AQA IGCSE Science: Acids and Bases Key Points | AQA IGCSE 科学：酸与碱考点精讲

📚 AQA IGCSE Science: Acids and Bases Key Points | AQA IGCSE 科学：酸与碱考点精讲

Acids and bases are fundamental to understanding chemical reactions in the world around us. This revision guide covers the essential concepts required for the AQA IGCSE Science syllabus, including pH, neutralisation, and the characteristic reactions of acids. Mastering these key points will help you tackle exam questions with confidence.

酸和碱是理解我们周围化学反应的基础。这份复习指南涵盖了 AQA IGCSE 科学课程大纲所要求的基本概念，包括 pH 值、中和反应以及酸的特征反应。掌握这些要点将帮助你自信地应对考试题目。

1. Introduction to Acids and Bases | 酸与碱简介

Acids are substances that release hydrogen ions (H⁺) when dissolved in water. They typically have a sour taste and can be corrosive. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Bases are substances that can neutralise acids, producing a salt and water. A base that dissolves in water is called an alkali; alkalis release hydroxide ions (OH⁻) in solution.

酸是溶于水时释放氢离子 (H⁺) 的物质。它们通常有酸味，并可能具有腐蚀性。实验室常见的酸包括盐酸 (HCl)、硫酸 (H₂SO₄) 和硝酸 (HNO₃)。碱是可以中和酸，生成盐和水的物质。溶于水的碱称为可溶碱；可溶碱在溶液中释放氢氧根离子 (OH⁻)。

It is important to remember that all alkalis are bases, but not all bases are alkalis. For example, copper(II) oxide is a base but it does not dissolve in water, so it is not an alkali. The distinction often appears in questions about neutralisation.

需要记住的是，所有可溶碱都是碱，但并非所有碱都是可溶碱。例如，氧化铜 (CuO) 是一种碱，但它不溶于水，因此不是可溶碱。这一区别经常出现在关于中和反应的问题中。

2. The pH Scale | pH值标度

The pH scale is a measure of the acidity or alkalinity of a solution. It ranges from 0 to 14. A pH less than 7 indicates an acidic solution; the lower the number, the more acidic the solution. A pH of 7 is neutral, like pure water. A pH greater than 7 indicates an alkaline solution, with higher numbers showing stronger alkalinity.

pH 值标度是衡量溶液酸碱性的指标，范围从 0 到 14。pH 值小于 7 表示酸性溶液；数字越小，酸性越强。pH 值等于 7 为中性，比如纯水。pH 值大于 7 表示碱性溶液，数字越大，碱性越强。

The pH scale is logarithmic, meaning each whole pH value below 7 is ten times more acidic than the next higher value. For instance, a solution of pH 3 is ten times more acidic than one of pH 4, and one hundred times more acidic than pH 5. This concept is often tested in data-analysis questions.

pH 值标度是对数标度，这意味着 pH 值每降低 1 个单位，酸性就增强 10 倍。例如，pH 值为 3 的溶液的酸性是 pH 值为 4 的溶液的 10 倍，是 pH 值为 5 的溶液的 100 倍。这一概念常在数据分析题中考查。

3. Indicators | 指示剂

Indicators are substances that change colour depending on the pH of the solution. Universal indicator is a mixture of dyes that shows a gradual colour change across the pH scale, from red in strong acids through green in neutral to violet in strong alkalis. Litmus is a simpler indicator: red in acid, blue in alkali, and purple in neutral.

指示剂是根据溶液的 pH 值而变色的物质。通用指示剂是一种混合染料，能在 pH 值标度上显示渐变的颜色变化：从强酸中的红色，经过中性时的绿色，到强碱中的紫色。石蕊是一种更简单的指示剂：酸性溶液中呈红色，碱性溶液中呈蓝色，中性时呈紫色。

Phenolphthalein is another common indicator, turning colourless in acidic and neutral solutions, and pink in alkaline solutions above about pH 8.3. Knowing the colour changes of these indicators is essential for titrations and identifying unknown solutions.

酚酞是另一种常见指示剂，在酸性和中性溶液中无色，在 pH 值约大于 8.3 的碱性溶液中呈粉红色。了解这些指示剂的颜色变化对于滴定和鉴定未知溶液至关重要。

Indicator	Acid colour	Neutral	Alkali colour
Universal indicator	Red, orange, yellow	Green	Blue, violet
Litmus	Red	Purple	Blue
Phenolphthalein	Colourless	Colourless	Pink

4. Acids and Metals | 酸与金属

When an acid reacts with a metal, a salt and hydrogen gas are produced. The general word equation is: acid + metal → salt + hydrogen. For example, magnesium reacts with hydrochloric acid to form magnesium chloride and hydrogen: Mg + 2HCl → MgCl₂ + H₂. The gas can be tested using a lit splint, which gives a ‘squeaky pop’ sound.

