醋酸溶液pH近似计算的浓度限制条件

To Estimate the pH of Acetic Acid Solution: The Concentration Limitation for the Approximate Calculation

实际工作中,根据浓度(c)差别,醋酸溶液的pH可用不同近似式求解,本文给出了使用近似式的浓度限制条件,对正确使用近似式获得醋酸溶液pH将提供很大便利。获得了准确氢离子浓度pH与醋酸溶液浓度c(pc=-lgc)的关系曲线,并得到以下结论:(1)当c≥1.89×10^(-3) mol?L^(-1)时,[H^+]=(cK_a)^(1/2),(2)当c≥4.30×10^(-7)mol?L^(-1)时,则[H^+]=(-K_a+(K_a^2+4cK_a)^(1/2))/2。近似结果与准确结果相对误差均满足±5.0%要求。

Calculating the pH of acetic acid solution is one of the most common work in analytical chemistry. If we know the concentration （c） and dissociation constant （K,）, it is possible to estimate the pH for the acetic acid solution. Two situations can be distinguished in depending on the concentration of＇acetic acid. （1）When c ≥ 1.89×10^-3 mol·L^-1,[H^＋]=√cka, the relative error excels 5.0 %. （2） When c ≥4.30×10^-7 mol·L^-1,[H^＋]=2/-ka＋√ka^2＋4cka,the relative error also excels -5.0 %.