Year 7 Cambridge Chemistry: Mock Unit Test Paper Walkthrough | Year 7 剑桥化学：单元测试模拟卷解析

📚 Year 7 Cambridge Chemistry: Mock Unit Test Paper Walkthrough | Year 7 剑桥化学：单元测试模拟卷解析

This walkthrough provides a full mock unit test designed for Year 7 Cambridge Lower Secondary Science (Chemistry), covering topics such as states of matter, particle theory, elements, compounds and mixtures, separation techniques, acids and alkalis, physical and chemical changes, and more. Each question is followed by a detailed explanation to reinforce key concepts and prepare you for your class assessments.

本文提供一套专为 Year 7 剑桥初中科学（化学）设计的完整单元模拟测试卷，覆盖物质状态、粒子理论、元素化合物混合物、分离技术、酸碱、物理与化学变化等重要主题。每道题后都有详细解析，帮助巩固核心概念，为课堂评估做好准备。

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1. Introduction: About the Mock Test | 引言：关于模拟测试

This mock test consists of 10 questions: multiple-choice and one short-answer question. It reflects the style of Cambridge Lower Secondary Checkpoint and school end-of-unit tests. Use it to identify your strengths and areas for improvement. The answer explanations include key facts, common misconceptions, and tips for remembering essential definitions.

本模拟卷包含 10 道题：选择题和一道简答题，题型贴近剑桥初中 Checkpoint 及校内单元测试风格。你可以借助它发现自己的强项和薄弱点。解析中包含关键知识点、常见误区以及记忆重要定义的技巧。

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2. Question 1: States of Matter | 第1题：物质的状态

Question: Which state of matter has a fixed volume but takes the shape of its container? A. Solid B. Liquid C. Gas D. Plasma

题目：哪种物质状态具有固定的体积但会呈现容器的形状？A. 固体 B. 液体 C. 气体 D. 等离子体

The correct answer is B, Liquid. Liquids have a definite volume because the particles are still in contact, but they can slide past each other, allowing the liquid to flow and adopt the shape of the bottom of the container. Solids (A) have a fixed shape and fixed volume. Gases (C) have neither a fixed shape nor a fixed volume — they spread out to fill their entire container. Plasma (D) is a high-energy state not typically covered at this level. Remember: ‘fixed volume, no fixed shape’ is the key description of liquids.

正确答案是 B 液体。液体具有确定的体积，因为粒子之间仍然相互接触，但它们能够相互滑动，因此液体可以流动并呈现容器的形状。固体 (A) 具有固定的形状和固定的体积。气体 (C) 既没有固定的形状也没有固定的体积——它们会扩散并充满整个容器。等离子体 (D) 是一种高能态，在 Year 7 阶段通常不涉及。请记住：“固定体积，无固定形状”是液体的关键特征。

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3. Question 2: Particle Theory — Gas Particles | 第2题：粒子理论——气体粒子

Question: The particle theory states that particles in a gas: A. Are tightly packed and vibrate in place B. Move freely and are far apart C. Are arranged in a regular pattern D. Have strong forces of attraction

题目：根据粒子理论，气体中的粒子：A. 堆积紧密并在原地振动 B. 自由运动且彼此间距很大 C. 以规则模式排列 D. 粒子间具有很强的吸引力

The correct choice is B. In a gas, particles have large spaces between them, move rapidly in all directions, and have very weak forces of attraction. Option A describes solids, where particles are tightly packed and only vibrate in fixed positions. Option C refers to the regular arrangement found in many solids (e.g. crystals). Option D is incorrect for gases because the forces of attraction are negligible. Understanding particle behaviour helps explain why gases can be compressed and spread out quickly.

正确选项是 B。在气体中，粒子之间有很大的空隙，它们快速向各个方向运动，粒子间的吸引力非常弱。选项 A 描述的是固体，其中粒子紧密堆积，只能在固定位置上振动。选项 C 指的是许多固体（如晶体）中存在的规则排列。选项 D 对气体而言是错误的，因为其吸引力几乎可以忽略。理解粒子行为有助于解释为什么气体容易被压缩并能迅速扩散。

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4. Question 3: Elements, Compounds and Mixtures | 第3题：元素、化合物和混合物

Question: Which of the following is a compound? A. Oxygen (O₂) B. Water (H₂O) C. Air D. Iron

题目：下列哪一项是化合物？A. 氧气 (O₂) B. 水 (H₂O) C. 空气 D. 铁

The answer is B, water. A compound is a pure substance made of two or more different types of atoms chemically bonded together. Water (H₂O) contains hydrogen and oxygen atoms bonded. Oxygen (O₂) is an element because it consists of only one type of atom. Air is a mixture of several gases (mainly nitrogen, oxygen, argon and carbon dioxide). Iron is an element. A quick way to check: if you can find it on the periodic table as a single symbol, it is an element; if it has two or more capital letters chemically combined, it is a compound.

