📚 IB Sciences: Acids and Bases Key Concepts | IB 科学：酸与碱 考点精讲
Mastering acids and bases is essential for success in IB Chemistry and related science courses. This guide breaks down the core concepts, from fundamental definitions to pH calculations and buffer systems, providing clear explanations and examples to support your revision.
掌握酸与碱是 IB 化学及相关科学课程取得成功的关键。本指南梳理了核心概念，从基本定义到 pH 计算和缓冲体系，提供清晰的解释和示例来支持你的复习。
1. Theories of Acids and Bases | 酸碱理论
Acids and bases can be defined using three major theories. The Arrhenius theory states that acids produce H⁺ ions in water, while bases produce OH⁻ ions. Although simple, it is limited to aqueous solutions.
酸和碱可以用三种主要理论来定义。阿伦尼乌斯理论指出，酸在水中产生 H⁺ 离子，而碱产生 OH⁻ 离子。虽然这个理论很简单，但它仅限于水溶液。
The Brønsted-Lowry theory broadens the definition: an acid is a proton (H⁺) donor, and a base is a proton acceptor. This theory applies to any solvent and introduces the concept of conjugate acid-base pairs.
布朗斯特-洛瑞理论扩展了定义：酸是质子（H⁺）供体，碱是质子受体。该理论适用于任何溶剂，并引入了共轭酸碱对的概念。
The Lewis theory is the most general: an acid is an electron-pair acceptor, and a base is an electron-pair donor. This covers reactions that do not involve protons at all, such as BF₃ + NH₃.
路易斯理论最为广义：酸是电子对受体，碱是电子对供体。这涵盖了根本不涉及质子的反应，例如 BF₃ + NH₃。
2. Conjugate Acid-Base Pairs | 共轭酸碱对
In a Brø by a single H⁺. For example, in the reaction HCl + H₂O → Cl⁻ + H₃O⁺, HCl and Cl⁻ form one pair, and H₂O and H₃O⁺ form another.
在布朗斯特-洛瑞反应中，酸提供一个质子后形成其共轭碱，而碱接受一个质子后形成其共轭酸。这对物质之间只相差一个 H⁺。例如，在反应 HCl + H₂O → Cl⁻ + H₃O⁺ 中，HCl 和 Cl⁻ 构成一对，H₂O 和 H₃O⁺ 构成另一对。
Strong acids have very weak conjugate bases that are essentially non-basic in water. Weak acids have relatively stronger conjugate bases, which can significantly hydrolyze water.
强酸的共轭碱非常弱，在水中基本上不显碱性。弱酸的共轭碱相对较强，可以显著地水解水。
3. Strong and Weak Acids/Bases | 强酸与弱酸 / 强碱与弱碱
A strong acid or base completely dissociates in water. Common strong acids include HCl, HBr, HI, HNO₃, H₂SO₄ (first dissociation) and HClO₄. Strong bases include Group 1 hydroxides and some Group 2 hydroxides like Ba(OH)₂.
强酸或强碱在水中完全解离。常见的强酸包括 HCl、HBr、HI、HNO₃、H₂SO₄（第一步解离）和 HClO₄。强碱包括第 1 族氢氧化物以及某些第 2 族氢氧化物，如 Ba(OH)₂。
Weak acids and bases partially dissociate, establishing an equilibrium. Examples of weak acids are CH₃COOH (ethanoic acid), H₂CO₃, and HF. Weak bases include NH₃ and amines. The degree of dissociation is given by Kₐ or Kb.
弱酸和弱碱部分解离，建立平衡。弱酸的例子有 CH₃COOH（乙酸）、H₂CO₃ 和 HF。弱碱包括 NH₃ 和胺类。解离度由 Kₐ 或 Kb 给出。
4. The pH Scale and Calculations | pH 标度与计算
n: pH = -log₁₀[H⁺]. Similarly, pOH = -log₁₀[OH⁻] and pH + pOH = 14 at 298 K in pure water.
pH 定义为氢离子浓度的负对数（以 10 为底）：pH = -log₁₀[H⁺]。类似地，pOH = -log₁₀[OH⁻]，在纯水中 298 K 时 pH + pOH = 14。
For strong monoprotic acids, [H⁺] equals the initial concentration of the acid. For strong bases like NaOH, [OH⁻] equals the base concentration. For weak acids, use the Kₐ expression and approximations if the dissociation is less than 5%.
