📚 Case Study Practice for Year 7 WJEC Chemistry | 七年级 WJEC 化学：案例分析实战演练
In Year 7 WJEC Chemistry, simply memorising facts is not enough. Real understanding comes from applying knowledge to unfamiliar situations – just like a scientist. This article takes you through case study practice, where you will act as a chemistry detective. You will explore observation skills, particle theory, changes of state, reactions, acids, gases and safety, all through worked examples that sharpen your thinking for exams and beyond. Each section presents a mini-case, followed by guided analysis. Let's begin the practical investigation of ideas.
在七年级 WJEC 化学中，仅仅记住事实是不够的。真正的理解来自将知识应用于陌生情境——就像科学家一样。本文带你进行案例分析实战演练，你将扮演化学侦探。通过观察技能、粒子理论、状态变化、反应、酸、气体和安全等实际示例，锻炼你的思维以应对考试及更广泛的挑战。每一部分都呈现一个小案例，并给出分析引导。让我们开始思想的实践探索吧。
1. Why Case Studies Matter | 为什么案例研究很重要
Case studies bridge the gap between textbook theory and real-world chemistry. They ask you to interpret data, spot patterns, and predict outcomes – exactly the skills WJEC examiners look for. When you practise with cases, you learn to think like a chemist, not just repeat definitions.
案例研究在教科书理论与现实世界的化学之间搭建了桥梁。它们要求你解读数据、发现模式并预测结果——这正是 WJEC 考官所看重的技能。当你用案例进行练习时，你学会像化学家一样思考，而不仅仅是重复定义。
Every case study contains clues: observations, measurements, and sometimes unexpected results. Your job is to explain these clues using scientific ideas such as the particle model or chemical change. This active learning makes concepts stick.
每个案例研究都包含线索：观察结果、测量数据，有时还有意想不到的结果。你的任务是用科学概念（如粒子模型或化学变化）来解释这些线索。这种主动学习能让概念牢牢记住。
In exams, you will meet application questions that look like mini-case studies. Regular practice gives you confidence to tackle any unfamiliar scenario with a calm, methodical approach.
在考试中，你会遇到看似迷你案例研究的应用题。经常练习能让你自信地以冷静、有条理的方法应对任何不熟悉的情境。
2. Observation: The First Step of a Chemical Detective | 观察：化学侦探的第一步
Good chemistry starts with careful observation. Before you can explain, you must notice what is actually happening. A case study often begins with a description of an experiment: a student mixes two colourless liquids, and the mixture becomes warm and cloudy. Your first task is to list the changes you spot.
好的化学始于仔细观察。在你能解释之前，你必须注意到实际发生了什么。案例研究常常以实验描述开始：一名学生混合两种无色液体，混合物变热且变浑浊。你的第一个任务是列出你发现的变化。
Ask yourself: What did you see, hear, feel or smell? (Never taste chemicals in the lab.) In the above case, you might note: colour change? Actually both liquids were colourless, but after mixing the solution turned white/cloudy. Temperature increased – the container felt warm. Bubbles? No mention. A solid appeared – the cloudiness suggests formation of an insoluble solid (precipitate). Write these observations as clear bullet points.
问问自己：你看到、听到、感觉到或闻到了什么？（切勿在实验室品尝化学品。）在上述案例中，你可能会注意到：颜色变化？其实两种液体原本无色，但混合后溶液变成白色/浑浊。温度升高——容器摸起来温暖。气泡？未提及。出现了固体——浑浊表明生成了不溶性固体（沉淀）。将这些观察结果写成清晰的要点。
Colourless liquids mixed
无色液体混合
Mixture turned cloudy (white solid appeared)
混合物变浑浊（出现白色固体）
Temperature increased (exothermic)
温度升高（放热）
Once observations are recorded, you can move on to inference. Cloudiness + warming often indicates a chemical reaction has taken place, producing a new substance. But you must check against physical changes too – for instance, mixing sand and water also gives cloudiness, but no energy change and it is reversible. Always link observations to evidence of chemical change: new substance formed, energy change, or irreversibility.
