📚 Year 7 CCEA Chemistry: Case Study Practical Practice | Year 7 CCEA 化学：案例分析实战演练
Chemistry is all about solving mysteries and understanding the substances around us. In CCEA Year 7, you will learn to apply your knowledge to real-life situations through case studies. These practical challenges help you build skills in observation, testing, and drawing conclusions – just like a real scientist. This article presents a series of case study scenarios that cover key topics such as acids and alkalis, separating mixtures, chemical reactions, and more. Use these examples to revise and sharpen your problem-solving abilities.
化学就是揭开谜团，了解我们身边的物质。在 CCEA 七年级课程中，你将通过案例分析，把学到的知识应用到实际情境里。这些实战演练能帮助你锻炼观察、测试和得出结论的能力——就像真正的科学家一样。本文呈现了一系列案例场景，涵盖了酸和碱、混合物分离、化学反应等重点主题。利用这些例子来复习，提升你解决问题的能力吧。
1. Identifying an Unknown White Powder | 识别未知白色粉末
Imagine you find a white powder in the kitchen. Is it baking soda, flour, or sugar? You can use simple tests to identify it. Add a few drops of vinegar to a sample. If it fizzes and produces bubbles, it is likely baking soda, because baking soda (sodium hydrogencarbonate) reacts with the acid in vinegar to produce carbon dioxide gas.
假设你在厨房里发现一种白色粉末。它是小苏打、面粉还是糖？你可以用简单的测试来找出答案。取一些样品滴几滴醋。如果嘶嘶起泡，那就很可能是小苏打，因为小苏打（碳酸氢钠）与醋中的酸反应产生二氧化碳气体。
If the powder dissolves in water and tastes sweet, it is sugar. Flour will form a paste in water and does not react with vinegar. Remember: never taste anything in a laboratory unless your teacher tells you it is safe. In a real investigation, you would also wear safety goggles and work in a well-ventilated area.
如果这种粉末溶于水且味道甜，就是糖。面粉在水中会形成糊状，遇醋不起泡。记住：在实验室里，除非老师明确说明安全，否则绝对不能品尝任何东西。在真实的探究中，你还需要佩戴护目镜，并在通风良好的地方操作。
The fizzing test is a classic example of a chemical reaction between an acid (vinegar) and a carbonate (baking soda). The bubbles contain CO₂ gas, which is the same gas you breathe out. You could confirm the gas by bubbling it through limewater, which turns cloudy in the presence of carbon dioxide.
嘶嘶起泡的测试是酸（醋）与碳酸盐（小苏打）之间化学反应的经典例子。冒出的气泡中含有二氧化碳气体，也就是我们呼出的气体。你可以将气体通入石灰水来验证，石灰水遇到二氧化碳会变浑浊。
2. Separating Sand and Salt | 分离沙子和食盐
A mixture of sand and salt has been spilled on the workbench. Your task is to obtain pure, dry salt from the mixture. First, add water to the mixture and stir. Salt dissolves in water, but sand does not. This creates a solution of salt in water, with sand settling at the bottom.
工作台上撒了一堆沙子和食盐的混合物。你的任务是从中提取出纯净干燥的食盐。首先，加水搅拌混合物。食盐能溶于水，而沙子不能。这样就得到了食盐溶液，沙子会沉淀在底部。
Next, filter the mixture through filter paper in a funnel. The sand stays in the filter paper as the residue, while the salt solution passes through as the filtrate. This process is called filtration and is used to separate an insoluble solid from a liquid.
接下来，用漏斗和滤纸过滤混合物。沙子作为滤渣留在滤纸上，食盐溶液则作为滤液流下去。这个过程叫过滤，用于分离不溶性固体和液体。
To recover the salt, heat the filtrate in an evaporating dish. The water will evaporate, leaving behind white salt crystals. This is evaporation. The salt is pure, and the sand has been successfully removed.
