Total hydrogen ion concentration scale

Dickson, A. G. (1993) pH Buffers for Sea Water Media Based on the Total Hydrogen Ion Concentration Scale, Deep-Sea Res. 40, 107-118. 

Dickson, A. G. (1990) Thermod5mamics of the dissociation of boric acid in S5mthetic seawater from 273.15 to 298.15 K. Deep-Sea Res. 37, 755-66. Dickson, A.G. (1993) pH buffers for sea water media based on the total hydrogen ion concentration scale. Deep-Sea Res. 40,107-18. 

This is conceptually the simplest of the seawater pH scales, but suffers from the problem that the concentration of free hydrogen ion cannot be determined analytically, since when acid is added to seawater at low pH a proportion of the added acid is bound to sulphate and fluoride ions. Since fluoride is only a minor component of seawater (see Chapter 11), Hans-son (1973) proposed fluoride-ffee synthetic seawater as the standard state, giving the total hydrogen ion concentration scale pH(T)... 

Clayton and Byrne (1993) determined pH as a function of Q for m-cresol purple at different temperatures and fitted this to an equation with the following result on the total hydrogen ion concentration scale (mol/(kg-seawater)), valid in the range 293[Pg.120]

Over the last 25 years, several groups have made reliable determinations of the stability constants defined in Eqs. (8-36) to (8-40). Unfortunately, these constants are not always directly comparable with one another since different groups have used different concentration scales and pH scales. The discussion will be restricted to the options recommended here for measurement and for reporting of results, Le., the mol/(kg-seawater) concentration scale and the total hydrogen ion concentration pH scale pH(T). 

Table 8-1 lists the constants which are recommended for use on the mol/(kg-seawater) concentration scale and the total hydrogen ion concentration pH scale pH(T). The determinations by Roy et al. (1993 1994) and Dickson (1990) listed in Table 8-1 supersede the careful determinations of Hansson (1973), which covered a mine limited salinity range and that had a somewhat higher standard deviation. Careful stability crmstant measurements have also been made on the seawater pH(SWS) scale (Xi, Kz, Goyet and Poisson, 1989 K, Dickson and Riley, 1979) and on the pH(NBS) scale (K, Kz, Mehrbach etaL, 1973 K- Culberson and Pytkowicz, 1973). In addition, Dickson and Millero (1987) recalculated the Ki and Kz values of Hansson (1973) and Mehrbach et aL (1973) to the pH(SWS) scale and found no consistent difference between them. 

The total hydrogen ion scale, pH. is defined in terms of the sum of free and complexed (total) hydrogen ion concentrations, where... 

Hydrogen ion concentration corresponding to pH scale definition, H )= Burette acid concentration in potentiometric titration, mol/L Total concentration of hydrogen ion CO2 solubility constant, mol/((kg-seawater)-atm)... 

Thus, when [H" "] = 1.0 x 10" 7 M, the pH is 7.0. Note that the pH scale is actually defined more precisely by pH = -log Aji+, where Ah+ is the "activity" of hydrogen ion in the given solution. For dilute aqueous solutions, where the total concentration of ions is less than about 0.01 M, Ah+ is approximately equal to [H" ]. For concentrated aqueous solutions and for nonaqueous solutions, this approximation is less useful because of the effects of electrical forces between ions. A pOH scale can be similarly defined pOH = -log [OH"]. Since the relation [H+][OH"] = = 1.0 x... 

The state variables that we will use to describe the instantaneous state of the membrane will be the proton ion fraction, ion potential, and water content (i/hA 3r>d X). The three fluxes we will use are the hydrogen flux N, the total charge flux Nj- = N + Z N, and the water flux N. The concentration associated with the total flux is just C which is constant in time. In terms of the scaled position variable, equation (8.25) becomes... 

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