一旦记录下观察结果，你就可以进行推理了。浑浊+变暖通常表明发生了化学反应，生成了新物质。但你也必须对比物理变化的可能性——例如，混合沙子和水也会产生浑浊，但无能量变化且可逆。始终将观察结果与化学变化的证据联系起来：生成新物质、能量变化或不可逆性。
3. Spotting Physical and Chemical Changes | 识别物理变化与化学变化
One of the most common case study themes is telling the difference between a physical and a chemical change. A physical change alters the state or appearance but does not produce new substances. A chemical change (a reaction) makes one or more new substances, often with an energy change that is hard to reverse.
最常见的案例研究主题之一是区分物理变化和化学变化。物理变化改变状态或外观，但不产生新物质。化学变化（反应）生成一种或多种新物质，通常伴随着难以逆转的能量变化。
Consider this case: A student heats a white powder (ammonium chloride) gently in a test tube. A white solid collects on the cooler part of the test tube, while the original powder disappears. Is this physical or chemical? At first, it seems chemical because a new solid appears elsewhere. However, ammonium chloride sublimes: it changes directly from solid to gas, then back to solid on a cold surface. The solid is still ammonium chloride. No new substance forms, so it is a physical change.
考虑这个案例：一名学生在试管中缓缓加热白色粉末（氯化铵）。白色固体聚集在试管较冷的部分，而原来的粉末消失了。这是物理变化还是化学变化？起初，似乎像是化学变化，因为别的地方出现了新固体。然而，氯化铵升华：它从固体直接变为气体，然后在冷表面重新变为固体。固体依然是氯化铵。没有新物质生成，所以是物理变化。
Use the following table to compare key indicators:
| Indicator | Physical change | Chemical change |
| New substance formed? | No | Yes |
| Energy change | Usually small, reversible | Often large, sometimes permanent |
| Reversible? | Often easily reversed | Usually difficult to reverse |
| Examples | Melting, boiling, dissolving | Burning, rusting, cooking |
指标 | 物理变化 | 化学变化
生成新物质？ | 否 | 是
能量变化 | 通常较小，可逆 | 通常较大，有时永久
可逆性 | 通常容易逆转 | 通常难以逆转
示例 | 熔化、沸腾、溶解 | 燃烧、生锈、烹饪
In WJEC questions, you may be given a scenario and asked to justify your choice. Always refer back to these criteria. Mention whether new substances are made, and what happened to energy.
在 WJEC 试题中，可能会给出一个情境并要求你证明你的选择。始终回顾这些标准。提及是否生成了新物质，以及能量发生了什么变化。
4. Applying the Particle Model | 应用粒子模型
The particle model is a powerful tool for explaining many phenomena in Year 7 chemistry. It describes how particles are arranged and behave in solids, liquids and gases. A case study might ask you to explain why a balloon inflates when vinegar and baking soda react, or why a deodorant can feels cold after spraying.
粒子模型是解释七年级化学中许多现象的有力工具。它描述了粒子在固体、液体和气体中的排列和行为。案例研究可能会要求你解释为什么醋和小苏打反应时气球会膨胀，或者为什么喷完除臭剂后罐子摸起来很冷。
Take the example of a sealed syringe half-filled with water. When you pull the plunger, the water does not expand, but the space above the water increases. Your task: explain using particles. Water particles are close together and attract each other strongly – they cannot be compressed easily. The space above contains water vapour particles, which are far apart and move quickly; pulling the plunger decreases the pressure, causing more liquid particles to escape into the vapour space until equilibrium is reached. This shows the difference between liquid and gas states.
