📚 Acids, Bases and Salts | 酸、碱和盐
Acids, bases and salts are fundamental categories of chemical substances that appear in every Edexcel IGCSE Science syllabus. Understanding their properties, reactions and real-world applications is not only key to exam success but also essential for making sense of the chemistry around us – from stomach acid and indigestion tablets to acid rain and fertiliser production. This article provides a comprehensive, bilingual revision guide covering all major subtopics with clear explanations, worked examples and exam-focused tips.
酸、碱和盐是化学物质的基本类别，出现在Edexcel IGCSE科学的每一份大纲中。理解它们的性质、反应和实际应用不仅是考试成功的关键，也是理解我们周围化学现象的基础——从胃酸和抗酸药片到酸雨和化肥生产。本文提供一份全面的双语复习指南，涵盖所有主要子主题，配有清晰的解释、示例和应考技巧。
1. What are Acids and Bases? | 酸和碱是什么？
Acids are substances that release hydrogen ions (H⁺) when dissolved in water. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Bases are substances that can neutralise acids to produce a salt and water; those that dissolve in water are called alkalis and release hydroxide ions (OH⁻). Sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)₂) are typical alkalis.
酸是溶于水时释放氢离子（H⁺）的物质。常见的实验室酸包括盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。碱是能够中和酸生成盐和水的物质；其中能溶于水的碱称为碱，会释放氢氧根离子（OH⁻）。氢氧化钠（NaOH）、氢氧化钾（KOH）和氢氧化钙（Ca(OH)₂）是典型的碱。
The strength of an acid is determined by the degree of ionisation in water. Strong acids like HCl and H₂SO₄ fully dissociate, giving a high concentration of H⁺ ions, whereas weak acids like ethanoic acid (CH₃COOH) only partially ionise. Similarly, strong alkalis such as NaOH fully dissociate in solution.
酸的强度由其在水中电离的程度决定。强酸如HCl和H₂SO₄完全解离，产生高浓度的H⁺离子；而弱酸如乙酸（CH₃COOH）仅部分电离。同样，强碱如NaOH在溶液中完全解离。
2. The pH Scale and Indicators | pH值标度和指示剂
The pH scale ranges from 0 to 14 and measures the acidity or alkalinity of a solution. A pH less than 7 indicates an acidic solution (higher concentration of H⁺), pH 7 is neutral (pure water), and pH greater than 7 indicates an alkaline solution (lower concentration of H⁺, higher OH⁻). The scale is logarithmic, meaning each unit change represents a tenfold change in hydrogen ion concentration.
pH值标度范围从0到14，用于测量溶液的酸性或碱性强弱。pH小于7表示酸性溶液（H⁺浓度较高），pH等于7为中性（纯水），pH大于7表示碱性溶液（H⁺浓度较低，OH⁻较高）。该标度为对数标度，每变化一个单位代表氢离子浓度变化十倍。
Indicators are substances that change colour depending on the pH. Litmus paper turns red in acid and blue in alkali. Universal indicator shows a range of colours from red (strongly acidic) through green (neutral) to purple (strongly alkaline) and can be used to estimate pH to an integer. More accurate measurements use a pH meter with a probe.
指示剂是根据pH改变颜色的物质。石蕊试纸在酸中变红，在碱中变蓝。通用指示剂显示一系列颜色，从红色（强酸性）经绿色（中性）到紫色（强碱性），可用于估算pH至整数。更精确的测量使用带有探头的pH计。
| pH range | Colour in universal indicator | Example |
|---|---|---|
| 0–2 strong acid 强酸 |
Red 红色 |
Battery acid, stomach acid 电池酸液、胃酸 |
| 3–4 weak acid 弱酸 |
Orange-yellow 橙色至黄色 |
Vinegar, lemon juice 醋、柠檬汁 |
| 5–6 very weak acid 极弱酸 |
Yellow-green 黄绿色 |
Rainwater (with dissolved CO₂) 雨水（溶有CO₂） |
| 7 neutral 中性 |
Green 绿色 |
Pure water 纯水 |
| 8–11 weak alkali 弱碱 |
Blue to violet 蓝色至紫色 |
Soap, ammonia solution 肥皂、氨水 |
| 12–14 strong alkali 强碱 |
Dark purple 深紫色 |
Sodium hydroxide solution 氢氧化钠溶液 |
3. Reactions of Acids with Metals | 酸与金属的反应
When a dilute acid reacts with a reactive metal (above hydrogen in the reactivity series), a salt and hydrogen gas are produced. The general word equation is: Metal + Acid → Salt + Hydrogen. For example, magnesium reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen gas. The mixture bubbles vigorously and the test tube becomes warm, indicating an exothermic reaction.
