Volumes of aqueous electrolyte solutions and the Tammann–Tait–Gibson model
Abstract
The Tammann–Tait–Gibson (TTG) equation for the partial molal volumes of aqueous electrolytes is compared with the Masson and Redlich equations. The TTG equation is shown to be equivalent to the Masson equation and the relationships between the coefficients are given. The TTG effective pressure function is derived for NaCl, NaBr, MgCl2, Na2SO4 and MgSO4 from reliable density data at 25 °C and shown to be entirely consistent with the corresponding compressibility data. The derivation was made using a number of constraints that ensured correct extrapolation to zero. The Masson and TTG coefficients in I½(I is the ionic strength) were found to be equivalent. Within the experimental and fitting errors, these coefficients are a linear function of the standard ionic entropies. The difference between the Debye–Hückel (DH) and TTG slopes for I½ is given by: +° – 1.4[ν−
−° + nΔ
diss°(H2O)]}
+°,
−° are the corresponding standard entropies (relative to
H+° = 0), Δ
diss°(H2O) is the entropy of ionization of water and n is the number of moles of water affected by 1 mole of the salt. This equation applies to seventy electrolytes with an average deviation of ± 0.23; the slopes range in value from 0 to 14.6 cm3 kg½ mol–
. The TTG volume is shown to be simply related to the standard entropies and when the ions become point charges S(TTG) = S(DH).