以一个装有一半水的密封注射器为例。当你拉动活塞时，水并没有膨胀，但水的上方空间增大了。你的任务：用粒子模型来解释。水粒子彼此靠近，吸引力强——它们不易被压缩。上方空间含有水蒸气粒子，它们相距很远且快速运动；拉动活塞降低压力，使更多液体粒子逸出进入蒸气空间，直至达到平衡。这显示了液态和气态的区别。
When a case involves temperature change, always describe particle energy. In an exothermic reaction, particles of the products have less chemical energy than the reactants – the difference is released as heat, making surrounding particles move faster. In an endothermic process, energy is taken in from surroundings, so surrounding particles slow down and the temperature drops.
当案例涉及温度变化时，始终描述粒子能量。在放热反应中，产物粒子的化学能比反应物少——差值以热量释放，使周围粒子运动更快。在吸热过程中，从周围环境吸收能量，因此周围粒子减速，温度下降。
A common exam case: a puddle of water eventually dries up even on a cold day. Explain why this happens with the particle model. Answer: In a liquid, some particles at the surface have enough energy to overcome attractions and escape into the air (evaporation). This can happen at any temperature as long as the air is not saturated. Over time, all liquid particles may escape.
一个常见的考题案例：即便是冷天，水坑最终也会干掉。用粒子模型解释原因。答案：在液体中，液面的一些粒子有足够能量克服吸引力进入空气（蒸发）。只要空气未达到饱和，任何温度下都可能发生。随时间推移，所有液体粒子都可能逸散。
5. Analysing Mass Changes | 分析质量变化
In many reactions, the total mass seems to change, but the law of conservation of mass tells us no atoms are created or destroyed. Case studies often focus on explaining apparent mass changes. A classic example: a student burns magnesium ribbon in a crucible. The magnesium turns into a white ash (magnesium oxide), and the final mass is greater than the initial mass of magnesium. How is this possible?
在许多反应中，总质量似乎变化了，但质量守恒定律告诉我们原子不会被创造或消灭。案例研究通常聚焦于解释表观质量变化。一个经典例子：一名学生在坩埚中燃烧镁条。镁变成白色灰烬（氧化镁），最终质量大于镁的初始质量。这怎么可能？
atoms add mass, but they were not weighed initially because they were in the air. If the experiment were done in a sealed container, the total mass of container + contents would stay exactly the same before and after the reaction.
答案在于坩埚是敞口的。镁与空气中的氧结合生成氧化镁：2Mg + O₂ → 2MgO。氧原子增加了质量，但由于它们来自空气，最初并未被称重。如果实验在密封容器中进行，容器及其内容物的总质量在反应前后将完全保持不变。
Conversely, heating a carbonate such as copper carbonate in an open crucible leads to a mass decrease because carbon dioxide gas escapes. Always check whether the system is open or closed. A closed system prevents matter from entering or leaving, so mass stays constant.
相反，在敞口坩埚中加热碳酸盐（如碳酸铜）会导致质量减少，因为二氧化碳气体逸出。始终检查系统是敞口还是封闭的。封闭系统防止物质进出，因此质量保持不变。
Case study practice: A student places a beaker of water on a balance and records the mass. After one week left open, the mass has decreased. Explain. The water evaporated – liquid water turned into water vapour that escaped. No atoms were lost; they simply moved into the air as gas. If the beaker had been sealed, mass would not change.
案例练习：一名学生将一只盛水的烧杯放在天平上并记录质量。敞口放置一周后，质量减少了。请解释。水蒸发了——液态水变成水蒸气逸出。没有原子被破坏；它们只是以气体形式进入了空气中。如果烧杯是密封的，质量就不会改变。
6. Understanding Acids and Alkalis | 理解酸和碱
Year 7 introduces acids and alkalis, their properties, and the pH scale. Case studies in this area might involve everyday substances such as stomach acid, indigestion tablets, or plant extracts as indicators. You might need to interpret colour changes of universal indicator or litmus, or explain why an alkali relieves an acid sting.
