Acids and Bases: Key Points for CCEA A-Level Science | 酸与碱：CCEA A-Level 科学考点精讲

📚 Acids and Bases: Key Points for CCEA A-Level Science | 酸与碱：CCEA A-Level 科学考点精讲

Mastering acids and bases is essential for success in A-Level Science. This guide covers the Bronsted-Lowry theory, pH calculations, weak acids, buffers, and titration curves exactly as required by the CCEA specification.

掌握酸与碱的知识对于在A-Level科学考试中取得好成绩至关重要。本指南依据CCEA考试局的要求，涵盖了布朗斯特-劳里理论、pH计算、弱酸、缓冲溶液以及滴定曲线等核心内容。

1. Bronsted-Lowry Theory | 布朗斯特-劳里酸碱理论

A Bronsted-Lowry acid is a proton (H⁺) donor, and a Bronsted-Lowry base is a proton acceptor. This definition extends acid-base behaviour beyond aqueous solutions, allowing us to classify substances like ammonia and hydrogen chloride gas as bases and acids respectively.

布朗斯特-劳里酸是质子（H⁺）的给予体，布朗斯特-劳里碱是质子的接受体。这一定义将酸碱行为扩展到了水溶液之外，使得我们能够将氨气和氯化氢气体等物质分别归类为碱和酸。

When hydrogen chloride dissolves in water, it donates a proton to water molecules, forming hydronium ions (H₃O⁺) and chloride ions.

当氯化氢溶于水时，它会将质子给予水分子，形成水合氢离子（H₃O⁺）和氯离子。

HCl + H₂O → H₃O⁺ + Cl⁻

In this reaction, HCl acts as the acid and H₂O acts as the base. The reverse reaction would see H₃O⁺ donating a proton to Cl⁻, demonstrating that acid-base reactions are often reversible.

在该反应中，HCl是酸，H₂O是碱。其逆反应是H₃O⁺将质子给予Cl⁻，这表明酸碱反应通常是可逆的。

2. Conjugate Acid-Base Pairs | 共轭酸碱对

Every acid has a conjugate base formed by the loss of a proton, and every base has a conjugate acid formed by the gain of a proton. These pairs differ by just one H⁺. For example, the acid HA and its conjugate base A⁻ form a conjugate pair.

每种酸失去一个质子后都会形成其共轭碱，每种碱获得一个质子后都会形成其共轭酸。这些酸碱对只相差一个H⁺。例如，酸HA及其共轭碱A⁻就构成一对共轭酸碱对。

In the equilibrium CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺, acetic acid (CH₃COOH) and the acetate ion (CH₃COO⁻) are a conjugate acid-base pair. Water and the hydronium ion form another pair.

在平衡体系CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺中，乙酸（CH₃COOH）和乙酸根离子（CH₃COO⁻）是一对共轭酸碱对。水和氢离子则构成另一对。

Recognising conjugate pairs helps predict the direction of acid-base equilibria. The stronger the acid, the weaker its conjugate base, and vice versa.

识别共轭酸碱对有助于预测酸碱平衡的方向。酸越强，其共轭碱越弱，反之亦然。

3. The Ionic Product of Water, Kw | 水的离子积Kw

Water undergoes slight self-ionisation: 2H₂O ⇌ H₃O⁺ + OH⁻. The equilibrium constant for this process is the ionic product of water, Kw = [H⁺][OH⁻]. At 25 °C, Kw has a value of 1.0 × 10⁻¹⁴ mol² dm⁻⁶.

水会发生微弱的自电离：2H₂O ⇌ H₃O⁺ + OH⁻。该过程的平衡常数即为水的离子积，Kw = [H⁺][OH⁻]。在25 °C时，Kw的值为1.0 × 10⁻¹⁴ mol² dm⁻⁶。

Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴

Kw is temperature-dependent; it increases with rising temperature. In pure water, [H⁺] = [OH⁻] = √Kw = 1.0 × 10⁻

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