IB Chemistry: Properties of Acids and Bases | IB化学：酸碱的性质

📚 IB Chemistry: Properties of Acids and Bases | IB化学：酸碱的性质

Acids and bases are fundamental to chemistry, influencing everything from industrial processes to biological systems. This article explores their key properties, definitions, and calculations as required by the IB Chemistry syllabus (CIE board).

酸碱是化学的基础，影响着从工业过程到生物系统的方方面面。本文根据IB化学教学大纲（CIE考试局）探讨它们的主要性质、定义和计算方法。

1. Defining Acids and Bases | 酸碱的定义

There are three main definitions of acids and bases that you need to know for IB Chemistry.

在IB化学中，你需要掌握酸碱的三种主要定义。

The Arrhenius definition states that an acid produces H⁺ ions in water, while a base produces OH⁻ ions.

阿伦尼乌斯定义指出，酸在水中产生H⁺离子，碱在水中产生OH⁻离子。

The Brønsted-Lowry definition is broader: an acid is a proton donor, and a base is a proton acceptor.

布朗斯特-劳里定义更为广泛：酸是质子给予体，碱是质子接受体。

The Lewis definition is the most general: an acid is an electron-pair acceptor, and a base is an electron-pair donor.

路易斯定义最为通用：酸是电子对接受体，碱是电子对给予体。

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2. The pH Scale | pH标度

The pH scale expresses the concentration of hydrogen ions in a solution. It is defined as:

pH标度表示溶液中氢离子的浓度。其定义如下：

pH = -log₁₀[H⁺]

easured in mol dm⁻³. A neutral solution at 25°C has [H⁺] = 1.0 × 10⁻⁷ mol dm⁻³, so pH = 7.

其中[H⁺]的单位是mol dm⁻³。在25°C时，中性溶液的[H⁺] = 1.0 × 10⁻⁷ mol dm⁻³，因此pH = 7。

ilarly, pOH is defined as pOH = -log₁₀[OH⁻]. At 25°C, pH + pOH = 14 for aqueous solutions.

类似地，pOH定义为pOH = -log₁₀[OH⁻]。在25°C时，水溶液的pH + pOH = 14。

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3. Strong and Weak Acids and Bases | 强酸与弱酸、强碱与弱碱

Acids and bases can be classified as strong or weak depending on their degree of dissociation in water.

根据在水中的电离程度，酸和碱可分为强与弱。

such as HCl, HNO₃ and H₂SO₄, dissociate completely in water. For example, HCl → H⁺ + Cl⁻.

强酸如HCl、HNO₃和H₂SO₄在水中完全电离。例如，HCl → H⁺ + Cl⁻。

Weak acids, such as CH₃COOH and H₂CO₃, dissociate only partially. The equilibrium is written with a ⇌ sign: CH₃COOH ⇌ H⁺ + CH₃COO⁻.

弱酸如CH₃COOH和H₂CO₃仅部分电离，其平衡用⇌表示：CH₃COOH ⇌ H⁺ + CH₃COO⁻。

Strong bases, such as NaOH and KOH, dissociate fully, releasing OH⁻ ions. Weak bases, such as NH₃, only partly accept protons from water: NH₃ + H₂O ⇌ NH₄⁺ + OH⁻.

强碱如NaOH和KOH完全电离，释放OH⁻离子。弱碱如NH₃仅部分从水中接受质子：NH₃ + H₂O ⇌ NH₄⁺ + OH⁻。

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4. Conjugate Acid-Base Pairs | 共轭酸碱对

In the Brønsted-Lowry theory, an acid and its conjugate base differ by one proton (H⁺).

在布朗斯特-劳里理论中，酸与其共轭碱相差一个质子（H⁺）。

For example, in the reaction HCl + H₂O ⇌ H₃O⁺ + Cl⁻, the acid HCl donates a proton to water, forming H₃O⁺. The conjugate pairs are HCl/Cl⁻ and H₃O⁺/H₂O.

例如，在反应HCl + H₂O ⇌ H₃O⁺ + Cl⁻中，酸HCl将质子给予水，生成H₃O⁺。共轭对为HCl/Cl⁻和H₃O⁺/H₂O。

The stronger the acid, the weaker its conjugate base, and vice versa.

酸越强，其共轭碱越弱，反之亦然。

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5. Acid-Base Reactions and Ionic Equations | 酸碱反应与离子方程式

Acid-base reactions are proton-transfer reactions. The simplest neutralisation reaction is between hydrogen ions and hydroxide ions:

酸碱反应是质子转移反应。最简单的中和反应是氢离子与氢氧根离子的反应：

H⁺(aq) + OH⁻(aq) → H₂O(l)

When writing ionic equations, species that do not change, known as spectator ions, are omitted. For example, for HCl + NaOH, the net ionic equation is the one above.

写离子方程式时，不参加反应、未发生变化的离子（称为旁观离子）被省略。例如，对于HCl + NaOH，净离子方程式就是上面的方程式。

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

Water undergoes self-ionisation: H₂O(l) ⇌ H⁺(aq) + OH⁻(aq). The equilibrium constant for this process is called the ionic product of water, Kw.

水会发生自耦电离：H₂O(l) ⇌ H⁺(aq) + OH⁻(aq)。该过程的平衡常数称为水的离子积Kw。

Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ mol² dm⁻⁶ at 25°C

Kw increases with temperature because self-ionisation is endothermic. Therefore pH of pure water is 7 only at 25°C; at higher temperatures it is lower, but the solution remains neutral.

Kw随温度升高而增大，因为自耦电离是吸热的。因此，纯水的pH仅在25°C时为7；在更高温度下pH更低，但溶液仍为中性。

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7. pH of Strong Acids and Bases | 强酸强碱的pH计算

ng acid with concentration c, since it dissociates completely, [H⁺] = c and pH = -log₁₀ c.

对于浓度为c的强酸，由于完全电离，[H⁺] = c，因此pH = -log₁₀ c。

a strong base with concentration c, [OH⁻] = c, pOH = -log₁₀ c, and pH = 14 - pOH at 25°C.

对于浓度为c的强碱，[OH⁻] = c，pOH = -log₁₀ c，在25°C时pH = 14 - pOH。

O₄. Since H₂SO₄ is diprotic, [H⁺] = 2 × 0.05 = 0.10 mol dm⁻³, so pH = -log₁₀(0.10) = 1.00.

例如：计算0.05 mol dm⁻³ H₂SO₄的pH。由于H₂SO₄是二元酸，[H⁺] = 2 × 0.05 = 0.10 mol dm⁻³，因此pH = -log₁₀(0.10) = 1.00。

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8. pH of Weak Acids | 弱酸的pH计算

For a weak acid HA, the equilibrium is HA ⇌ H⁺ + A⁻. If the initial concentration is c₀ and the acid dissociation constant is Kₐ, we can approximate [

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