Migration of Ions

When a electrolyte is dissolved in plenty of water, it breaks up into positively and negatively charged particles called cautions and anions respectively. When a potential differences is applied between the electrodes dipping the electrolyte, the positive ions move towards the cathode and the negative ions move towards the ions move toward the cathode and the negative ions move towards the anode. They will soon acquire a terminal velocity (constant velocity) due to collisions with the rest of the ions and neutral molecules. The terminal velocity acquired by ion depends chiefly on the potential gradient, the size of the ion and the viscosity acquired by an ion under unit potential gradient.

Cautions are generally heavier than the anions and so their mobility is less than that of the anions. As result of this differing motilities and concentration of the electrolyte near the electrodes become different. The study of ionic mobility and the consequent change in concentration near the electrodes is known as transport phenomena.