酸碱滴定:滴定剂液滴尺寸与滴定突跃

Acid-Base Titration: Volume of One Drop from a Burette and p H Range of Titration Jump

存在滴定突跃是滴定分析可以进行的先决条件。国内教科书讨论突跃范围的概念时均利用了滴定分数100±0.1%的条件,即按照滴定分数99.9%和100.1%来计算突跃范围。实际上,滴定过程中滴定剂是以液滴为单位加入到被测溶液中的,指示剂滴定法中也是以一滴或半滴标准溶液加入后被测溶液颜色发生改变来确定终点的,因此,按照化学计量点前后欠缺或过量半滴标准溶液来计算突跃范围更具科学性和实用价值。本文将计量点附近单滴滴定剂加入被测溶液引起的p H变化定义为突跃范围。对强碱滴定一元强酸体系的突跃范围进行了数学计算。结果表明,突跃范围与被测溶液的体积和浓度、滴定剂的浓度和液滴尺寸、被测溶液和滴定剂的浓度比等因素都有密切相关性,给出了不同于教科书的某些重要结论,这些新结论与实际滴定情形相符,对指导滴定分析具有重要参考价值。

The p H range of the titration jump is very important for the acid-base titration reactions directed by using an acid-base indicator. In this paper,the p H range has been calculated by a new way,namely around the volume ranges of Vep± 0. 5Vdrop,where Vepis the titrant volume at the right equivalence point,and Vdropis the volume of a single drop of the titrant delivered from a burette. The results showed that the p H jump ranges of the acid base reactions are closely related to titrant concentration,titrant volume of a single drop,the concentration and volume of the solution to be determined. Some new important conclusions can be deduced from the calculation of an example of acid base titration. For example,the volume of a single drop delivered from a burette should not be too small,ensuring an easy way of finding the end point of an acid base titration. The small volume of a single drop would be expected to give the lower titration error for the titration analysis.