Ion transport number

Ion transport number, also called the transference number, is the fraction of the total current carried in an electrolyte by a given ion. Differences in transport number arise from differences in electrical mobility. For example, in a solution of sodium chloride, less than half of the current is carried by the positively charged sodium cations and more than half is carried by the negatively charged chloride anions because the chloride ions are able to move faster, i.e., chloride ions have higher mobility than sodium cations. The sum of the transport numbers for all of the ions in solution equals unity.