对于强一元酸，[H⁺] 等于酸的初始浓度。对于像 NaOH 这样的强碱，[OH⁻] 等于碱的浓度。对于弱酸，使用 Kₐ 表达式，如果解离度小于 5% 则可以采用近似计算。
Kₐ = [H⁺][A⁻] / [HA]
The quadratic formula or the approximation [H⁺] = √Kₐ × c may be used, where c is the initial concentration, provided c/Kₐ > 1000.
可以使用二次公式或近似公式 [H⁺] = √Kₐ × c，其中 c 是初始浓度，前提是 c/Kₐ > 1000。
5. The Ionic Product of Water, Kw | 水的离子积 Kw
Water undergoes self-ionization: 2H₂O ⇌ H₃O⁺ + OH⁻. The equilibrium constant is Kw = [H⁺][OH⁻]. At 298 K, Kw = 1.0 × 10⁻¹⁴.
水发生自解离：2H₂O ⇌ H₃O⁺ + OH⁻。平衡常数是 Kw = [H⁺][OH⁻]。在 298 K 时，Kw = 1.0 × 10⁻¹⁴。
The value of Kw ter decreases as temperature rises, but the solution remains neutral because [H⁺] = [OH⁻].
Kw 的值随温度升高而增加，因为自解离是吸热的。因此，纯水的 pH 随温度升高而降低，但溶液仍保持中性，因为 [H⁺] = [OH⁻]。
6. Acid Deposition and Environmental Impact | 酸沉降与环境影响
Acid deposition, commonly known as acid rain, occurs when sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) are released into the atmosphere. These gases react with water and oxygen to form sulfuric acid and nitric acid, lowering the pH of precipitation below 5.6.
酸沉降，通常称为酸雨，当二氧化硫（SO₂）和氮氧化物（NOₓ）排放到大气中时发生。这些气体与水及氧气反应生成硫酸和硝酸，使降水的 pH 降至 5.6 以下。
Impacts include leaching of toxic aluminum ions from soils into water bodies, damage to plant leaves, corrosion of limestone and marble buildings, and acidification of lakes leading to loss of aquatic life.
影响包括有毒铝离子从土壤浸出进入水体、损害植物叶片、侵蚀石灰石和大理石建筑，以及湖泊酸化导致水生生物灭绝。
7. Buffer Solutions and the Henderson-Hasselbalch Equation | 缓冲溶液与亨德森-哈塞尔巴尔赫方程
A buffer is a solution that resists changes in pH upon addition of small amounts of acid or base. It consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in significant concentrations.
缓冲溶液是一种在加入少量酸或碱时能抵抗 pH 变化的溶液。它由浓度可观的弱酸及其共轭碱（或弱碱及其共轭酸）组成。
The pH of an acidic buffer can be calculated using the Henderson-Hasselbalch equation:
酸性缓冲液的 pH 可以用亨德森-哈塞尔巴尔赫方程计算：
pH = pKₐ + log₁₀([A⁻] / [HA])
Buffers are crucial in biological systems (blood pH 7.4 maintained by carbonic acid/hydrogencarbonate) and in industrial processes.
缓冲液在生物系统（血液 pH 7.4 由碳酸/碳酸氢盐维持）和工业过程中至关重要。
8. Acid-Base Indicators and Titration Curves | 酸碱指示剂与滴定曲线
forms shifts, typically around pKₐ ± 1. Common indicators include phenolphthalein (pH 8.2–10.0, colorless to pink) and methyl orange (pH 3.1–4.4, red to yellow).
指示剂是在特定 pH 范围内变色的弱酸或弱碱。颜色变化发生在两种形式的比例改变时，通常在 pKₐ ± 1 左右。常见的指示剂包括酚酞（pH 8.2–10.0，无色到粉红）和甲基橙（pH 3.1–4.4，红到黄）。
Titration curves plot pH against volume of titrant added. The shape depends on the strengths of the acid and base:
滴定曲线绘制 pH 随加入滴定剂体积的变化。曲线形状取决于酸和碱的强度：
- Strong acid – strong base: Equivalence point at pH 7, sharp vertical region. / 强酸–强碱：等量点 pH = 7，有陡峭的垂直区。
- Weak acid – strong base: Equivalence point pH > 7 due to conjugate base hydrolysis. Buffer region before equivalence. / 弱酸–强碱：等量点 pH > 7，因为共轭碱水解。等量点前有缓冲区域。
- Weak base – strong acid: Equivalence point pH < 7. / 弱碱–强酸：等量点 pH < 7。
9. Lewis Acids and Bases in Coordination Chemistry | 配位化学中的路易斯酸碱
Lewis acid-base theory explains the formation of complex ions. A metal cation acts as a Lewis acid (electron-pair acceptor) and ligands act as Lewis bases (electron-pair donors). For example, in [Cu(NH₃)₄]²⁺, Cu²⁺ is the Lewis acid and NH₃ is the Lewis base.
