Monograph - Metrohm

Titration of basesThe lowest pH values at the end of the titration were:with HClO 4 ; –5.7 in MIBK/glacial acetic acid/toluene/El.1 and –5.5 inacetone/El.1with HCl; –3.7 in MIBK/glacial acetic acid/toluene/El.1 and –3.4 inthe same solvent/El.2Very good solvents for medium-strength bases are acetone, acetonitrileand toluene/IPA/H 2 O.B) Aniline (pK B = 9.42)Except for ethanol the jumps with HClO 4 were larger, steeper and neater. In fourcases the curves were identical with each electrode, in two cases Electrode 1was better (MIBK/glacial acetic acid/toluene and toluene/IPA/H 2 O).Summary of the delta pH values (mean value of 3 determinations, delta «pH init»to «pH end»):Solvent HClO 4/El.1 HCl/El.1 HClO 4/El.2 HCl/El.2Ethanol 5.8 5.5 5.7 5.1Acetone 7.0 4.3 7.0 4.4Acetonitrile 7.5 4.8 7.4 4.6Dioxane/IPA 5.2 3.8 5.2 3.9MIBK/glacial acetic acid/toluene5.8 4.0 5.7 4.0Toluene/IPA/H 2O 5.6 3.6 5.3 3.8The lowest pH values at the end of the titration were:with HClO 4 ; –5.6 in MIBK/glacial acetic acid/toluene - El.1 and –5.3in acetone - El.1with HCl; –3.6 in MIBK/glacial acetic acid/toluene - El. 1 and –3.2in the same solvent - El.2Very good solvents for weak bases are acetone, MIBK/glacial acetic acid/toluene and also ethanol.C) Urea (pK B = 13.80)This very weak base could not be determined in any of the solvents tested. Notitration curves that could be evaluated were obtained!Non-aqueous titration of acids and bases with potentiometric endpoint indication 13