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Maharashtra State BoardHSC Science (Computer Science) 12th Standard Board Exam
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Overview of Electrochemistry

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Topics

Estimated time: 27 minutes
Maharashtra State Board: Class 12

Definition: Metallic conduction

The conduction of electricity through metals by movement of electrons is called metallic conduction.

Maharashtra State Board: Class 12

Definition: Ionic conduction

The conduction of electricity through molten electrolytes or aqueous solutions by movement of ions is called electrolytic or ionic conduction.

Maharashtra State Board: Class 12

Definition: Electrolyte

A substance which dissociates into ions in aqueous solution or molten state and conducts electricity is called electrolyte.

Maharashtra State Board: Class 12

Definition: Conductivity

The electrical conductance of a conductor of unit length and unit area of cross section is called conductivity.

k = 1 / ρ
k = G × l / a

Maharashtra State Board: Class 12

Definition: Electrolysis

The process of breaking down of an ionic compound in molten state or aqueous solution by passage of electricity is called electrolysis.

Maharashtra State Board: Class 12

Definition: Electrolytic cell

An electrochemical cell in which non-spontaneous reaction is forced by passing direct current is called electrolytic cell.

Maharashtra State Board: Class 12

Definition: Molar conductivity

The electrical conductance of all the ions produced by 1 mole of an electrolyte dissolved in a given volume of solution is called molar conductivity.

\[{}_{\Lambda}=\frac{k}{c}\]

Maharashtra State Board: Class 12

Law: Kohlrausch’s Law of Independent Migration of Ions

  1. Kohlrausch’s law states that at infinite dilution each ion migrates independent of co-ion and contributes to total molar conductivity of an electrolyte irrespective of the nature of the other ion to which it is associated.
  2. At zero concentration (infinite dilution), both cation and anion contribute to the molar conductivity of the electrolyte.
  3. The molar conductivity at infinite dilution (Λ°) is the sum of molar conductivities of the cation and the anion.
  4. The mathematical expression of the law is:
    Λ° = n₊ λ₊° + n₋ λ₋°
    where λ₊° and λ₋° are molar conductivities of cation and anion, and n₊ and n₋ are the number of moles of cation and anion in the formula of electrolyte.
  5. The law is useful in calculating molar conductivity at zero concentration and in determining Λ° values of weak electrolytes from those of strong electrolytes.
Maharashtra State Board: Class 12

Definition: Galvanic or Voltaic cell

An electrochemical cell in which spontaneous reaction produces electricity is called galvanic or voltaic cell.

Maharashtra State Board: Class 12

Key Points:

  1. Electrode potential is the potential difference established due to an electrode half reaction occurring at the surface of contact between metal and its ion solution.
  2. The potential associated with oxidation reaction is called oxidation potential, while the potential associated with reduction reaction is called reduction potential.
  3. The overall cell potential (emf) of a galvanic cell is the algebraic sum of the electrode potentials of anode and cathode. Ecell = Eoxi(anode) + Ered(cathode)
  4. When the galvanic cell operates, electrons are produced at the anode and move through the external circuit to the cathode due to the cell potential.
  5. Standard potential is the electrode or cell potential measured under standard conditions of 1 M concentration, 1 atm pressure and 25°C.
  6. According to IUPAC convention, standard potential of an electrode is taken as the standard reduction potential and the standard cell potential is given by: E∘cell = E∘(cathode) − E∘(anode)
 
Maharashtra State Board: Class 12

Key Points: Classification of Voltaic (or galvanic) cells

Basis Primary Cell Secondary Cell
Meaning A cell in which chemicals are consumed during current generation and cannot be regenerated. A cell in which chemicals consumed during current generation can be regenerated by applying external potential.
Recharging Cannot be recharged. Can be recharged by applying external potential.
Reaction Nature Cell reaction cannot be reversed. Cell reaction is reversed during charging.
Working Type Works only as galvanic cell. Acts as galvanic cell during discharge and electrolytic cell during charging.
Examples Dry cell Lead storage battery, Mercury cell, Nickel-cadmium cell
Maharashtra State Board: Class 12

Key Points: Fuel cells

Topic Details
Meaning A fuel cell converts chemical energy of a redox reaction directly into electrical energy.
Fuel & Oxidant In hydrogen–oxygen fuel cell, hydrogen acts as fuel and oxygen acts as oxidizing agent.
Anode Reaction (Oxidation)

Hydrogen is oxidized at anode (–).

2H₂(g) + 4OH⁻(aq) → 4H₂O(l) + 4e⁻
Cathode Reaction (Reduction)

Oxygen is reduced at cathode (+).

O₂(g) + 2H₂O(l) + 4e⁻ → 4OH⁻(aq)
Overall Reaction

Sum of anode and cathode reactions.

2H₂(g) + O₂(g) → 2H₂O(l) E°cell = 1.23 V
Advantages Non-polluting (water is product) and high efficiency (~70%).
Drawback Hydrogen gas is hazardous and costly to prepare.
Applications Used in automobiles (experimental), space programmes and power generation.
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