Fundamentals of Electrolysis and Electrochemical Cells

Fundamentals of Electrolysis

Electrolysis is the decomposition of a compound, in solution or in the molten state, brought about by the passage of electric current through it.

Definitions and Components

• An electrolyte is a substance in the molten state or as a solution in water, which allows the passage of electricity.
• A non-electrolyte is a substance in a solution that does not conduct electric current.
• A conductor is a substance which conducts or allows the passage of electricity.
• An insulator is a solid substance which does not conduct electricity.

Electrolysis Laws and Quantities

The amount of substance deposited or liberated is directly proportional to the quantity of electricity (Q) passed through the solution during electrolysis.

The moles of substances deposited or liberated are inversely proportional to the valency of the elements, respectively.

One Faraday is the quantity of electricity (96,500 coulombs) required to produce one mole of a univalent element.

Electrochemical Processes

• Electroplating is a process to coat one metal with a thin layer of another metal by electrolysis.
• An oxidant is an acceptor of electrons and is reduced in a chemical reaction.
• A reductant is a donor of electrons and is oxidised in a chemical reaction.

Electrochemical Cells

• An electrolytic cell is the cell in which electrical energy is transformed into chemical energy.
• A chemical cell is the cell in which chemical energy is transformed into electrical energy by forcing the electrons to travel through a wire.

Factors Affecting Electrolysis

Factors affecting the position of ions in the electrochemical series include:

• Concentration of the electrolyte.
• Nature of the electrode.

Arrhenius Theory and Solutions

Arrhenius stated that electrolytes contain electrically charged particles called ions. Electrolytes can conduct electricity due to the movement of these ions, whereas non-electrolytes do not contain ions and so they cannot conduct electricity.

A molar solution of a compound is a solution which contains one mole of the compound in one cubic decimetre (1 dm³) of the solution.

Hofmann's Votameter

Hofmann's Votameter is mentioned in relation to these concepts.

Example: Ionization and Electrode Reactions

Ionization Equation

K[Ag(CN)₂](aq) → K⁺(aq) + Ag⁺(aq) + 2CN⁻(aq)

Reaction at the Cathode:

Ag⁺(aq) + e⁻ → Ag(s)
(Silver deposits)

Reaction at the Anode:

Ag(s) → Ag⁺(aq) + e⁻
(Silver dissolves)