Additivity of Electrolyte Limiting Conductivity

The limiting molar conductivity of an electrolyte, A°, is a sum of the limiting ionic conductivities, taking into account the number of ions, v in the electfolyte formula, 

FIGURE 3.20 Molar conductivity of strong [Chapter 10, Table 10.11] and weak [1] electrolytes 

The limiting ionic conductivity is a transport property of an ion, which does not depend on concentration but depends on tanperature and pressure (or density of the solvent). Contrary to any tliamodynamic property of an individual ion, the limiting ionic conductivities of individual ions can experimentally be obtained and are tabulated in [Chapter 10, Table 10.12] for a number of anions and cations. Therefore, the molar conductivity of an electrolyte at infinite dilution. A , is an additive value and can be calculated using the limiting ionic conductivities. This possibility is particularly useful for the weak electrolytes, whai A cannot be experimentally obtained using Kohlrausch s law by an extrapolation to the infinite dilution. For example, the limiting molar conductivity of acetic add, CHjCOOHCaq), can be calculated as follows  

As another example to use Equation 3.13, the limiting molar conductivity of CaCl2(aq) can be calculated using the limiting ionic conductivities of ions [Chapter 10, Table 10.12] and then compared with A of CaCl2(aq) given in [Chapter 10, Table 10.11]. Both values should be the same and are equal to 271.54 S cm mol .  

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