多元酸碱滴定系统的PH,PX,δ,η,β随φ的变化规律

Variation law of pH,pX,δ,η,β with φ for polybasic acid-base titration system

从酸碱平衡的Henderson-Hasselbalch方程出发,运用物料守恒和质子守恒等基本原理,确定多元酸碱滴定的滴定方程[H^+]=f(φ),并解析平衡浓度负对数pX、分布系数δ、敏锐指数η和缓冲指数β等衍生量φ随滴定分数φ的变化规律.以OH^-滴定H_3PO_4为例,为避免求解关于[H^+]的高次方程,运用Excel求解数据集(pH,φ)和(φ,φ),运用Origin绘制pH-φ和φ-φ曲线,并具体分析滴定系统的特征.多元酸碱的滴定曲线在计量点时存在滴定突跃,当滴定至第i个计量点时,作为主要型体的第i级解离产物存在pX拐折,分布系数δ近似于1,而作为次要型体的第i-1和i+1级解离产物存在pX突跃,分布系数δ近似于0.敏锐指数η和缓冲指数β在计量点时分别存在极大值和极小值.突跃、拐折和极值具有随多元酸碱初始分析浓度递增的趋势.

Based on Henderson Hasselbaleh equation of acidbase equilibrium,matter conservation and protonconservation were.used as basie prineiple.the titration equation[H]=f(ó)for polybasic acidbase titration wasdetermined,simultaneously,the.variation law of derivative variable p such as negative logarithm of equilibriumconcentration pX,distribution coefficient 6,sensitivity index n and buffer indexèwith titration index Q wasinterpreted and analyzed.Taking the system that HsPO4 was titrated with OH for example,to avoid solving equationof higher degree for[H'].Excel was used to solvedatasets(pH,ó)and(o,ó),Origin was used to draw pH-óand Q-Q eurves,simultaneously,the characteristies of titration system was analyzed concretely.The titration eurveof polybasie acidbase existed titration jump in stoichiometric point,when titrated to the stoichiometric point i.thedissociative product in grade i which was the primary style existed pX inflexion and its distribution coeffieient 6 wasapproximate to 1,while the dissoeiative produets in grade.il and i+l which were the secondary style existed pXjump and their distribution coefficients 6 were approximate to 0.Sensitivity index n and buffer index B existedmaximum and minimum value in stoichiometric point,respectively.The jump,inflexion and extremum had inereasingtrend with the initial analytical concentration of polybasie acidbase.