📚 Year 7 SQA Chemistry: Case Study Practical Drill | 七年级 SQA 化学：案例分析实战演练
In SQA Year 7 Chemistry, case studies are a fantastic way to connect classroom theory with real-world problems. By investigating a specific situation—like identifying an unknown substance or finding out why a lake has become acidic—you can sharpen your observation, analytical and experimental skills. This article walks you through four detailed case studies, each carefully designed to build your confidence in applying chemical concepts. You will explore how to test for carbonates, recover dissolved solids, understand neutralisation reactions and investigate rusting. Get ready to think like a real chemist!
在 SQA 七年级化学中，案例分析是将课堂理论与实际问题联系起来的绝佳方式。通过调查特定情景——例如鉴定一种未知物质，或找出湖泊变酸的原因——你可以锻炼观察、分析和实验技能。本文将带你走进四个详细的案例分析，每一个都旨在帮助你建立运用化学概念的信心。你将探索如何检测碳酸盐、回收溶解的固体、理解中和反应以及探究铁生锈的原因。准备好像真正的化学家一样思考吧！
1. What Is a Case Study in Chemistry? | 什么是化学案例分析？
A case study in chemistry presents a practical problem or scenario that requires scientific investigation. You are given clues—such as observations, data tables or test results—and you must apply your knowledge of chemical properties, reactions and separation techniques to solve it. In Year 7, case studies often involve simple experiments like mixing substances, heating solutions or using indicators.
化学案例分析是指一个需要通过科学调查来解决的实际问题或情景。你会得到一些线索——例如观察结果、数据表或测试结果——然后你必须运用化学性质、反应和分离技术的知识来解决问题。在七年级，案例分析通常涉及混合物质、加热溶液或使用指示剂等简单实验。
2. Case 1: Mystery White Powder | 案例一：神秘白色粉末
Imagine you find a small jar labelled only "Sample X". The powder is white, odourless and looks like baking soda, table salt or chalk dust. Your task is to identify it using tests available in the school laboratory. A case study sheet provides the following initial observations: the powder is soluble in water and does not melt when heated gently over a Bunsen burner. What could it be?
假设你发现一个小瓶子，上面只标着 "样品 X"。粉末是白色的、无味的，看起来像小苏打、食盐或粉笔灰。你的任务是利用学校实验室现有的测试来鉴定它。案例分析表给出了以下初始观察结果：粉末可溶于水，在本生灯上温和加热时不会熔化。它可能是什么呢？
3. Observing and Testing the Powder | 观察与测试粉末
, you expect brisk effervescence with the release of carbon dioxide gas. The chemical equation is: NaHCO₃ + HCl → NaCl + H₂O + CO₂. If it is chalk (calcium carbonate, CaCO₃), a similar reaction occurs: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. However, table salt (NaCl) does not react with acid. So the presence of fizzing would rule out salt.
首先，取一小勺样品 X 放入试管，加入稀盐酸。如果它是小苏打（碳酸氢钠，NaHCO₃），你会观察到迅速起泡，并释放二氧化碳气体。化学方程式为：NaHCO₃ + HCl → NaCl + H₂O + CO₂。如果它是粉笔灰（碳酸钙，CaCO₃），也会发生类似反应：CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂。然而，食盐（NaCl）不会与酸反应。因此，出现气泡就可以排除食盐。
Next, you test the solution with red and blue litmus paper. Baking soda dissolved in water is weakly alkaline and turns red litmus blue. Chalk is almost insoluble, but a tiny amount dissolves to give a slightly alkaline solution. Salt solution is neutral. This difference helps narrow down the candidate.
