Ionic conductivities at infinite dilution

Sometimes in the literature the equivalent ionic conductivity at infinite dilution is erroneously termed ion mobility however, eqn. 2.17 clearly shows the interesting linear relationship between both properties with the faraday as a factor. 

This equation is valid for both strong and weak electrolytes, as a = 1 at the limiting dilution. The quantities A = zf- FU have the significance of ionic conductivities at infinite dilution. The Kohlrausch law of independent ionic conductivities holds for a solution containing an arbitrary number of ion species. At limiting dilution, all the ions conduct electric current independently the total conductivity of the solution is the sum of the contributions of the individual ions. 

Table 2.1 Ionic conductivities at infinite dilution (Q 1 cm2 mol ) at various temperatures. (According to R. A. Robinson and R. H. Stokes)...

Wagner s solution See Wagner s reagent. vag narz sa.Iu shan 1 Walden s rule phys chem A rule which states that the product of the viscosity and the equivalent ionic conductance at infinite dilution In electrolytic solutions is a constant, independent of the solvent It Is only approximately correct. wol-danz, rul ... 

Table 4.1—The equivalent ionic conductivities at infinite dilution in water at 25 "C...

Table 6.10. Some Ionic Conductivities at Infinite Dilution at 298 K (A 8 Sm2/kmoI)<621...

Table 5. Equivalent ionic conductances at infinite dilution (25 C)...

The cohesive energy of the solvent also is related to the boiling point, so there is a correlation of boiling point ot solvent viscosity as well. A further relationship of the equivalent conductance at infinte dilution is that it is composed of the individual ionic conductances at infinite dilution ... 

Calculate the limiting molar conductivities, A°, at 25°C for the following electrolytes NaNOa, Mg(OH)2, CaS04, K2SO4, (CH3COO)2Mg, La2(S04)3 given the following information on individual ionic conductivities at infinite dilution, i.e. A and... 

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 first term is due to the viscous drag of the solvent on the moving ion. When interionic effects vanish, this is the only remaining force and determines the ionic conductance at infinite dilution,. Fy is the force acting on the ion j due to the stress exerted by the local fluid on its surface. Fy is the force due to electrostatic interactions with the ions surrounding y, at low concentrations, the relaxation effect stems from this force. 

Start the complete numerical calculation described in sect. 5.4.2, When Ka is very large the value of the conductance at infinite dilution obtained by these methods has a rather large uncertainty hence Ka will be even more uncertain. In these cases A° is estimated by a different method, employing Walden s rule or using known values for the ionic conductances at infinite dilution. 

Dipolar aprotic solvents behave as differentiating solvents with the polarisability of the anions largely determining their interactions with the solvent molecules. Ionic conductances at infinite dilution show that the mobility of Br is roughly double that of supporting the idea that small halide ions are poorly solvated in these solvents. 

Table 3.2. Some molar ionic conductivities at infinite dilution at 25 °C...

Electrolytes in solution such as KCl dissociate into cations and anions and diffuse more rapidly than the undissociated molecule because of their small size. Diffusion coefficients can be estimated using ionic conductance at infinite dilution in water. Equations and data are given elsewhere (S5, T2). Both the negatively and positively charged ions diffuse at the same rate so that electrical neutrality is preserved. 

Molar ionic conductivities. At infinite dilution, each ionic species present contributes a fixed amount to the total ionic conductivity, regardless of the nature of any other ions present. This means that the total conductivity of a sufficiently dilute solution is given by the sum of the individual ionic conductivities of the i different ionic species present [Eq. (D.7)] ... 

X+ and X ° being the ionic conductivities at infinite dilution. Equation (4.9) has been written for infinite dilution since it is only under such conditions, when ion-ion interactions are at a minimum, that the law strictly holds. It is then applicable to both strong and weak electrolytes. Its validity is demonstrated in the data of Table 4.2. 

Example 6.1-5 Calcium chloride diffusion from conductance Estimate the diffusion coefficient of CaCl2 from conductance measurements. The equivalent ionic conductance at infinite dilution is 59.5 for Ca and 76.4 for chloride. The experimental value of the diffusion coefficient is about 1.32 lO cm /sec. 

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