📚 Year 9 AQA Chemistry: Case Study Practice | Year 9 AQA 化学：案例分析实战演练
Welcome to this case study practice for Year 9 AQA Chemistry. In this article, we will explore real-world scenarios where chemical concepts are applied to solve problems. By analysing these cases, you will deepen your understanding of key topics such as acids and alkalis, separation techniques, chemical reactions, and environmental chemistry. Each case includes a description, the chemistry behind it, and practice questions to test your knowledge.
欢迎来到 Year 9 AQA 化学的案例分析实战。本文将通过真实情境，运用化学概念解决问题。分析这些案例，你会加深对酸和碱、分离技术、化学反应和环境化学等关键主题的理解。每个案例包括描述、背后的化学原理，以及练习题来检验你的知识。
1. Acid Rain and Limestone Buildings | 酸雨与石灰岩建筑
Case Description: The ancient limestone cathedral of St. Paul's has suffered surface erosion over the decades. Rainwater in the area is often acidic due to air pollution. Chemists were called to investigate why the stone was crumbling.
案例描述：圣保罗大教堂古老的石灰岩外墙几十年来遭受表面侵蚀。该地区因空气污染，雨水常呈酸性。化学家受邀调查石材为何碎裂。
rom sulfur dioxide and nitrogen oxides in the atmosphere. When acid rain contacts limestone, a neutralisation reaction occurs: CaCO₃(s) + H₂SO₄(aq) → CaSO₄(aq) + H₂O(l) + CO₂(g). The solid calcium carbonate dissolves, causing erosion.
化学背景：石灰岩主要成分是碳酸钙（CaCO₃）。酸雨含有硫酸（H₂SO₄）和硝酸（HNO₃），由大气中的二氧化硫和氮氧化物形成。当酸雨接触石灰岩，发生中和反应：CaCO₃(s) + H₂SO₄(aq) → CaSO₄(aq) + H₂O(l) + CO₂(g)。固态碳酸钙溶解，导致侵蚀。
Practice: Explain why using limestone for statues in polluted cities is not a good long-term choice. Propose a method to protect such structures.
练习：解释为什么在污染城市用石灰岩制作雕像不是长期的好选择。提出一种保护这类结构的方法。
2. Purifying Drinking Water | 净化饮用水
Case Description: A village relies on a well that has become contaminated with mud, leaves and bacteria after heavy rain. The local health authority must provide safe drinking water using simple chemistry techniques.
案例描述：一个村庄依赖的水井在暴雨后被泥沙、树叶和细菌污染。当地卫生部门必须用简单的化学方法提供安全的饮用水。
acts with water to form hypochlorous acid (HOCl), which kills bacteria: Cl₂(g) + H₂O(l) → HOCl(aq) + HCl(aq). Filtration cannot remove dissolved substances or microbes, but chlorine disinfects the water effectively.
化学背景：净化过程包括过滤以去除不溶性固体，然后进行氯化消毒。氯气（Cl₂）与水反应生成次氯酸（HOCl），可杀灭细菌：Cl₂(g) + H₂O(l) → HOCl(aq) + HCl(aq)。过滤不能除去溶解物质或微生物，但氯可以有效消毒。
Practice: Explain why the water must be filtered before adding chlorine. What would happen if the order were reversed?
练习：解释为什么必须先过滤再加氯消毒。如果顺序颠倒，会发生什么？
3. Rusting of Iron | 铁的锈蚀
Case Description: An old iron bridge near the coast shows orange-brown flaking on its surface. Engineers need to understand why the corrosion is worse than inland and how to stop further damage.
案例描述：海岸附近一座古老的铁桥表面出现橙褐色的剥落。工程师需要了解为什么腐蚀比内陆更严重，以及如何阻止进一步损坏。
lled rust: 4Fe(s) + 3O₂(g) + 2xH₂O(l) → 2Fe₂O₃·xH₂O(s). Salt water accelerates the process because ions increase conductivity, speeding up electron transfer. Prevention methods include painting, oiling, or galvanising with a more reactive metal like zinc (sacrificial protection).
