I do a potentiometric titration for ligands( like amino acids ) and ligand metal complexes to calculate dissociation constant of ligands and formation constant of it's metal complexes.
You should calculate a concentration constant – ionic product of water (Kw) on the basis of thermodynamic constants (Kw0, table value), and the values of the activity coefficients of the ions H+ and OH-, calculated for a given ionic strength
KW=KW0/(yH*yOH), KW0=1,00∙10–14 (at 298.15 К)
logyi=(-A*zi2*I1/2)/(1+B*ai*I1/2) - bi*I - ci*I3/2
In the case of using of potassium nitrate KNO3 as the background electrolyte: А298К = 0,5091; zi=1 (i = H+ or ОН–); B298К = 0,03286; аН = 8,02 nm; aOH = 1,34 nm; bH = 9.2∙10–2; bOH = 11.3∙10–2; cH = cOH = 0;
I - ionic strength.
The autodissociation constant (Kw) of the solvent water were determined using Gran´s method. For all the information about this to see:
- G. Gran, Analyst (London) 1952, 77, 661.
- F.J. Rossotti and H. Rossotti, J. Chem. Educ., 1965, 42, 375.
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