路易斯酸碱理论解释了配离子的形成。金属阳离子充当路易斯酸（电子对受体），配体充当路易斯碱（电子对供体）。例如，在 [Cu(NH₃)₄]²⁺ 中，Cu²⁺ 是路易斯酸，NH₃ 是路易斯碱。
The strength of a Lewis acid depends on factors such as charge density and polarizability. This theory is essential for understanding transition metal chemistry and bonding.
路易斯酸的强度取决于电荷密度和极化率等因素。该理论对于理解过渡金属化学和成键至关重要。
10. Experimental Techniques and Common Errors | 实验技术与常见错误
In titration, a burette delivers the titrant, and a conical flask holds the analyte with indicator. The endpoint is when the indicator changes color; the equivalence point is the theoretical point of complete reaction. Careful technique ensures the two are close.
在滴定中，滴定管递送滴定剂，锥形瓶盛放含有指示剂的待测溶液。终点是指示剂变色的时刻；等量点是理论上反应完全的点。小心操作可确保两者接近。
Common errors include parallax error when reading the burette, not rinsing the burette with the titrant, and adding titrant too quickly past the endpoint. Distilled water does not change the number of moles, so it does not affect the titre if added to the flask.
常见错误包括读取滴定管时的视差误差、未用滴定剂润洗滴定管，以及过快加入滴定剂超过终点。蒸馏水不会改变摩尔数，所以加入锥形瓶不会影响滴定体积。
11. Polyprotic Acids and Stepwise Dissociation | 多元酸与分步解离
cid is strong in its first dissociation (H₂SO₄ → H⁺ + HSO₄⁻) but weak in the second (HSO₄⁻ ⇌ H⁺ + SO₄²⁻, Kₐ₂ = 1.2 × 10⁻²).
多元酸可以提供多个质子，分步解离。每一步都有自己的解离常数。例如，硫酸的第一步解离是强解离（H₂SO₄ → H⁺ + HSO₄⁻），但第二步解离较弱（HSO₄⁻ ⇌ H⁺ + SO₄²⁻，Kₐ₂ = 1.2 × 10⁻²）。
overall pH of a polyprotic acid solution is largely determined by the first dissociation.
磷酸（H₃PO₄）有三个不同的 Kₐ 值：Kₐ₁ = 7.5 × 10⁻³，Kₐ₂ = 6.2 × 10⁻⁸，Kₐ₃ = 4.8 × 10⁻¹³。多元酸溶液的总体 pH 值主要由第一步解离决定。
12. Exam Tips and Common Pitfalls | 考试技巧与常见陷阱
Always distinguish between strength and concentration: a strong acid is fully dissociated regardless of concentration; a weak acid is partially dissociated even at high concentration. Use precise language in explanations, for example, 'hydrogen ions' rather than just 'acid'.
始终区分强度与浓度：强酸无论浓度高低都完全解离；弱酸即使浓度高也只是部分解离。在解释中使用精确的语言，例如用“氢离子”而不只是“酸”。
When calculating pH of weak bases, remember to find [OH⁻] first, then convert to pOH and finally to pH. For buffer solutions, do not forget that the Henderson-Hasselbalch equation uses concentrations at equilibrium, not initial amounts.
计算弱碱的 pH 时，记得先求出 [OH⁻]，然后转换为 pOH，最后得到 pH。对于缓冲溶液，别忘了亨德森-哈塞尔巴尔赫方程使用的是平衡浓度，而不是初始量。
Finally, link concepts to real-world applications where possible, such as the role of ocean acidification (CO₂ dissolving to form carbonic acid) and the use of antacids (bases neutralizing excess stomach acid).
最后，尽可能将概念与实际应用联系起来，例如海洋酸化的作用（CO₂ 溶解形成碳酸）以及抗酸剂的使用（碱中和过多的胃酸）。
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