七年级介绍酸和碱、它们的性质以及 pH 等级。这一领域的案例研究可能涉及日常物质，如胃酸、消化药片，或作为指示剂的植物提取物。你可能需要解读通用指示剂或石蕊的颜色变化，或解释为什么碱可以缓解酸引起的刺痛。
Consider this: A student tests three unknown solutions with universal indicator. Solution A turns red; Solution B turns green; Solution C turns purple. What can you deduce? Solution A is strongly acidic (pH 1-2). Solution B is neutral (pH 7). Solution C is strongly alkaline (pH 11-14). Using the pH scale, you can also estimate approximate values. A follow-up question might ask: which solution would sting a cut? An acidic solution stings, but a strong alkali can also cause burns. Safety note: both strong acids and strong alkalis are corrosive.
考虑这个案例：一名学生用通用指示剂测试三种未知溶液。溶液 A 变红；溶液 B 变绿；溶液 C 变紫。你能推断出什么？溶液 A 是强酸性（pH 1-2）。溶液 B 是中性（pH 7）。溶液 C 是强碱性（pH 11-14）。利用 pH 等级，你还可以估计出近似值。可能还会有后续问题：哪种溶液会刺痛伤口？酸性溶液会导致刺痛，但强碱也能引起灼伤。安全提示：强酸和强碱都具有腐蚀性。
ther scenario: A wasp sting is alkali; a bee sting is acidic. How would you treat each one? is is a real-life neutralisation case. Neutralisation is a chemical reaction where an acid and an alkali react to form a salt and water: acid + alkali → salt + water. The general equation is H⁺(aq) + OH⁻(aq) → H₂O(l).
另一种情境：黄蜂蜇伤是碱性的；蜜蜂蜇伤是酸性的。你会如何分别处理？黄蜂蜇伤（碱性）可以用醋（弱酸）中和。蜜蜂蜇伤（酸性）可以用小苏打膏（弱碱）处理。这是一个真实的中和案例。中和是一种化学反应，酸和碱反应生成盐和水：酸 + 碱 → 盐 + 水。一般离子方程式为 H⁺(aq) + OH⁻(aq) → H₂O(l)。
When writing about indicators, remember that red litmus turns blue in alkali; blue litmus turns red in acid. Universal indicator gives a rainbow spectrum from red (strong acid) to violet (strong alkali). Practise describing colours accurately – 'pinkish-red' rather than just 'pink', for example.
在谈到指示剂时，记住红色石蕊试纸在碱中变蓝；蓝色石蕊试纸在酸中变红。通用指示剂呈现从红色（强酸）到紫色（强碱）的彩虹色谱。练习准确描述颜色——例如用“粉红色调的红色”而不仅是“粉红色”。
7. Gas Test Cases | 气体测试案例
WJEC expects Year 7 students to know standard tests for hydrogen, oxygen and carbon dioxide. A case might describe a gas being produced during a reaction and ask you to identify which gas it is based on test results, or to design a test yourself.
WJEC 期望七年级学生了解氢气、氧气和二氧化碳的标准检测方法。一个案例可能会描述反应产生的气体，要求你根据测试结果判断是哪种气体，或自行设计一个检测方案。
is held at the mouth of the test tube, there is a squeaky pop sound. Which gas is present? equation for the reaction: magnesium + hydrochloric acid → magnesium chloride + hydrogen.
案例：一名学生将镁加入盐酸中。迅速产生气泡。当一根点燃的木条放在试管口时，听到一声轻微的爆鸣声。存在哪种气体？爆鸣声是检验氢气的经典方法。氢气与空气中的氧气燃烧，产生小型爆炸。反应的文字方程式：镁 + 盐酸 → 氯化镁 + 氢气。
Another case: A sample of pond weed is placed under a funnel in water, and a test tube filled with water is inverted over the funnel. After a few days in sunlight, a gas collects. A glowing splint relights when inserted. This confirms oxygen gas, produced by photosynthesis. The glowing splint relight test is specific to oxygen; it does not work for other gases.
