📚 CAIE Year 7 Chemistry Mock Test Analysis | CAIE 七年级化学单元测试模拟卷解析
Mock tests are one of the most powerful tools for mastering Year 7 CAIE Chemistry. They help you move from simply memorising facts to applying concepts under time pressure, revealing exactly where your understanding is strong and where it needs reinforcement. This article takes you through a representative mock paper, question by question, unpacking the key scientific ideas, common pitfalls, and the precise answers that earn full marks. Whether you use this as a practice run before tackling the questions yourself or as a detailed review after an attempt, you will sharpen your ability to think like a chemist and write answers that examiners expect.
模拟测试是掌握七年级 CAIE 化学的最有力工具之一。它们帮助你从简单记忆事实，转变为在时间压力下应用概念，准确揭示你理解扎实的地方和需要加强的地方。本文带你逐题解析一份具有代表性的模拟试卷，剖析关键的科学概念、常见错误以及能获得满分的精准答案。无论你是将此作为自己答题前的演练，还是尝试后的详细复盘，你都将提升像化学家一样思考的能力，并学会写出考官期望的答案。
1. States of Matter and Particle Arrangement | 物质状态与粒子排列
Question: Compare the arrangement and movement of particles in ice, liquid water, and steam. Use the particle model to explain why ice has a fixed shape but liquid water takes the shape of its container.
题目：比较冰、液态水和水蒸气中粒子的排列和运动。用粒子模型解释为什么冰有固定的形状，而液态水会随容器形状改变。
Answer: In ice, particles are packed closely together in a regular, fixed arrangement. They vibrate in fixed positions but cannot move past one another. This locked structure gives ice a definite shape and volume. In liquid water, particles are still close together but no longer in a regular pattern. They can slide and flow past each other, so the liquid takes the shape of the bottom of its container while maintaining a fixed volume. In steam, particles are far apart, moving rapidly in all directions with no fixed arrangement. Steam has neither a fixed shape nor a fixed volume; it spreads out to fill the entire space available.
答案：在冰中，粒子紧密堆积，呈规则、固定的排列。它们在固定位置上振动，但不能相互越过。这种锁定的结构使冰具有确定的形状和体积。在液态水中，粒子仍然紧密，但不再有规则的排列模式。它们可以相互滑动和流动，因此液体在保持固定体积的同时，呈现容器底部的形状。在水蒸气中，粒子相距很远，向各个方向快速运动，没有固定的排列。水蒸气既没有固定的形状，也没有固定的体积；它会扩散充满整个可用空间。
Explanation: A common mistake is stating that particles in a liquid are 'further apart' than in a solid. In reality, the spacing is very similar for most substances; the key difference is the loss of fixed positions. For the second part, students must explicitly link the particle-level freedom to move with the macroscopic property of changing shape. Weak answers say 'because particles move' without connecting this movement to the loss of a rigid structure. Strong answers use precise phrases such as 'slide past each other' and 'fixed positions', demonstrating a clear grasp of the CAIE particle model.
解析：一个常见错误是说液体中的粒子比固体中的“间距更大”。实际上，对大多数物质而言，间距非常相似；关键区别在于失去了固定的位置。对于第二部分，学生必须明确地将粒子层面的自由移动与宏观上形状改变的性质联系起来。较弱的答案只说“因为粒子运动”，而没有将这种运动与刚性结构的丧失联系起来。有力的答案使用“相互滑动”和“固定位置”等精确表述，显示出对 CAIE 粒子模型的清晰掌握。
2. Pure Substances, Mixtures, and Dissolving | 纯净物、混合物与溶解
Question: A student stirs a spoonful of salt into a beaker of warm water. The salt seems to disappear. Is salt water a pure substance or a mixture? Explain your answer using scientific terms. What happens to the salt particles during dissolving?