接着，你用红色和蓝色石蕊试纸测试溶液。小苏打溶于水呈弱碱性，能使红色石蕊试纸变蓝。粉笔灰几乎不溶，但极少量溶解也会形成弱碱性溶液。食盐溶液为中性。这个差异有助于缩小范围。
4. Analysing Results and Drawing Conclusions | 分析结果并得出结论
After testing, you record: Sample X effervesces vigorously with acid, and the solution turns red litmus paper blue. Since both baking soda and chalk produce CO₂ with acid, you need an extra check. A flame test can distinguish them: sodium compounds give a bright yellow flame, while calcium compounds produce a brick-red flame. If your flame test shows a yellow colour, you confirm the powder is sodium hydrogencarbonate.
测试后你记录：样品 X 与酸剧烈起泡，溶液使红色石蕊试纸变蓝。由于小苏打和粉笔灰遇酸都会产生二氧化碳，你需要额外验证。焰色反应可以区分它们：钠化合物产生亮黄色火焰，而钙化合物产生砖红色火焰。如果你的焰色测试显示黄色，你就能确认该粉末是碳酸氢钠。
This case study teaches the importance of using multiple tests and linking observations to chemical properties. A good case study conclusion always explains the reasoning step by step.
这个案例说明了使用多种测试方法并将观察结果与化学性质联系起来的重要性。一份好的案例分析结论总是会逐步解释推理过程。
5. Case 2: The Disappearing Solids | 案例二：消失的固体
A farmer notices that after heavy rain, the white fertiliser pellets he spread on his field seem to have disappeared. The soil is damp but no solid remains are visible. He knows the fertiliser is ammonium nitrate (NH₄NO₃), which is highly soluble. Your task is to explain what happened and design a method to recover the fertiliser from a sample of the wet soil, using evaporation and crystallisation.
一位农民注意到，大雨过后，他撒在田里的白色化肥颗粒似乎消失了。土壤潮湿，但看不到固体残留。他知道这种化肥是硝酸铵（NH₄NO₃），极易溶于水。你的任务是解释发生了什么，并设计一种方法，利用蒸发和结晶从湿土样品中回收化肥。
The disappearance is due to dissolving: ammonium nitrate separates into NH₄⁺ and NO₃⁻ ions surrounded by water molecules. Because it is so soluble, the solid seems to vanish. To recover it, you could mix the soil with warm water, filter out the insoluble sand and clay, and then evaporate the water from the filtrate. However, to obtain pure crystals you must allow the solution to cool slowly so that crystals form rather than a powder.
消失是因为溶解：硝酸铵分离成 NH₄⁺ 和 NO₃⁻ 离子，被水分子包围。由于它极易溶解，固体看似消失了。要回收它，你可以将土壤与温水混合，滤掉不溶的沙子和黏土，然后蒸发滤液中的水。但要得到纯净的晶体，必须让溶液缓慢冷却，这样才会形成晶体而不是粉末。
6. Recovering Pure Salt from Solution | 从溶液中回收纯盐
In the laboratory, you set up evaporation and crystallisation as follows: First, heat the salt solution in an evaporating dish over a water bath. As water evaporates, the solution becomes more concentrated. Once small crystals begin to appear at the edge, stop heating and leave the dish in a warm place. Over time, large, well-shaped crystals of ammonium nitrate will grow. The key is slow evaporation; rapid boiling would give a crusty solid that traps impurities.
在实验室中，你按以下步骤进行蒸发和结晶：首先，在水浴上加热蒸发皿中的盐溶液。随着水蒸发，溶液变得更浓。一旦边缘开始出现小晶体，就停止加热，将蒸发皿放在温暖的地方。一段时间后，硝酸铵大而规则的晶体就会生长出来。关键是缓慢蒸发；快速沸腾会产生包裹杂质的外壳状固体。
You can check the purity by measuring the melting point: pure ammonium nitrate melts sharply at around 170 °C. The recovered crystals should match this known value.
你可以通过测定熔点来检查纯度：纯硝酸铵在约 170 °C 时快速熔化。回收的晶体应与此已知值相符。
7. Case 3: Acid Rain Attack | 案例三：酸雨的侵袭
In a nearby forest, park rangers find that a small
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