📚 IGCSE CIE Chemistry: Acid-Base Theory Key Points | IGCSE CIE 化学：酸碱理论 考点精讲
Acids, bases, and alkalis are fundamental topics in IGCSE CIE Chemistry. You need to understand their definitions in terms of proton transfer, be able to describe characteristic reactions, interpret the pH scale, and explain neutralisation. This article summarises the key points, providing bilingual explanations to help you master every aspect of acid-base theory for the exam.
酸、碱和可溶性碱是 IGCSE CIE 化学的基础课题。你需要掌握根据质子转移的定义，能够描述特征反应，解释 pH 标度，并说明中和反应。本文总结核心考点，提供双语解释，帮助你全面掌握酸碱理论，轻松应对考试。
1. Defining Acids and Bases | 酸碱的定义
In IGCSE Chemistry, the Bronsted-Lowry theory is the primary definition used. An acid is a proton (H⁺) donor, and a base is a proton acceptor. This definition focuses on the transfer of a hydrogen ion.
在 IGCSE 化学中，主要采用布朗斯特-劳里理论。酸是质子（H⁺）给予体，碱是质子接受体。该定义关注氢离子的转移过程。
When an acid dissolves in water, it donates a proton to a water molecule, forming the hydronium ion, H₃O⁺. This can be simplified as the presence of H⁺(aq) ions.
酸溶于水时，会将一个质子给予水分子，形成水合氢离子 H₃O⁺。可简化为存在 H⁺(aq) 离子。
Alkalis are soluble bases that release hydroxide ions, OH⁻, in water. When a base accepts a proton, it often forms a hydroxide ion or directly takes H⁺ from an acid.
碱是可溶性的碱，在水中释放氢氧根离子 OH⁻。碱接受质子时，通常会生成氢氧根离子或直接从酸中夺取 H⁺。
A typical proton transfer: HCl + H₂O → H₃O⁺ + Cl⁻. Here, HCl is the acid, and H₂O acts as a base.
典型的质子转移：HCl + H₂O → H₃O⁺ + Cl⁻。在此反应中，HCl 是酸，H₂O 充当碱。
2. Characteristic Reactions of Acids | 酸的特征反应
Acids react with reactive metals, bases, carbonates and hydrogencarbonates. These reactions produce salts and are often used to identify acids.
酸与活泼金属、碱、碳酸盐和碳酸氢盐反应。这些反应生成盐，常用于鉴别酸。
Reaction with metals (above hydrogen in the reactivity series): acid + metal → salt + hydrogen gas. Example: 2HCl + Mg → MgCl₂ + H₂.
与金属（金属活动性顺序位于氢之前）反应：酸 + 金属 → 盐 + 氢气。例如：2HCl + Mg → MgCl₂ + H₂。
Reaction with bases (neutralisation): acid + base → salt + water. With alkalis: HCl + NaOH → NaCl + H₂O.
与碱反应（中和）：酸 + 碱 → 盐 + 水。与可溶性碱：HCl + NaOH → NaCl + H₂O。
Reaction with carbonates: acid + carbonate → salt + water + carbon dioxide. Example: 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂. Effervescence confirms CO₂.
与碳酸盐反应：酸 + 碳酸盐 → 盐 + 水 + 二氧化碳。例如：2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂。起泡现象证明有 CO₂ 生成。
Reaction with hydrogencarbonates: acid + hydrogencarbonate → salt + water + carbon dioxide. Similar to carbonates, with rapid bubbling.
与碳酸氢盐反应：酸 + 碳酸氢盐 → 盐 + 水 + 二氧化碳。与碳酸盐类似，迅速产生气泡。
3. Properties of Bases and Alkalis | 碱和可溶性碱的性质
Bases neutralise acids to form salt and water. Alkalis are bases that dissolve in water and produce OH⁻ ions. Common alkalis include sodium hydroxide, potassium hydroxide and calcium hydroxide.
碱能中和酸生成盐和水。可溶性碱是能溶于水并产生 OH⁻ 离子的碱。常见的可溶性碱有氢氧化钠、氢氧化钾和氢氧化钙。
Alkalis react with ammonium salts on heating to produce ammonia gas. For example: NaOH + NH₄Cl → NaCl + H₂O + NH₃. This is a test for ammonium ions.
