The calculated pH that a solution would have if it were in equilibrium with calcium carbonate. Numerically, pHc* is equal to (pK2 - pKc) + p(Ca) + pAlk, where p(Ca) and pAlk are the negative logarithms of the molar concentrations of Ca and of the equivalent concentration of (CO3 + HCO3), respectively, and pK2 and pKc are the negative logarithms of the second dissociation constant of H2CO3 and the solubility constant of CaCO3, respectively, both corrected for ionic strength. It is used in conjunction with the measured pH of a water to determine if CaCO3 will precipitate from the water, or if the water will dissolve CaCO3 as it passes through a calcareous soil.