题目：一名学生将一勺盐搅拌进一杯温水中。盐似乎消失了。盐水是纯净物还是混合物？请用科学术语解释你的答案。溶解过程中盐粒子发生了什么变化？
Answer: Salt water is a mixture, specifically a solution. A mixture contains two or more different substances that are not chemically joined. In this solution, salt is the solute (the substance that dissolves) and water is the solvent (the substance that does the dissolving). The salt does not disappear; its particles separate from the giant crystal lattice and spread out evenly between the water particles. The salt particles become surrounded by water particles and move freely throughout the liquid, forming a transparent, homogeneous mixture. This is a physical change, not a chemical reaction, because no new substance is formed. The salt can be recovered by evaporating the water.
答案：盐水是混合物，具体来说是溶液。混合物包含两种或更多种没有通过化学方式结合的不同物质。在该溶液中，盐是溶质（被溶解的物质），水是溶剂（进行溶解的物质）。盐并没有消失；其粒子从巨大的晶格中分离出来，均匀地分散在水粒子之间。盐粒子被水粒子包围，在液体中自由移动，形成透明、均匀的混合物。这是一个物理变化，而不是化学反应，因为没有新物质生成。通过蒸发水分可以回收盐。
Explanation: The word 'disappear' in the question is a deliberate trap. Students who interpret dissolving as vanishing do not yet understand the particle model. Examiners look for the precise vocabulary: solute, solvent, solution, mixture, not chemically combined. Many Year 7 learners also confuse dissolving with melting. Emphasise that melting is one substance changing state, while dissolving involves two substances interacting but not reacting chemically. Mentioning reversibility through evaporation further strengthens the answer by showing a clear distinction from chemical reactions.
解析：题目中“消失”一词是故意设置的陷阱。将溶解理解为消失的学生，还没有理解粒子模型。考官看重精准的词汇：溶质、溶剂、溶液、混合物、非化学结合。许多七年级学生还会混淆溶解和熔化。要强调熔化是单一物质的状态改变，而溶解涉及两种物质相互作用但不发生化学反应。提及通过蒸发可逆这一事实，能进一步强化答案，清晰表明与化学反应的区别。
3. Separation Techniques and Experimental Choices | 分离技术与实验选择
Question: You are given a mixture of sand, salt, and water. Describe, in correct order, the separation steps you would use to obtain dry sand and pure salt crystals. Name each technique and explain why you chose it for each step.
题目：给你一份沙子、盐和水的混合物。请按正确顺序描述你将用于获得干燥沙子和纯净盐晶体的分离步骤。说出每种技术的名称，并解释每一步选择它的原因。
Answer: Step one is filtration. Pour the mixture through filter paper in a funnel. The sand particles are too large to pass through the tiny holes in the filter paper, so they are trapped as residue. The salt water (filtrate) passes through. This separates the insoluble sand from the soluble salt and the water. Step two is evaporation or crystallisation. Heat the salt water solution gently in an evaporating dish. The water evaporates, leaving solid salt crystals behind. Filtration is chosen because particle size is the property that differs between sand and the salt-water solution. Evaporation is chosen because the salt has a much higher boiling point than water, so the water turns into vapour while the salt remains.
答案：第一步是过滤。将混合物通过漏斗中的滤纸倒入。沙子颗粒太大，无法通过滤纸上的微小孔隙，因此作为残渣被截留。盐水（滤液）则通过。这便将不溶的沙子与可溶的盐和水分离开。第二步是蒸发或结晶。在蒸发皿中缓缓加热盐水溶液。水分蒸发，留下固态盐晶体。选择过滤是因为颗粒大小是沙子与盐水溶液之间不同的性质。选择蒸发是因为盐的沸点远高于水，因此水转变为蒸汽而盐留存下来。
Explanation: The key skill here is justifying choices based on physical properties. Sand differs by being insoluble and having larger particle size; salt differs by being soluble and having a vastly higher boiling point. Students lose marks by merely naming the techniques without explanation. The correct sequence is crucial: filtration must come first, because heating the whole mixture would just boil off water and leave a sand-and-salt solid mix, not achieving separation. Also note that 'evaporation' works, but 'crystallisation' is often preferred in CAIE when pure, larger crystals are desired; both are acceptable if justified.
