Neutralization and Acid Dissociation of Hydrogen Carbonate Ion : A Thermochemical Approach
Neutralization and Acid Dissociation of Hydrogen Carbonate Ion : A Thermochemical Approach
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碳酸氢根离子的中和和酸解：热化学方法
DOI：
10.1021/ed300090g
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发表时间：
2013
期刊：
影响因子：
3
通讯作者：
S. Mishima
中科院分区：
文献类型：
--
作者：
N. Koga;K. Shigedomi;T. Kimura;T. Tatsuoka;S. Mishima
本文对NaHCO3和NaOH水溶液反应中的热化学关系进行了实验室探讨。用量热法测定了该反应的热变ΔRh，以及强酸与氢氧化钠(AQ)中和反应的热变ΔnH，对此差异的解释是学生提问的依据。学生们认为，碳酸氢根离子的酸解离对整个反应的贡献可能是造成这种差异的原因。利用赫斯定律，学生提出了酸解离热变化Δdh的正值。然后，他们被要求提供Δdh阳性的实验证据。学生通过测量不同温度下NaHCO3和NaOH水溶液反应的半中和点溶液的pH来检验酸离解常数与温度的关系。这为预测ΔdH的符号提供了第二种方法；然后，通过引入范特霍夫方程，可以计算出ΔdH的数值。探究活动的目的是使用ΔRh、ΔNh和ΔDh的评估实验值来验证赫斯定律。本实验活动适用于高中的高级化学课程或大学的普通化学课程。此外，从学生数据中计算碳酸氢离子酸解的吉布斯能量变化ΔdG和熵变化ΔdS可用于高级实验室活动。
A laboratory inquiry into the thermochemical relationships in the reaction between aqueous solutions of NaHCO3and NaOH is described. The enthalpy change for this reaction, ΔrH, and that for neutralization of strong acid and NaOH(aq), ΔnH, are determined calorimetrically; the explanation for the difference is the basis for the student inquiry. The contribution of acid dissociation of the hydrogen carbonate ion to the overall reaction is considered by students as a possible explanation for the difference. Using Hess’s law, students propose a positive value for the acid dissociation enthalpy change ΔdH. Then, they are required to show experimental evidence of the positive ΔdH. Examination of the temperature dependence of the acid dissociation constantKais performed by students through pH measurements of the solution at the half-neutralization point of the reaction between aqueous solutions of NaHCO3and NaOH at different temperatures. This provides a second means of predicting the sign of ΔdH; then, through introduction of the van’t Hoff equation, a numerical value for ΔdHcan be calculated. The goal of the inquiry activity is to verify Hess’s law using the evaluated experimental values of ΔrH, ΔnH, and ΔdH. This lab activity is appropriate for advanced chemistry courses at high schools or general chemistry courses at colleges. Further, calculations of the Gibbs energy change ΔdGand entropy change ΔdSof acid dissociation of the hydrogen carbonate ion from the student data for the temperature dependence ofKacan be applied in an advanced lab activity.