另一个案例：将水草样本放在水中的漏斗下，并将装满水的试管倒扣在漏斗上。在阳光下放置几天后，有气体收集。插入带火星的木条后木条复燃。这证实了是氧气，由光合作用产生。带火星木条复燃的检测对氧气是特异的；其他气体不会产生此现象。
Carbon dioxide is tested by bubbling the gas through limewater (calcium hydroxide solution). If the limewater turns milky/cloudy, carbon dioxide is present. This reaction forms calcium carbonate, which is insoluble. A common classroom case: mixing vinegar and baking soda produces CO₂. Bubbling the gas through limewater gives cloudiness. Always detail colour change from colourless to milky.
二氧化碳检测是将气体通入石灰水（氢氧化钙溶液）。如果石灰水变浑浊/乳白，则存在二氧化碳。该反应生成碳酸钙，不溶于水。常见的课堂案例：混合醋和小苏打产生 CO₂。将气体通入石灰水会变浑浊。始终详细描述颜色从无色变为乳白色。
8. Safety Analysis | 安全分析
Every chemistry experiment requires safety awareness. Case studies may present a set-up and ask you to identify hazards, suggest precautions, or explain why a rule is in place. This tests your ability to apply laboratory safety knowledge.
每个化学实验都需要安全意识。案例研究可能给出一个实验装置，要求你识别危险、提出预防措施，或解释为何要遵守某项规定。这考查你应用实验室安全知识的能力。
Example case: A student plans to heat a flammable liquid like ethanol using a Bunsen burner. The diagram shows the beaker of ethanol directly over the flame with no gauze, and the student is wearing no goggles. What are the safety concerns? First, heating flammable liquids directly over a naked flame can cause a fire or explosion. A water bath or electric heater should be used. Second, no eye protection: corrosive or hot splashes could injure eyes. Third, no heatproof mat under the Bunsen. Always list hazards and then corrections.
案例举例：一名学生计划使用本生灯加热易燃液体如乙醇。图中显示烧杯中的乙醇直接在火焰上加热，没有垫石棉网，且学生未佩戴护目镜。有哪些安全问题？首先，用明火直接加热易燃液体可能导致火灾或爆炸。应使用水浴或电加热器。其次，没有眼部防护：腐蚀性或高温飞溅物可能伤害眼睛。第三，本生灯下没有耐热垫。始终列出危险点然后给出纠正措施。
Another scenario: A student accidentally breaks a test tube and there is a spill of a strong acid. The case asks for emergency actions. The correct sequence: alert the teacher immediately; avoid touching the spill; if acid is on skin, wash with plenty of water for 15 minutes; for spills on the bench, the teacher will neutralise with sodium carbonate or damp cloth, never bare hands. Knowing these procedures shows scientific maturity.
另一种情境：一名学生不慎打碎试管，并有强酸溢出。案例要求给出紧急处理步骤。正确顺序：立即通知老师；避免接触溢出物；如果酸溅到皮肤上，用大量水冲洗 15 分钟；对于台面溢出，老师会用碳酸钠或湿布中和处理，严禁赤手接触。了解这些程序显示了科学上的成熟。
You might also be asked to explain hazard symbols. For example, a substance labelled with a skull and crossbones means 'toxic' or 'deadly'. A flame symbol means 'flammable'. A cross means 'irritant' or 'harmful'. Be ready to match symbols to their meaning and suggest safe handling: use in fume cupboard, wear gloves, keep away from flames.
