Electrochemistry Notes: Electrolysis is defined as a process of decomposing electrolytes into their elements by passing a direct electric current through its aqueous solution or molten state (fused).
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Faraday’s law of electrolysis
Faraday’s first law of electrolysis:
During electrolysis by a current is proportional to the quantity of electricity passed through the electrolyte (solution or melt).
W ∞ Q
Faraday’s second law of electrolysis:
The amounts of different substances liberated by the same quantity of electricity passing through the electrolytic solution are proportional to their equivalent weights.
w1/w2 = E1/E2 where E is the equivalent weight.
Faraday’s first law of electrolysis: During electrolysis by a current is proportional to the quantity of electricity passed through the electrolyte (solution or melt).
W ∝ Q (Q = quantity of electricity passed)
W = ZQ
Q = I × t Current (I), “t” is time in second
W = Z × I × t
Where Z is electrochemical equivalent of the substance deposited and Z = Eq. wt. of substance.
Z = Eq. wt. of substance / 96500
Ag +(aq) + e– → Ag(s)
One mole of the electron is required for the reduction of one mole of silver ions.
C = 96487 C 𝑚𝑜𝑙−1
This quantity of electricity is called Faraday (F)
1F ≃96500 C 𝑚𝑜𝑙−1
Electrochemical Cells or galvanic or a voltaic cell or Daniell cell:
An electrochemical cell that converts the chemical energy of a spontaneous redox reaction into electrical energy.
Functions of salt bridge
1. Its U-shaped glass tube filled with a relatively inert electrolyte.
2. Its Contain saturated solution of KCl, KNO3, NH4NO3, Agar-Agar and Gelatin
3. It maintain electrical neutrality of the solution
4. It complete the electrical circuit by allowing the ions to flow from one solution to another
5. It minimizes the potential in liquid-liquid junction
Effect of external voltage on Electrochemical Cells
To electrical energy and has an electrical potential equal to 1.1 V
When concentration of Zn2+and Cu2+ions is unity
Electrode potential (E)
1. If the metal rod is dipped into the aqueous solution of it salt, the rod become either positively or negatively charged with respect to solution.
2. Thus a potential difference get developed between metal rod and solution, this potential difference is called electro potential
Standard Electrode Potential (𝑬°)
Measurement of Electrode Potential
It is assigned a zero potential at all temperatures corresponding to the reaction
Cell Potential or EMF of cell
The potential difference between the two electrodes of a galvanic cell is called the cell potential and is measured
in volts. The cell potential is the difference between the electrode potentials (reduction potentials) of the cathode and anode.
The arrangement of elements in order of their decreasing electrode potential values.
Electrochemical Series Important Points
1. In the electrochemical series, the reduction potential of an element is taken in reference to the hydrogen (𝐸°=0)
1. The greater the reduction potential of an element the more easily it will be reduced. Elements that have low reduction potential will get oxidized much quickly and easily.
2. Stronger reducing agents that have negative standard reduction potential are usually situated below the hydrogen in the electrochemical series. On the other hand, weaker reducing agents with positive standard reduction potential are found above the hydrogen in the series.
3. As we move down in the group the reducing agent’s strength increases while the oxidizing agents’ strength decreases.
4. When we move from top to bottom in the series, the electro positivity, and activity of metals increase. In the case of non-metals, it decreases.
Application of Electrochemical Series
1. Oxidizing and Reducing Strengths
2. Calculation of Standard emf(Eocell) of Electrochemical Cell
3. Predicting the Feasibility of Redox Reaction
4. To compare relative activity of metals
Factors affecting electrolytic conduction
1. Nature of electrolyte: Strong electrolytes ionize almost completely in the solution whereas weak electrolytes ionize to a small extent.
2. Size of ions: larger the ion, smaller will be its conductance.
3. Nature of solvent and viscosity: Greater the polarity of the solvent, greater is the conductance. Greater the viscosity, lesser will be the conductance.
4. Concentration of solution: Higher the concentration of the solution, less is the conduction.
5. Temperature: On increasing the T, the dissociation increases and the conduction increases.
Limiting molar conductivity (Λ°𝑚)
The molar conductivity of a solution at infinite dilution is known as limiting molar conductivity. In other words, when the concentration of the electrolyte approaches zero, the molar conductivity is known as limiting molar conductivity.
1. The conductivity and molar conductivity of an electrolyte change with the concentration of the electrolyte.
2. As concentration decreases, conductivity decreases for both strong and weak electrolytes.
3. But molar conductivity increases as concentration decreases.
4. The variation is different for strong electrolytes and weak electrolytes.
Λ = K x V
Variation of molar conductivity with concentration
It is shown by Debye-Huckel-Onsager equation as follows
Here, Λ𝑚°= Molar conductivity at infinite dilution
(Limiting molar conductivity)
Λ𝑚= Molar conductivity at V-dilution
A = Constant which depends upon nature of solvent and temperature
C = Concentration
Limiting molar conductivity of Strong electrolytes
The limiting molar conductivity of an electrolyte can be represented as the sum of the individual contributions of the anion and cationof the electrolyte.