Conductivity molar ionic

Magnetic field strength H Molar ionic conductivity A, A... 

Example 3.7 Use molar ionic conductivity data in Table 3-1 to calculate the mobility and diffusivity of Na+, Cl and NaCl at infinite dilution and 298.15 K. 

The ionic mobility is related to the molar ionic conductivity of the ion k... 

Ionic mobility — Quantity defined by the velocity of an ion moving in a unit electric field (SI unit m2 V-1 s-1). The ionic mobility of ion i (uf) is related to its molar ionic conductivity (A ) by A = zfFui, where Z is the charge number of the ion. The ionic mobility is also related to the -> diffusion coefficient (A) by the Nernst-Einstein... 

Molar ionic conductivity — This quantity, first introduced by -> Kohlrausch, is defined by A = Zi Fui (SI unit Sm2 mol-1), where Zj and 14 are the charge number and -> ionic mobility of an ion, respectively. The molar -> conductivity of an electrolyte M +X (denoted by A) is given by A = u+X+ + i/ A, where A+ and A are the molar ionic conductivities of the cation and anion. The A value of an ion at infinite dilution (denoted by A°°) is specific to the ion. For alkali metal ions and halide ions, their A values in water decrease in the orders K+ > Na+ > Li+ and Br- > Cl- > F-. These orders are in conflict with those expected from the crystal ionic radii, because the smaller ions are more highly hydrated, so that the -> hydrated ions become larger and thus less mobile. Based on Stokes law, the radius of a hydrated ion... 

Eq. (11) shows that the signal observed during solute ion elution is also proportional to the difference in limiting molar ionic conductivities between the eluent and the solute ions. 

Values of limiting molar ionic conductivities for a few common ions are shown in Table 1. The data tabulated are referred to 25°C temperature. The term limiting molar ionic conductivity is used according to lU-PAC recommendation, rather than the formerly used limiting ionic equivalent conductivity. The molar and equivalent values are interconvertible through stoichiometric coefficient z. 

Table 1 limiting Molar Ionic Conductivities of some Anions and Cations (S cm /mol) at 25°C... 

It is common to introduce A the molar ionic conductivity for electrolytes, which is the conductivity of a specific volume of an electrolyte containing one mole of solution between electrodes placed one meter apart ... 

The transport number has been defined in Section 9.1 as the fraction of the total current carried by a given ion. This is the definition most useful to the determination of transport numbers from emfs. In Chapter 11 the transport number is defined in terms of ionic mobilities, and/or individual molar ionic conductances (see Section 11.17), which are more directly linked to the methods described in that chapter. 

Analysis of the situation for such acids and bases will be given (Section 11.14), once individual molar ionic conductivities have been discussed (see Section 11.11 below). 

After correcting for the conductivity of the solvent, the conductivity of a saturated solution of silver bromide in water is 6.99 x 10 S cm at 18°C. If the molar ionic conductivities of Ag" (aq) and Br (aq) are 53.5 and 68.0 S cm mol respectively, find the solubility of silver bromide in water. From this calculate the solubility product for silver bromide. 

The values for the transport numbers are internally self consistent between the calculation from molar ionic conductivities and from the ionic mobilities. This is as it should be. The sum of the transport numbers for the ions of a given electrolyte is unity. This, again, is as it should be. 

It is very important to be able to measure transport numbers over a range of concentrations as this is the only way to determine the dependence of individual molar ionic conductivities as a function of concentration. If this can be done, then it means that observed molar conductivities for any electrolyte at given concentrations can be split up into the contributions from the ions of the electrolyte. 

Varying the concentration of the KCl solution will allow determination of the transport numbers for both ions over a range of concentrations. From these the individual molar ionic conductivities for KCl(aq) over a range of concentrations can be found. 

The actual ionic molar conductivity which is a value for situations where non-ideality must be considered is equal to the ideal molar ionic conductivity at infinite dilution modified by the term 1 — AX/X. AX is a sum of aU the terms which are taken to lead to non-ideality. 

The equation for the molar ionic conductivity for a symmetrical electrolyte is ... 

Table 6.3 Individual Molar Ionic Conductivities (Q cm mo ") in Water at 25 C...

The (specific) electrolytic conductivity of a saturated solution of silver chloride, AgCl, in pure water at 25 C is 1.26 x 10 O " cm higher than that of the water used. Calculate the solubility of AgCl in water if the molar ionic conductivities are Ag", 61,8 Cl , 76.4 cm moPh... 

This paper provides a calculated value of 250 for K for nickel sulphate complexation based on the earlier measurements of Franke [1895FRA] (at the two lowest molarities for which results were reported, 9.768 x lO" and 19.53 x lO M) at 25°C. The value of A was based on estimates of the molar ionic conductivities of sulphate (158 S cm moF ), and for Ni (112.2 S cm -moF ). There are no new experimental data. 

Once we have measured transference numbers, we can calculate the values of the molar ionic conductivities using Eq. (31.39)... 

At 25 °C, a solution of KCl having a conductivity of 0.14088 S/m exhibits a resistance of 654 in a particular conductivity cell In this same cell, a 0.10 mol/L solution of NH4OH has a resistance of2524 Q. The limiting molar ionic conductivities are available in Table 31.5. Calculate... 

In Appendices 5.12.1 to 5.12.12 are given tables of limiting molar ionic conductances in those organic solvents for which both accurate conductances and at least reasonably accurate transference numbers are at present available. Inspection of the figures in the appendices yields the following broad generalisations ... 

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