化学背景：锈蚀是一种同时需要氧气和水的氧化反应。铁反应生成水合氧化铁（通常称为铁锈）：4Fe(s) + 3O₂(g) + 2xH₂O(l) → 2Fe₂O₃·xH₂O(s)。盐水加速了该过程，因为离子提高了导电性，加快了电子转移。防护方法包括涂漆、涂油或使用更活泼的金属如锌进行镀锌（牺牲保护）。
Practice: Suggest why galvanising provides longer-lasting protection than paint. Include the term 'sacrificial protection' in your answer.
练习：说明为什么镀锌能比油漆提供更持久的保护。在你的回答中包括'牺牲保护'这一术语。
4. Combustion of Fuels | 燃料的燃烧
Case Description: A family's gas boiler releases fumes that trigger a carbon monoxide alarm. The technician explains that incomplete combustion of the natural gas is occurring. The family wants to understand the difference between complete and incomplete combustion.
案例描述：一个家庭的燃气锅炉释放的烟气触发了一氧化碳报警器。技术人员解释说，天然气发生了不完全燃烧。这家人想了解完全燃烧与不完全燃烧的区别。
. When oxygen supply is limited, incomplete combustion produces toxic carbon monoxide (CO) and soot (C): 2CH₄(g) + 3O₂(g) → 2CO(g) + 4H₂O(g) or CH₄(g) + O₂(g) → C(s) + 2H₂O(g). Carbon monoxide binds to haemoglobin, reducing oxygen transport in blood.
化学背景：天然气的主要成分是甲烷（CH₄）。完全燃烧产生二氧化碳和水：CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)。当氧气供应有限时，不完全燃烧会产生有毒的一氧化碳（CO）和碳黑（C）：2CH₄(g) + 3O₂(g) → 2CO(g) + 4H₂O(g) 或 CH₄(g) + O₂(g) → C(s) + 2H₂O(g)。一氧化碳与血红蛋白结合，降低血液的氧运输能力。
Practice: Explain why a yellow, smoky flame indicates incomplete combustion. Write a balanced equation for the incomplete combustion of butane (C₄H₁₀) to form carbon monoxide and water.
练习：解释为什么黄焰和多烟的火焰表明不完全燃烧。写出丁烷（C₄H₁₀）不完全燃烧生成一氧化碳和水的配平方程式。
5. Neutralising Stomach Acid | 中和胃酸
Case Description: After a heavy meal, a person suffers from heartburn caused by excess hydrochloric acid (HCl) in the stomach. They take an indigestion tablet containing calcium carbonate. The relief is rapid, accompanied by burping.
案例描述：一个人在大餐后出现胃灼热，这是由胃中过量盐酸（HCl）引起的。他服用了含有碳酸钙的抗酸片。症状迅速缓解，并伴有打嗝。
) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). The carbon dioxide gas produced causes burping. Other antacid ingredients include magnesium hydroxide (Mg(OH)₂) and aluminium hydroxide, which react similarly but without producing gas, e.g., Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O.
化学背景：抗酸片通过中和起作用。有效成分碳酸钙与胃酸反应：CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)。产生的二氧化碳气体引起打嗝。其他抗酸成分包括氢氧化镁（Mg(OH)₂）和氢氧化铝，它们反应类似但不产生气体，例如：Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O。
formula mass (CaCO₃ = 100, Mg(OH)₂ = 58) to decide which tablet can neutralise more acid.
练习：比较 1 g CaCO₃ 和 1 g Mg(OH)₂ 的中和能力。使用相对分子质量（CaCO₃=100，Mg(OH)₂=58）判断哪种药片能中和更多的酸。
6. Chromatography in Forensics | 法医中的色谱分析
Case Description: A forged cheque is discovered at a bank. Forensic scientists suspect the ink used is from a specific brand of pen. They extract ink from the cheque and compare it with ink samples from three pens using paper chromatography.
