质子平衡方程各组分浓度动态图与碳酸氢钠溶液pH计算

Dynamic Diagram of Component Concentration in Proton Balance Equation and pH Calculation of NaHCO_(3)Aqueous Solution

NaHCO_(3)水溶液的质子平衡方程为:[H_(2)CO_(3)]+[H^(+)]=[OH^(-)]+[CO_(3)^(2-)]。随溶液浓度c的变化,H_(2)CO_(3),H^(+),OH^(-)和CO_(3)^(2-)的相对含量也会发生变化。提出并绘制了质子平衡方程中各组分浓度随溶液浓度c变化的动态图。从动态图上,可以直观地观察到哪些组分是主要组分,哪些组分是次要组分,哪些组分相对含量可以忽略不计,从而得到不同浓度区间溶液的不同pH近似式。对动态图的研究,不仅可以发现新的pH近似式,还可以帮助正确解读pH近似式的物理意义。值得强调的是,动态图对溶液中存在的各类质子转移平衡也能提供全新的认识。较浓溶液中,质子转移平衡HCO_(3)^(-)+HCO_(3)^(-)⇌H_(2)CO_(3)+CO_(3)^(2-)占据支配地位。9.1×10^(-6)mol·L^(-1)稀溶液中,反应H_(2)O+HCO_(3)^(-)⇌H_(2)CO_(3)+OH^(-)占据支配地位。

The proton balance equation of NaHCO_(3)aqueous solution is displayed as[H_(2)CO_(3)]+[H^(+)]=[OH^(-)]+[CO_(3)^(2-)],and the relative content of the species including H_(2)CO_(3),H^(+),OH^(-),and CO_(3)^(2-) would be changed as the analytical concentration of NaHCO_(3)solution is varied.In this paper,the dynamic diagram of the concentration of each component in the proton balance equation with the solution concentration c is presented and plotted.From the dynamic diagram,the major,the minor,and the negligible species in the proton balance equation are directly and easily determined,thus,different pH formulas of solutions with different concentrations were obtained.The dynamic diagram can not only find new pH formulas,but also help students understand the physical meaning of the pH formulas correctly.It should be emphasized that the dynamic diagrams can provide new insights into the proton transfer reactions.For example,in concentrated solutions,the proton transfer reaction HCO_(3)^(-)+HCO_(3)^(-)⇌H_(2)CO_(3)+CO_(3)^(2-) dominates.In 9.1×10^(-6)mol·L^(-1)solution,the proton transfer reaction H_(2)O+HCO_(3)^(-)⇌H_(2)CO_(3)+OH^(-) dominates.