Transport Number or Transference Number

(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 t_c and t_a or n_c and n_a”.

From this definition,

evidently,

(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.

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

Ionic mobility and transport number are related as,

Absolute ionic mobilityis the mobility with which the ion moves under unit potential gradient. It's unit is .

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