Electrochemistry is the study of the relationship between chemical energy and electrical energy. Many spontaneous reactions and corrosion reactions liberate electrical energy. In electrolysis, electrical energy is converted directly into chemical energy. The products of an electrolytic reaction depend on the nature of the material being electrolysed and the type of electrode used. Oxidising and reducing species present in the electrolyte cell and their standard electrode potentials affect the products of electrolysis. Electrolysis plays an important role in most people's daily lives, whether it is for the manufacturing of aluminium, electroplating of metals, or the synthesis of chemical compounds.
Michael Faraday was the first scientist who proposed two laws to explain the quantitative aspects of electrolysis, popularly known as Faraday's laws of electrolysis. Faraday's laws of electrolysis provide a basis for mathematical analysis of the mass deposited at electrodes and the amount of charge passed through them.
Faraday's laws are fundamental in various applications, including electroplating, metal extraction, battery technology and chemical synthesis. These laws also help in environmental monitoring and in various chemistry experiments.
Question: 1
Predict the products of electrolysis in each of the following: An aqueous solution of CuCl\(_2\)
Show Hint
In CuCl\(_2\) electrolysis: Cu at cathode, Cl\(_2\) at anode.
Faraday’s Second Law:
When the same quantity of electricity is passed through different electrolytes, the masses of substances deposited are proportional to their equivalent weights.
Mathematically:
\[
\frac{m_1}{m_2} = \frac{E_1}{E_2}
\]
Where:
\( m \) = mass deposited
\( E \) = equivalent weight
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Question: 5
The following reactions occur at the anode during electrolysis of aqueous sodium chloride solution:
\[
Cl^- \rightarrow \frac{1}{2}Cl_2 + e^- \quad E^\circ = 1.36\,V
\]
\[
2H_2O \rightarrow O_2 + 4H^+ + 4e^- \quad E^\circ = 1.23\,V
\]
Which reaction is feasible at the anode and why?
Show Hint
In brine electrolysis, Cl\(_2\) forms instead of O\(_2\) due to overvoltage effect.
Although oxidation of water has lower potential (1.23 V), in aqueous NaCl:
Overvoltage for oxygen evolution is high.
Chloride ions are present in high concentration.
Thus, chloride oxidation occurs preferentially:
\[
2Cl^- \rightarrow Cl_2 + 2e^-
\]
Answer:
Chlorine evolution is feasible at the anode due to lower overvoltage and high Cl\(^-\) concentration.