案例描述：银行发现一张伪造支票。法医专家怀疑所用墨水来自特定品牌的笔。他们从支票上提取墨水，并用纸色谱法将其与三支笔的墨水样本进行比较。
Chemical Background: Paper chromatography separates mixtures of soluble dyes. A spot of the ink mixture is placed on chromatography paper and dipped in a solvent. The solvent moves up the paper, carrying the dyes at different rates because of differences in solubility and attraction to the paper. The pattern of spots (the chromatogram) is unique for each mixture. The Rf value (distance moved by substance ÷ distance moved by solvent) helps identify components.
化学背景：纸色谱法可以分离可溶性染料的混合物。将墨水混合物点样在色谱纸上，放入溶剂中。溶剂沿纸上升，因溶解度和与纸的吸附力不同，各种染料以不同速率移动。色斑的图谱（色谱图）对每种混合物都是独特的。Rf 值（物质移动距离 ÷ 溶剂移动距离）有助于鉴别组分。
Practice: A blue dye travels 4.2 cm while the solvent front moves 7.0 cm. Calculate its Rf value. Explain why an Rf value is always less than 1.
练习：一种蓝色染料移动了 4.2 cm，而溶剂前沿移动了 7.0 cm。计算其 Rf 值。解释为什么 Rf 值总是小于 1。
7. Displacement Reactions in Industry | 工业中的置换反应
Case Description: A mining company extracts copper from low-grade ores using scrap iron. They soak the ore in acid to produce a copper sulfate solution, then add iron powder. A reddish-brown solid forms, which is purified copper.
案例描述：一家矿业公司用废铁从低品位矿石中提取铜。他们将矿石浸泡在酸中制成硫酸铜溶液，然后加入铁粉。形成红棕色固体，即纯化的铜。
u(s). This is a redox reaction: Fe loses electrons (oxidation) while Cu²⁺ ions gain electrons (reduction). Ionic equation: Fe(s) + Cu²⁺(aq) → Fe²⁺(aq) + Cu(s). Displacement reactions are also used to extract metals like titanium using sodium.
化学背景：铁比铜活泼，因此能将铜从其化合物中置换出来。反应为：Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)。这是一个氧化还原反应：铁失去电子（氧化），而铜离子得到电子（还原）。离子方程式：Fe(s) + Cu²⁺(aq) → Fe²⁺(aq) + Cu(s)。置换反应还可用于用钠提取钛等金属。
Practice: Predict and explain what would happen if magnesium ribbon were added to copper(II) sulfate solution. Write the balanced equation, including state symbols.
练习：预测并解释将镁条加入硫酸铜溶液中会发生什么。写出配平的方程式，包括状态符号。
8. The Greenhouse Effect | 温室效应
Case Description: Scientists studying climate change monitor atmospheric CO₂ levels at Mauna Loa Observatory. The data show a steady annual rise. Policymakers ask how greenhouse gases work and what can be done to reduce emissions.
案例描述：研究气候变化的科学家在莫纳罗亚天文台监测大气 CO₂ 浓度。数据显示每年稳步上升。政策制定者询问温室气体如何起作用，以及如何减少排放。
Chemical Background: Greenhouse gases, such as carbon dioxide (CO₂), methane (CH₄) and water vapour, absorb infrared radiation reflected from the Earth's surface. This trapped energy warms the atmosphere — the greenhouse effect. Human activities, including burning fossil fuels and deforestation, increase CO₂ levels, enhancing the effect and causing global warming. The carbon cycle describes how carbon moves between the atmosphere, oceans, and living organisms.