要回收食盐，就把滤液放在蒸发皿里加热。水分蒸发后，就会留下白色的食盐晶体。这是蒸发。得到的盐很纯净，沙子已经被成功分离。
Key equipment used: beaker, stirring rod, filter funnel, filter paper, evaporating dish, Bunsen burner or hot plate. Always use safety goggles and be careful with hot glassware.
使用的关键器材：烧杯、搅拌棒、过滤漏斗、滤纸、蒸发皿、本生灯或加热板。务必佩戴护目镜，小心烫手玻璃器皿。
3. Testing for Carbon Dioxide in Soft Drinks | 检验软饮料中的二氧化碳
Soft drinks fizz when you open the bottle. The gas responsible for this fizz is carbon dioxide (CO₂). To prove it, you can set up a simple apparatus. Connect a tube from the bottle to a test tube containing limewater (calcium hydroxide solution). Shake the bottle gently so that the gas travels through the tube and bubbles into the limewater.
打开软饮料瓶时会有嘶嘶声。造成这种气泡的气体是二氧化碳。要证明这一点，可以搭建一个简单的装置。用一根导管将饮料瓶连接到装有石灰水（氢氧化钙溶液）的试管。轻轻摇晃瓶子，让气体沿导管进入石灰水里冒出气泡。
If the limewater turns milky or cloudy, carbon dioxide is present. The chemical reaction is: calcium hydroxide + carbon dioxide → calcium carbonate (white solid) + water. This is a reliable test for CO₂ gas.
如果石灰水变成牛奶状或浑浊，说明有二氧化碳存在。化学反应为：氢氧化钙 + 二氧化碳 → 碳酸钙（白色固体） + 水。这是检验二氧化碳气体的可靠方法。
You can also compare the effect by using a straw to blow exhaled breath into fresh limewater. It will also turn cloudy, proving that we exhale carbon dioxide. This link between chemistry and biology highlights the usefulness of case studies.
你还可以用吸管向新鲜的石灰水中吹气进行对比。呼出的气体同样会使石灰水变浑浊，证明我们呼出二氧化碳。化学与生物之间的这种联系凸显了案例分析学习的价值。
4. The Mystery of the Invisible Ink | 隐形墨水的奥秘
You receive a blank piece of paper with a secret message. Using a paintbrush, you carefully brush lemon juice over the paper and then gently heat it with a hairdryer or by holding it near a radiator. Brown writing slowly appears. Lemon juice is an invisible ink, and heating causes the acids and sugars in the juice to oxidise and turn brown, revealing the message.
你收到一张看似空白的纸，上面有秘密信息。用画笔小心地把柠檬汁涂在纸上，然后用电吹风微微加热，或者靠近暖气片加热。棕色的字迹就会慢慢显现。柠檬汁是一种隐形墨水，加热使汁液中的酸和糖分氧化变褐，从而显露出信息。
This is a classic example of a chemical change brought about by heat. Compare this with an acid-base ink: if you write with a baking soda solution and then paint over with grape juice (a natural pH indicator), the writing changes colour. The grape juice turns red in acidic conditions and green-blue in alkaline conditions, making the hidden baking soda message visible.
这是一个由热量引起化学变化的经典例子。与酸碱墨水对比一下：如果你用小苏打溶液写字，然后再涂上葡萄汁（天然 pH 指示剂），字迹会变色。葡萄汁在酸性条件下变红，在碱性条件下变绿蓝色，从而让隐藏的小苏打信息现形。
In a lab, you would record the colour changes and explain why they happen. This case study reinforces concepts of acids, bases, and pH indicators.
在实验室里，你会记录颜色变化并解释原因。这个案例能巩固酸、碱和 pH 指示剂的概念。
5. Burning Magnesium: A Bright Reaction | 燃烧镁条：明亮的反应
Hold a strip of magnesium ribbon with tongs and place it in a Bunsen burner flame. It ignites with a brilliant white light and leaves behind a white ash. This dramatic reaction is a classic demonstration of a chemical change. Magnesium reacts with oxygen in the air to form magnesium oxide.
