Molar conductance limiting

Table 9. Ionic radii and ionic limiting molar conductivities of some anions in PC at 25°C, taken from Ref. 1211]...

Radii of anions of lithium salts and limiting molar conductivities in solvents of... 

A,. limiting molar conductivity of electrolyte in presence of ligand III.7 ... 

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 ... 

Method for the Determination of Limiting Molar Conductivities of Ions... 

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]. 

Hittorf transport method — Only at infinite dilution can the molar conductivity of a solution be split into the two limiting molar conductivities associated with the individual ions, which are independent of each other. This is because only at infinite dilution can we completely neglect interionic interactions. However, in order to determine the values of the individual ionic conductivities, an additional measurement is necessary in order to partition Ao into AJ and Ag we must determine the so-called -> transport numbers of the individual ions. The total current i, can be written as the sum of partial currents i+ and i, corresponding to the currents carried by the cations and anions. We define the transport number of the cations, t+, as t+ = -fi— = and simi-... 

As a result of prolonged and careful study of the conductance of salt solutions down to low concentrations, Kohlrausch found that the difference in molar conductivities of pairs of salts, containing similar anions and always the same two cations, is constant and independent of the nature of the anion. He found for example that the following differences of limiting molar conductivities (measured at 18°C in cm2 Q 1 mol-1 units)... 

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... 

Table limiting molar conductivity, ion-pair formation constant and ion size parameters. 

Limiting molar conductivities of the complex ions ( A °°(M" /n)) obtained were expressed as a fiinction of temperature (/ in 0 by the equation ... 

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.

Table 6.2 Limiting Molar Conductivities of Single Ions in Water at 25°C [7] ...

Estimate the molar conductivity of 0.1 M HCl at 25°C given that its limiting molar conductivity is 426.2 cm mol and assuming an ionic size parameter a of 0.45 nm. 

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... 

This is in stark contrast to the situation where hmiting ionic conductivities are concerned (see Sections 11.11 to 11.13). Here limiting molar conductivities can be split up into individual limiting ionic conductivities for the cation and the anion, so that a table of these can be constmcted, e.g. ... 

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

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