当酸与金属反应时，会生成盐和氢气。通用文字方程式为：酸 + 金属 → 盐 + 氢气。例如，镁与盐酸反应生成氯化镁和氢气：Mg + 2HCl → MgCl₂ + H₂。可以用点燃的木条检验这种气体，会发出 ‘噗’ 的一声。

Not all metals react with acids at the same rate. More reactive metals, like potassium, sodium and calcium, react vigorously, while less reactive metals, such as copper, do not react at all with dilute acids. This is linked to the reactivity series; only metals above hydrogen in the series will displace hydrogen from acids.

并非所有金属与酸的反应速率都相同。较活泼的金属，如钾、钠和钙，反应剧烈；而活泼性较低的金属，如铜，则完全不能与稀酸反应。这与金属活动性顺序有关；只有排在氢前面的金属才能从酸中置换出氢。

5. Acids and Carbonates | 酸与碳酸盐

Carbonates react with acids to produce a salt, water and carbon dioxide gas. The general equation is: acid + carbonate → salt + water + carbon dioxide. For instance, calcium carbonate (limestone) reacts with hydrochloric acid: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Carbon dioxide can be identified using limewater, which turns milky (cloudy).

碳酸盐与酸反应生成盐、水和二氧化碳气体。通用方程式为：酸 + 碳酸盐 → 盐 + 水 + 二氧化碳。例如，碳酸钙（石灰石）与盐酸反应：CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂。可以用石灰水检验二氧化碳，石灰水会变浑浊。

This reaction is often used to produce salts in the laboratory. However, because carbon dioxide is released, the reaction is not suitable for making salts that require evaporation to dryness if the product is heat-sensitive. The reaction can be seen as a specific example of neutralisation, where the carbonate acts as the base.

该反应常用于实验室制备盐。但由于会释放二氧化碳，如果产物对热敏感，此反应不适合用于需要通过蒸发至干来制盐的情况。这种反应可以看作中和反应的一个特例，其中碳酸盐充当碱。

6. Neutralisation | 中和反应

Neutralisation is the reaction between an acid and a base (or alkali) to produce a salt and water. The general ionic equation for neutralisation is: H⁺(aq) + OH⁻(aq) → H₂O(l). In the reaction between hydrochloric acid and sodium hydroxide, the products are sodium chloride and water: HCl + NaOH → NaCl + H₂O.

中和反应是酸和碱（或可溶碱）反应生成盐和水的反应。中和反应的通用离子方程式为：H⁺(aq) + OH⁻(aq) → H₂O(l)。在盐酸与氢氧化钠的反应中，产物是氯化钠和水：HCl + NaOH → NaCl + H₂O。

Neutralisation has many everyday applications. Farmers use lime (calcium oxide) to neutralise acidic soil. Antacid tablets contain bases like magnesium hydroxide to neutralise excess stomach acid. In the lab, neutralisation is exactly determined by titration using an indicator to find the equivalence point.

中和反应有许多日常应用。农民用石灰（氧化钙）来中和酸性土壤。抗酸药片含有氢氧化镁等碱，用于中和过多的胃酸。在实验室中，通过滴定并使用指示剂来确定等当点，从而精确进行中和。

7. Strong and Weak Acids | 强酸与弱酸

A strong acid is one that completely ionises in water, releasing all its hydrogen ions. Examples include hydrochloric acid, sulfuric acid and nitric acid. A weak acid only partially ionises in solution, establishing an equilibrium between the molecules and ions. Ethanoic acid (in vinegar) and citric acid are common weak acids.

强酸是指在水中完全电离，释放出全部氢离子的酸。例如盐酸、硫酸和硝酸。弱酸在溶液中仅部分电离，在分子和离子之间建立平衡。乙酸（食醋中）和柠檬酸是常见的弱酸。

The strength of an acid is not the same as its concentration. A concentrated weak acid may still have a relatively low concentration of hydrogen ions compared to a dilute strong acid. This means the pH of a weak acid is typically higher than that of a strong acid at the same concentration.

酸的强度并不等同于其浓度。与稀强酸相比，浓弱酸中氢离子的浓度可能仍然相对较低。这意味着在相同浓度下，弱酸的 pH 值通常高于强酸。

8. Bases and Alkalis | 碱与可溶碱

Bases include metal oxides, metal hydroxides and metal carbonates. Soluble bases (alkalis) such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) dissociate in water to give OH⁻ ions. Insoluble bases, like copper(II) oxide, can still neutralise acids, but they do not significantly raise pH until the acid is consumed.

