📚 Acids and Bases: WJEC GCSE Science Revision Guide | 酸与碱：WJEC GCSE 科学考点精讲
Acids and bases are all around us, from the citric acid in lemons to the sodium hydrogencarbonate in baking powder. In WJEC GCSE Science (Chemistry), you need to understand the properties of acids and bases, how to measure acidity using the pH scale, and what happens during neutralisation reactions. This guide covers every essential topic, with equations, practical methods, and common pitfalls so you can feel confident in your exam.
酸和碱无处不在，从柠檬中的柠檬酸到发酵粉中的碳酸氢钠。在 WJEC GCSE 科学（化学）中，你需要理解酸和碱的性质、如何使用 pH 标度测量酸度，以及中和反应会发生什么。本指南涵盖所有必考主题，包含方程式、实验方法和常见错误，让你在考试中信心十足。
1. Understanding Acids and Bases | 理解酸和碱
An acid is a substance that produces hydrogen ions, H⁺, when dissolved in water. For example, hydrogen chloride gas, HCl, dissolves to form hydrochloric acid, releasing H⁺ ions. The presence of H⁺ ions gives acids their characteristic properties, including a sour taste and the ability to turn blue litmus red.
酸是溶于水时产生氢离子（H⁺）的物质。例如，氯化氢气（HCl）溶解形成盐酸，释放出 H⁺ 离子。H⁺ 离子的存在赋予酸特有的性质，包括酸味和使蓝色石蕊试纸变红的能力。
A base is a substance that can neutralise an acid, and an alkali is a soluble base that releases hydroxide ions, OH⁻, in water. Common alkalis include sodium hydroxide (NaOH) and potassium hydroxide (KOH). All alkalis are bases, but not all bases are alkalis; for instance, copper(II) oxide is a base but is insoluble in water.
碱是可以中和酸的物质，而可溶性碱在水中释放氢氧根离子 OH⁻，称为碱溶液。常见碱液包括氢氧化钠（NaOH）和氢氧化钾（KOH）。所有碱液都是碱，但并非所有碱都是碱液；例如氧化铜是碱，但不溶于水。
You should be able to recall the general word equation for the reaction between an acid and an alkali: acid + alkali → salt + water. This is a neutralisation reaction, where H⁺ from the acid combines with OH⁻ from the alkali to form water, H₂O.
你应当记住酸与碱液反应的一般文字方程式：酸 + 碱液 → 盐 + 水。这是一个中和反应，酸中的 H⁺ 与碱液中的 OH⁻ 结合生成水 H₂O。
2. The pH Scale | pH 值标度
The pH scale goes from 0 to 14 and measures how acidic or alkaline a solution is. It is a logarithmic scale: a solution with pH 3 is ten times more acidic than one with pH 4. Acids have pH values less than 7, with strong acids like hydrochloric acid having values close to 0. Alkalis have pH values greater than 7, with strong alkalis such as sodium hydroxide solution reaching pH 14. A pH of 7 is neutral – neither acidic nor alkaline – as shown by pure water.
pH 标度从 0 到 14，用于衡量溶液的酸性或碱性程度。它是对数标度：pH 为 3 的溶液酸性是 pH 为 4 的溶液的十倍。酸的 pH 值小于 7，强酸（如盐酸）的 pH 值接近 0。碱液的 pH 值大于 7，强碱液（如氢氧化钠溶液）的 pH 值可达 14。pH 7 为中性——既非酸性也非碱性，纯水即如此。
For WJEC, you must state the pH ranges for acidic, neutral and alkaline solutions, and understand that pH is determined by the concentration of H⁺ ions. A higher concentration of H⁺ means a lower pH. You are not required to calculate concentration from pH at GCSE, but you should link low pH to more acidic and high H⁺ concentration.
在 WJEC 考试中，你必须说出酸性、中性和碱性溶液的 pH 范围，并理解 pH 由 H⁺ 离子浓度决定。H⁺ 浓度越高，pH 越低。GCSE 不要求从 pH 计算浓度，但你应当将低 pH 与更强的酸性以及高 H⁺ 浓度联系起来。
Certain everyday substances have characteristic pH values: gastric acid (stomach) ~ pH 1-2, lemon juice ~ pH 2-3, vinegar ~ pH 3, pure water pH 7, blood ~ pH 7.4, and household bleach ~ pH 12-13.
