确定乙酸乙酯和氢氧化钠等浓度下的皂化反应速率常数的多种方法

Various Methods for Determining the Saponification Reaction Rate Constant at the Same Concentration of Ethyl Acetate and Sodium Hydroxide

摘要: 在物理化学实验的课程中常用电导法测定乙酸乙酯和氢氧化钠等浓度下的皂化反应速率常数，通过测量不同反应时间下的电导率，再根据二级反应特点，找出反应物浓度与时间的关系，然后处理数据给出反应速率常数，发现误差与处理数据的模型有关。本文为了说明不同误差的原因，能够更清晰比较各种处理模型的特点，详细推导了五种处理模型的拟合公式，并用其分别处理5组平行实验数据。其中四种模型是建立在电导率与浓度是线性关系的基础上，包括非线性拟合和线性拟合，其处理数据的反应速率常数相对误差都较大，在65.16%到138.11%之间，而建立在电导率与浓度是非线性关系的基础上的第五种模型，用数值法处理数据，发现其误差最低，平均值为23.95%。本文通过比较不同模型处理的结果，指出学生处理实验数据时需要根据实验情况而选择合适的拟合模型的必要性。只有选择合适的拟合模型才能得到较准确的反应速率常数。

Abstract: In the course of physical chemistry experiment, the conductance method was commonly used in the saponification reaction of the same concentration of ethyl acetate and sodium hydroxide to measure the reaction rate constant. By measuring the conductivity under different reaction times, the relationship between the concentration of reactants and time was found according to the characteristics of the second-order reaction, and then the reaction rate constant was given by processing the data. The errors were found to be related to the model of processing the data. In order to explain the causes of different errors and compare the characteristics of various processing models more clearly, this paper derived the five fitting formulas of processing models in detail and used them to process five groups of parallel experimental data respectively. Among the five models, there were four ones that were based on the linear relationship between conductivity and concentration, including nonlinear fitting and linear fitting, and the relative errors of the reaction rate constants of the processed data were large, ranging from 65.16% to 138.11%. The fifth model which was based on the nonlinear relationship between conductivity and concentration had the lowest error, with an average of 23.95%. By comparing the results of different models, this paper pointed out that it was necessary for students to choose an appropriate fitting model according to the experimental situation when processing experimental data. Only by choosing a suitable fitting model could we get a more accurate reaction rate constant.