碱包括金属氧化物、金属氢氧化物和金属碳酸盐。可溶性碱（即可溶碱）如氢氧化钠 (NaOH) 和氢氧化钾 (KOH) 在水中解离出 OH⁻ 离子。不溶性碱，如氧化铜，也能中和酸，但在酸被消耗完之前，溶液的 pH 值不会明显升高。

Ammonia solution is a common weak alkali used in cleaning products. It partially ionises in water to form ammonium ions and hydroxide ions: NH₃ + H₂O ⇌ NH₄⁺ + OH⁻. Because the equilibrium lies far to the left, the concentration of hydroxide ions is low, making it a weak alkali.

氨水是清洁产品中常见的一种弱碱。它在水中部分电离，形成铵离子和氢氧根离子：NH₃ + H₂O ⇌ NH₄⁺ + OH⁻。由于平衡极大地偏向左侧，氢氧根离子浓度较低，因此它是一种弱碱。

9. Making Soluble Salts | 制备可溶性盐

There are several methods to prepare a soluble salt, depending on the solubility of the reactants and the stability of the salt. One common approach is to react an acid with an excess insoluble base, such as a metal oxide or carbonate. After the reaction stops, the excess solid is removed by filtration, and the salt solution is crystallised by evaporation.

根据反应物的溶解性和盐的稳定性，有多种方法可以制备可溶性盐。一种常见的方法是将酸与过量不溶性碱（如金属氧化物或碳酸盐）反应。反应停止后，通过过滤除去多余的固体，然后通过蒸发结晶得到盐溶液。

For salts that decompose on heating, gentle heating in a water bath is used. If both the acid and the base are soluble, titration is needed to exactly neutralise the acid without using excess base. The salt is then obtained by evaporation and recrystallisation if high purity is required.

对于加热易分解的盐，需采用水浴缓慢加热。如果酸和碱均可溶，则需要通过滴定来精确中和酸，而不使用过量的碱。随后通过蒸发得到盐；如果需要高纯度，还可以进行重结晶。

Example: Preparation of copper(II) sulfate crystals. Add excess copper(II) oxide to warm sulfuric acid, stir, filter the unreacted solid, heat the filtrate to evaporate some water, then allow it to cool slowly to form blue crystals.

示例： 制备硫酸铜晶体。将过量氧化铜加入温热的硫酸中，搅拌，过滤未反应的固体，加热滤液蒸发部分水分，然后让其缓慢冷却，形成蓝色晶体。

CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)

10. Everyday Examples and Environmental Context | 日常实例与环境背景

Acids and bases appear in many everyday products. Citric acid is in lemons and oranges; ethanoic acid is in vinegar; carbonic acid is in fizzy drinks. Household cleaners often contain alkalis like sodium hydroxide or ammonia. Understanding their properties helps explain why they are used and how to handle them safely.

酸碱存在于许多日常产品中。柠檬和橙子中含有柠檬酸；食醋中含有乙酸；碳酸存在于汽水中。家用清洁剂通常含有氢氧化钠或氨水等碱性物质。了解它们的性质有助于解释其用途和如何安全使用。

In the environment, acid rain is a significant problem. It forms when sulfur dioxide and nitrogen oxides from burning fossil fuels dissolve in rainwater, producing weak sulfuric and nitric acids. Acid rain can lower the pH of soil and lakes, harming plants and aquatic life. Limestone buildings are eroded because calcium carbonate reacts with the acid.

在环境中，酸雨是一个严重的问题。它是由燃烧化石燃料产生的二氧化硫和氮氧化物溶于雨水中，形成稀硫酸和稀硝酸而形成的。酸雨会降低土壤和湖泊的 pH 值，危害植物和水生生物。石灰石建筑因碳酸钙与酸反应而受到侵蚀。

Even the human body maintains a delicate pH balance. Blood is kept at a pH of about 7.4; small deviations can be dangerous. The stomach produces hydrochloric acid to help digestion, while the small intestine is slightly alkaline. This interplay demonstrates how vital acid-base chemistry is to life.

甚至人体也维持着精密的 pH 值平衡。血液的 pH 值保持在约 7.4；微小的偏差都可能造成危险。胃产生盐酸帮助消化，而小肠则呈弱碱性。这种相互作用表明酸碱化学对生命至关重要。

Published by TutorHao | IGCSE Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

AQA IGCSE Science: Acids and Bases Key Points | AQA IGCSE 科学：酸与碱 考点精讲