用坩埚钳夹住一段镁条，放到本生灯的火焰上。镁条会发出耀眼的白光燃烧，留下白色灰烬。这个剧烈的反应是化学变化的典型示范。镁与空气中的氧气反应，生成氧化镁。
Word equation: magnesium + oxygen → magnesium oxide. This is a combination reaction. Never look directly at the intense light; wear safety goggles. The product, magnesium oxide, is a base: if you add a few drops of water and test with red litmus, it turns blue, indicating its alkaline nature.
文字表达式：镁 + 氧气 → 氧化镁。这是一个化合反应。切勿直视强光，要戴护目镜。生成的氧化镁是一种碱：滴几滴水，用红色石蕊试纸测试，会变蓝，表明其碱性。
This case study shows how a metal can combine with a non-metal to produce a compound with very different properties. The original shiny, malleable magnesium becomes a crumbly white powder.
这个案例演示了金属与非金属如何结合，生成性质截然不同的化合物。原本有光泽、可弯曲的镁变成了松脆的白色粉末。
6. Growing Copper Sulfate Crystals | 制作硫酸铜晶体
You can grow beautiful blue crystals from a copper sulfate solution. First, heat water and dissolve as much copper sulfate powder as possible until no more dissolves, creating a saturated solution. Let it cool slowly. Filter the warm solution to remove any undissolved solid, then leave it in a shallow dish to cool and evaporate slowly.
你可以用硫酸铜溶液培养美丽的蓝色晶体。首先，加热水并尽可能多地溶解硫酸铜粉末，直到不再溶解，制成饱和溶液。让它慢慢冷却。将温热的溶液过滤，去除任何未溶解的固体，然后放在浅盘里，让它缓慢降温和蒸发。
Over several days, the water will evaporate, and copper sulfate will come out of solution, forming large, deep blue crystals. This separation technique is called crystallisation. It is used to obtain pure solid crystals from a solution.
几天后，水分蒸发，硫酸铜会从溶液中析出，形成深蓝色的大块晶体。这种分离技术叫作结晶。它用来从溶液中获得纯净的固体晶体。
The shape of the crystals is regular and characteristic, showing that the particles are arranged in a repeating pattern. When a crystal is fully formed, you can use a spatula to lift it out and dry it on filter paper. Never touch the solid with bare hands; use tools.
晶体形状规则，特征明显，表明粒子排列成重复的模式。当晶体完全形成时，你可以用刮勺把它取出来，放在滤纸上晾干。切勿用手直接触摸固体，要用工具。
7. Investigating Solubility: How Much Dissolves? | 探究溶解度：能溶解多少？
Take 100 cm³ of water at room temperature. Slowly add teaspoons of salt, stirring after each addition until the salt dissolves. Count the number of teaspoons added before solid begins to settle at the bottom and will not dissolve, no matter how much you stir. This point is called the saturation point.
取室温下 100 cm³ 水。逐匙加入食盐，每加一勺就搅拌至溶解。数一数加入的匙数，直到有固体沉底，无论怎么搅拌都不再溶解。这个点就叫饱和点。
Repeat the experiment with sugar and then with baking soda. You will find that different substances have different solubilities in the same volume of water at the same temperature. Sugar is much more soluble than salt, and the exact masses can be recorded as ‘grams per 100 g of water’.
用糖和小苏打重复这个实验。你会发现，在相同温度和水量下，不同物质的溶解度不同。糖的溶解度远大于食盐，具体的质量可以记录为“每 100 克水中溶解的克数”。
This case study introduces the concept of solubility and the difference between a solute (the substance that dissolves) and a solvent (the liquid). Temperature affects solubility: heating the water usually allows more solid to dissolve. You could plot a bar chart of your results.
