# JEE Main & Advanced Chemistry Electrochemistry Transport Number Or Transference Number

Transport Number Or Transference Number

Category : JEE Main & Advanced

(1) Definition : “The fraction of the total current carried by an ion is known as transport number, transference number or Hittorf number may be denoted by sets symbols like t+ and t or tc and ta or nc and na.

From this definition,

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

${{t}_{c}}=\frac{\text{Current carried by a cation}}{\text{Total current passed through the solution}}$

evidently, ${{t}_{a}}+{{t}_{c}}=1.$

(2) Determination of transport number : Transport number can be determined by Hittorf's method, moving boundary method, emf method and  from ionic mobility.

(3) Factors affecting transport number

A rise in temperature tends to bring the transport number of cation and anion more closer to 0.5

(4) Transport number and Ionic mobility : Ionic mobility or Ionic conductance is the conductivity of a solution containing 1 g ion, at infinite dilution, when two sufficiently large  electrodes are placed 1 cm apart.

$\text{Ionic mobilities }({{\lambda }_{a}}\,\text{or}\,{{\lambda }_{c}})\propto \,\text{speeds of ions}\,\text{(}{{u}_{a}}\text{or}\,{{u}_{c}})$

Unit of ionic mobility is Ohm–1 cm2 or V–1S-1cm2

Ionic mobility and transport number are related as,

${{\lambda }_{a}}\,\text{or}{{\lambda }_{c}}={{t}_{a}}\,\text{or}\,{{t}_{c}}\times {{\lambda }_{\infty }}$

Absolute ionic mobility is the mobility with which the ion moves under unit potential gradient. It's unit is $cm\,{{\sec }^{-1}}$.

$\text{Absolute ionic mobility }=\frac{\text{Ionic mobility}}{\text{96,500}}$

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