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**物理化学：离子平衡** 本课程深入探讨了导电水溶液（电解质）相关的核心概念，重点关注酸、碱和盐的行为。我们将研究强电解质和弱电解质的电离过程，以及弱电解质中存在的电离平衡。 **核心主题包括：** * **酸碱理论：** * Arrhenius 理论：酸提供氢离子，碱提供氢氧根离子。 * Brønsted-Lowry 理论：酸是质子供体，碱是质子受体，引出共轭酸碱对的概念。 * Lewis 理论：酸是电子对受体，碱是电子对供体，是更广义的定义。 * **弱电解质的电离：** * 推导弱酸 (Ka) 和弱碱 (Kb) 的电离（平衡）常数表达式。 * 分析电离度如何受浓度和同离子效应影响。 * **pH 概念：** * 介绍 pH (pH = -log[H+]) 以及相关的 pOH, pKa, pKb, pKw 的概念。 * 探讨水的电离，以及 pH + pOH = pKw 的基本关系。 * **盐的水解：** * 分析强酸弱碱盐、强碱弱酸盐以及强弱酸碱盐在水溶液中的水解现象。 * **缓冲溶液：** * 定义缓冲溶液及其重要性。 * **溶解度平衡：** * 讨论难溶盐的溶解度平衡，引入溶度积常数 (Ksp) 及其与溶解度的关系。 * 计算盐的沉淀和溶解条件。 * 探讨同离子效应如何影响难溶盐的溶解度。 **实践活动建议：** * 使用 pH 试纸测定各种果蔬汁、饮料、体液和水样的 pH 值。 * 测量不同盐溶液的 pH 值，判断其由强酸/弱酸和强碱/弱碱组成的依据。 * 通过混合乙酸钠和乙酸溶液配制缓冲溶液，并测量其 pH 值。 * 观察不同 pH 值溶液中指示剂颜色的变化。 * 进行酸碱滴定并使用指示剂。 * 观察同离子效应对难溶盐溶解度的影响。 * （如果条件允许）使用 pH 计测量 pH 值，并与 pH 试纸的结果进行比较。
SUMMARYAll substances that conduct electricity in aqueous solutions are called electrolytes. Acids, bases and salts are electrolytes and the conduction of electricity by their aqueous solutions is due to anions and cations produced by the dissociation or ionization of electrolytes in aqueous solution. The strong electrolytes are completely dissociated. In weak electrolytes there is equilibrium between the ions and the unionized electrolyte molecules. According to Arrhenius, acids give hydrogen ions while bases produce hydroxyl ions in their aqueous solutions. Brönsted-Lowry on the other hand, defined an acid as a proton donor and a base as a proton acceptor. When a Brönsted-Lowry acid reacts with a base, it produces its conjugate base and a conjugate acid corresponding to the base with which it reacts. Thus a conjugate pair of acid-base differs only by one proton. Lewis further generalised the definition of an acid as an electron pair acceptor and a base as an electron pair donor. The expressions for ionization (equilibrium) constants of weak acids (Ka ) and weak bases (Kb ) are developed using Arrhenius definition. The degree of ionization and its dependence on concentration and common ion are discussed. The pH scale (pH = -log[H+ ]) for the hydrogen ion concentration (activity) has been introduced and extended to other quantities (pOH = - log[OH-]) ; pKa = -log[Ka] ; pKb = -log[Kb]; and pKw = -log[Kw] etc.). The ionization of water has been considered and we note that the equation: pH + pOH = pKw is always satisfied. The salts of strong acid and weak base, weak acid and strong base, and weak acid and weak base undergo hydrolysis in aqueous solution.The definition of buffer solutions, and their importance are discussed briefly. The solubility equilibrium of sparingly soluble salts is discussed and the equilibrium constant is introduced as solubility product constant (Ksp ). Its relationship with solubility of the salt is established. The conditions of precipitation of the salt from their solutions or their dissolution in water are worked out. The role of common ion and the solubility of sparingly soluble salts is also discussed.SUGGESTED ACTIVITIES FOR STUDENTS REGARDING THIS UNIT (a) The student may use pH paper in determining the pH of fresh juices of various vegetables and fruits, soft drinks, body fluids and also that of water samples available. (b) The pH paper may also be used to determine the pH of different salt solutions and from that he/she may determine if these are formed from strong/weak acids and bases. (c) They may prepare some buffer solutions by mixing the solutions of sodium acetate and acetic acid and determine their pH using pH paper. (d) They may be provided with different indicators to observe their colours in solutions of varying pH. (e) They may perform some acid-base titrations using indicators. (f) They may observe common ion effect on the solubility of sparingly soluble salts. (g) If pH meter is available in their school, they may measure the pH with it and compare the results obtained with that of the pH paper
