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 tc and ta or nc and na”.
From this definition,
(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 .