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This article in SSSAJ

  1. Vol. 35 No. 5, p. 710-714
    Received: Sept 30, 1970
    Accepted: May 12, 1971

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Buffer Curves and Acid Strength of Humic Acid and Two Resins1

  1. J. T. Gilmour and
  2. N. T. Coleman2



Two humic acids, Cellex-CM, and IRC-50 were placed in 10-1, 10-2, and 10-3M NaCl or CaCl2 and titrated potentiometrically with NaOH or Ca(OH)2, respectively. Titration curves of Cellex-CM and IRC-50 in the NaOH-NaCl system showed parallel 1 pH unit displacements for a 10-fold change in NaCl concentration, while humic acid showed a 0.5 pH unit displacement. Buffer curves of humic acid, Cellex-CM, and IRC-50 in the Ca(OH)2-CaCl2 system showed a 0.4 pH unit displacement for a 10-fold change in CaCl2 concentration. The regular displacement of buffer curves led to development of a theory using ion exchange and surface ionization of H that described the buffer curves and assigned a salt independent pKa to the weak acid adsorbents.

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