当稀酸与活泼金属（在金属活动顺序表中位于氢之前）反应时，生成盐和氢气。通用的文字方程式为：金属 + 酸 → 盐 + 氢气。例如，镁与稀盐酸反应生成氯化镁和氢气。混合物剧烈冒泡，试管变热，表明这是一个放热反应。
The hydrogen can be tested by bringing a lit splint to the mouth of the test tube; it burns with a ‘squeaky pop’ sound. Metals such as copper, which are below hydrogen in the reactivity series, do not react with dilute acids because they cannot displace hydrogen ions.
氢气可以通过将点燃的木条靠近试管口来检验；氢气燃烧发出“噗”的一声。在金属活动顺序中位于氢以下的金属（如铜）不与稀酸反应，因为它们不能将氢离子置换出来。
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
4. Neutralisation – Acids and Bases | 中和反应 – 酸与碱
Neutralisation occurs when an acid reacts with a base (or alkali) to form a salt and water. The H⁺ ions from the acid combine with OH⁻ ions from the alkali to produce water: H⁺(aq) + OH⁻(aq) → H₂O(l). The remaining ions form the salt. If the exact reacting quantities are used, the resulting solution is neutral (pH 7).
当酸与碱（或碱溶液）反应生成盐和水时，发生中和反应。酸中的H⁺离子与碱中的OH⁻离子结合生成水：H⁺(aq) + OH⁻(aq) → H₂O(l)。剩余的离子形成盐。如果使用恰好完全反应的量，得到的溶液呈中性（pH 7）。
A common laboratory example is the titration of sodium hydroxide with hydrochloric acid using phenolphthalein indicator. As acid is added, the pink colour fades and disappears when all the alkali has been neutralised. This is a typical method for preparing a soluble salt.
实验室中一个常见的例子是用酚酞作指示剂，用盐酸滴定氢氧化钠。随着酸的加入，粉红色逐渐褪去，当碱被完全中和时颜色消失。这是制备可溶性盐的一种典型方法。
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
5. Reactions of Acids with Carbonates | 酸与碳酸盐的反应
Acids react with metal carbonates and hydrogencarbonates to produce a salt, water and carbon dioxide gas. Lime-scale (calcium carbonate) reacting with vinegar is a familiar example. In the lab, marble chips (CaCO₃) are often used with dilute hydrochloric acid. Effervescence occurs as CO₂ gas is given off.
酸与金属碳酸盐和碳酸氢盐反应生成盐、水和二氧化碳气体。水垢（碳酸钙）与醋反应是一个常见的例子。实验中常用大理石碎片（CaCO₃）与稀盐酸反应。释放出CO₂气体时会产生泡腾现象。
Carbon dioxide turns limewater milky due to the formation of insoluble calcium carbonate. This test can distinguish CO₂ from other gases. The general reaction can be written as: Metal carbonate + Acid → Salt + Water + Carbon dioxide.
二氧化碳会使石灰水变浑浊，这是因为生成了不溶性的碳酸钙。该检验可以区分CO₂与其他气体。该反应的通式可写为：金属碳酸盐 + 酸 → 盐 + 水 + 二氧化碳。
CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
6. Making Soluble Salts | 制备可溶性盐
Soluble salts can be prepared by reacting a dilute acid with an insoluble solid (metal, metal oxide, hydroxide or carbonate) and then filtering off the excess solid, or by neutralising an acid with an alkali via titration. For example, copper(II) sulfate can be made by reacting copper(II) oxide with sulfuric acid. The insoluble oxide is added in excess to the warm acid until no more reacts, the mixture is filtered, and the filtrate is evaporated to obtain blue crystals.