解析：这里的核心技能是基于物理性质来论证选择。沙子的不同之处在于不溶解且颗粒尺寸较大；盐的不同之处在于可溶解且沸点极高。学生如果只说出技术名称而不加解释，就会失分。正确的顺序至关重要：必须首先进行过滤，因为加热整个混合物只会蒸走水分，留下沙子和盐的固体混合物，无法实现分离。还要注意，“蒸发”是可行的，但 CAIE 中若希望得到纯净、更大的晶体，通常更倾向使用“结晶”；只要能合理论证，两者都接受。
4. Chemical vs. Physical Changes | 化学变化与物理变化
Question: Classify each of the following as a physical change or a chemical change, giving one clear reason for each: (a) melting butter, (b) baking a cake, (c) rusting of iron, (d) chopping wood.
题目：将以下各项分类为物理变化或化学变化，并分别给出一个明确的理由：(a) 融化黄油，(b) 烘烤蛋糕，(c) 铁生锈，(d) 劈柴。
Answer: (a) Melting butter is a physical change. The butter changes from solid to liquid, but it is still butter; no new substance is made. This is a reversible change of state. (b) Baking a cake is a chemical change. The ingredients react together with heat to form entirely new substances with different properties; the change is irreversible. (c) Rusting of iron is a chemical change. Iron reacts with oxygen and water in the air to form a new substance called iron oxide (rust), which has completely different properties from iron. (d) Chopping wood is a physical change. The wood is cut into smaller pieces, but each piece is still wood; no new substance is produced.
答案：(a) 融化黄油是物理变化。黄油从固态变为液态，但它仍然是黄油；没有新物质生成。这是一个可逆的物态变化。(b) 烘烤蛋糕是化学变化。各种原料与热量一起反应，形成具有不同性质的、全新的物质；该变化不可逆。(c) 铁生锈是化学变化。铁与空气中的氧气和水反应，形成一种叫做氧化铁（铁锈）的新物质，其性质与铁完全不同。(d) 劈柴是物理变化。木头被切成小块，但每一块仍然是木头；没有新物质产生。
Explanation: The critical discriminator in CAIE is the formation of new substances, not just changes in appearance. A substance has a fixed chemical composition. When butter melts, the chemical composition of the fat molecules does not change. When a cake bakes, the proteins, starches, and sugars undergo chemical reactions like denaturation and Maillard browning, producing molecules that were not present in the raw dough. Students often misclassify chopping as a chemical change because the appearance changes dramatically; drilling the definition—'no new substance formed'—helps correct this.
解析：在 CAIE 中，关键的区分标准是是否有新物质生成，而不仅仅是外观改变。一种物质具有固定的化学组成。黄油融化时，脂肪分子的化学组成没有改变。烘烤蛋糕时，蛋白质、淀粉和糖发生变性、美拉德褐变等化学反应，产生出面团中原本不存在的新分子。学生常因为外观变化巨大而将劈柴错误地归类为化学变化；反复练习“没有新物质生成”这一判断标准有助于纠正。
5. Laboratory Equipment Identification and Use | 实验室器材识别与使用
Question: Name the piece of laboratory equipment best suited for each task, and briefly explain your choice: (a) measuring exactly 25.0 cm³ of water, (b) holding a small amount of solid for heating over a Bunsen burner, (c) supporting a beaker on a tripod during heating.
