Q. 17 II.4.0( 2 Votes )

In the electrolysis of aqueous sodium chloride solution which of the half-cell reaction will occur at anode?
A.

B.

C.

D.

Answer :

The products of molten sodium chloride and aqueous solution of sodium chloride are not the same. In molten NaCl electrolysis, the products are only Na and Cl2. In the electrolysis of aqueous NaCl, apart from Na+ and Cl- ions, H+ and OH- ions also exist because of presence of H2O. At the cathode, there is competition between two reduction reactions –


(i) Na+(aq) + e Na(s) where standard electrode potential Ecell = 2.71 V


(ii) H+(aq) + e 1/2 H2(g) Ecell = 0.00 V


The reaction with higher potential value is preferred, hence the second equation takes place. But H+ is produced as a product of dissociation of H2O, which is given by H2O(l) H+ + OH-. The net reaction at the cathode is written as H2O (l) + e 1/2H2 (g) + OH.


At anode, two oxidation reactions are possible.


(i) Cl (aq) 1/2 Cl2 (g) + e Ecell = 1.36 V


(ii) 2H2O (l) O2 (g) + 4H+ (aq) + 4e Ecell = 1.23 V


Here, the issue of overpotential arises. Some electrochemical processes which are possible at an electrode, are so slow kinetically that at lower voltages these cannot take place and an extra potential (called overpotential) needs to be applied. The reaction at anode with lower value of E cell is preferred and accordingly, water should get oxidised in preference to Cl(aq). However, because of overpotential of oxygen, second reaction is preferred. Hence, the correct option is (ii).

Rate this question :

How useful is this solution?
We strive to provide quality solutions. Please rate us to serve you better.
Related Videos
Electrochemistry - 07Electrochemistry - 07Electrochemistry - 0763 mins
Electrochemistry - 04Electrochemistry - 04Electrochemistry - 0464 mins
Nernst Equation - Learn the ConceptNernst Equation - Learn the ConceptNernst Equation - Learn the Concept33 mins
Electrochemistry - 06Electrochemistry - 06Electrochemistry - 0621 mins
Difference between electrochemical and electrolysisDifference between electrochemical and electrolysisDifference between electrochemical and electrolysis45 mins
Master Concept of Oxidising and Reducing agentMaster Concept of Oxidising and Reducing agentMaster Concept of Oxidising and Reducing agent42 mins
Electrochemistry - 05Electrochemistry - 05Electrochemistry - 0560 mins
Nernst Equation (Conceptual Class)Nernst Equation (Conceptual Class)Nernst Equation (Conceptual Class)66 mins
Qualitative Aspect of ElectrolysisQualitative Aspect of ElectrolysisQualitative Aspect of Electrolysis58 mins
Practice Questions on faraday's lawPractice Questions on faraday's lawPractice Questions on faraday's law44 mins
Try our Mini CourseMaster Important Topics in 7 DaysLearn from IITians, NITians, Doctors & Academic Experts
Dedicated counsellor for each student
24X7 Doubt Resolution
Daily Report Card
Detailed Performance Evaluation
caricature
view all courses