📚 Case Study Practical Exercises | 案例分析实战演练
Case studies are a vital part of Year 9 CCEA Chemistry, bridging the gap between theory and real-world application. They challenge you to apply your knowledge of chemical principles, experimental techniques, and data analysis to solve practical problems. Mastering case studies not only prepares you for exams but also develops scientific thinking that is essential for further study.
案例分析是CCEA九年级化学的重要组成部分，它在理论与实践之间架起了桥梁。它要求你运用化学原理、实验技能和数据分析知识，解决实际问题。掌握案例分析不仅能帮助你在考试中取得好成绩，还能培养科学思维，为今后的学习打下坚实基础。
1. Introduction to Case Studies | 案例分析导论
In CCEA Chemistry, a case study typically presents a real-life scenario, a set of experimental data, or a problem that needs solving. You are expected to interpret results, suggest explanations and evaluate methods. These exercises test your ability to think like a scientist, not just recall facts. Key skills include observation, classification, measurement, identifying variables, drawing conclusions and suggesting improvements.
在CCEA化学中，案例分析通常会给出一个现实场景、一组实验数据或一个待解决的问题。你需要解读结果、提出解释并评估方法。这些练习考察你是否能像科学家一样思考，而不只是回忆事实。关键技能包括观察、分类、测量、识别变量、得出结论以及提出改进建议。
2. Case Study 1: Identifying an Unknown White Powder | 案例一：鉴别未知白色粉末
A technician has left three unlabelled jars on the bench, each containing a white powder: sodium chloride (table salt), sucrose (sugar) and sodium hydrogen carbonate (baking soda). Your task is to design a sequence of tests to safely identify each powder. Start by adding a spatula of each solid to separate test tubes of distilled water. All three dissolve, so further tests are needed. Add a few drops of dilute hydrochloric acid to each solution: the sample that fizzes and releases a colourless gas is sodium hydrogen carbonate. To distinguish the remaining two, test the electrical conductivity of their solutions using a circuit with a bulb. The salt solution conducts electricity and the bulb glows brightly, while the sugar solution does not. Finally, heating a small sample on a spoon over a Bunsen flame provides confirmation: sugar melts, turns brown and eventually chars, whereas salt does not change.
一位实验员把三个未贴标签的广口瓶留在了台面上，里面分别装有白色粉末：氯化钠（食盐）、蔗糖（白糖）和碳酸氢钠（小苏打）。你的任务是设计一系列检测安全地鉴别每种粉末。首先，用药匙取少量固体分别放入装有蒸馏水的试管中。三者全都溶解了，所以需要进一步检测。向各溶液中滴加几滴稀盐酸：冒泡并放出无色气体的样品是碳酸氢钠。为了区分剩余两种，用带小灯泡的电路测试它们溶液的导电性。食盐溶液能导电，灯泡明亮；而糖溶液不能。最后，用药匙取少量样品在本生灯上加热可以确认：糖会熔化、变褐并最终碳化，而食盐没有变化。
3. Case Study 2: Investigating the Reaction of Metals with Acid | 案例二：探究金属与酸的反应
d. Observations are recorded over five minutes. The magnesium ribbon reacts vigorously, producing many bubbles and feeling warm. Zinc reacts moderately with steady bubbling. Iron shows slow bubbling, and the solution gradually turns pale green. Copper does not react at all. Students collect the gas released in each tube and test it with a burning splint – ity series. The balanced equation for magnesium is Mg + 2HCl → MgCl₂ + H₂. Iron’s reaction is Fe + 2HCl → FeCl₂ + H₂; the pale green colour indicates Fe²⁺ ions. Copper’s lack of reaction is because it is below hydrogen in the reactivity series and cannot displace hydrogen from the acid.
在一次探究中，大小相同的镁带、锌条、铁丝和铜片分别加入盛有稀盐酸的试管中，记录五分钟内的观察现象。镁带反应剧烈，产生大量气泡，试管变热。锌反应中等，持续冒泡。铁丝冒出缓慢气泡，溶液逐渐变为淡绿色。铜则完全不反应。学生们收集每支试管中放出的气体，用燃着的木条检验——听到尖锐的爆鸣声，证明是氢气。反应性由强到弱的顺序是：Mg > Zn > Fe > Cu。这符合它们在反应性顺序中的位置。镁反应的配平方程式为 Mg + 2HCl → MgCl₂ + H₂。铁的反应是 Fe + 2HCl → FeCl₂ + H₂；淡绿色表明有 Fe²⁺ 离子。铜不反应是因为它在反应性顺序中位于氢之后，不能把氢从酸中置换出来。
4. Case Study 3: Separating Sand, Salt and Water | 案例三：分离沙子、盐和水
A mixture of sand, salt and water is given. The task is to obtain pure dry sand and pure dry salt from it. First, pour the mixture through a filter paper in a funnel. The residue left on the filter paper is sand, which can be rinsed with distilled water and then dried in a warm oven to give pure dry sand. The filtrate, which passes through, is a salt solution. To recover the salt, transfer the solution to an evaporating dish and heat gently over a water bath until crystals start to form. Then allow it to cool slowly so that more crystals develop. Finally, filter and dry the crystals between sheets of filter paper. This process uses filtration followed by evaporation and crystallisation. Each step relies on physical changes, not chemical changes, because no new substances are made.
