📚 Year 7 Cambridge Chemistry: Unit Test Mock Paper Analysis | Year 7 Cambridge 化学：单元测试模拟卷解析
Welcome to the Year 7 Cambridge Chemistry Unit Test Mock Paper Analysis. In this article, we present sample questions from a mock paper that covers the core topics of the Cambridge Lower Secondary Science chemistry syllabus. By going through each question and its detailed explanation, you will strengthen your understanding of key concepts, common pitfalls, and exam techniques. Let’s dive in and build your confidence for the upcoming test.
欢迎来到 Year 7 Cambridge 化学单元测试模拟卷解析。本文展示了一套模拟卷中的典型题目，涵盖了剑桥初中科学化学课程的核心主题。通过逐一分析每个问题及其详细解析，你将加深对关键概念的理解，识别常见错误，并掌握答题技巧。现在，让我们一起提升应试信心吧。
1. States of Matter and Changes of State | 物质状态与状态变化
Question 1: Describe the arrangement and movement of particles in a solid, a liquid and a gas. Explain what happens to the particles when ice is heated and eventually turns into steam.
问题1：描述固体、液体和气体中粒子的排列和运动方式。解释当冰被加热并最终变成水蒸气时，粒子发生了什么变化。
Answer: In a solid, particles are tightly packed in a regular pattern and they only vibrate in fixed positions. In a liquid, particles are still close together but can move past each other, so the liquid flows and takes the shape of its container. In a gas, particles are far apart and move rapidly in all directions. When ice is heated, particles gain kinetic energy, vibrate more strongly and overcome some of the forces holding them in place – the solid melts into liquid water. As heating continues, particles gain enough energy to break free from the liquid’s surface and escape as a gas (steam). This change from liquid to gas is called boiling or evaporation.
答案：固体中，粒子紧密排列成规则的图案，只能在固定位置振动。液体中，粒子仍然彼此靠近，但可以相互滑动，因此液体能够流动并呈现容器的形状。气体中，粒子相距很远，快速向各个方向运动。当冰被加热时，粒子获得动能，振动更剧烈，克服了部分束缚力——固体熔化成液态水。继续加热，粒子获得足够的能量，从液体表面挣脱并逸出成为气体（水蒸气）。这种从液体到气体的变化称为沸腾或蒸发。
Common mistake: Adding energy does not change the particles themselves; it only changes their arrangement and movement. Melting and boiling are physical changes, not chemical reactions.
常见错误：输入能量并不会改变粒子本身，只会改变它们的排列和运动方式。熔化和沸腾是物理变化，而不是化学反应。
2. Physical and Chemical Changes | 物理变化与化学变化
Question 2: Classify the following changes as physical or chemical: melting butter, rusting iron, dissolving sugar in water, baking a cake. Explain your reasoning.
问题2：将以下变化分类为物理变化或化学变化：黄油融化、铁生锈、糖溶于水、烘焙蛋糕。解释你的理由。
Answer: Physical changes: melting butter, dissolving sugar in water. Chemical changes: rusting iron, baking a cake.
答案：物理变化：黄油融化，糖溶于水。化学变化：铁生锈，烘焙蛋糕。
Explanation: In physical changes, the substance keeps its chemical identity – only its state or appearance changes. Melted butter is still butter; dissolved sugar can be recovered by evaporation. In chemical changes, new substances with different properties are formed. Rusting iron produces iron oxide, which is chemically different from iron. Baking a cake involves irreversible reactions that create new compounds, such as carbon dioxide gas, and changes in texture and taste.
解析：在物理变化中，物质保持其化学身份不变——只有状态或外观改变。融化的黄油仍然是黄油；溶解的糖可以通过蒸发回收。在化学变化中，会形成性质不同的新物质。铁生锈产生氧化铁，与铁的化学性质不同。烘焙蛋糕涉及不可逆的反应，生成新的化合物（如二氧化碳气体），并且质地和味道都发生了改变。
3. Elements, Compounds and Mixtures | 元素、化合物与混合物
Question 3: Identify each substance as an element, compound or mixture: oxygen gas (O₂), water (H₂O), air, iron (Fe), sodium chloride (NaCl). Give a brief definition for each category.
问题3：判断下列物质属于元素、化合物还是混合物：氧气（O₂）、水（H₂O）、空气、铁（Fe）、氯化钠（NaCl）。并为每一类给出简短的定义。
Answer: Elements: O₂, Fe. Compounds: H₂O, NaCl. Mixture: air.
答案：元素：O₂、Fe。化合物：H₂O、NaCl。混合物：空气。
Definitions: An element is a pure substance made of only one type of atom. A compound is a pure substance composed of two or more different elements chemically combined in a fixed ratio. A mixture contains two or more substances that are physically combined but not chemically bonded and can be separated by physical means.
定义：元素是仅由一种原子组成的纯净物。化合物是由两种或多种不同元素以固定比例化学结合而成的纯净物。混合物含有两种或多种物质，它们物理混合在一起但未发生化学键合，可以用物理方法分离。
Note: Oxygen gas (O₂) is an element because both atoms are oxygen; water is a compound of hydrogen and oxygen; air is a mixture of nitrogen, oxygen, argon and other gases.
注意：氧气（O₂）是元素，因为两个原子都是氧；水是氢和氧的化合物；空气是氮气、氧气、氩气和其他气体的混合物。
4. The Periodic Table and Symbols | 元素周期表与符号
Question 4: Write the chemical symbols for carbon, sodium, chlorine, gold and lead. What three pieces of information can you find in a typical periodic table box?