这个案例引入了溶解度的概念，以及溶质（被溶解的物质）和溶剂（液体）的区别。温度会影响溶解度：加热水通常能让更多固体溶解。你可以把你的实验结果画成柱状图。
8. Neutralising a Spilled Acid Safely | 安全中和溢出的酸
An acid spill has occurred in the science lab. Your teacher asks you to help clean it up safely. You are given a jar of calcium carbonate powder (limestone chippings). When the powder is sprinkled onto the acid (for example, dilute hydrochloric acid), it fizzes immediately. The calcium carbonate neutralises the acid, producing carbon dioxide gas, water, and a harmless calcium salt.
科学实验室发生酸泄漏。老师请你帮忙安全清理。你得到一罐碳酸钙粉末（石灰石碎屑）。把粉末撒在酸上（例如稀盐酸），立刻会嘶嘶起泡。碳酸钙中和了酸，生成二氧化碳气体、水以及无害的钙盐。
The word equation is: calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide. The carbon dioxide escapes as bubbles, and the spill eventually stops fizzing when all the acid has been neutralised. Afterwards, the neutralised solid can be swept up and disposed of safely.
文字表达式：碳酸钙 + 盐酸 → 氯化钙 + 水 + 二氧化碳。二氧化碳以气泡形式逸出，当所有酸都被中和后，冒泡就会停止。之后，中和后的固体可以扫除并安全处置。
You could also use sodium hydrogencarbonate (baking soda), which works in a similar way. This case study emphasises the importance of pH and neutralisation reactions in real-world safety situations, and it links to the earlier identification case study.
也可使用碳酸氢钠（小苏打），效果类似。这个案例分析强调了真实安全情境下 pH 值与中和反应的重要性，并且与前面的鉴别案例相呼应。
9. Separating Inks with Chromatography | 用色谱法分离墨水
A black marker pen is used to write a label, which then gets wet. The ink spreads into different colours, revealing that black ink is actually a mixture of several pigments. You can investigate this using paper chromatography. Draw a line of black ink near the bottom of a strip of filter paper, then suspend the paper so that the tip just dips into water (or a suitable solvent) without submerging the ink line.
用一支黑色马克笔写标签，标签被打湿后，墨水晕开出现不同颜色，揭开黑色墨水实际上是数种颜料混合物的秘密。你可以用纸色谱法来探究。在滤纸条底部附近画一条黑墨线，然后将滤纸悬挂起来，使底端刚好浸入水中（或合适的溶剂），但不要淹没墨水线。
As the water travels up the paper, it carries the ink pigments with it. Different pigments travel at different speeds and separate, producing a pattern of coloured bands. This is called a chromatogram. The more soluble a pigment is, the further it travels up the paper.
水沿滤纸上行时，会把墨水中的颜料带上去。不同颜料的移动速度不同，从而分离开，形成彩色条带的图案，这称为色谱图。颜料的溶解度越高，在纸上爬升得越远。
You can also compare different black pens from different brands. Each will produce a unique chromatogram, which acts as a fingerprint for the ink. This technique is used in forensic science to match ink samples.
你还可以比较不同品牌的黑笔。每一支都会产生独特的色谱图，就像墨水的指纹一样。这种技术被用于法医学中比对墨水样品。
10. The Case of the Fizzing Indigestion Tablet | 泡腾消食片的谜案
A student drops an effervescent indigestion tablet into a glass of water. It fizzes vigorously, releasing gas and eventually dissolving completely. The tablet contains citric acid and sodium hydrogencarbonate. When the two solids dissolve in water, they react to produce carbon dioxide, sodium citrate, and water.
一位学生把一片泡腾消食片丢进一杯水中。药片猛烈冒泡，释放出气体，并最终完全溶解。该药片含有柠檬酸和碳酸氢钠。这两种固体溶于水后发生反应，生成二氧化碳、柠檬酸钠和水。
The fizzing is evidence of a chemical reaction. To find out if mass is conserved, you could place the glass on a balance before and after the reaction. The mass decreases slightly because the carbon dioxide gas escapes into the air. If you carry out the reaction in a sealed plastic bag, the total mass remains the same, proving the law of conservation of mass.
