高周波容量分析 (第2報)

弱酸の中和滴定

抄録

Neutralization titration of weak acids was carried out using the high frequency volumetric analytical apparatus described in the previous report (This Journal 71, 705 (1951)). By the ordinary method, it is difficult to determine the end point but an excellent method was devised by the use of two procedures. One is the titration of definite amount of 0.1 N sodium hydroxide solution by the solution of weak acids to be tested, and the other is the addition of a very small amount of pyridine in the weak acid solution being tested. In the case of the latter, acids with a dissociation constants of around 10^-7, i.e. acids with dissociation above that of the first dissociation of carbonic acid, can correctly be determined. In both cases, the solvent used is water. In the case of a mixture of two acids, as long as their dissociation constant is less than 10^-3, they can separately be titrated without the addition of pyridine. Phenol, boric acids and others whose dissociation constant is less than 10^-9 fail to react by this means even by the addition of pyridine that the presence of these compounds do not constitute a hazzard in this titration. It was found, however, that it was possible to titrate these very weak acids with dissociation constants less than 10^-9 by the use of pyridine as the sole solvent.