📚 GCSE AQA Science: Acids and Bases - Core Concepts | GCSE AQA 科学：酸与碱 考点精讲
This article covers the essential GCSE AQA Science topic of acids and bases, including definitions, indicators, pH, neutralisation, reactions of acids, strength versus concentration, and key practical skills such as titration. Understanding these core ideas will prepare you for exam questions on chemical reactions and quantitative chemistry.
本文涵盖GCSE AQA科学中酸与碱的核心考点，包括定义、指示剂、pH值、中和反应、酸的反应特性、强弱酸与浓度的区别，以及滴定等关键实验技能。掌握这些核心概念将帮助你应对化学反应和定量化学的考试题目。
1. What are Acids and Bases? | 什么是酸和碱？
In aqueous solutions, acids produce hydrogen ions, H⁺. For example, hydrochloric acid (HCl) ionises to give H⁺ and Cl⁻. Sulfuric acid (H₂SO₄) produces two H⁺ ions per molecule.
在水溶液中，酸产生氢离子(H⁺)。例如，盐酸(HCl)电离生成H⁺和Cl⁻。硫酸(H₂SO₄)每个分子产生两个H⁺。
Bases are substances that can neutralise acids. Metal oxides and metal hydroxides are typical bases. A base that dissolves in water is called an alkali and releases hydroxide ions, OH⁻.
碱是能中和酸的物质。金属氧化物和金属氢氧化物是典型的碱。可溶于水的碱称为碱溶液，并释放氢氧根离子(OH⁻)。
Remember: all alkalis are bases, but not all bases are alkalis. For instance, copper(II) oxide is a base but insoluble in water, so it is not an alkali.
记住：所有碱溶液都是碱，但并非所有碱都是碱溶液。例如，氧化铜(II)是碱，但不溶于水，因此不是碱溶液。
2. Indicators and pH | 指示剂与pH
Indicators are dyes that change colour depending on whether a solution is acidic or alkaline. Common indicators include litmus, phenolphthalein, and methyl orange.
指示剂是能根据溶液酸性或碱性而改变颜色的染料。常用指示剂包括石蕊、酚酞和甲基橙。
Litmus turns red in acid and blue in alkali. Phenolphthalein is colourless in acid and pink in alkali. Methyl orange is red in acid and yellow in alkali.
石蕊在酸中变红，在碱中变蓝。酚酞在酸中无色，在碱中变粉红。甲基橙在酸中呈红色，在碱中呈黄色。
Universal indicator is a mixture of dyes that shows a range of colours across the pH scale, from red (strong acid) to violet (strong alkali). It can be used as a solution or on pH paper.
通用指示剂是混合染料，能根据pH标度显示一系列颜色，从红色（强酸）到紫色（强碱）。它可以作为溶液使用，也可以浸在pH试纸上。
3. The pH Scale and Hydrogen Ion Concentration | pH标度与氢离子浓度
The pH scale measures the acidity or alkalinity of a solution. It ranges from 0 (very acidic) to 14 (very alkaline). A pH of 7 is neutral, like pure water.
pH标度衡量溶液的酸碱性。范围从0（强酸）到14（强碱）。pH 7为中性，如纯水。
pH is related to the concentration of hydrogen ions: the higher the H⁺ concentration, the lower the pH. Each decrease of 1 on the pH scale means a tenfold increase in H⁺ concentration.
pH与氢离子浓度相关：H⁺浓度越高，pH值越低。pH每降低1，表示H⁺浓度增加10倍。
For alkalis, pH is determined by the concentration of hydroxide ions. Diluting an acid or alkali moves the pH closer to 7.
对于碱溶液，pH由氢氧根离子浓度决定。稀释酸或碱溶液会使pH向7靠拢。
4. Neutralisation Reactions | 中和反应
A neutralisation reaction occurs when an acid reacts with a base to produce a salt and water. The H⁺ ions from the acid combine with OH⁻ ions from the base to form water molecules.
中和反应是酸与碱反应生成盐和水的过程。酸中的H⁺与碱中的OH⁻结合形成水分子。
H⁺ + OH⁻ → H₂O
salt + water. For example, hydrochloric acid + sodium hydroxide → sodium chloride + water.
通式为：酸 + 碱 → 盐 + 水。例如，盐酸 + 氢氧化钠 → 氯化钠 + 水。
Neutralisation is exothermic, meaning it releases heat energy. The exact temperature change can be measured in a calorimetry experiment.
