THEORETICAL EVALUATION OF ENTROPY TITRATION METHOD FOR CALORIMETRIC DETERMINATION OF EQUILIBRIUM CONSTANTS IN AQUEOUS SOLUTION

The effect of random errors in the titrant and solution concentrations and in the heat data on the accuracy of the equilibrium constant values obtained from thermometric titration data has been determined. Systems of the type HA + B− = HB + A− where KR is the equilibrium constant for the reaction as written and K is the equilibrium constant for the reaction HB = H+ + B− were investigated. The equilibrium constant for the reaction HA = A− + H+ is assumed to be known. The accuracy with which K can be determined depends on the magnitude of KRi- the most accurate log K values being obtained when log KR is greater than −1 and less than 2. For log KR values in this range, the cumulative effect of a 0.4% random error in the experimental heat data and of a 0.1% random error in the solution and titrant concentrations will normally cause an error of less than 0.01 unit in log K. Through the proper choice of titrant, the entropy titration method can be used to accurately determine any pK value less than 15 or greater than −1 for proton dissociation in aqueous solution. © 1968, American Chemical Society. All rights reserved.