| 柳青,王海水.化学通报,2020,83(5):476-479. |
| 近似计算的普适性：一元弱酸的滴定突跃范围 |
| The Universal Approximation Calculation: Range of Abrupt Change in Titration of a Monoprotic Weak Acid |
| 投稿时间：2019-11-05 修订日期：2020-01-26 |
| DOI： |
| 中文关键词: 滴定 一元弱酸 化学计量点 突跃范围 |
| 英文关键词:Titration Monoprotic weak acid Stoichiometric point Range of abrupt change |
| 基金项目:国家自然科学基金项目（21773072）、广东省普通高校青年创新人才项目（2018KQNCX005）和中央高校基本科研业务费专项资金（2019MS031）资助 |
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| 中文摘要: |
| 突跃范围是选择指示剂的主要依据，也是决定能否准确滴定的重要条件。滴定一元弱酸HB溶液时，计量点前（滴定分数a=0.999），许多溶液中cHB与［OH-］或cHB与［H+］具有相同数量级，因此通用教科书介绍的近似式pH=pKa+lg（cB-）/（cHB）存在较大局限性。本文新推导出了满足误差要求（在±0.02pH以内）的适用滴定各种浓度一元弱酸HB的pH的近似公式。计量点前，溶液酸性情形（pKa≤4.0），溶液［H+］=10-3cKa/c+2Ka；溶液碱性情形（pKa>4.0），溶液［H+］=cKa+√cKa（cKa+8×10-8）/2000c。计量点后（a=1.001），考虑弱碱B-对溶液pH影响，则有溶液［H+］=-cKa+√cKa（cKa+8×10-8）/2000c。 |
| 英文摘要: |
| The range of abrupt change in the titration curve plays a key role in selecting an indicator, and also is the important factor to determine whether or not the titration proceeds accurately. Before the stoichiometric point of the chemical reaction, the approximate formula pH=pKa+lg(cB-)/(cHB) can be normally used to obtain the solution pH. However, if[OH-] is close to cHB or[H+] approaches cHB, the above approximation should be a serious problem. In this paper, pH approximation formulas for monoprotic weak acid with different concentrations are derived, which satisfy the error requirement (within ±0.02 pH). Before the stoichiometric point (a=0.999), if the solution is acidic (pKa ≤ 4.0 case),[H+]=10-3cKa/c+2Ka; if the solution is alkaline (pKa>4.0 case),[H+]=cKa+√cKa(cKa+8×10-8)/2000c. After the stoichiometric point (a=1.001),[H+]=-cKa+√cKa(cKa+8×10-8)/2000c. The three equations works more properly than the formula pH=pKa+lgcB-/cHB. |
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