Fraction of current carried

The fraction of current carried by the cations is clearly 7 /(7 + 7 ) tliis fraction is tenned the transport number of the cations, and evidently... 

Both the anions and cations can contribute to the current. In the absence of concentration gradients, the transference number relates the fraction of current carried by each species... 

The ion transport number is defined as the fraction of current carried through the membrane by counterions. If the concentration of fixed charges in the membrane is high compared to the concentration of the ambient solution, then the mobile ions in the IX membrane are mosdy counterions, co-ions are effectively excluded, and the ion transport number then approaches 1. Commercial membranes have ion transport numbers in dilute solutions of ca 0.85—0.95. The relationship between ion transport number and current efficiency is shown in Figure 3 where is the fraction of current carried by the counterions (anions) through the AX membrane and is the fraction of current carried by the counterions (cations) through the CX membrane. The remainder of the current (1 — in the case of the AX membranes and (1 — in the case of the CX membranes is carried by co-ions and... 

Transport numbers for several non-haloaluminate ionic liquids generated from ionic liquid self-diffusion coefficients are listed in Table 3.6-7. The interesting, and still open, question is whether the NMR-generated transport numbers provide the same measure of the fraction of current carried by an ion as the electrochemically... 

It is clear from these relationships that the transport number of an ion is different in different electrolytes. Thus when solutions of, say, potassium chloride and lithium chloride are electrolyzed, the fraction of current carried by the chloride ions is not the same in the two cases. 

The transport (or transference) numbers (/ ) represent the fractions of current carried out by such specific ions in the absence of concentration gradients. In dilute solutions can be estimated by dividing the equivalent ion conductance (Hq ) by A0. When concentration gradients are present, some of the current arises from diffusion and this affects the effective numbers. Generally, the transference numbers are weak functions of concentration and temperature and may be regarded as practically independent of salt concentration (Prentice, 1991 Robinson and Stokes, 2002). 

True and Apparent Transference Numbers.—The fundamental assumption of the Hittorf method for evaluating transference numbers from concentration changes is that the water remains stationary. There is ample evidence, however, that ions are solvated in solution and hence they carry water molecules with them in their migration through the electrolyte this will result in concentration changes which affect the measured or apparent transference number. Suppose that each cation and anion has associated with it and w- molecules of water, respectively let T+ and be the true transference numbers, i.e., the actual fraction of current carried by cations and anions, respectively. For the passage of one faraday of electricity the cations will carry w T+ moles of water in one direction and the anions will transport W-T- moles in the opposite direction there will consequently be a resultant transfer of... 

Ionic conduction is the conductive migration of dissolved ions in the applied electromagnetic field. This ion migration is a flow of current that results in PR losses (heat production) due to resistance to ion flow. All ions in a solution contribute to the conduction processes however, the fraction of current carried by any given species is determined by its relative concentration and its inherent mobility in the medium. Therefore, the losses due to ionic migration depend on the size, charge and conductivity of the dissolved ions, and are subject to the effects of ion interaction with the solvent molecules [18]. 

A laboratory membrane brine electrolysis cell, designed for automated operation, was constructed ( 1,2). This system enables the measurement of the sodium ion transport number of a membrane under specific sets of conditions using a radiotracer method. In such an experiment, the sodium chloride anolyte solution is doped with 22Na radio-tracer, a timed electrolysis is performed, and the fraction of current carried by sodium ion through the membrane is determined by the amount of radioactivity that has transferred to the sodium hydroxide catholyte solution. The voltage drop across the membrane during electrolysis is simultaneously measured, so that the overall performance of the material can be evaluated. 

For mixtures of charged species, the fraction of current carried by the yth species is and the amount of the total current, /, carried by theyth species is The number of moles... 

Guerrero, A., Singer, J.J., and Fay, F.S. (1994b) Simultaneous measurement of Ca release and influx into smooth muscle cells in response to caffeine. A novel approach for calculating the fraction of current carried by calcium. Journal of General Physiology, 104 395-422. 

For each mole of silver deposited in the coulometer the number of moles of KCl transferred from anode to cathode, being equal to the fraction of current carried by the potassium ions, is... 

The P/Q channel component is pharmacologically isolated by 2 pM co-conotoxin MVllC or co-conotoxin MVIID, or by 2 pM co-agatoxin IVA. In bovine chromaffin cells, co-conotoxin MVllD blocks the N current reversibly while co-conotoxin MVllC does so irreversibly [17]. Thus, the use of co-conotoxin MVIID followed by its washout can be a convenient tool to isolate the P/Q channel. The blocking effects of co-conotoxin MVIIC are extraordinarily slowed down and decreased in the presence of excessive concentrations (i.e., more than 2 mM) of Ba " [79,85] or Ca " [15]. Taking into consideration these methodological problems, we believe that the fraction of current carried out by P/Q channels in bovine chromaffin cells amounts to 50% [79]. This fraction is even higher (60%) in human chromaffin cells [65]. The opposite occurs in pig [63] and cat chromaffin cells [64] where P/Q channels carry only 5% of the cnrrent. Finally, in rat chromaffin cells, P/Q channels contribute 20% to the current [47] and in the monse 30% [62]. More recent studies show that this component is about 15% in mouse chromaffin cells [92]. 

Circulating current is thus mainly carried by hydroxyl ions, so that most of the alkahnity produced by the cathodic reaction is removed from the reinforcement surface. On the other hand, the fraction of current carried by chlorides is modest... 

The transport numbers, U and ta, of an electrolyte are defined as the fractions of the current carried, respectively, by the cation and anion. The calculation of these quantities from transport number measurements implies a knowledge of the nature of the ion carriers present, and this usually presents no difficulties. For a pure KCl solution, for instance, the ion carriers can confidently be stated to be and Cl ions, and the value of ta = 0.5102 for a 0.10 mol dm" solution of KCl at 25 shows that the fractions of current carried by and Cl" are 0.4898 and 0.5102, respectively. Combined with the measured molar conductivity of the salt at this concentration, A = 128.9012" cm the molar conductivity of the ion in this solution is 0.4898 x 128.90 = 63.14 and that of Cl" is 65.76 cm. ... 

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