中和反应是放热的，意味着它会释放热能。在量热实验中可以测量确切的温度变化。
5. Reactions of Acids with Metals | 酸与金属的反应
produce a salt and hydrogen gas. The general equation is: acid + metal → salt + hydrogen.
稀酸与某些金属（如镁、锌和铁）反应，生成盐和氢气。通式为：酸 + 金属 → 盐 + 氢气。
For instance, magnesium reacts with hydrochloric acid to form magnesium chloride and hydrogen.
例如，镁与盐酸反应生成氯化镁和氢气。
Mg + 2HCl → MgCl₂ + H₂
Copper does not react with dilute acids because it is below hydrogen in the reactivity series. The test for hydrogen is a lighted splint producing a 'squeaky pop'.
铜不与稀酸反应，因为它在金属活动性顺序中位于氢之后。检验氢气的方法是用点燃的火柴靠近，产生“爆鸣声”。
6. Reactions of Acids with Metal Oxides, Hydroxides and Carbonates | 酸与金属氧化物、氢氧化物和碳酸盐的反应
lt and water only. For example, sulfuric acid + copper(II) oxide → copper sulfate + water.
酸与金属氧化物和金属氢氧化物反应，只生成盐和水。例如，硫酸 + 氧化铜(II) → 硫酸铜 + 水。
With metal carbonates, acids produce a salt, water, and carbon dioxide gas. The fizzing (effervescence) confirms CO₂, which turns limewater milky.
酸与金属碳酸盐反应，生成盐、水和二氧化碳气体。起泡（冒泡）证实CO₂，使石灰水变浑浊。
General equations:
通式：
acid + metal oxide → salt + water
酸 + 金属氧化物 → 盐 + 水
acid + metal hydroxide → salt + water
酸 + 金属氢氧化物 → 盐 + 水
acid + metal carbonate → salt + water + CO₂
酸 + 金属碳酸盐 → 盐 + 水 + 二氧化碳
7. Strong and Weak Acids | 强酸与弱酸
A strong acid is completely ionised in aqueous solution, meaning all its molecules release H⁺ ions. Examples include hydrochloric acid, sulfuric acid, and nitric acid.
强酸在水溶液中完全电离，即所有分子都释放H⁺离子。例子包括盐酸、硫酸和硝酸。
A weak acid only partially ionises, so the solution contains a mixture of molecules and ions. Ethanoic acid (CH₃COOH) is a typical weak acid.
弱酸仅部分电离，因此溶液中含有分子和离子的混合物。乙酸(CH₃COOH)是典型的弱酸。
For solutions of the same concentration, a strong acid has a lower pH (more acidic) than a weak acid because it produces a higher concentration of H⁺.
对于相同浓度的溶液，强酸的pH值更低（酸性更强），因为它产生的H⁺浓度更高。
8. Concentration versus Strength | 浓度与强度的区别
Concentration refers to how much acid is dissolved in a given volume of water. It is measured in mol/dm³ or g/dm³. Diluting an acid reduces its concentration.
浓度是指一定体积水中溶解了多少酸，用mol/dm³或g/dm³表示。稀释酸会降低其浓度。
Strength refers to the degree of ionisation. A concentrated weak acid may still have a higher pH than a dilute strong acid because the strong acid is fully ionised.
强度指电离的程度。浓的弱酸仍然可能比稀的强酸的pH值高，因为强酸是完全电离的。
When comparing acids, it is essential to specify both concentration and strength. For example, 0.1 mol/dm³ HCl has a lower pH than 0.1 mol/dm³ ethanoic acid.
在比较酸时，必须同时说明浓度和强度。例如，0.1 mol/dm³ HCl的pH低于0.1 mol/dm³乙酸。
9. Making Salts – Soluble Salts from Insoluble Bases | 制备盐——从不溶碱制可溶盐
A pure dry sample of a soluble salt can be prepared by reacting an acid with an insoluble base, such as a metal oxide or carbonate. The excess solid base is added until no more reacts, then filtered off.
可用酸与不溶碱（如金属氧化物或碳酸盐）反应制备纯净干燥的可溶盐样品。加入过量的固体碱，直到不再反应，然后过滤掉多余固体。
For example, to make copper(II) sulfate crystals: add black copper(II) oxide
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