化学背景：温室气体，如二氧化碳（CO₂）、甲烷（CH₄）和水蒸气，吸收从地球表面反射的红外辐射。这些被捕获的能量使大气变暖——称为温室效应。人类活动，包括燃烧化石燃料和砍伐森林，增加了 CO₂ 浓度，加剧了温室效应并导致全球变暖。碳循环描述了碳在大气、海洋和生物体之间的迁移。
Practice: Explain why reducing deforestation helps to control atmospheric CO₂. Suggest two other methods to lower your carbon footprint.
练习：解释为什么减少森林砍伐有助于控制大气中的 CO₂。提出另外两种降低碳足迹的方法。
9. Plastics and Recycling | 塑料与回收
Case Description: A coastal town is overwhelmed by plastic waste washed ashore. The council wants to recycle the plastics but must first sort them by polymer type. Some items melt and reshape easily, while others char and burn.
案例描述：一个沿海小镇被冲上岸的塑料垃圾淹没。议会想回收这些塑料，但必须先按聚合物类型分拣。有些物品容易熔化再塑形，而另一些则会烧焦燃烧。
Chemical Background: Plastics are polymers — long chains of repeating monomer units. Thermoplastics (e.g., polyethene, polystyrene) soften when heated and can be remoulded, because their polymer chains are held by weak intermolecular forces without cross-links. Thermosets (e.g., bakelite) have strong covalent cross-links, so they do not melt; heating causes decomposition. Recycling involves sorting, shredding, melting and remoulding thermoplastics into new products, saving resources and reducing landfill.
化学背景：塑料是聚合物——由重复单体单元组成的长链。热塑性塑料（如聚乙烯、聚苯乙烯）加热时软化并可重新塑形，因为它们的聚合物链仅由弱分子间力维持，没有交联。热固性塑料（如电木）具有强共价交联，因此不会熔化；加热会导致分解。回收包括分类、切碎、熔融并将热塑性塑料重新塑造成新产品，节约资源并减少填埋。
Practice: Suggest a simple heating test to distinguish a thermoplastic from a thermoset. Explain why thermosets are used for saucepan handles.
练习：提出一个简单的加热测试来区分热塑性塑料和热固性塑料。解释为什么锅柄使用热固性塑料。
10. Hard Water and Descaling | 硬水与除垢
Case Description: A household notices white scale building up inside kettles and on showerheads. The water supply is from a limestone aquifer. A plumber recommends using white vinegar for cleaning and explains the chemistry behind it.
案例描述：一个家庭发现水壶内部和淋浴喷头上积聚了白色水垢。供水来自石灰岩含水层。水管工建议用白醋清洁，并解释其背后的化学原理。
pitation of calcium carbonate (scale): Ca(HCO₃)₂(aq) → CaCO₃(s) + H₂O(l) + CO₂(g). Vinegar (ethanoic acid, CH₃COOH) removes scale by reacting with calcium carbonate: CaCO₃(s) + 2CH₃COOH(aq) → Ca(CH₃COO)₂(aq) + H₂O(l) + CO₂(g). This is an acid-carbonate reaction that releases carbon dioxide gas, effectively dissolving the scale.
化学背景：硬水含有溶解的钙离子（Ca²⁺）和镁离子（Mg²⁺）。加热时，暂时硬度导致碳酸钙（水垢）沉淀：Ca(HCO₃)₂(aq) → CaCO₃(s) + H₂O(l) + CO₂(g)。醋（乙酸，CH₃COOH）通过与碳酸钙反应除垢：CaCO₃(s) + 2CH₃COOH(aq) → Ca(CH₃COO)₂(aq) + H₂O(l) + CO₂(g)。这是一个碳酸盐与酸的反应，释放二氧化碳气体，有效地溶解水垢。
Practice: Write a word equation for the descaling reaction. Explain why stronger acids like hydrochloric acid are not recommended for domestic descaling.
练习：写出除垢反应的文字方程式。解释为什么不建议在家用除垢中使用盐酸等强酸。
Published by TutorHao | Chemistry Revision Series | aleveler.com
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