冒泡是该化学反应的证据。要验证质量是否守恒，可以把玻璃杯放在天平上，测量反应前后的质量。由于二氧化碳气体逸散到空气中，质量会略微减少。如果在密封的塑料袋中进行反应，总质量保持不变，这就证明了质量守恒定律。
This case study ties together gas tests, acid-carbonate reactions, and the idea of conservation of mass. It is a perfect example of how everyday products can teach important chemical principles.
这个案例把气体检验、酸-碳酸盐反应和质量守恒思想结合在了一起，是一个极好的例子，展示了日常用品如何能用来教授重要的化学原理。
11. Using pH to Diagnose Soil for a Garden | 用 pH 值诊断花园土壤
A gardener wants to grow blueberries, which need acidic soil. She sends you a sample of soil and asks you to test its pH. You mix the soil with distilled water to make a paste, then dip a piece of universal indicator paper into the mixture. Compare the wet strip to the pH colour chart.
一位园艺师想种蓝莓，需要酸性土壤。她寄给你一份土壤样品，请求帮忙检测 pH 值。你先把土壤与蒸馏水混合调成糊状，然后把一片通用指示剂纸浸入混合物中。将湿润的试纸与 pH 比色卡进行比对。
If the paper turns green (pH around 7), the soil is neutral. Blue or purple indicates alkaline soil (pH 8-14). Red, orange, or yellow indicates acidity (pH 1-6). Blueberries prefer a pH of about 4.5-5.5, so if the soil is too alkaline, the gardener can add acidic material like peat moss or ericaceous compost to lower the pH.
如果试纸变为绿色（pH 值约 7），则是中性土壤。蓝色或紫色表示碱性土壤（pH 8-14）。红色、橙色或黄色表示酸性（pH 1-6）。蓝莓喜欢 pH 值约 4.5-5.5 的环境，所以如果土壤偏碱，园艺师可以添加泥炭苔或杜鹃科植物堆肥等酸性物质来降低 pH。
This case study applies pH testing to a real-life situation and reinforces the idea that different plants require specific soil conditions. You can also discuss the use of litmus paper to quickly test whether a substance is an acid or an alkali.
这个案例把 pH 测试应用到了实际生活中，并巩固了不同植物需要特定土壤条件的概念。你也可以讨论用石蕊试纸快速检测某物质是酸还是碱的方法。
12. Mystery Substance: Solid, Liquid, or Gas? | 神秘物质：固体、液体还是气体？
A sealed jar contains an unknown substance at room temperature. The substance takes the shape of the container, but when you tip some out, it flows and forms a puddle on the desk. It can be compressed only slightly, and its volume does not change much when moved. Is it a solid, a liquid, or a gas?
一个密封的罐子中装有室温下的某种未知物质。该物质呈容器的形状，但倒出来一些后，它会流动并在桌面上形成一滩。它只能被轻微压缩，移动时体积变化不大。它是固体、液体还是气体？
Liquids have a fixed volume but take the shape of their container, and they flow easily. Gases have no fixed shape or volume and can be compressed significantly. Solids keep their own shape. Therefore, the mystery substance is a liquid. You could also test it by pouring it into another container to see if it takes the new shape.
液体有固定的体积，但形状随容器而变，并且很容易流动。气体没有固定的形状或体积，并且能被显著压缩。固体保持自己的形状。因此，这个神秘物质是液体。你也可以把它倒入另一个容器，看它是否呈新形状，以此验证。
This simple case study reinforces the particle model: particles in a liquid are close together but can slide past one another, giving the liquid its ability to flow. A gas’s particles are far apart and move rapidly in all directions.
这个简单的案例巩固了粒子模型：液体中的粒子排列紧密，但能互相滑过，从而使液体具有流动性。气体的粒子相隔很远，并向各个方向快速运动。
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