两性物质NaHA溶液pH计算的新近似公式

New Approximate Formula for pH Calculation of Amphiprotic NaHA Solution

NaHA可分为酸性物质(K_(a1)K_(a2)>K_(w))和碱性物质(K_(a1)K_(a2)<K_(w))。NaHA酸性物质溶液,其pH范围为:(pK_(a1)+pK_(a2))/2<pH<7.00。NaHA碱性物质溶液,其pH范围为:7.00<pH<(pK_(a1)+pK_(a2))/2。根据NaHA溶液性质,合理舍弃次要组分,分别得到了酸性物质或碱性物质溶液pH的近似公式。本文推导的近似公式具有如下特点:物理意义清楚,适用浓度范围广。例如,对于极稀溶液(1.0×10^(-5) mol·L^(-1)),计算结果也满足±5%误差要求。

The amphiprotic NaHA can be divided into acidic and alkaline substances.If NaHA is acidic,its solution has a pH range of(pK_(a1)+pK_(a2))/2<pH<7.00.If NaHA is alkaline,the pH range of its solution covers 7.00<pH<(pK_(a1)+pK_(a2))/2.Based on the acid-base properties of NaHA solution,ignoring the minor components,the approximate formula of pH for acidic or alkaline solution is obtained,respectively.The new approximate formula derived in this paper has the following characteristics:It can be used in very dilute solution(1.0×10^(-5) mol·L^(-1)),its physical meaning is clear,and the approximate result satisfies the requirement of ±5% error.