Some Electrical, Optical, and Transport Properties of the Mixtures

2 Some Electrical, Optical, and Transport Properties of the Mixtures The relative permittivity and the dynamic viscosity of binary mixtures of water with cosolvents are also relevant to the solvation and behavior of electrolytes and ions in these mixtures. These, again, are intensive properties, so that rather than dealing with excess quantities deviations from ideal behavior according to eq. (3.43), with AT replacing i , should be used. 

The relative permittivities obey Equation 3.43 with two or three terms, the values of which for 25°C, adapted from [56], except where noted, are shown in Table 3.15. Except for aqueous formamide and Af-methylformamide, in which the pure cosolvents have larger relative permittivities than that of water, the permittivities drop with increasing cosolvent contents, but not hnearly. 

The variation of the refractive index, n, between that of water and that of the neat water-miscible cosolvents does not exceed 13% (Table 3.5). Hence for some purposes, linear interpolation according to the mole fractions provides a sufficiently good approximation for of the mixture. A better one is obtained when is back-calculated from the molar refraction, assumed to be independent of the arrangements and bonding of the atoms, according to  

However, if the refractive index of the mixtures is to be used for calculation of the composition, as is sometimes done, then direct calibration is preferable to the use of Equation 3.49. 

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