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Keywords:

  • pH—profiles versus solubility, weak acids, weak bases;
  • Solubility—profiles versus pH, weak acids, weak bases

Abstract

The pH–solubility profile of a weak acid or base is shown to be a function of its pKsp, and pKa, and uncharged species solubility. Equations are presented that can be used to calculate the solubility as a function of pH. These equations can also be used when there is added salt present. Experimental data was obtained in three cosolvent systems consisting of methanol–water and ethanol–water. Also, the effect of different acids on the solubility of a weak base is reported. A pronounced effect on the solubility by the addition of salt is explained in terms of the Ksp.