📚 Year 7 CIE Chemistry Case Study Practical Exercises | CIE 七年级化学案例分析实战演练
Welcome to our collection of real-world case studies designed to sharpen your chemistry skills for Year 7 CIE. In each scenario, you will apply your knowledge of particles, separation techniques, acids and bases, chemical reactions, and more. Read through the situations carefully and think like a scientist to solve the puzzles.
欢迎来到我们为 CIE 七年级化学设计的真实世界案例集。在每个场景中，你将运用关于粒子、分离技术、酸与碱、化学反应等方面的知识。仔细阅读情境，像科学家一样思考，解决这些难题。
1. Ink Chromatography Detective Case | 墨水色谱侦探案例
A threatening letter was found at a crime scene, written with a black pen. The police suspect it came from a particular office with several pens. As a forensic scientist, you need to identify which pen was used. You perform paper chromatography on the ink from the letter and on inks from three suspect pens (A, B, C). You place spots of each ink on a pencil line on chromatography paper, and dip the paper into water. The water travels up the paper, separating the ink dyes. The letter ink separates into blue and yellow spots. Pen A shows blue and yellow spots that match the letter ink exactly, while Pen B shows only blue, and Pen C shows red and yellow.
犯罪现场发现一封威胁信，用黑色墨水书写。警方怀疑它来自一间有多支笔的办公室。作为法医科学家，你需要确定使用了哪支笔。你对信件墨水和三支嫌疑笔（A、B、C）的墨水进行纸色谱分析。在色谱纸的铅笔线上点上各墨水点，将纸浸入水中。水沿着纸上升，分离墨水染料。信件墨水分离出蓝色和黄色斑点。笔A显示蓝色和黄色斑点，与信件墨水完全匹配；笔B只显示蓝色；笔C显示红色和黄色。
Paper chromatography works because different coloured compounds dissolve differently in the solvent (water) and travel at different speeds up the paper. A mixture of dyes separates into its component colours, allowing us to compare ink patterns. In this case, the match between the letter and Pen A strongly suggests that Pen A was used to write the threat.
纸色谱的原理是不同有色化合物在溶剂（水）中溶解程度不同，并在纸上以不同速度上升。染料混合物分离成各组成颜色，使我们能比较墨水图案。在本例中，信件与笔A的匹配强烈表明笔A被用来写威胁信。
2. Separating Salt and Sand from a Beach Mixture | 海滩混合物的盐沙分离
A student collected a bucket of sandy, salty water at the beach and wants to obtain pure salt and clean sand. How can this be done using simple laboratory techniques? First, the mixture is filtered. The sand gets trapped on the filter paper, while the salt water passes through as the filtrate. The sand residue can be washed and dried. Next, the salt solution is heated gently in an evaporating dish. The water evaporates, leaving behind pure salt crystals. This process uses physical changes; no new substances are formed.
一名学生在海边收集了一桶含有沙子的咸水，想要获得纯盐和干净的沙子。如何使用简单的实验室技术实现呢？首先，将混合物过滤。沙子被截留在滤纸上，而盐水作为滤液通过。沙子残余物可以洗涤并干燥。接着，将盐溶液放在蒸发皿中缓缓加热。水蒸发后留下纯盐晶体。这个过程利用物理变化，没有新物质生成。
Key separation methods involved: filtration separates insoluble solid from liquid; evaporation separates a soluble solid from a solution. This case highlights the difference between soluble and insoluble substances and how to recover them.
涉及的关键分离方法：过滤分离不溶性固体与液体；蒸发从溶液中分离可溶性固体。这个案例凸显了可溶与不可溶物质之间的区别以及如何回收它们。
3. Testing Soil pH for a Vegetable Garden | 蔬菜花园的土壤 pH 测试
A gardener wants to grow cabbages, which prefer a soil pH between 6.5 and 7.5. She tests a sample of her garden soil by shaking it with distilled water and adding a few drops of universal indicator. The solution turns greenish-blue, indicating a pH of about 8. Is the soil suitable? The gardener needs to lower the pH by adding an acidic material like composted oak leaves or sulfur. Universal indicator provides a range of colours: red (strong acid), orange/yellow (weak acid), green (neutral), blue/violet (alkaline). The soil at pH 8 is slightly alkaline, so not ideal for cabbages.
一位园丁想种植卷心菜，它们偏好 pH 6.5 至 7.5 的土壤。她取了一份花园土壤样品，与蒸馏水摇匀后加入几滴通用指示剂。溶液变成蓝绿色，表明 pH 约为 8。土壤合适吗？园丁需要通过添加酸性物质如腐叶土或硫磺来降低 pH。通用指示剂提供一系列颜色：红色（强酸）、橙/黄（弱酸）、绿色（中性）、蓝/紫（碱性）。pH 8 的土壤呈弱碱性，因此不适合卷心菜。
This case applies the pH scale and use of indicators. It also shows that chemistry helps us solve real gardening problems. Remember: pH values below 7 are acidic, 7 is neutral, and above 7 are alkaline.
本案例应用了 pH 标度和指示剂的使用。它也表明化学能帮助我们解决真实的园艺问题。记住：pH 值低于 7 为酸性，7 为中性，高于 7 为碱性。
4. The Mystery of the Floating Ice Cube | 冰块漂浮之谜
On a hot day, a child places an ice cube into a glass of water and notices it floats instead of sinking. Is this unusual? Most solids sink in their own liquids, but ice is an exception because of its special particle arrangement. In liquid water, particles are close but can slide past each other. When water freezes, the particles arrange into a regular, open framework held by bonds, creating more space between them. This makes ice less dense than liquid water, so it floats.
在一个炎热的日子，一个孩子将一块冰放入一杯水中，注意到它浮在水面而不是沉下去。这反常吗？大多数固体在其同种液体中会下沉，但冰是一个
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