Automatic titration by stepwise addition of equal volumes of titrant. Part III. Use of linear equations to calculate equivalence volumes in acid-base titrations

Potentiometric titrations in which the titration curve is plotted or the titration is interrupted at a pre-set end-point have important disadvantages. The following conditions must be met to obtain satisfactory results: (1) reaction between titrant and titrand must be rapid; (2) the response time of the indicator electrode must be short; and (3) electrode potentials near the equivalence point must be stable and reproducible.These disadvantages can be avoided by using the method of stepwise addition of titrant. In this method, equivalence volumes cannot be read directly and must be calculated. A computational procedure allowing the calculation of equivalence volumes for the titration of monoprotic acids, bases and ampholytes with log K values up to 11 is described. The procedure is based on the solution of a set of linear equations and requires only a few sets of measurements of e.m.f. versus volume of titrant plus initial volume and titrant concentration. Log K values are not required and e.m.f. measurements may have a constant systematic error up to ±6 mV, corresponding to ±0.1 pH unit. Only concentrations and concentration constants are used. No estimated values of equivalence volumes or stability constants are necessary.