某些日常物质有典型的 pH 值：胃酸约 pH 1-2，柠檬汁约 pH 2-3，醋约 pH 3，纯水 pH 7，血液约 pH 7.4，家用漂白水约 pH 12-13。
3. Indicators and Colour Changes | 指示剂与颜色变化
An indicator is a substance that changes colour depending on the pH of the solution. The most common indicators for GCSE are litmus, methyl orange and phenolphthalein. Litmus turns red in acids and blue in alkalis. Methyl orange is red in acidic solutions and yellow in alkaline solutions. Phenolphthalein is colourless in acids and pink in alkalis.
指示剂是一种根据溶液 pH 值改变颜色的物质。GCSE 最常见的指示剂为石蕊、甲基橙和酚酞。石蕊在酸性溶液中变红，在碱性溶液中变蓝。甲基橙在酸性溶液中呈红色，在碱性溶液中呈黄色。酚酞在酸中无色，在碱中呈粉红色。
Universal indicator is a mixture of several indicators that changes colour gradually across the whole pH range. It is often used as a solution or on paper strips. It shows red-orange for pH 1-3, yellow-green for pH 4-6, green for neutral pH 7, blue for pH 8-11, and violet-purple for pH 12-14. In WJEC practicals, you may need to record the colour of universal indicator when testing unknown solutions.
通用指示剂是多种指示剂的混合物，可在整个 pH 范围内逐渐变色。通常以溶液或试纸条形式使用。pH 1-3 时呈红橙色，pH 4-6 呈黄绿色，中性 pH 7 呈绿色，pH 8-11 呈蓝色，pH 12-14 呈紫紫色。在 WJEC 实验中，你可能需要记录测试未知溶液时通用指示剂的颜色。
Always describe colour changes precisely in the exam. For example, ‘methyl orange turns from red to yellow as the solution changes from acidic to alkaline,’ not just ‘it changes colour.’
在考试中要精确描述颜色变化。例如，“随着溶液由酸性变为碱性，甲基橙由红色变为黄色”，而不是只说“颜色变了”。
4. Neutralisation and Salt Formation | 中和与盐的形成
Neutralisation is a chemical reaction in which an acid and a base react to form a salt and water. In terms of ions, the hydrogen ions from the acid react with the hydroxide ions from the alkali: H⁺(aq) + OH⁻(aq) → H₂O(l). This is the ionic equation for neutralisation of a strong acid with a strong alkali.
中和是酸与碱反应生成盐和水的化学反应。从离子角度来看，酸中的氢离子与碱中的氢氧根离子反应：H⁺(aq) + OH⁻(aq) → H₂O(l)。这是强酸与强碱中和的离子方程式。
The salt produced depends on the acid used: hydrochloric acid produces chlorides, sulfuric acid produces sulfates, and nitric acid produces nitrates. The other part of the salt comes from the metal (or ammonium) in the base or alkali. For example, sodium hydroxide + hydrochloric acid → sodium chloride + water: NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l).
生成的盐取决于所用的酸：盐酸产生氯化物，硫酸产生硫酸盐，硝酸产生硝酸盐。盐的另一部分来自碱或碱液中的金属（或铵根）。例如，氢氧化钠 + 盐酸 → 氯化钠 + 水：NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)。
It is important to write balanced symbol equations for neutralisation reactions. Remember to balance the number of atoms of each element on both sides. For example, sulfuric acid reacting with sodium hydroxide: H₂SO₄(aq) + 2NaOH(aq) → Na₂SO₄(aq) + 2H₂O(l).
写出中和反应的配平符号方程式非常重要。记得平衡两边每种元素的原子数目。例如，硫酸与氢氧化钠反应：H₂SO₄(aq) + 2NaOH(aq) → Na₂SO₄(aq) + 2H₂O(l)。
5. Reactions of Acids with Metals | 酸与金属的反应
When an acid reacts with a metal (above hydrogen in the reactivity series), a salt and hydrogen gas are produced. The general word equation is: acid + metal → salt + hydrogen. For example, magnesium + sulfuric acid → magnesium sulfate + hydrogen: Mg(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂(g).