题目：说出最适合以下每项任务的实验室器材名称，并简要解释你的选择：(a) 精确量取 25.0 cm³ 的水，(b) 盛放少量固体并在本生灯上加热，(c) 加热时在三脚架上支撑烧杯。
Answer: (a) A volumetric pipette, or a measuring cylinder. A volumetric pipette measures a fixed volume very precisely. A 25 cm³ measuring cylinder is an acceptable alternative if handled with care (reading the bottom of the meniscus at eye level). A beaker is unsuitable because its scale is only approximate. (b) A crucible, or an evaporating dish. These are designed to withstand strong, direct heating without cracking. A test tube is also acceptable for very small amounts of powder. (c) A wire gauze. It spreads the flame's heat evenly across the bottom of the beaker and provides a stable, flat surface. Without gauze, the beaker could tip or crack from concentrated heat.
答案：(a) 移液管，或量筒。移液管能非常精确地量取固定体积。如果操作得当（在视线水平读取弯月面底部），25 cm³ 量筒是可接受的替代选择。烧杯不合适，因为它的刻度只是近似值。(b) 坩埚，或蒸发皿。它们被设计成能承受强烈的直接加热而不破裂。对于极少量粉末，试管也可接受。(c) 石棉网。它将火焰的热量均匀地分散在烧杯底部，并提供稳定、平整的表面。没有石棉网，烧杯可能因热量集中而倾倒或破裂。
Explanation: This question tests practical knowledge, which CAIE emphasises from Year 7 onward. The explanation matters as much as the name. For (a), 'precision' is the keyword: students must show awareness that different glassware has different levels of accuracy. For (b), 'direct heating' requires heat-resistant material. For (c), 'even heat distribution' is the function of wire gauze. Practical questions often include safety considerations: using tongs, wearing goggles, keeping hair tied back. Even if the question does not explicitly ask for safety, weaving in one relevant safety point can sometimes gain credit in extended-response questions.
解析：这道题考察实践知识，CAIE 从七年级起就强调这一方面。解释与名称同样重要。对于 (a)，“精确度”是关键词：学生必须意识到不同的玻璃器皿具有不同的准确度水平。对于 (b)，“直接加热”需要耐热材料。对于 (c)，“均匀分散热量”是石棉网的功能。实践题经常包括安全考量：使用坩埚钳、佩戴护目镜、扎好头发。即使题目没有明确要求安全内容，在扩展回答题中穿插一个相关的安全要点有时也能得分。
6. The pH Scale and Everyday Substances | pH 值标度与日常物质
Question: Orange juice has a pH of around 3.5, pure water has a pH of 7, and bleach has a pH of around 12. (a) Which substance is the most acidic? (b) Which substance is the most alkaline? (c) Describe a safe method to test the pH of a household liquid without using a digital probe, and explain the colour change you might observe for orange juice.
题目：橙汁的 pH 值约为 3.5，纯水为 7，漂白剂约为 12。(a) 哪种物质酸性最强？(b) 哪种物质碱性最强？(c) 描述一种不使用数字探头来测试家用液体 pH 值的安全方法，并解释橙汁可能引起的颜色变化。
Answer: (a) Orange juice is the most acidic because it has the lowest pH value. (b) Bleach is the most alkaline because it has the highest pH value. (c) Use universal indicator, which is a mixture of several dyes that change colour across the entire pH scale. Add a few drops of universal indicator to a small sample of the liquid in a test tube, or touch a glass rod dipped in the liquid onto universal indicator paper. Observe the colour. For orange juice (pH ~3.5), universal indicator turns orange or red-orange, indicating a weak to moderate acid. Never taste or touch unknown substances. Wear safety goggles.
答案：(a) 橙汁酸性最强，因为它的 pH 值最低。(b) 漂白剂碱性最强，因为它的 pH 值最高。(c) 使用通用指示剂，它是由几种在不同 pH 值下变色的染料混合而成。向试管中少量液体样品滴入几滴通用指示剂，或用蘸取液体的玻璃棒轻触通用指示纸。观察颜色变化。对于橙汁（pH 约 3.5），通用指示剂会变成橙色或红橙色，表明是弱酸到中强酸。切勿品尝或触摸未知物质。佩戴安全护目镜。
Explanation: The pH scale seems simple, but students often confuse 'strong acid' with 'concentrated acid' and 'weak acid' with 'dilute acid'. At Year 7, the focus is on the numerical scale: lower pH means stronger acid, higher pH means stronger alkali. pH 7 is neutral. The method description must be practical and safe. Universal indicator (liquid or paper) is the expected answer. Litmus paper only tells acid or alkali, not the strength, so it is insufficient for a question asking for a comparison of pH. Including safety points—no tasting, wear protection, handle glass carefully—shows good laboratory practice.
