计算一元弱酸溶液pH的标准化解题方法

A Normalized Method to Find the pH of a Solution Containing a Weak Monoprotic Acid

本文提出了计算一元弱酸HA(浓度c,离解常数K_a)溶液pH的标准化解题方法。第一类情形,比较c与K_a大小。如果c≥105K_a,则[H^+]=(cK_a+K_w)^(1/2);如果K_a≥19c,则弱酸溶液可按强酸溶液来处理,通常情况下可认为[H^+]=c。第二类情形,如果1/19K_a<c<105K_a,则比较cK_a与10K_w(K_w水的离子积)大小,cK_a≥10K_w时,[H^+]=1/2(-cK_a+(K_a^2+4cK_a)^(1/2));cK_a<10K_w时,[H+]=(cK_a+K_w)^(1/2)。标准化解题具有以下特点:两类情形判据清晰;求算过程简单;普适性好,常见浓度的(c≥6×10^(-6)mol·L^(-1))一元弱酸溶液pH计算均可适用。

This paper presents a normalized method to find the pH of a solution containing a weak monoprotic acid. The normalized method has the following characteristics： Its results is very close to the true values. The calculation steps arc clear and normalized. The universality of this new method is good, applicable to the pH calculation for all weak monoprotic acids except very dilute solution （6×10^-6 mol·L-1）.