无机化学课程教学中一元酸碱溶液pH的定量计算问题

doi:10.3866/PKU.DXHX202003085

Abstract

Abstract:

The quantitative calculation of pH of monoacid/monobasic solution is a basic problem for inorganic chemistry teaching. The qualitative description and quantitative calculation of pH are connected by approximation conditions. It is very important for the students to understand these approximation conditions, which will help them solve problems about ionic equilibrium in aqueous solution. However, how to use these approximation conditions correctly in solution of low concentration and weak acids is often difficult. Even in some textbooks, the description of concepts is not accurate and not consistent with the associated courses. Thus, to solve the problems mentioned above, the derivations of the approximation conditions are introduced and examples are analyzed in detail in this paper. The problems of quantitative calculation of pH of monoacid/monobasic solution which should be paid attention to in the course teaching of inorganic chemistry are discussed.

Key words: Inorganic chemistry, Course teaching, pH, Quantitative calculation

MSC2000:

Ting Wang, Zongpei Zhang, Zhanhang He, Kai Li. The Quantitative Calculation of pH in Monoacid/Monobasic Solution in Teaching of Inorganic Chemistry[J].University Chemistry, 2020, 35(8): 129-134.

相对误差<	1%	2%	2.5%	4%	5%
K_a[HA] >	49.3K_w	24.3K_w	19.3K_w	11.8K_w	9.26K_w

相对误差<	1%	2%	2.5%	4%	5%
c/K_a >	2130	637	417	162	105

K_ac	c/K_a	计算方法
< 20K_w	< 400	${[{{\rm{H}}^ + }]^3} + {K_{\rm{a}}}{[{{\rm{H}}^ + }]^2} - ({K_{\rm{a}}}c + {K_{\rm{w}}})[{{\rm{H}}^ + }] - {K_{\rm{a}}}{K_{\rm{w}}} = 0$
< 20K_w	> 400	$[{{\rm{H}}^ + }] = \sqrt {{K_{\rm{a}}}c + {K_{\rm{w}}}} $
> 20K_w	< 400	$[{{\rm{H}}^ + }] = \frac{{ - {K_{\rm{a}}} + \sqrt {{K_{\rm{a}}}^2 + 4{K_{\rm{a}}}c} }}{2}$
> 20K_w	> 400	$[{{\rm{H}}^ + }] = \sqrt {{K_{\rm{a}}}c} $

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The Quantitative Calculation of pH in Monoacid/Monobasic Solution in Teaching of Inorganic Chemistry

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