可溶性盐可以通过将稀酸与不溶性固体（金属、金属氧化物、氢氧化物或碳酸盐）反应，然后过滤掉过量固体来制备，或者通过滴定用碱中和酸来制备。例如，硫酸铜可以通过氧化铜与硫酸反应制得。将不溶性氧化铜过量加入到温热的酸中，直到不再反应，过滤，将滤液蒸发结晶，即可得到蓝色晶体。
The sequence of steps – reaction, filtration, evaporation and crystallisation – is a core practical skill. When using an alkali and acid titration, no excess solid is involved; instead the exact volumes are mixed, and the solution is evaporated to yield the salt. This method is particularly useful for preparing sodium, potassium and ammonium salts.
反应、过滤、蒸发和结晶这一系列步骤是核心实验技能。当使用酸碱滴定时，不涉及过量固体；而是将精确体积的酸和碱混合，然后将溶液蒸发得到盐。这种方法特别适用于制备钠盐、钾盐和铵盐。
7. Preparation of Insoluble Salts by Precipitation | 沉淀法制备不溶性盐
Insoluble salts are prepared by mixing two soluble solutions that contain the required ions. A precipitate of the insoluble salt forms immediately. For instance, barium sulfate (BaSO₄), used in X-ray imaging, can be prepared by mixing barium chloride solution with sodium sulfate solution. The solid is filtered, washed with distilled water and dried.
不溶性盐通过混合两种含有所需离子的可溶性溶液来制备，立即生成不溶性盐的沉淀。例如，X射线成像中使用的硫酸钡（BaSO₄）可以通过混合氯化钡溶液和硫酸钠溶液制备。将固体过滤，用蒸馏水洗涤并干燥。
To choose suitable starting solutions, you need to know the solubility rules. All nitrates are soluble, all sodium, potassium and ammonium salts are soluble, but most sulfates are soluble except barium, lead and calcium sulfates. Hydroxides are generally insoluble except Group I and ammonium hydroxides. This knowledge is often tested in the Edexcel IGCSE exam.
要选择合适的起始溶液，你需要了解溶解性规则。所有硝酸盐都可溶，所有钠盐、钾盐和铵盐都可溶，但大多数硫酸盐可溶，除了硫酸钡、硫酸铅和硫酸钙。氢氧化物一般不溶，除了第一主族和氢氧化铵。这些知识在Edexcel IGCSE考试中经常考查。
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
8. Testing for Common Gases | 常见气体的检验
IGCSE students must be able to recall the tests for hydrogen, oxygen, carbon dioxide, chlorine and ammonia. A lit splint gives a ‘squeaky pop’ for hydrogen; a glowing splint relights in oxygen; carbon dioxide turns limewater cloudy; chlorine bleaches damp litmus paper and has a sharp smell; ammonia turns damp red litmus paper blue and has a pungent odour.
IGCSE学生必须能够记住氢气、氧气、二氧化碳、氯气和氨气的检验方法。点燃的木条在氢气中发出“噗”的爆鸣声；带火星的木条在氧气中复燃；二氧化碳使石灰水变浑浊；氯气使湿润的石蕊试纸漂白并具有刺激性气味；氨气使湿润的红色石蕊试纸变蓝并具有刺鼻气味。
These tests are vital for identifying products in acid reactions. For example, when an acid reacts with a carbonate, the gas produced is always carbon dioxide. When an acid reacts with a metal, the gas is hydrogen. Recognising these links helps in both practical assessments and written papers.
