Difference Between Ionic Mobility and Ionic Velocity

The key difference between ionic mobility and ionic velocity is that ionic mobility defines the ability of ions to move through a medium whereas ionic velocity defines how fast the ions move through the medium.

The conductance of an electrolyte arises from the movement of ions through the electrolytic medium. However, they do not move in a well-ordered manner. Therefore, the velocity of this movement is different from one ion to another. The movement of ions is due to an externally applied electrostatic field.

1. Overview and Key Difference
2. What is Ionic Mobility
3. What is Ionic Velocity
4. Side by Side Comparison – Ionic Mobility vs Ionic Velocity in Tabular Form
5. Summary

What is Ionic Mobility?

Ionic mobility or electrical mobility is the ability of ions to move through a medium upon the effect of an electric field. Ions are charged particles; thus, they have either a negative or positive electrical charge. Therefore, an electric field can affect the movement of these ions. We name the process of separating ions according to their mobility in the gas phase as “ion mobility spectrometry”. Moreover, if we do this separation in the liquid phase, we call it “electrophoresis”.

Difference Between Ionic Mobility and Ionic Velocity

Figure 1: Ion Mobility Spectrometry

Furthermore, in mathematical terms, we can define the ionic mobility as the ratio of the drift velocity to the magnitude of the electric field. It is as follows:

μ=v_d/E

μ is ionic mobility while V_d is drift velocity of ion and E is the magnitude of the applied electric field. This equation is valid for either gas phase or liquid phase. However, the electric field should be uniform throughout the medium.

What is Ionic Velocity?

Ionic velocity is the speed obtained by an ion moving through a medium under a unit electric field. We name it as drift velocity, and it is an average value. Here, the electric field has to be uniform, and it can exert a force on the moving charged particle. Moreover, we can give this ionic velocity as follows:

V_d = μE

V_d is the ionic velocity, and μ is the ionic mobility while E is the magnitude of the external electric field. The unit of measurement for this velocity is ms^-1.

What is the Difference Between Ionic Mobility and Ionic Velocity?

Ionic mobility and ionic velocity are highly related chemical concepts. The key difference between ionic mobility and ionic velocity is that ionic mobility defines the ability of ions to move through a medium whereas ionic velocity defines how fast the ions move through the medium. Moreover, another significant difference between ionic mobility and ionic velocity is that the unit of measurement of ionic mobility is m² V⁻¹ s⁻¹ while the unit of measurement of ionic velocity is ms⁻¹.

Summary – Ionic Mobility vs Ionic Velocity

Ions are charged particles. There are two major forms as cations and anions. However, both these ions can contribute to the conductance of an electrolyte. In brief, ionic mobility and ionic velocity are two chemical concepts that describe the movement of these ions through a medium. The key difference between ionic mobility and ionic velocity is that ionic mobility defines the ability of ions to move through a medium whereas ionic velocity defines how fast the ions move through the medium.

Reference:

1. “Ionic Mobility and Electrophoresis.” Chemistry LibreTexts, National Science Foundation, 26 Nov. 2018, Available here.
2. Libretexts. “8.9D: Ionic Migration.” Chemistry LibreTexts, National Science Foundation, 26 Nov. 2018, Available here.