酸与金属（在金属活动性顺序中排在氢之前的）反应，生成盐和氢气。一般文字方程式为：酸 + 金属 → 盐 + 氢气。例如，镁 + 硫酸 → 硫酸镁 + 氢气：Mg(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂(g)。
You can test for hydrogen gas by placing a lit splint over the mouth of the test tube – a squeaky pop indicates hydrogen. In the lab, this reaction is carried out by adding a small piece of metal to dilute acid and observing the vigorous fizzing as hydrogen is released.
你可以通过将燃着的木条放在试管口来检验氢气——听到尖锐的爆鸣声即表明有氢气。在实验室中，该反应通过向稀酸中加入一小块金属进行，可以观察到剧烈的冒泡现象，氢气随之逸出。
Note that copper and metals below hydrogen in the reactivity series do not react with dilute acids, as they cannot displace hydrogen from the acid.
注意，铜以及排在氢之后的金属不与稀酸反应，因为它们无法从酸中置换出氢。
6. Reactions of Acids with Carbonates | 酸与碳酸盐的反应
Carbonates react with acids to produce a salt, water and carbon dioxide gas. The word equation is: acid + carbonate → salt + water + carbon dioxide. For instance, calcium carbonate (limestone, marble) with hydrochloric acid: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g).
碳酸盐与酸反应生成盐、水和二氧化碳气体。文字方程式为：酸 + 碳酸盐 → 盐 + 水 + 二氧化碳。例如，碳酸钙（石灰石、大理石）与盐酸反应：CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)。
The production of carbon dioxide can be tested by bubbling the gas through limewater – it turns limewater cloudy or milky because insoluble calcium carbonate forms. This is a key identification test for CO₂. Fizzing and effervescence are also visible signs.
二氧化碳的生成可以通过将气体通入石灰水中来检验——石灰水变浑浊或变成乳白色，因为生成了不溶的碳酸钙。这是 CO₂ 的关键鉴定试验。冒泡和起泡也是可见的迹象。
All metal carbonates react in a similar way. Sodium carbonate + sulfuric acid → sodium sulfate + water + carbon dioxide: Na₂CO₃(s) + H₂SO₄(aq) → Na₂SO₄(aq) + H₂O(l) + CO₂(g). Learning to write balanced equations for these reactions is a core skill.
所有金属碳酸盐均以类似方式反应。碳酸钠 + 硫酸 → 硫酸钠 + 水 + 二氧化碳：Na₂CO₃(s) + H₂SO₄(aq) → Na₂SO₄(aq) + H₂O(l) + CO₂(g)。学会书写这些反应的配平方程式是一项核心技能。
7. Making Copper(II) Sulfate Crystals | 制备硫酸铜晶体
A classic WJEC practical involves preparing pure, dry copper(II) sulfate crystals from copper(II) oxide and dilute sulfuric acid. This is a neutralisation reaction between an insoluble base and an acid. The word equation is: copper(II) oxide + sulfuric acid → copper(II) sulfate + water: CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l).
一个经典的 WJEC 实验涉及用氧化铜和稀硫酸制备纯净干燥的硫酸铜晶体。这是不溶性碱与酸之间的中和反应。文字方程式为：氧化铜 + 硫酸 → 硫酸铜 + 水：CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)。
The steps are: (1) warm the dilute sulfuric acid in a beaker; (2) add black copper(II) oxide powder one spatula at a time while stirring until the solid no longer dissolves – excess solid is indicated by a black residue at the bottom; (3) filter the mixture to remove the unreacted copper(II) oxide, collecting the clear blue filtrate; (4) evaporate some of the water by gentle heating or place the solution in an evaporating basin and allow it to cool and crystallise slowly; (5) dry the crystals by pressing between filter papers.
步骤为：(1) 在烧杯中温热稀硫酸；(2) 一勺一勺地加入黑色氧化铜粉末并搅拌，直至固体不再溶解——多余的固体表现为底部有黑色残留物；(3) 过滤混合物除去未反应的氧化铜，收集清澈的蓝色滤液；(4) 通过温和加热蒸发掉部分水分，或将溶液放入蒸发皿中让其慢慢冷却结晶；(5) 用滤纸压干晶体。
You should be able to explain why an excess of the base is used – to ensure all the acid is neutralised. Filtration removes the insoluble unreacted base, and crystallisation produces the pure hydrated crystals, CuSO₄·5H₂O.
