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pKi values and sensitivity of acid-base indicators in the mixed solvent systems of water-alcohols and water-acetone at differential pH and in concentration media were determined by spectrophotometric method. When the concentration of the organic solvents were increased, the pKi values of sulfophthalein indicators, thymol blue and bromcresol purple, became larger whereas those of an azo indicator, methyl yellow, became smaller and the pH values of the equivalent points of acids became higher than those in the aqueous solution. Potassium bicarbonate, a standard compound used in acid-base titration, can be titrated with hydrochloric acid solution in the organic solvent systems without a prerequisite procedure of expelling carbon dioxide by boiling.
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