Standard Electrode Potential

When a metal is placed in 1 M solution of its ions at 25°C then a potential difference develops between metal and its solution. This potential difference is known as standard electrode potential.

According to IUPAC convention, the reduction potential is known as standard electrode potential.

Electrolytic cell

Electrolytic cell is the cell in which electrical energy converts into chemical energy. Charge passes through the movement of cations and anions. Cations move towards the negative electrode i.e., cathode and anion moves towards the positive electrode i.e., anode. This process is known as electrolysis.

Product of Electrolysis: According to preferential discharge theory, that ion will discharge first which requires less energy. The potential at which ion gets discharged is known as deposition potential or discharge potential.

Discharge potential = electrode potential + over voltage

Overvoltage: When an e- transfers from electrode to solution or vice-versa then certain activation energy (due to transfer from solid to liquid state or vice-versa) is involved, which is termed as overvoltage. It can be as high as 1V for O₂.

1. Electrolysis of NaCl Solution:

NaCl  Na⁺ + Cl^-, H₂O  H⁺ + OH^-
Cathode: 2e^- + 2H⁺--> H₂
Anode: 2Cl^---> Cl₂ + 2e^-

Note: For a very dilute NaCl solution, O2 is liberated at anode instead of Cl2.

2. Electrolysis of CuSO₄ Solution (Pt-electrodes):

CuSO₄  Cu⁺² + SO₄^-2
H₂O  H⁺ + OH^-
Cathode: Cu⁺² + 2e^---> Cu
Anode: 4OH^---> 2H₂O + O₂ + 4e^-

3. Electrolysis of CuSO₄ solution using Cu electrodes:

Electrolysis of CuSO₄ solution (using Cu electrode)
CuSO₄  Cu²⁺+ SO₄^-2
Cathode: Cu⁺² + 2e^- --> Cu
Anode: Cu --> Cu⁺² + 2e^-

4. Electrolysis of Acidulated water using inert electrodes:

Electrolysis acidulated water containing some H₂SO₄ using inert electrode
H₂SO₄  2H⁺ + SO₄^-2, H₂O H⁺+ OH^-
Cathode: 2H⁺+ 2e^- --> H₂
Anode: 4OH^- --> 2H₂O + O₂ + 4e^-

5. Electrolysis of NaCl solution using Hg-electrodes:

Cathode: Na⁺+e^- --> Na
Anode: 2Cl^- --> Cl₂ + 2e^-

FARADAY'S LAWS OF ELECTROLYSIS

1. Faraday's First Law of Electrolysis: According to this law, the mass of a substance deposited or liberated at any electrode is directly proportional to the charge passed.

m  q
m = Zq
m = Zit

Z = electrochemical equivalent
m = mass deposited, q = charge passed
i = current, t = time

Electrochemical equivalent: It is mass of substance deposit or liberated by one coulomb of charge.

2. Faradays's Second Law of Electrolysis: When same quantity of charge is passed through the solution of different electrolytes, the mass of substance deposited or liberated at electrode is directly proportional to its equivalent weight.

m  E,  E = Equivalent weight