你还可能被要求解释危害警示符号。例如，贴有骷髅和交叉骨符号表示“有毒”或“致命”。火焰符号表示“易燃”。叉号表示“刺激”或“有害”。准备好将符号与其含义匹配，并建议安全操作：在通风橱中使用、戴手套、远离明火。
9. Data Interpretation and Graphs | 数据解释与图表
WJEC case studies sometimes include tables or graphs, such as temperature changes during heating or cooling, or mass changes over time. You need to interpret the data to draw conclusions. A typical case: a graph of temperature vs. time for heating stearic acid (a pure compound). The temperature rises steadily, then stays flat for a while, then rises again. The flat section shows melting – the temperature remains constant while the solid turns to liquid because energy is used to overcome forces between particles, not to raise temperature.
WJEC 案例研究有时会包括表格或图表，如加热或冷却过程中的温度变化，或质量随时间的变化。你需要解读数据以得出结论。一个典型案例：加热硬脂酸（一种纯物质）的温度-时间曲线图。温度均匀上升，然后保持平坦一段时间，然后再度上升。平坦段显示熔化——固体变成液体时温度保持不变，因为能量用于克服粒子间作用力，而不是升高温度。
When you see a plateau on a heating curve, identify the state change. Melting point is the temperature at this plateau. Boiling point shows another plateau at a higher temperature. For impure substances, you will notice the melting temperature is lower and the melting happens over a range rather than a sharp point – this is a common multiple-choice clue.
当你在加热曲线上看到一个平台时，识别出状态变化。该平台处的温度即为熔点。沸点则在更高的温度处显示另一个平台。对于不纯物质，你会发现熔点较低，并且熔化发生在一个范围内而非一个锐点——这是常见的选择题线索。
Another data interpretation case: measuring the pH of a solution as an acid is gradually added to an alkali (titration concept, simplified). The pH falls slowly at first, then drops sharply, then flattens. The steep part represents neutralisation. You may be asked to estimate how much acid was needed to reach pH 7. Always read values carefully from the graph, and use a ruler to project lines if needed.
另一个数据解读案例：在往碱溶液中逐渐加入酸的过程中测量 pH 值（简化的滴定概念）。pH 起初缓慢下降，然后急剧下降，最后趋于平坦。陡降部分代表中和过程。你可能会被要求估算达到 pH 7 所需的酸量。始终仔细从图中读取数值，必要时用直尺引线。
Practise explaining trends using words like 'increase', 'decrease', 'constant', 'rapid', 'gradual'. Link the trend to particle theory or chemical concepts. For example, 'the temperature stopped rising because melting requires energy to break bonds between particles, so the energy supplied is used for that rather than heating.'
练习使用“增加”、“减少”、“恒定”、“迅速”、“逐渐”等词语解释趋势。将趋势与粒子理论或化学概念联系起来。例如，“温度停止上升是因为熔化需要能量来打破粒子间的结合，因此所供应的能量用于此目的而非加热。”
10. Integrated Case: The Burning Mystery | 综合案例：燃烧之谜
To pull everything together, let's work through an integrated case that combines several Year 7 topics. A student finds a dull grey metal weight in the laboratory. She decides to clean it with sandpaper, revealing a shiny, silver-coloured metal. She then strongly heats it in a crucible using a Bunsen burner. The metal glows bright white and turns into a white powder. The mass of the product is greater than the original shiny metal. When a few drops of water are added to the cooled white powder, it fizzes and produces a gas that turns damp red litmus paper blue. The mixture feels warm and soapy to touch.
为了融会贯通，我们来完成一个综合了多个七年级主题的综合案例。一名学生在实验室发现一块暗灰色的金属块。她决定用砂纸打磨，露出闪亮的银白色金属。然后她用本生灯在坩埚中强热。金属发出明亮的白光并变成白色粉末。产物的质量大于原始发亮金属的质量。当在冷却的白色粉末上滴加少量水时，它嘶嘶作响，产生的气体使湿润的红色石蕊试纸变蓝。混合物摸起来温热且有滑腻感。
What observations suggest a chemical change? New white powder formed, bright light and heat given out, mass increased, gas produced with water. Several indicators of a reaction.
