| 林道广,王海水.化学通报,2019,82(6):563-565,533. |
| 一元弱酸溶液氢离子浓度近似计算的课程新设计 |
| A New and Easy Understanding Way to Derive Approximation Formulas for Estimating the Hydrogen Ion Concentration of a Monoprotic Weak Acid Solution |
| 投稿时间：2018-11-30 修订日期：2019-01-28 |
| DOI： |
| 中文关键词: 一元弱酸 氢离子浓度 近似式 判据 |
| 英文关键词:Monoprotic weak acid Hydrogen ion concentration Approximation formula Criterion |
| 基金项目:国家自然科学基金 |
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| 中文摘要: |
| 通常情况下，一元弱酸HA溶液氢离子浓度可按近似式[H+]AV1=1/2(-K_a+√(K_a^2+4cK_a ))或[H+]AV2=√(cK_a )估算。不同于现有教科书，本文以新的方式导出上述公式，并用数学方法推导出了[H+]AV1和[H+]AV2近似式的使用条件。(1)溶液中[H+]??[OH-]时，可忽略水离解产生的氢离子，此时可用[H+]AV1估算溶液pH。[H+]AV1与氢离子准确浓度[H+]T相对误差不大于?5%时，需要满足两条件c?6.0?10-6mol?L-1和cKa?10Kw；（2）用[H+]AV2估算溶液pH的条件为[H+]??[OH-]和[HA]?c，即同时忽略水的离解和忽略HA的离解（HA离解很少情形）。[H+]AV2与[H+]T相对误差不大于?5%时，要求满足cKa?10Kw和c?105Ka。本文用数学方法推导出cKa?10Kw或c?105Ka等条件，与现教科书有关内容比较，判据严谨，边界条件清晰，学生容易理解，对提高教学效果具有积极意义。 |
| 英文摘要: |
| Among the mainstream analytical chemistry textbooks, the hydrogen ion concentration of a monoprotic weak acid solution can be estimated by approximation formulas[H^+ ]_AV1=1/2(-K_a+√(K_a^2+4cK_a ))or[H^+ ]_AV2=√(cK_a ). In this paper, the two above formulasare derived from a new and easy understandingway.(ⅰ)If[H+]??[OH-], [H+]AV1can be used to estimate the pH of the solution. If the relative error between [H+]AV1and the accurate hydrogen ion concentration[H+]Tis within?5%,then both c?6?10-6mol?L-1 and cKa?10Kw are required. (ⅱ)When use [H+]AV2 to estimate the pH of the solution, it needs two conditions: [H+]??[OH-] and c?[HA]. If the relative error between[H+]AV2 and [H+]T is less than ?5%, bothcKa?10Kw and c?105Ka are required. The conclusions obtained in this study are more accurate and reliable,the physical meaningsof the approximation formulas areclear. Therefore, it is easy for the students to understand and master the related approximate calculation correctly. |
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