1.23.5: Water: Self-Dissociation
A significant contribution to the chemistry of aqueous solutions stems from the self dissociation of water(\(\ell\))(see also \(\mathrm{D}_{2}\mathrm{O}(\ell\)) [1]). At \(298.15 \mathrm{~K}\) and ambient pressure, \(\mathrm{pK}_{\mathrm{a}} equals 14.004 [2]. Olofsson and Hepler [3] recommended a ‘best value’ for the standard enthalpy of self dissociation at ambient pressure and \(298.15 \mathrm{~K}\) equal to \(55.81 \mathrm{~kJ mol}^{-1}\) [4,5]. Hepler and colleagues recommend a best value for\(\Delta_{\mathrm{d}} C_{\mathrm{p}}^{0}\) equal to \(- 215 \mathrm{~J K}^{-1} \mathrm{~mol}^{-1}\) [5]; see also [6-8] together with [1] for details characterizing \(\mathrm{D}_{2}\mathrm{O}\).
The standard volume of self-dissociation for water(\(\ell\)) at \(298 \mathrm{~K}\) is negative, approx. \(- 20 \mathrm{cm}^{3} \mathrm{~mol}^{-1}\), decreasing with increase in temperature [8,9].
An extensive literature describes the thermodynamics of self-dissociation of water in binary liquid mixtures [11]; see also [12] for \(\mathrm{D}_{2}\mathrm{O}\).
Footnotes
[1] A. K. Covington, R. A. Robinson and R. G. Bates, J. Phys. Chem., 1966, 70 , 3820.
[2] A. K. Covington, M. I. A. Ferra and R. A. Robinson, J. Chem. Soc. Faraday Trans.,1,1977, 73 ,1721.
[3] G. Olofsson and L. G. Hepler, J. Solution Chem.,1975, 4 ,127.
[4] G. Olofsson and I. Olofsson, J. Chem. Thermodyn.,1973, 5, 533; 1977, 9 , 65.
[5] O. Enea, P. P. Singh, E. M. Woolley, K. G. McCurdy and L. G. Hepler, J. Chem. Thermodyn., 1977, 9 ,731.
[6] G. C. Allred and E. M. Woolley, J. Chem. Thermodyn..,1981, 13 , 147.
[7] P. P. Singh, K. G. McCurdy, E. M. Woolley and L. G. Hepler, J. Solution Chem., 1977, 6 ,327.
[8] J. J. Christensen, G. L .Kimball, H. D. Johnston and R. M. Izatt, Thermochim. Acta,1972, 4 ,141.
[9]
- D. A. Lown, H. R. Thirsk and Lord Wynne-Jones, Trans. Faraday Soc., 1968, 64 ,2073.
- F. J. Millero, E. V. Hoff and L. Kahn, J. Solution Chem.,1972, 1 ,309.
[10] J. P. Hershey, R. Damasceno and F. J. Millero, J. Solution Chem.,1984, 13 ,825.
[11]
- DMSO + water(\(\ell\)); A. K. Das and K. K. Kundu, J. Chem. Soc. Faraday Trans.1,1973, 69 ,730.
- \(\left(\mathrm{CH}_{3}\right)_{3}\mathrm{COH} + \text { water}(\ell)\); H. Gillet., L. Avedikian and J.-P. Morel, Can. J.Chem.,1975, 53 ,455.
- MeOH + water(\(\ell\)); C.H.Rochester, J. Chem. Soc., Dalton Trans.,1972,5.
- Alcohol + water(\(\ell\)); E. M. Woolley, D. G. Hurkot and L. G. Hepler, J. Phys. Chem., 1970, 74 ,3908.
- \(\mathrm{CH}_{3}\mathrm{CN} + \text { water}(\ell)\); U. Mandal, S. Bhattacharya and K. K. Kundu, Indian J. Chem. Sect. A,1985, 24 ,191.
- E. M. Woolley, and L.G.Hepler, Anal. Chem.,1972, 44 ,1520.
- Urea+water; A. K. Das and K. K. Kundu, J. Phys.Chem.,1975, 79 ,2604.
[12] R. E.George and E. M. Woolley, J. Solution Chem.,1972, 1 ,279.