可溶性碱与铵盐加热反应，释放氨气。例如：NaOH + NH₄Cl → NaCl + H₂O + NH₃。这是检验铵根离子的方法。
Alkalis feel soapy and turn red litmus paper blue. They have a pH greater than 7.
可溶性碱触感滑腻，能使红色石蕊试纸变蓝。它们的 pH 大于 7。
4. The pH Scale and Indicators | pH 标度与指示剂
The pH scale measures the acidity or alkalinity of a solution. It ranges from 0 to 14. A lower pH means higher concentration of H⁺ ions (more acidic), while a higher pH means lower concentration of H⁺ ions (more alkaline).
pH 标度衡量溶液的酸碱性，范围为 0 至 14。pH 越低，H⁺ 离子浓度越高（酸性越强）；pH 越高，H⁺ 离子浓度越低（碱性越强）。
pH 7 is neutral, where the concentrations of H⁺ and OH⁻ are equal. Pure water is neutral at 25 °C. Universal indicator gives a range of colours according to pH.
pH 7 为中性，此时 H⁺ 和 OH⁻ 离子浓度相等。25 °C 时纯水呈中性。通用指示剂会根据 pH 显示一系列颜色。
Litmus: red in acid, blue in alkali. Methyl orange: red in acid, yellow in alkali. Phenolphthalein: colourless in acid, pink in alkali.
石蕊：酸性溶液中呈红色，碱性溶液中呈蓝色。甲基橙：酸性呈红色，碱性呈黄色。酚酞：酸性无色，碱性呈粉红色。
Indicator comparison:
指示剂对比：
| Indicator | Colour in acid | Colour in alkali | 指示剂 | 酸性颜色 | 碱性颜色 |
|---|---|---|---|---|---|
| Litmus | Red | Blue | 石蕊 | 红 | 蓝 |
| Methyl orange | Red | Yellow | 甲基橙 | 红 | 黄 |
| Phenolphthalein | Colourless | Pink | 酚酞 | 无色 | 粉红 |
5. Strong and Weak Acids | 强酸和弱酸
A strong acid is completely ionised in aqueous solution. Every molecule donates its proton, so the concentration of H⁺ ions is high for a given concentration. Examples: HCl, HNO₃, H₂SO₄.
强酸在水溶液中完全电离。每个分子都给出质子，因此在相同浓度下 H⁺ 离子浓度较高。例如：HCl、HNO₃、H₂SO₄。
A weak acid is only partially ionised in water. Most of the molecules remain undissociated, so the H⁺ concentration is much lower than that of a strong acid of the same molar concentration. Examples: CH₃COOH (ethanoic acid), H₂CO₃, citric acid.
弱酸在水中仅部分电离。大部分分子保持未解离状态，因此相同摩尔浓度下 H⁺ 浓度远低于强酸。例如：CH₃COOH（乙酸）、H₂CO₃、柠檬酸。
This difference explains why strong acids have a lower pH than weak acids of the same concentration. The degree of ionisation determines strength, not concentration.
这一差异解释了为何同浓度的强酸 pH 低于弱酸。酸性的强弱取决于电离程度，而非浓度。
Strong bases, like NaOH and KOH, fully dissociate to release OH⁻ ions. Weak bases like NH₃ only partially ionise.
强碱如 NaOH 和 KOH 完全解离，释放 OH⁻ 离子。弱碱如 NH₃ 仅部分电离。
6. Neutralisation – The Core of Acid-Base Chemistry | 中和反应——酸碱化学的核心
Neutralisation is the reaction between an acid and a base to produce salt and water. The ionic equation for neutralisation using a strong acid and a strong alkali is: H⁺(aq) + OH⁻(aq) → H₂O(l).
中和反应是酸与碱反应生成盐和水的过程。强酸与强碱反应的离子方程式为：H⁺(aq) + OH⁻(aq) → H₂O(l)。
During neutralisation, the pH moves towards 7. The exact salt formed depends on the acid and base used. For example, HCl + KOH → KCl + H₂O gives potassium chloride.
中和过程中，pH 趋于 7。具体生成的盐取决于所用的酸和碱。例如 HCl + KOH → KCl + H₂O 生成氯化钾。
Neutralisation is exothermic. Temperature increase can be observed. CIE exams often ask about the energy change and salt preparation.