解析：pH 标度看似简单，但学生经常混淆“强酸”与“浓酸”、“弱酸”与“稀酸”。在七年级，重点是数值标度：pH 值越低表示酸性越强，pH 值越高表示碱性越强。pH 7 为中性。方法描述必须既实用又安全。通用指示剂（液体或试纸）是预期的答案。石蕊试纸只能辨别酸或碱，无法显示强度，因此对于要求比较 pH 值的问题来说不够充分。包含安全要点——不品尝、佩戴防护装备、小心处理玻璃——能展示良好的实验室操作规范。
7. Combustion Reactions and the Fire Triangle | 燃烧反应与火三角
Question: A candle burns inside a sealed jar until the flame goes out. (a) Name the three things required for a fire to burn, as described by the fire triangle. (b) Explain, using the fire triangle, why the candle flame eventually goes out. (c) What gas is produced during complete combustion that turns limewater cloudy?
题目：一支蜡烛在密封的罐子里燃烧，直到火焰熄灭。(a) 根据火三角理论，说出燃烧所需的三要素。(b) 运用火三角解释为什么蜡烛火焰最终会熄灭。(c) 完全燃烧过程中产生的何种气体会使石灰水变浑浊？
Answer: (a) The fire triangle consists of fuel, heat (ignition temperature), and oxygen. Remove any one of these three, and the fire goes out. (b) The candle's fuel is the wax, and the initial heat and oxygen are present inside the jar. However, the jar is sealed, so no fresh air can enter. As the candle burns, it uses up the oxygen inside the jar. Once the oxygen concentration falls below the level needed to sustain combustion, the fire goes out because one side of the fire triangle is removed. (c) Carbon dioxide is the gas produced during complete combustion. It reacts with limewater (calcium hydroxide solution) to form a white precipitate of calcium carbonate, turning the limewater cloudy or milky.
答案：(a) 火三角由燃料、热量（着火温度）和氧气组成。移除这三者中的任何一个，火就会熄灭。(b) 蜡烛的燃料是蜡，罐内初始时有热量和氧气存在。然而，罐子是密封的，没有新鲜空气能进入。随着蜡烛燃烧，它消耗掉罐内的氧气。一旦氧气浓度降至维持燃烧所需的水平以下，火焰就熄灭了，因为火三角的一边被移除了。(c) 二氧化碳是完全燃烧过程中产生的气体。它与石灰水（氢氧化钙溶液）反应，形成白色的碳酸钙沉淀，使石灰水变浑浊或呈乳白色。
Explanation: The phrase 'uses up the oxygen' is scientifically acceptable at this level, though more precise students might say 'the oxygen reacts with the wax to form carbon dioxide and water'. The fire triangle is a model that CAIE explicitly requires. For part (c), students must remember the carbon dioxide test: bubble the gas through limewater, or shake the gas with limewater. 'Turns milky' or 'turns cloudy' are the exact phrases examiners look for. Do not confuse this with the test for water (anhydrous copper sulfate turns from white to blue) or the test for oxygen (relights a glowing splint).
解析：“消耗掉氧气”这一说法在此阶段科学上是可接受的，不过更严谨的学生可能会说“氧气与蜡反应生成二氧化碳和水”。火三角是 CAIE 明确要求的模型。对于 (c) 部分，学生必须记住二氧化碳的检验方法：使气体通过石灰水冒泡，或与石灰水一起摇匀。“变乳白色”或“变浑浊”正是考官寻找的准确表述。不要将此与水的检验（无水硫酸铜由白变蓝）或氧气的检验（使带火星的木条复燃）相混淆。
8. Atomic Structure Basics for Year 7 | 七年级基础原子结构
Question: An atom of carbon has 6 protons, 6 neutrons, and 6 electrons. (a) Where in the atom are protons and neutrons found? (b) Where are electrons found? (c) Explain why the carbon atom has no overall electric charge.