这些检验对于鉴定酸反应中的产物至关重要。例如，当酸与碳酸盐反应时，产生的气体总是二氧化碳。当酸与金属反应时，气体是氢气。认识这些联系有助于实验评估和笔试。
| Gas 气体 | Test 检验方法 | Result 现象 |
|---|---|---|
| Hydrogen 氢气 | Lit splint at mouth of test tube 点燃的木条放在试管口 |
Squeaky pop “噗”的爆鸣声 |
| Oxygen 氧气 | Glowing splint inserted 将带火星的木条伸入 |
Splint relights 木条复燃 |
| Carbon dioxide 二氧化碳 | Bubble through limewater 通入石灰水 |
Limewater turns milky 石灰水变浑浊 |
| Chlorine 氯气 | Damp blue litmus paper held in gas 将湿润的蓝色石蕊试纸置于气体中 |
Bleached white; pungent smell 漂白变白；刺激性气味 |
| Ammonia 氨气 | Damp red litmus paper held in gas 将湿润的红色石蕊试纸置于气体中 |
Turns blue; pungent smell 变蓝；刺鼻气味 |
9. Acid Rain – Causes and Effects | 酸雨 – 成因与影响
Acid rain is mainly caused by the dissolution of sulfur dioxide and nitrogen oxides in rainwater. Sulfur dioxide comes from burning fossil fuels containing sulfur impurities, especially coal, while nitrogen oxides are produced in car engines at high temperatures. These oxides react with water and oxygen in the atmosphere to form sulfuric acid and nitric acid, lowering the pH of rain to around 4 or below.
酸雨主要由二氧化硫和氮氧化物溶解在雨水中造成。二氧化硫来自燃烧含硫杂质的化石燃料，尤其是煤；而氮氧化物是在汽车发动机高温下产生的。这些氧化物与大气中的水和氧气反应生成硫酸和硝酸，使雨水的pH值降至约4或以下。
Acid rain damages ecosystems by acidifying lakes and soils, dissolving toxic aluminium ions that harm aquatic life and tree roots. It also erodes buildings made of limestone and marble, reacting with calcium carbonate to form soluble calcium sulfate, which is washed away. Reducing acid rain requires scrubbing flue gases and using catalytic converters in cars.
酸雨通过酸化湖泊和土壤、溶出有毒的铝离子来损害水生生物和树木根系，从而破坏生态系统。它还会侵蚀由石灰石和大理石建造的建筑物，与碳酸钙反应生成可溶性硫酸钙而被冲走。减少酸雨需要净化烟道废气和在汽车中使用催化转换器。
SO₂(g) + H₂O(l) → H₂SO₃(aq) then 2H₂SO₃(aq) + O₂(g) → 2H₂SO₄(aq)
10. Key Equations and Exam Tips | 关键方程式与考试技巧
For Edexcel IGCSE, memorising and applying chemical equations is essential. The following compilation links reactants to products and includes state symbols, which are often required for full marks. Practice writing ionic equations for neutralisation and precipitation, and learn the patterns behind salt formation rather than memorising isolated examples.
对于Edexcel IGCSE，记住并运用化学方程式至关重要。以下汇编将反应物与产物联系起来，并包括状态符号，这在获得满分时通常是必需的。练习书写中和反应和沉淀反应的离子方程式，并学习盐形成的规律，而不是死记孤立的例子。
Mg + H₂SO₄ → MgSO₄ + H₂
ZnO + 2HCl → ZnCl₂ + H₂O
Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
When approaching questions on making salts, always identify the required salt and decide whether it is soluble or insoluble. Then choose the appropriate preparation route. State clearly the steps: add excess solid, filter, heat the filtrate to evaporate water, leave to crystallise. Label diagrams of apparatus if asked. For pH, understand the difference between strength and concentration – two different concepts frequently confused.
在解答关于制备盐的题目时，始终先确定所需的盐并判断它是可溶还是不可溶。然后选择合适的制备路线。清晰地陈述步骤：加入过量固体、过滤、加热滤液蒸发水分、静置结晶。如需要，标注装置图。对于pH，要理解强度与浓度的区别——这两个不同的概念经常被混淆。
Finally, practice describing the observation of colour changes with indicators, effervescence, formation of precipitate, and heat change. Use correct chemical terminology: ‘colourless’ not ‘clear’, ‘precipitate’ not ‘cloudy substance’. These small details make a significant difference in the Edexcel mark scheme.
最后，练习描述指示剂颜色变化、泡腾现象、沉淀生成和热量变化等观察结果。使用正确的化学术语：“无色”而非“透明”，“沉淀”而非“浑浊物”。这些细节在Edexcel评分方案中有显著影响。
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