问题4：写出碳、钠、氯、金和铅的元素符号。在周期表的一个典型方框中，你可以找到哪三条信息？
Answer:
| Element (English) | Symbol | 元素（中文） |
|---|---|---|
| Carbon | C | 碳 |
| Sodium | Na | 钠 |
| Chlorine | Cl | 氯 |
| Gold | Au | 金 |
| Lead | Pb | 铅 |
答案：见上表。在周期表方框中，通常可以找到元素符号、原子序数（原子中质子的数目）和相对原子质量。
Periodic table box: Each box typically shows the element symbol, the atomic number (number of protons) and the relative atomic mass. Some tables also include the full element name.
周期表方框：每个方框通常显示元素符号、原子序数（质子数）和相对原子质量。有些周期表还包括元素全名。
5. Chemical Reactions and Word Equations | 化学反应与文字方程式
Question 5: When magnesium ribbon burns in air, it reacts with oxygen to form magnesium oxide. Write a word equation for this reaction. State the reactants and the product.
问题5：当镁条在空气中燃烧时，它与氧气反应生成氧化镁。写出该反应的文字方程式。指明反应物和生成物。
Answer: magnesium + oxygen → magnesium oxide
答案：镁 + 氧气 → 氧化镁
Explanation: The reactants are magnesium and oxygen. The product is magnesium oxide. The arrow (→) means ‘reacts to form’. During the reaction, white light and heat are released, and a white powder (magnesium oxide) is produced. This is a synthesis (combination) reaction.
解析：反应物是镁和氧气。生成物是氧化镁。箭头 (→) 表示“反应生成”。在反应过程中，释放出白光和热量，并生成白色粉末（氧化镁）。这是一个化合反应。
6. Acids, Alkalis and the pH Scale | 酸、碱和pH值
Question 6: A student tests a colourless solution with universal indicator and it turns green. What is the pH of the solution? Is it acidic, alkaline or neutral? Name a common household liquid that would give a similar result.
问题6：一名学生用通用指示剂检测一种无色溶液，指示剂变为绿色。该溶液的pH值是多少？它是酸性、碱性还是中性？举出一种会得到类似结果的家庭常见液体。
Answer: The pH is 7. The solution is neutral. Pure water (distilled water) would give a green colour with universal indicator; tap water may also be close to neutral but can vary slightly.
答案：pH值为7。该溶液是中性。纯水（蒸馏水）遇通用指示剂呈绿色；自来水也可能接近中性，但会略有差异。
Key points: Universal indicator green corresponds to pH 7. Values below 7 are acidic (red, orange, yellow); values above 7 are alkaline (blue, purple).
要点：通用指示剂变绿对应于pH 7。低于7的值为酸性（红、橙、黄）；高于7的值为碱性（蓝、紫）。
7. Separating Mixtures: Filtration and Distillation | 分离混合物：过滤与蒸馏
Question 7: You are given a mixture of sand, salt and water. Describe the steps you would take to obtain pure dry sand and pure salt.
问题7：给你一份沙子、食盐和水的混合物。描述你将采取哪些步骤，以获得纯净的干沙子和纯净的食盐。
Answer: First, filter the mixture using filter paper and a funnel. The sand, being insoluble, will be trapped in the filter paper as a residue. Wash it with a little water and dry it to obtain pure dry sand. The filtrate (salt solution) is collected. Then, heat the salt solution in an evaporating dish or use a gentle evaporation method to remove the water. Salt crystals will be left behind. Further drying gives pure salt.
答案：首先，使用滤纸和漏斗过滤混合物。沙子不溶于水，会留在滤纸上作为残渣。用少量水冲洗并干燥，即得到纯净的干沙子。收集滤液（食盐水）。然后，将食盐水在蒸发皿中加热或采用缓慢蒸发的方法除去水。最后留下盐的晶体。进一步干燥即得到纯盐。
Methods used: Filtration separates an insoluble solid from a liquid. Evaporation (or crystallisation) is used to obtain a soluble solid from a solution.
所用方法：过滤用于分离不溶性固体和液体。蒸发（或结晶）用于从溶液中获取可溶性固体。
8. The Reactivity Series and Displacement | 金属活动性与置换反应
Question 8: A piece of zinc metal is added to a blue copper sulfate solution. The mixture is left for a few minutes. State two observations you would make and write the word equation for the reaction.
问题8：将一小块锌加入蓝色的硫酸铜溶液中，静置几分钟。陈述你会观察到的两个现象，并写出该反应的文字方程式。
Answer: Observations: The blue colour of the solution fades (or becomes colourless). A reddish-brown solid (copper) coats the zinc or settles at the bottom. The zinc strip may appear smaller.
答案：现象：溶液的蓝色变浅（或变为无色）。锌表面出现红棕色固体（铜）或沉淀在底部。锌片可能变小。
Word equation: zinc + copper sulfate → zinc sulfate + copper
文字方程式：锌 + 硫酸铜 → 硫酸锌 + 铜
Explanation: Zinc is more reactive than copper, so it displaces copper from the copper sulfate solution. This is a displacement reaction.
解析：锌比铜活泼，因此它能将铜从硫酸铜溶液中置换出来。这是一个置换反应。
9. Laboratory Safety and Common Apparatus | 实验室安全与常用仪器
Question 9: List three safety rules to follow when heating a liquid
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