题目：一个碳原子有 6 个质子、6 个中子和 6 个电子。(a) 质子和中子位于原子的何处？(b) 电子位于何处？(c) 解释为什么碳原子整体不带电荷。
Answer: (a) Protons and neutrons are found in the nucleus, which is the very small, dense central part of the atom. (b) Electrons are found in shells or energy levels orbiting around the nucleus. (c) Protons carry a positive electric charge (+1), and electrons carry a negative electric charge (-1). Neutrons have no charge. In this carbon atom, there are 6 protons (total charge +6) and 6 electrons (total charge -6). The positive and negative charges balance each other out exactly, resulting in a net charge of zero. The atom is therefore electrically neutral.
答案：(a) 质子和中子位于原子核中，原子核是原子中心极小、极密的部分。(b) 电子位于围绕原子核的电子层或能级中，绕核运动。(c) 质子带正电荷（+1），电子带负电荷（-1）。中子不带电荷。在这个碳原子中，有 6 个质子（总电荷 +6）和 6 个电子（总电荷 -6）。正负电荷恰好相互抵消，净电荷为零。因此该原子是电中性的。
Explanation: At Year 7, CAIE introduces the simple model of an atom: a central nucleus containing protons and neutrons, with electrons in shells surrounding it. Charged particles are called ions, but the term 'ion' is not formally required until later years; students should still recognise that a neutral atom has equal numbers of protons and electrons. A common error is stating that 'neutrons cancel out the charge of protons', which is incorrect because neutrons have no charge. Only electrons balance protons. Diagrams are often helpful: a small circle for the nucleus with a surrounding ring for an electron shell makes the concept concrete.
解析：在七年级，CAIE 引入原子的简单模型：中心是含有质子和中子的原子核，电子分布在核外的电子层中。带电荷的粒子叫做离子，但“离子”这个术语在更高年级才正式要求；学生仍应认识到中性原子的质子数与电子数相等。一个常见错误是说“中子抵消了质子的电荷”，这是不正确的，因为中子不带电。只有电子才能平衡质子。图示往往很有帮助：一个小圆圈表示原子核，外面加上一个环绕的圆环表示电子层，能让概念变得具体。
9. Key Chemical Reactions and Word Equations | 关键化学反应与文字方程式
Question: Write word equations for the following reactions: (a) magnesium reacting with oxygen to form magnesium oxide, (b) the thermal decomposition of calcium carbonate (limestone), (c) zinc reacting with hydrochloric acid to produce zinc chloride and hydrogen gas.
题目：写出下列反应的文字方程式：(a) 镁与氧气反应生成氧化镁，(b) 碳酸钙（石灰石）的热分解反应，(c) 锌与盐酸反应生成氯化锌和氢气。
onate → calcium oxide + carbon dioxide. (The reaction requires heat, indicated by the word 'heat' red as requiring strong heating.) (c) zinc + hydrochloric acid → zinc chloride + hydrogen.
答案：(a) 镁 + 氧气 → 氧化镁。 (b) 碳酸钙 → 氧化钙 + 二氧化碳。（该反应需要加热，可在箭头上方注明“加热”，或简单记住需要强热。） (c) 锌 + 盐酸 → 氯化锌 + 氢气。
ion: Word equations are the foundation of chemical literacy at Year 7. The arrow (→) means 'reacts to form' or 'produces' ry because it does not show the direction of reaction. For (b), thermal decomposition means breaking down a substance using heat. The word 'thermal' cid would produce zinc sulfate instead. Students should begin to recognise these patterns.
