Question

Define ionic mobility. Explain the factors affecting ionic mobility. How is it related to transport number?

Answer 1

Part 1: Ionic mobility:

• The average velocity with which a given ion drifts through a specified medium under the influence of an electric field is called ionic mobility.
• It is denoted by (μ).

Part 2:Factors affecting ionic mobility:

• Temperature: Ionic mobility is directly proportional to the temperature. The higher the temperature more will be the speed of the ion.
• Nature of electrolyte: Ionic mobility also depends upon the nature of the electrolyte.
• Size of ion: Ionic mobility is inversely proportional to the size of the ion. The larger the size of the ion less will be the ionic mobility.

Part 3: Transport number:

• The transport number is also called the transference number.
• It is the fraction of the total current carried in an electrolyte by a given ion.
• Differences in transport numbers arise from differences in electrical mobility.
• It is denoted by t_a or t_c.

${\mathrm{t}}_{\mathrm{a}}=\frac{\mathrm{Current}\mathrm{carried}\mathrm{by}\mathrm{an}\mathrm{anion}}{\mathrm{Total}\mathrm{current}\mathrm{passed}\mathrm{through}\mathrm{the}\mathrm{solution}}$

${\mathrm{t}}_{\mathrm{c}}=\frac{\mathrm{Current}\mathrm{carried}\mathrm{by}\mathrm{cation}}{\mathrm{Total}\mathrm{current}\mathrm{passed}\mathrm{through}\mathrm{the}\mathrm{solutiuon}}$

Relation between ionic mobility and transportation number:

The relationship between ionic mobility and transportation numbers is:

${\mathrm{\lambda }}_{\mathrm{a}}={\mathrm{t}}_{\mathrm{a}}\times {\mathrm{\lambda }}^{\infty }$

Or

${\mathrm{\lambda }}_{\mathrm{c}}={\mathrm{t}}_{\mathrm{c}}\times {\mathrm{\lambda }}^{\infty }$

Where ${\mathrm{\lambda }}_{\mathrm{a}}\mathrm{or}{\mathrm{\lambda }}_{\mathrm{c}}$ is ionic mobilities.