分布分数计算式推导及应用中的对应性和规律性问题探讨

doi:10.3866/PKU.DXHX202204009

Abstract

Abstract:

The calculation of equilibrium concentrations of each component in the acid-base system is a critical knowledge point in teaching analytical chemistry. Its teaching impact depends on the mastery of the derivation, application, and potential meaning of the distribution fraction (δ) formula. The derivation and application of δ as the focus are time-consuming and tedious. δ has good application in calculating the pH, concentration of each species in the acid-base and complex system, buffer capacity, and titration error. In this study, the methods for the rapid derivation and convenient application of δ in n-ary acid-base solutions were examined. The application of this study helps stimulate students' interest, improve cognition, and enhance understanding.

Key words: Analytical chemistry, Distribution fractions, Distribution curve, Acid-base systems

Kaiti Abulizi Xiao, Mulati Areyi, Ronglan Wu. Discussion of Correspondence and Regularity Problem in Deriving and Applying Distribution Fraction Calculations[J].University Chemistry, 2023, 38(2): 233-238.

Figures/Tables 2

溶液酸度	溶液中的组分及其变化	实例(磷酸溶液)
pH < pK_a1	主组分H_nA、次组分H_n−1A⁻；其他存在形式因浓度极低可忽略。随着pH渐近pK_a1，因H_nA解离出现H_n−1A⁻组分，[H_nA]渐近[H_n−1A⁻]，即H_nA的曲线渐降，H_n−1A⁻的渐增，相交在pH = pK_a1点	pH < 2.12	主组分H₃PO₄，次组分H₂PO₄⁻
pH = pK_a1	主组分H_nA、H_n−1A⁻，即[H_nA] = [H_n−1A⁻]；其他存在形式因浓度极低可忽略	pH = 2.12	主组分H₃PO₄、H₂PO₄⁻，即[H₃PO₄] = [H₂PO₄⁻]
pK_a1 < pH < pK_a2	主组分H_n−1A⁻，次组分H_nA和H_n−2A²⁻；其他存在形式因浓度极低可忽略。随pH增大，[H_nA]渐近最低值，[H_n−1A⁻]渐增至最大值，之后，因H_n−1A⁻开始解离出现H_n−2A²⁻组分，[H_n−1A⁻]渐近[H_n−2A²⁻]，即H_n−1A⁻的曲线渐降，H_n−2A²⁻的渐增，将相交在pH = pKa₂点	2.12 < pH < 7.20	主组分H₂PO₄⁻、次组分H₃PO₄、HPO₄²⁻， 2.12 < pH < 4.66时， [H₃PO₄] > [HPO₄²⁻] pH = 4.66时， [H₃PO₄] = [HPO₄²⁻] 4.66 < pH < 7.20时 [HPO₄²⁻] > [H₃PO₄]
以此类推	以此类推……	pH = 7.20	主组分H₂PO₄⁻、HPO₄²⁻，即[H₂PO₄⁻] = [HPO₄²⁻]
pK_an−1 < pH < pK_an	主组分H₁A⁽ⁿ⁻¹⁾⁻，次组分H₂A⁽ⁿ⁻²⁾⁻、Aⁿ⁻；其他存在形式因浓度极低可忽略。相交点后，随pH增大，[H₂A⁽ⁿ⁻²⁾⁻]渐近最低值，[H₁A⁽ⁿ⁻¹⁾⁻]渐增至最大值，然后H₁A⁽ⁿ⁻¹⁾⁻开始解离，[H₁A⁽ⁿ⁻¹⁾⁻]渐近[Aⁿ⁻]，即代表H₁A⁽ⁿ⁻¹⁾⁻的线渐降，Aⁿ⁻的渐增，趋向于相交点，相交在pH = pK_an点	7.20 < pH < 12.36	主组分HPO₄²⁻、次组分H₂PO₄⁻、PO₄³⁻， 7.20 < pH < 9.78时， [H₂PO₄⁻] > [PO₄³⁻] pH = 9.78时， [H₂PO₄⁻] = [PO₄³⁻] 9.78 < pH < 12.36时， [PO₄³⁻] > [H₂PO₄⁻]
pH = pK_an	主组分H₁A⁽ⁿ⁻¹⁾⁻、Aⁿ⁻；即[H₁A⁽ⁿ⁻¹⁾⁻] = [Aⁿ⁻]；其他存在形式因浓度极低可忽略	pH = 12.36	主组分HPO₄²⁻、PO₄³⁻，即[HPO₄²⁻] = [PO₄³⁻]
pK_an < pH	主组分Aⁿ⁻，次组分H₁A⁽ⁿ⁻¹⁾⁻；其他存在形式因浓度极低可忽略。相交点后，随pH增大，[H₁A⁽ⁿ⁻¹⁾⁻]渐近最低值，[Aⁿ⁻]渐增至最大值	12.36 < pH	主组分PO₄³⁻，次组分HPO₄²⁻

项	pH = 4.66		pH = 11.07
[H⁺]³	3 × 4.66 = 13.98	10^−13.98	3 × 11.07 = 33.21	10^−33.21
K_a₁[H⁺]²	2.12 + 2 × 4.66 = 11.44	10^−11.44	2.12 + 2 × 11.07 = 24.26	10^−24.26
K_a₁K_a₂[H⁺]	2.12 + 7.20 + 4.66 = 13.98	10^−13.98	2.12 + 7.20 + 11.07 = 20.39	10^−20.39
K_a₁K_a₂K_a₃	2.12 + 7.20 + 12.36 = 21.68	10^−21.68	2.12 + 7.20 + 12.36 = 21.68	10^−21.68

1	华东理工大学分析化学教研组; 四川大学工科化学基础教程教学基地. 分析化学, 第7版北京: 高等教育出版社, 2009.
2	武汉大学. 分析化学(上册), 第6版北京: 高等教育出版社, 2010.
3	李娜. 大学化学, 2021, 36 (9), 2108032.
4	何蔓; 陈贝贝; 胡斌. 大学化学, 2021, 36 (6), 2006036.
5	李爱峰; 王术皓; 贾文丽; 薛庆旺. 化学教育, 2018, 39 (22), 22.

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Discussion of Correspondence and Regularity Problem in Deriving and Applying Distribution Fraction Calculations

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