解析：文字方程式是七年级化学素养的基础。箭头（→）表示“反应生成”或“产生”。反应物在左边，生成物在右边。常见错误是把箭头方向写反，或使用等号，这在化学中是不正确的，因为它不能显示反应的方向。对于 (b)，热分解是指用热量将物质分解。“热”字意味着加热，因此必须与反应条件相联系。对于 (c)，注意盐酸提供了盐中的氯化部分；硫酸则会产生硫酸锌。学生应开始识别这些模式。
10. Scientific Enquiry and Graph Skills | 科学探究与图表技能
Question: A student heats water in a beaker and records the temperature every minute until boiling. The data: 0 min: 20°C, 1 min: 32°C, 2 min: 44°C, 3 min: 56°C, 4 min: 68°C, 5 min: 80°C, 6 min: 92°C, 7 min: 100°C, 8 min: 100°C, 9 min: 100°C. (a) Plot these points on graph paper and draw the best-fit line. (b) Identify the point where boiling begins. (c) Explain why the temperature remains constant after 7 minutes, even though heating continues.
题目：一名学生加热烧杯中的水，每分钟记录一次温度直到沸腾。数据如下：0 分钟: 20°C, 1 分钟: 32°C, 2 分钟: 44°C, 3 分钟: 56°C, 4 分钟: 68°C, 5 分钟: 80°C, 6 分钟: 92°C, 7 分钟: 100°C, 8 分钟: 100°C, 9 分钟: 100°C。(a) 在坐标纸上绘制这些点并画出最佳拟合线。(b) 指出沸腾开始的时刻。(c) 解释为什么尽管继续加热，7 分钟后的温度却保持不变。
Answer: (a) The graph should have 'Time (minutes)' on the x-axis and 'Temperature (°C)' on the y-axis. Points are plotted accurately, and a line of best fit is drawn. It will rise steadily before flattening into a horizontal plateau at 100°C. (b) Boiling begins at the 7-minute mark, where the line becomes horizontal. (c) Once water reaches its boiling point, the energy supplied by the Bunsen burner is used to overcome the forces of attraction between water particles so they can escape as steam, rather than to increase their kinetic energy. This is latent heat of vaporisation. Therefore, the temperature stays steady at 100°C until all the water has boiled away.
答案：(a) 图表中 x 轴为“时间（分钟）”，y 轴为“温度（°C）”。准确描点，画出最佳拟合线。线条先稳定上升，然后在 100°C 处变为水平的平台。(b) 沸腾始于第 7 分钟，此时线条变为水平。(c) 一旦水达到沸点，本生灯提供的能量被用来克服水粒子之间的吸引力，使它们能够以蒸汽形式逸出，而不是增加它们的动能。这就是汽化潜热。因此，温度稳定在 100°C，直到所有的水都蒸发完。
Explanation: Graph skills are assessed throughout CAIE science. Students must label axes with the quantity and unit, choose sensible scales that use more than half the graph paper, and plot crosses (not dots). The 'line of best fit' for this data set is two straight lines: one sloping up, one horizontal. Many Year 7 students incorrectly try to join every point with a zigzag line. For the explanation of the plateau, the CAIE mark scheme expects an energy-based answer: heat energy is used to change state (overcoming inter-particle forces), not to raise temperature. Simply saying 'because it is boiling' does not explain why the temperature stops rising.
解析：图表技能在 CAIE 科学中贯穿始终。学生必须标注坐标轴及其对应的量和单位，选择使用图表纸一半以上的合理刻度，并用叉号（而非圆点）描点。对于本数据集，“最佳拟合线”是两条直线：一条向上倾斜，一条水平。许多七年级学生错误地试图用锯齿线连接每个点。对于平台期的解释，CAIE 评分标准期望一个基于能量的答案：热能用于改变状态（克服粒子间作用力），而不是提高温度。简单地说“因为它正在沸腾”并不能解释为什么温度停止上升。
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