给你一份沙子、食盐和水组成的混合物，任务是从中获得纯净的干沙子和纯净的干食盐。首先，把混合物倒入装有滤纸的漏斗中过滤。留在滤纸上的残余物就是沙子，可以用蒸馏水冲洗，然后在温烘箱中干燥，得到纯净的干沙子。透过滤纸的滤液是食盐溶液。为了回收食盐，将溶液转移到蒸发皿中，在水浴上缓慢加热，直到有晶体出现。然后让其缓缓冷却，析出更多晶体。最后，过滤并用滤纸吸干晶体。这个过程依次运用了过滤、蒸发和结晶。每一步都属于物理变化，而非化学变化，因为没有产生新物质。
5. Case Study 4: The Effect of Acid Rain on Marble Chips | 案例四：酸雨对大理石碎片的影响
furic acid. Bubbles of carbon dioxide are seen immediately. After the reaction stops, the remaining solid is rinsed, dried and weighed. The final mass is lower than the initial mass, showing that some marble has been consumed. The chemical equation is CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂. However, calcium sulfate is only slightly soluble and can form a protective layer that slows further reaction – ues. This case study highlights how a lab model can illustrate a concept but may not fully replicate environmental conditions.
大理石的主要成分是碳酸钙 (CaCO₃)。为模拟酸雨的影响，一位学生将已知质量的大理石碎片放入盛有稀硫酸的烧杯。立即看到有二氧化碳气泡产生。反应停止后，将剩余固体冲洗、干燥并称重。最终质量比初始质量小，说明部分大理石已被消耗。化学方程式为 CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂。然而，硫酸钙仅是微溶的，可能形成一层保护膜，减缓后续反应——这是该模型的一个局限性。在现实中，酸雨含有硫酸和硝酸的混合物，而硝酸钙是可溶的，因此侵蚀会持续进行。这个案例表明，实验室模型可以阐明概念，但可能无法完全复制环境条件。
6. Case Study 5: Electrolysis of Water | 案例五：水的电解
bbles form at both platinum electrodes. Twice as much gas collects at the cathode (negative electrode) as at the anode (positive electrode). When tested, the cathode gas burns with a squeaky pop, confirming hydrogen (H₂). The anode gas relights a glowing splint, confirming oxygen (O₂). The overall reaction is 2H₂O(l) → 2H₂(g) + O₂(g). The volume ratio of hydrogen to oxygen is 2:1, exactly matching the ratio of atoms in water. Adding acid makes the water conduct electricity; without it, very little current would flow. This case study reinforces the idea that water is a compound made of hydrogen and oxygen, and it demonstrates the relationship between chemical formulae and gas volumes.
通过电流可以将水分解为组成它的单质。在霍夫曼电解仪中，加入少量稀硫酸的水被电解。两个铂电极上都产生气泡。阴极（负极）收集到的气体体积是阳极（正极）的两倍。检验发现，阴极气体燃烧发出尖锐爆鸣声，证明是氢气 (H₂)；阳极气体能使带火星的木条复燃，证明是氧气 (O₂)。总反应为 2H₂O(l) → 2H₂(g) + O₂(g)。氢气与氧气的体积比为 2:1，恰好等于水中原子的比例。加入酸是为了让水导电；不加酸，几乎不会有电流通过。这个案例分析巩固了“水是由氢和氧组成的化合物”这一概念，并展示了化学式与气体体积之间的关系。
7. Case Study 6: Combustion Reactions and Energy Changes | 案例六：燃烧反应与能量变化
Combustion reactions release energy as heat and light. A simple calorimetry experiment can measure the energy released when a fuel burns. A student places 100 g of water in a copper can, records its initial temperature (20 °C), lights a spirit burner containing ethanol and heats the water. After burning for several minutes, the final temperature is 45 °C. The temperature change (ΔT) is 25 °C. The heat energy absorbed by the water can be calculated using:
Q = m × c × ΔT
00 × 4.2 × 25 = 10 500 J (10.5 kJ). This energy came from burning a small mass of ethanol. The experiment can be repeated with other fuels, such as hexane or candle wax, to compare their energy outputs per gram. It demonstrates that combustion is exothermic and that different fuels release different amounts of energy. Common errors include heat loss to the surroundings and incomplete combustion, which can be discussed as improvements.
