Electrochemical Equivalent
Definition and meaning of Electrochemical Equivalent in chemistry.
Electrochemical equivalent is the mass of a substance deposited or liberated at an electrode per unit of electric charge (typically one coulomb) passed through an electrolyte during electrolysis.
In more detail
It is calculated as Z = M/(nF), where M is the molar mass of the substance, n is the number of electrons transferred per ion in the electrode reaction, and F is the Faraday constant (96,485 C/mol). This quantity is the proportionality constant in Faraday's first law of electrolysis, m = Z × Q, allowing the mass of metal deposited or gas released to be predicted directly from the charge passed. Electrochemical equivalents underpin coulometric analysis, electroplating calculations, and historically defined the ampere via the silver voltameter.
Key facts
| Symbol | Z |
|---|---|
| Formula | Z = M/(nF) |
| Typical units | g/C (or kg/C in SI) |
| Field | Physical Chemistry |
For silver deposition, Ag⁺ + e⁻ → Ag, so Z = 107.87 g/mol ÷ (1 × 96,485 C/mol) = 1.118 × 10⁻³ g/C. Passing 1 coulomb of charge through a silver nitrate solution therefore deposits 1.118 mg of silver on the cathode.
Frequently asked questions
How does electrochemical equivalent relate to Faraday's laws?
It is the constant of proportionality in Faraday's first law of electrolysis: the mass deposited or liberated, m, equals Z multiplied by the total charge passed, Q (m = ZQ).
What is the electrochemical equivalent of copper?
For Cu2+ + 2e- → Cu, Z = 63.55 g/mol ÷ (2 × 96,485 C/mol) ≈ 3.29 × 10⁻4 g/C.