iii) CH3NHCH(CH3 )2
(iv) (CH3 )3CNH2 (v) C6H5NHCH3 (vi) (CH3CH2 )2NCH3 (vii) m–BrC6H4NH2
Give one chemical test to distinguish between the following pairs of compounds.
(i) Methylamine and dimethylamine
(ii) Secondary and tertiary amines
(iii) Ethylamine and aniline
(iv) Aniline and benzylamine
(v) Aniline and N-methylanilineAccount for the following:
(i) pKb of aniline is more than that of methylamine.
(ii) Ethylamine is soluble in water whereas aniline is not.
(iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.
(iv) Although amino group is o– and p– directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.
(v) Aniline does not undergo Friedel-Crafts reaction.
(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines. (vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines.
Top CBSE CLASS XII Electrolytic Cells and Electrolysis Questions
Top CBSE CLASS XII Questions
- 2, b, c are in A.P. and the range of determinant $\begin{vmatrix}1&1&1\\ 2&b&c\\ 4&b^{2}&c^{2}\end{vmatrix}$ is [2, 16]. Then find range of c is
- A boy of mass 50 kg is standing at one end of a, boat of length 9 m and mass 400 kg. He runs to the other, end. The distance through which the centre of mass of the boat boy system moves is
- A capillary tube of radius r is dipped inside a large vessel of water. The mass of water raised above water level is M. If the radius of capillary is doubled, the mass of water inside capillary will be
- A circular disc is rotating about its own axis. An external opposing torque 0.02 Nm is applied on the disc by which it comes rest in 5 seconds. The initial angular momentum of disc is
- A circular disc is rotating about its own axis at uniform angular velocity \(\omega.\) The disc is subjected to uniform angular retardation by which its angular velocity is decreased to \(\frac {\omega}{2}\) during 120 rotations. The number of rotations further made by it before coming to rest is