燃烧反应以热和光的形式释放能量。一个简单的量热实验可以测量燃料燃烧时放出的能量。一位学生将 100 g 水放入铜罐，记录初始温度（20 °C），点燃装有乙醇的酒精灯，加热水。燃烧几分钟后，最终温度为 45 °C。温度变化 (ΔT) 为 25 °C。水吸收的热量可通过下式计算：
Q = m × c × ΔT
其中 m 是水的质量 (100 g)，c 是水的比热容 (4.2 J/g°C)，ΔT 是升高的温度。代入数字：Q = 100 × 4.2 × 25 = 10 500 J (10.5 kJ)。这些能量来自燃烧少量乙醇。可以用己烷或蜡烛蜡等其他燃料重复实验，比较它们每克放出的能量。实验证明燃烧是放热反应，且不同燃料释放的能量不同。常见误差包括热量散失到周围环境和燃烧不完全，这些可作为改进点进行讨论。
8. Case Study 7: Making a Natural pH Indicator from Red Cabbage | 案例七：用红甘蓝制作天然 pH 指示剂
Red cabbage contains a pigment called anthocyanin that changes colour depending on pH. By chopping some leaves, boiling them in water for ten minutes and filtering, you obtain a deep purple solution that acts as a pH indicator. The student tests the indicator with household substances: lemon juice turns it pink (acid), baking soda solution turns it blue-green (alkali) and tap water leaves it purple (neutral). A colour scale can be built by testing solutions of known pH from 1 to 14. This case study highlights the nature of acids and alkalis and introduces the concept of indicators. It also provides a practical example of extracting chemicals from natural sources – an important technique in chemistry. Discussion can then link to synthetic indicators like litmus and universal indicator, noting that the cabbage indicator gives a wide colour range but is hard to store.
红甘蓝含有一种叫花青素的色素，其颜色随 pH 值变化。将一些甘蓝叶切碎，在水中煮沸十分钟后过滤，就能得到一种深紫色溶液，它可作为 pH 指示剂。学生用这种指示剂测试家用物质：柠檬汁使其变为粉红色（酸），小苏打溶液使其变为蓝绿色（碱），自来水则使其保持紫色（中性）。通过测试已知 pH 值从 1 到 14 的溶液，可以制作色阶。这个案例分析突出了酸和碱的性质，并引入了指示剂的概念。它也提供了一个从天然原料中提取化学物质的实例——这是化学中的重要技术。随后可以讨论石蕊和通用指示剂等合成指示剂，并注意到甘蓝指示剂虽然颜色范围广但不易保存。
9. Case Study 8: Investigating the Effect of Temperature on the Rate of Dissolving | 案例八：探究温度对溶解速率的影响
Dissolving is a physical process that can be influenced by several factors. To investigate temperature, three identical sugar cubes are added to beakers containing water at 20 °C, 40 °C and 60 °C. Each is stirred at the same speed, and the time taken for the cube to completely disappear is recorded. Results show that at 20 °C dissolving takes 180 seconds, at 40 °C it takes 95 seconds, and at 60 °C it takes only 45 seconds. The higher the temperature, the faster the sugar dissolves. This can be explained by particle theory: in hotter water, water particles move faster and collide with the sugar surface more frequently and with greater energy, pulling sugar particles into solution more quickly. The case study can be extended by asking what other variables must be controlled (mass of sugar, volume of water, stirring rate) and what equipment would improve accuracy (thermometer, stopwatch, water bath).
溶解是一个物理过程，可受多种因素影响。为了研究温度的影响，将三块相同的方糖分别放入盛有 20 °C、40 °C 和 60 °C 水的烧杯中。以相同速度搅拌，记录方糖完全消失所需的时间。结果显示，20 °C 时溶解需 180 秒，40 °C 时需 95 秒，60 °C 时仅需 45 秒。温度越高，糖溶解得越快。这可以用粒子理论解释：在更热的水中，水粒子运动更快，更频繁且更强有力地撞击糖的表面，把糖粒子更快地拉入溶液。这个案例可以拓展，提问还有哪些变量必须控制（糖的质量、水的体积、搅拌速度）以及哪些设备可提高准确性（温度计、秒表、水浴）。
10. Examination Tips and Common Pitfalls | 考试技巧与常见误区
When answering case study questions, always read the provided information carefully. Underline key data such as masses, temperatures, times and observations. Structure your answers logically: state what the data shows, explain using scientific principles, and then evaluate the method or suggest improvements. Common pitfalls include forgetting to quote data from the question, using vague language like 'it reacted', and failing to mention controlled variables. In calculations, always write the formula, show substitution steps and include units. If you are asked to draw a conclusion, make sure it clearly answers the original problem and is supported by evidence. Finally, check if your answer fits the context – an environmental case study, for example, may require you to link chemical reactions to real-world impacts.
在回答案例分析问题时，务必仔细阅读所给信息。划出关键数据，如质量、温度、时间和观察结果。答案要有条理：先说数据反映了什么，再用科学原理解释，然后评价方法或提出改进建议。常见误区包括忘记引用题目中的数据、使用“它反应了”这样含糊的表述，以及遗漏控制变量。计算时，一定要写出公式、展示代入步骤并带上单位。如果要求得出结论，要确保结论清楚地回答了原始问题并有证据支持。最后，检查你的答案是否切合情境——例如，环境类案例分析可能需要你把化学反应与现实影响联系起来。
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