答案是 B 水。化合物是由两种或两种以上不同原子通过化学键结合而成的纯物质。水 (H₂O) 含有氢原子和氧原子，并以化学键结合。氧气 (O₂) 是单质（元素），因为它只由一种原子构成。空气是几种气体（主要是氮气、氧气、氩气和二氧化碳）的混合物。铁是元素。一个快速判断方法：如果能在元素周期表中找到其单一符号，则是元素；如果化学式含有两个或以上大写字母并通过化学方式结合，则是化合物。

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5. Question 4: Separation of a Mixture — Sand and Salt | 第4题：混合物的分离——沙和食盐

Question: A mixture of sand and salt can be separated by: A. Filtration then evaporation B. Distillation C. Chromatography D. Magnetism

题目：分离沙和食盐的混合物可以通过：A. 过滤然后蒸发 B. 蒸馏 C. 色谱法 D. 磁力

The correct sequence is A. First, add water to dissolve the salt, leaving the insoluble sand. Filter the mixture to separate the sand (residue) from the salt solution (filtrate). Then heat the filtrate gently so the water evaporates, leaving solid salt behind. Distillation (B) would also collect the water, but it is more complex and not required for this simple solid-solid separation. Chromatography (C) separates dissolved coloured substances. Magnetism (D) separates magnetic from non-magnetic materials, which does not apply here.

正确步骤是 A。首先，加水溶解食盐，不溶的沙则保持不变。过滤混合物，将沙（残渣）与食盐溶液（滤液）分离。然后缓慢加热滤液，使水蒸发，留下固体食盐。蒸馏 (B) 虽然也能收集水，但装置更复杂，对于这种简单的固-固分离并非必需。色谱法 (C) 用于分离溶解的有色物质。磁力 (D) 用来分离磁性物质与非磁性物质，此处不适用。

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6. Question 5: Acids, Alkalis and Indicators | 第5题：酸、碱和指示剂

Question: Universal indicator turns red in a solution. The solution is probably: A. Neutral B. A strong acid C. A weak alkali D. A strong alkali

题目：通用指示剂在某溶液中变红，该溶液很可能是：A. 中性 B. 强酸 C. 弱碱 D. 强碱

The answer is B, a strong acid. Universal indicator shows a range of colours depending on pH. Red typically indicates pH 1–2, which corresponds to a strong acid. Weak acids give orange or yellow. Green indicates neutral (pH 7). Weak alkalis turn the indicator blue, and strong alkalis give purple. It is important to link the colour with approximate pH values and not just with ‘acid’ or ‘alkali’.

答案是 B 强酸。通用指示剂根据 pH 显示不同颜色。红色通常对应 pH 1–2，属于强酸。弱酸呈橙色或黄色。绿色表示中性（pH 7）。弱碱使指示剂变蓝，强碱则呈紫色。重要的是将颜色与大致 pH 值关联起来，而不能仅仅停留在“酸”或“碱”的层面。

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7. Question 6: Physical and Chemical Changes | 第6题：物理变化与化学变化

Question: Which process is a chemical change? A. Ice melting B. Boiling water C. Burning wood D. Dissolving sugar

题目：下列哪个过程是化学变化？A. 冰融化 B. 水沸腾 C. 木材燃烧 D. 糖溶解

The answer is C, burning wood. A chemical change produces one or more new substances with different properties, and it is usually difficult to reverse. Burning wood makes ash, carbon dioxide and water vapour — all new substances. Ice melting (A), boiling water (B), and dissolving sugar (D) are physical changes because no new substance is formed; the change can be easily reversed (e.g. freezing, condensing, evaporating the water from sugar solution). Look out for signs of a chemical reaction: colour change, gas production, temperature change without heating, or a precipitate forming.

