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溴酚蓝(BPB)是分析化学中常用的指示剂,它有一个等吸收点的特征吸收谱图,利用这种吸收谱图可以确定溴酚蓝热力学解离常数K°.用通常的化学法和电化学法测定弱电解质的解离度,不能区分没解离的部分是分子还是离子对.用分光光度法测定解离度,可以找出这个区别,因为分子和离子有不同的吸收光谱.在溶液中离子对的形成主要靠离子间的库伦力,而光学性质通常受库伦力影响不大.因此,用具有等吸收点的吸收谱图来确定弱电解质的解离度的方法被称作真解离度测定法.在pH=2—5范围内,溴酚蓝的解离是从第二个羟基上脱下质子的过程
Bromophenol blue (BPB) is commonly used in analytical chemistry indicator, which has a characteristic absorption isotherm absorption spectrum, the use of this absorption spectrum can determine the thermodynamic K Br Phenol blue dissociation constant K °. By the usual chemical method Electrochemical methods can be used to determine the dissociation of weak electrolytes, and it is not possible to distinguish between molecules that are not dissociated or ion pairs. To determine the degree of dissociation by spectrophotometry, this difference can be found because of the different absorption spectra of molecules and ions. The formation of ion pairs in solution mainly depends on the Coulomb’s force between the ions, and the optical properties are generally not significantly affected by Coulombness Therefore, a method of determining the degree of dissociation of a weak electrolyte with an absorption spectrum having equal absorption points is called True Dissociation Assay The dissociation of bromophenol blue is the process of taking off protons from the second hydroxyl group in the pH range of 2-5