中和反应为放热反应，可观察到温度升高。CIE 考试中常会询问能量变化及盐的制备方法。
7. Making Salts from Acids | 由酸制备盐
Salts can be prepared by reacting an acid with an insoluble base (like CuO), a metal (like Mg), or a carbonate. The method involves adding excess solid to the acid, heating, filtering, and evaporating to obtain crystals.
可以通过酸与不溶性碱（如 CuO）、金属（如 Mg）或碳酸盐反应来制备盐。方法包括向酸中加入过量固体、加热、过滤，再蒸发得到晶体。
For example, to make copper(II) sulfate: CuO + H₂SO₄ → CuSO₄ + H₂O. Add excess black CuO to warm sulfuric acid, filter, and crystallise the blue salt.
例如制备硫酸铜：CuO + H₂SO₄ → CuSO₄ + H₂O。将过量黑色氧化铜加入温热硫酸中，过滤后结晶得到蓝色盐。
When using an alkali (soluble base), titration is necessary to exactly neutralise, as there is no visible excess solid. This yields sodium, potassium, or ammonium salts.
当使用可溶性碱时，必须通过滴定精确中和，因为没有可见的过量固体。这样可制得钠盐、钾盐或铵盐。
8. Titration – A Closer Look | 滴定详解
Titration is used to find the exact volumes of acid and alkali that neutralise each other. A pipette measures a fixed volume of alkali, and a burette is used to add acid dropwise until the indicator changes colour.
滴定用于测定酸和碱恰好中和所需的精确体积。用移液管量取固定体积的碱液，用滴定管逐滴加入酸液，直至指示剂变色。
In CIE practicals, you are often asked to carry out titration with methyl orange or phenolphthalein, record readings to 0.05 cm³, and calculate concentration. Repeating until consistent results is essential.
在 CIE 实验考试中，常要求用甲基橙或酚酞进行滴定，读数精确到 0.05 cm³，并计算浓度。必须重复至获得一致结果。
Once the endpoint is reached, the solution contains only salt and water. This solution can be evaporated to obtain pure salt crystals.
达到终点后，溶液中只有盐和水。可蒸发此溶液获得纯的盐晶体。
9. Controlling pH in Real Life | 现实生活中的 pH 控制
Soil pH is crucial for plant growth. Most crops prefer a pH between 6 and 7. If soil is too acidic, farmers add lime (calcium carbonate or calcium hydroxide) to raise the pH.
土壤 pH 对植物生长至关重要。大多数作物喜欢 pH 6–7。若土壤过酸，农民会施加石灰（碳酸钙或氢氧化钙）来提高 pH。
Acid rain, caused by dissolved SO₂ and NOₓ, lowers the pH of lakes and rivers. This harms aquatic life. Liming is also used to neutralise acidified lakes.
酸雨由溶解的 SO₂ 和 NOₓ 引起，会降低湖泊和河流的 pH，危害水生生物。同样采用撒石灰的方法中和酸化水体。
In the human stomach, excess hydrochloric acid can cause discomfort. Antacids containing magnesium hydroxide or calcium carbonate neutralise the acid.
人体胃中过多的盐酸会引起不适。含有氢氧化镁或碳酸钙的抗酸剂可中和胃酸。
10. Key Definitions and Exam Tips | 关键定义与应试技巧
Remember: Acid = proton donor. Base = proton acceptor. Alkali = soluble base producing OH⁻. Neutralisation = H⁺ + OH⁻ → H₂O. Strong acid/base = fully ionised. Weak acid/base = partially ionised.
记住：酸 = 质子供体。碱 = 质子受体。可溶性碱 = 可溶的碱，产生 OH⁻。中和 = H⁺ + OH⁻ → H₂O。强酸/强碱 = 完全电离。弱酸/弱碱 = 部分电离。
Common mistakes: confusing concentration with strength, forgetting that weak acids still have pH below 7, and writing incorrect ionic equations. Always use state symbols (aq),(s),(l),(g).
常见错误：混淆浓度与强度，认为弱酸的 pH 仍高于 7，以及写错离子方程式。务必标注状态符号 (aq)(s)(l)(g)。
For CIE paper 4 and 6, be ready to describe an investigation to compare the pH of strong and weak acids, or to plot a pH curve showing neutralisation.
在 CIE 卷 4 和卷 6 中，准备好描述对比强、弱酸 pH 的实验探究，或绘制表示中和过程的 pH 曲线。
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