答案是 C 木材燃烧。化学变化会产生一种或多种具有不同性质的新物质，并且通常难以逆转。木材燃烧生成灰烬、二氧化碳和水蒸气——这些都是新物质。冰融化 (A)、水沸腾 (B) 和糖溶解 (D) 都是物理变化，因为没有新物质生成，而且很容易逆向恢复（例如结冰、冷凝、蒸发糖水溶液）。识别化学反应的标志包括：颜色变化、放出气体、无外界加热时温度改变或生成沉淀。

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8. Question 7: Diffusion | 第7题：扩散

Question: When a perfume bottle is opened, the smell spreads across the room. This is due to: A. Evaporation B. Diffusion C. Condensation D. Conduction

题目：当打开香水瓶时，气味会弥漫整个房间，这是因为：A. 蒸发 B. 扩散 C. 冷凝 D. 热传导

The correct term is B, diffusion. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. The gas particles of the perfume drift through the air randomly until they are evenly spread. Evaporation (A) is the change from liquid to gas at the surface, which does happen to the perfume but does not explain the spreading. Condensation (C) is gas to liquid. Conduction (D) is the transfer of heat through solids. Remember, diffusion is a consequence of the random motion of particles in liquids and gases.

正确的术语是 B 扩散。扩散是指粒子从高浓度区域向低浓度区域的运动。香水的蒸气粒子在空气中随机飘动，直到均匀分布。蒸发 (A) 是液体在表面转变为气体的过程，香水确实会发生蒸发，但这并不能解释气味的扩散。冷凝 (C) 是气体变为液体。热传导 (D) 是热量在固体中的传递。请记住，扩散是液体和气体中粒子随机运动的结果。

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9. Question 8: Melting and Boiling Points | 第8题：熔点与沸点

Question: A substance melts at 0°C and boils at 100°C. What is its state at 25°C? A. Solid B. Liquid C. Gas D. Cannot tell

题目：某物质的熔点为 0°C，沸点为 100°C。在 25°C 时它是什么状态？A. 固体 B. 液体 C. 气体 D. 无法确定

The substance is B, liquid at 25°C. Below 0°C it is solid (ice); between 0°C and 100°C the substance is liquid; above 100°C it becomes a gas. Since 25°C falls in the liquid range, the answer is liquid. Interestingly, this substance matches water, which is used here to illustrate a familiar example. Always compare the given temperature with the melting point and boiling point: if temperature > melting point and < boiling point → liquid.

该物质在 25°C 为 B 液体。低于 0°C 时它是固体（冰）；在 0°C 到 100°C 之间是液体；高于 100°C 则变为气体。因为 25°C 处于液体区间，所以答案是液体。有趣的是，该物质与水吻合，这里用熟悉的例子帮助理解。始终将给定温度与熔点和沸点进行比较：若温度 > 熔点且 < 沸点，则为液态。

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10. Question 9: Solutions — Solvents and Solutes | 第9题：溶液——溶剂与溶质

Question: In a solution of salt water, which is the solvent? A. Salt B. Water C. Salt and water D. Neither

题目：在食盐水中，哪一个是溶剂？A. 食盐 B. 水 C. 食盐和水都是 D. 都不是

The solvent is B, water. A solvent is the liquid in which a solute dissolves. In a salt water solution, salt (sodium chloride) is the solute that dissolves, and water is the solvent that does the dissolving. The solute is often a solid, but can be a liquid or gas. Water is known as the ‘universal solvent’ because it dissolves so many substances. Be careful not to confuse solute and solvent: the solvent is the substance present in the larger amount (usually water).

溶剂是 B 水。溶剂是能够溶解溶质的液体。在食盐水中，食盐（氯化钠）是被溶解的溶质，而水是进行溶解的溶剂。溶质通常是固体，但也可以是液体或气体。水被称为“万能溶剂”，因为它能溶解许多物质。注意不要混淆溶质和溶剂：溶剂一般是在溶液中含量较多的那个物质（通常是水）。

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11. Question 10: Obtaining Pure Water from Seawater | 第10题：从海水中获取纯水

Question: Describe how to obtain pure water from a sample of seawater. Name the separation method used.

题目：描述如何从一份海水样品中获取纯水，并命名所使用的分离方法。

The method is distillation. Pour seawater into a round-bottom flask and set up a distillation apparatus with a condenser and a collecting beaker. Heat the flask gently. The water evaporates, turning into water vapour, while the dissolved salt remains in the flask. The water vapour travels into the inner tube of the condenser, which is surrounded by cold water flowing in the outer jacket. The vapour cools, condenses back into pure liquid water, and is collected in the beaker as distillate. This process separates a liquid from a soluble solid based on differences in boiling points.

该分离方法是蒸馏。将海水倒入圆底烧瓶中，搭建好蒸馏装置，包括冷凝管和收集烧杯。缓慢加热烧瓶。

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