你应当能够解释为何使用过量的碱——以确保所有酸都被中和。过滤除去未反应的不溶性碱，结晶得到纯净的水合晶体 CuSO₄·5H₂O。
8. Everyday Examples and Safety | 日常例子与安全
Acids and bases have many everyday applications. Stomach acid (containing hydrochloric acid) helps digest food, and antacids (bases like magnesium hydroxide and calcium carbonate) neutralise excess acid to relieve indigestion. The pH of soil is adjusted by adding lime (calcium oxide, a base) to raise pH when soil is too acidic for crop growth.
酸和碱有许多日常应用。胃酸（含有盐酸）帮助消化食物，抗酸剂（如氢氧化镁和碳酸钙等碱）可中和过多胃酸以缓解消化不良。土壤 pH 可通过添加石灰（氧化钙，一种碱）来调节，当土壤过酸不利于作物生长时提高 pH。
In the laboratory, acids and alkalis are corrosive or irritant, so you must always wear safety goggles and handle them with care. When diluting concentrated acids, always add acid to water (never the reverse) while stirring slowly to avoid splashing due to the exothermic reaction. Know the hazard symbols for corrosive substances.
在实验室中，酸和碱液具有腐蚀性或刺激性，因此必须始终佩戴护目镜并小心操作。稀释浓酸时，务必把酸加入水中（切勿反过来），同时缓慢搅拌，以避免放热反应引起的飞溅。识别腐蚀性物质的危险标志。
Bee stings are acidic and can be treated with baking soda (a base), while wasp stings are alkaline and can be treated with vinegar (an acid). This is a real-life neutralisation concept that appears in many exam contexts.
蜜蜂蜇伤是酸性的，可用小苏打（一种碱）处理，而黄蜂蜇伤是碱性的，可用醋（一种酸）处理。这是现实生活中应用中和概念的实例，经常出现在考试情境中。
9. Summary of Equations and Key Terms | 方程式和关键术语总结
Below are the essential general equations you must know for WJEC GCSE acids, bases and salts:
以下是 WJEC GCSE 酸、碱和盐必考的基本方程式：
- acid + alkali → salt + water (neutralisation) | 酸 + 碱液 → 盐 + 水（中和）
- acid + metal → salt + hydrogen (metal above hydrogen) | 酸 + 金属 → 盐 + 氢气（金属在氢之上）
- acid + carbonate → salt + water + carbon dioxide | 酸 + 碳酸盐 → 盐 + 水 + 二氧化碳
- acid + base (insoluble) → salt + water | 酸 + 碱（不溶）→ 盐 + 水
A salt is an ionic compound formed when a metal (or ammonium) replaces the hydrogen in an acid. Key terms: base (any substance that neutralises an acid), alkali (soluble base that releases OH⁻), pH (measure of acidity, related to H⁺ concentration), indicator (dye that changes colour with pH).
盐是金属（或铵根）取代酸中氢而形成的离子化合物。关键术语：碱（任何可中和酸的物质）、碱液（可溶性碱，释放 OH⁻）、pH（酸度衡量量，与 H⁺ 浓度相关）、指示剂（随 pH 改变颜色的染料）。
In naming salts: hydrochloric acid → … chloride; sulfuric acid → … sulfate; nitric acid → … nitrate. For example, potassium + nitric acid → potassium nitrate + hydrogen. Memorising these patterns will help you construct any formula.
盐的命名：盐酸 → 某氯化物；硫酸 → 某硫酸盐；硝酸 → 某硝酸盐。例如，钾 + 硝酸 → 硝酸钾 + 氢气。记住这些规律有助于你构建任何化学式。
State symbols are required when writing equations: (s) solid, (l) liquid, (g) gas, (aq) aqueous (dissolved in water). For example, CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). Including correct state symbols shows a deeper understanding and is often rewarded in mark schemes.
书写方程式时需要标明状态符号：(s) 固体，(l) 液体，(g) 气体，(aq) 水溶液（溶于水）。例如，CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)。写上正确的状态符号能体现更深入的理解，通常会在评分方案中给分。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply