Ionic Migration
Definition and meaning of Ionic Migration in chemistry.
Ionic migration is the directed movement of ions through a solution or molten electrolyte toward the oppositely charged electrode when an external electric field is applied.
In more detail
The applied electric field exerts a force on each ion proportional to its charge, pushing cations toward the cathode and anions toward the anode. This ionic motion is what carries electric current through an electrolyte and is described quantitatively by ionic mobility (drift velocity per unit field) and the transport number (the fraction of total current carried by a given ion). Migration is distinct from diffusion, which is driven by a concentration gradient rather than an electric field, though both processes contribute to the net flux of ions described by the Nernst-Planck equation. Faster, smaller, more highly charged ions generally migrate more quickly and carry a larger share of the current.
Key facts
| Field | Physical Chemistry |
|---|---|
| Driving force | Applied electric (potential) field |
| Quantified by | Ionic mobility and transport number |
| Contrast with | Diffusion (driven by concentration gradient) |
During the electrolysis of aqueous sodium chloride, Na+ ions migrate through the solution toward the cathode while Cl- ions migrate toward the anode, completing the electric circuit inside the cell.
Frequently asked questions
How does ionic migration differ from diffusion?
Migration is the movement of ions caused by an applied electric field, while diffusion is movement caused by a concentration gradient; total ion transport in solution is the sum of both contributions.
What is the transport number in ionic migration?
The transport number is the fraction of the total electric current in an electrolyte carried by a particular ion, which depends on that ion's mobility relative to all other ions present.