The limiting molar conductivity

The value of A is a measure of the ion-solvent interaction and, within the scope of the continuum hydrodynamic model, is related to the bulk viscosity of the solvent, t], through the Nemst-Einstein equation or its empirical equivalent, Walden s law (t .A = constant). However, it is well known that the simple continuum model is not valid in aqueous systems even at room temperature. 

Marshall analyzed the limiting molar conductivity of simple electrolytes up to 800 °C and 400 MPa and proposed (Marshall, 1987) a reduced state relationship for the limiting conductivity of aqueous ions on the basis of the experimental information available at that time. He found that A was a linear function of density 

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In Section 7.1, molar conductivities of electrolytes of various degrees of dissociation were considered. The limiting molar conductivity of electrolyte MxAy (A°°) is given by ... 

The method for the determination of limiting molar conductivities of electrolytes A°° was discussed in Section 7.1. The limiting molar conductivities of individual ions (7 ) can be obtained by the following methods. 

The limiting molar conductivity of an electrolyte (A°°) and the limiting transference numbers of the ions constituting the electrolyte are determined ex-... 

The limiting molar conductivity, A°°, for a reference electrolyte [(i-Am)4N+B(i-Am)4, (i-Am)3BuN+BPh4, etc.] is determined experimentally and t100/2 is considered to be the limiting conductivity of the constituent ions. 

When the limiting molar conductivities are to be obtained for a series of ions in a given solvent, the first step is to get the limiting molar conductivity of an ion by one of the above methods. Then, the limiting molar conductivities for other ions can be obtained sequentially by applying Kohlrausch s law of independent ionic migration (Section 5.8). 

The limiting molar conductivities of ions in various solvents are listed in Table 7.4. The following are some general points about ionic conductivities in non-aque-ous solutions ... 

As mentioned in Section 7.1, if we determine the molar conductivity of an electrolyte as a function of its concentration and analyze the data, we can get the value of limiting molar conductivity A°° and quantitative information about ion association and triple-ion formation. If we determine the limiting molar conductivity of an ion (7 °) by one of the methods described in Section 7.2, we can determine the radius of the solvated ion and calculate the solvation number. It is also possible to judge the applicability of Walden s rule to the ion under study. These are the most basic applications of conductimetry in non-aqueous systems and many studies have been carried out on these problems [1-7]. 

A selected number of ionic mobilities at 18°C and 25°C is shown in Table 1.4. This table may be utilized for the calculation of the limiting molar conductivities of any electrolytes made up of the ions listed. Thus, for acetic acid at 25°C... 

Fig. 6.7 Plots of the molar conductivity against the square root of the electrolyte concentration for three strong electrolytes ( ) and one weak electrolyte ( ). The data for the strong electrolytes were fitted to a straight line at lower concentrations in order to obtain the limiting molar conductivity Aq.

Use the Henderson equation to estimate the liquid junction potentials for the following systems assume that the limiting molar conductivities given in table 6.2 can be used to calculate the ionic mobility. 

A° (m /Q/mol) is the limiting molar conductivity of ions at infinite dilution. The typical values of Xj are around 10 /Q. For comparison, the bulk conductivity, is given by... 

The limiting value to which A approaches as Cs,oich 0 is called the limiting molar conductivity, A° and ... 

It is used for calculating the limiting molar conductivity, JsP, of an electrolyte from tabulated individual limiting ionic conductivities, X°, i.e. for very, very low concentrations. Under such conditions, the law can handle calculations of predicted limiting molar conductivities for both strong and weak electrolytes. 

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... 

Calculate the limiting molar conductivities at infinite dilution, A", for the following weak acids at 25°C. 

What is first required is the value for the limiting molar conductivity of NHaCaq) in terms of the values given for the strong electrolytes NaOH(aq), NH4Cl(aq) and NaCl(aq). 

E21.25(b) The limiting molar conductivity of a dissolved salt is the sum of that of its ions, so... 

Acetic acid is so weak in methanol Ka = 9.63 at 25°C) that it is impracticable to attempt to determine Ka from measurements on solutions of the weak acid alone. The solvent corrections for these solutions are uncertain. Moreover, a long extrapolation is required to obtain the limiting molar conductance according to eqn. 3.5.3. It is better to find A° independently by using Kohlrausch s law ... 

AJ is the limiting molar conductance at infinitesimal ionic strength, and the relaxation and electrophoretic parameters a and jS, respectively, are defined in eqn. 5.2.3. From eqns. 5.8.3 and 5.10.1 the transference number of a completely dissociated symmetrical electrolyte is given by... 

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