哪些观察结果提示发生了化学变化？生成了新的白色粉末，发出明亮的光和热，质量增加，与水反应产生气体。多个反应标志。
tal (likely magnesium) reacted with oxygen from the air: Mg + O₂ → MgO. Oxygen added mass.
解释质量增加的原因。该金属（很可能是镁）与空气中的氧气反应：Mg + O₂ → MgO。氧气增加了质量。
What is the white powder? Magnesium oxide, a metal oxide.
白色粉末是什么？氧化镁，一种金属氧化物。
ition of water produced a gas that turned damp red litmus paper blue. This gas was ammonia? de are basic. They react with water to form an alkaline solution: MgO + H₂O → Mg(OH)₂. The 'fizzing' and gas production is unusual – gO does not fizz with water. The description suggests perhaps the metal was sodium instead? H₂O → 2NaOH, and sodium metal itself fizzes, producing hydrogen which may lift the litmus? lver afterwards, white powder with water fizzes and gives a gas that turns red litmus blue – s sodium, the product sodium oxide reacts with water to give NaOH solution, no gas. However, the student added water to the powder and it fizzed – implying a gas. Could it be unreacted sodium metal? If there was leftover sodium? lkaline solution turned red litmus blue, and the fizzing was due to the reaction of sodium? But litmus paper would be affected only by the solution, not the gas. The clue says 'produces a gas that turns damp red litmus paper blue' – t with nitrogen: 3Mg + N₂ → Mg₃N₂. Magnesium nitride reacts with water to produce ammonia gas: Mg₃N₂ + 6H₂O → 3Mg(OH)₂ + 2NH₃. Ammonia is alkaline and turns damp red litmus blue. This is a subtle extension suitable for Year 7 high-achievers. The case can thus reveal deeper thinking. The shiny metal is magnesium, burning gave MgO and some Mg₃N₂. Adding water to the mixture produced ammonia (from nitride) and felt warm and soapy due to alkaline magnesium hydroxide. This is a perfect integrated case.
加入水产生了一种气体，使湿润的红色石蕊试纸变蓝。该气体是氨气吗？等等，红色石蕊在碱性中变蓝。金属氧化物如氧化镁是碱性的。它们与水反应生成碱性溶液：MgO + H₂O → Mg(OH)₂。但“嘶嘶作响”和产生气体是不寻常的——纯 MgO 与水不会嘶嘶作响。这描述暗示金属可能是钠？氧化钠与水剧烈反应：Na₂O + H₂O → 2NaOH，但钠单质会嘶嘶作响产生氢气，氢气不影响石蕊试纸。实际上，如果金属是镁，强烈加热时镁不仅与氧气反应，还可能与空气中的氮气反应：3Mg + N₂ → Mg₃N₂。氮化镁与水反应生成氨气：Mg₃N₂ + 6H₂O → 3Mg(OH)₂ + 2NH₃。氨气是碱性的，使湿润的红色石蕊试纸变蓝。这就完美解释了所有现象。亮的金属是镁，燃烧生成氧化镁和少量氮化镁。加水产生氨气（嘶嘶声）和氢氧化镁（温热、滑腻感，碱性）。这是一个绝妙的综合案例。
Let's frame the integrated case explanation simply for Year 7: Metal X burns to form oxides. Some oxide reacts with water to make an alkaline solution (soapy feel). Another compound formed with nitrogen reacts with water to release ammonia gas, which is alkaline and turns litmus blue. This deepens understanding of metal chemistry and gas tests.
针对七年级，我们可以简化：金属 X 燃烧生成多种氧化物。部分氧化物与水反应生成碱性溶液（滑腻感）。另一种与氮形成的化合物与水反应释放氨气，氨气呈碱性使石蕊变蓝。这加深了对金属化学和气体检测的理解。
Published by TutorHao | WJEC Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图