📚 Year 7 WJEC Chemistry: Unit Test Mock Paper Analysis | Year 7 WJEC 化学：单元测试模拟卷解析
Preparing for a Year 7 chemistry unit test can feel a lot like learning a new language – but mock papers are the best tool in your revision kit. This analysis breaks down a typical WJEC-style mock paper, covering states of matter, particle models, separation techniques, acids and alkalis, and essential lab skills. Each question is followed by a detailed answer and key revision notes so you can understand exactly what examiners expect and where marks are awarded.
备战七年级化学单元测试就像学习一门新语言——而模拟卷是你复习包里最棒的工具。本文细致讲解了一份典型 WJEC 风格的模拟卷，涵盖物质状态、粒子模型、分离技术、酸和碱以及基本的实验技能。每道题后都附有详细答案和核心复习点，让你准确理解命题人的期待以及分数是怎样给的。
1. Question 1: Naming Changes of State | 问题1：命名状态变化
The question: A student places a sealed container of pure water in a freezer at -15 °C. After three hours the water has become solid ice. Name the change of state that has taken place and state the temperature at which this change begins for pure water. [2 marks]
题目：一名学生将一个密封的纯水容器放入 -15 °C 的冰箱中。三个小时后水变成了固体冰。请写出所发生的状态变化名称，并说明纯水开始发生该变化的温度。[2分]
Answer & analysis: The change is called freezing (or solidification). Freezing is the process where a liquid turns into a solid. For pure water this occurs at 0 °C – the freezing point. At this temperature the particles lose enough energy that they can no longer slide past one another; they become locked into a fixed, regular arrangement. [2 marks: 1 for 'freezing', 1 for 0 °C]
答案与解析：该变化称为凝固（或冻结）。凝固是液体变为固体的过程。对于纯水，这一过程发生在 0 °C（凝固点）。在这个温度下，粒子失去了足够的能量，不能再互相滑动，而是被固定在规则排列的位置上。[2分：答出“凝固”得1分，答出 0 °C 得1分]
2. Question 2: Particle Model – Solid and Liquid | 问题2：粒子模型——固体与液体
The question: Draw and label particle diagrams to show the arrangement and movement of particles in a solid and in a liquid. Explain why a solid has a definite shape but a liquid takes the shape of its container. [4 marks]
题目：画出并标注粒子示意图，分别展示固体和液体中粒子的排列与运动。解释为何固体有固定形状而液体会取容器的形状。[4分]
Answer & analysis: In a solid diagram, particles should be drawn touching in neat rows (regular arrangement) with small vibration arrows; they cannot move from place to place. In a liquid diagram, particles are close together but randomly arranged; arrows show them sliding past each other. Explanation: solid particles are held in fixed positions by strong forces, giving a definite shape; liquid particles can move and slide, so the liquid flows and fits the container. [1 mark for each correct diagram, 1 for movement arrows, 1 for explanation]
答案与解析：固体图中，粒子应紧挨着排列成整齐的行列（规则排列），并画上表示微小振动的箭头；它们不能移动位置。液体图中，粒子彼此靠近但随机分布，箭头表示它们相互滑动。解释：固体粒子被强作用力固定在原位，因此有固定形状；液体粒子可以移动和滑动，因此液体流动并填满容器。[每张正确图得1分，运动箭头得1分，解释得1分]
3. Question 3: Classifying Elements, Compounds and Mixtures | 问题3：分类元素、化合物和混合物
The question: Look at the list of substances: gold, carbon dioxide, air and table salt (sodium chloride). State whether each one is an element, a compound or a mixture. [4 marks]
题目：观察以下物质清单：金、二氧化碳、空气和食盐（氯化钠）。写出它们各自是元素、化合物还是混合物。[4分]
Answer & analysis: Gold (Au) is an element – it contains only one type of atom. Carbon dioxide (CO₂) is a compound – it contains carbon and oxygen atoms chemically bonded together. Air is a mixture – it is made of different gases (mainly nitrogen, oxygen) that are not chemically joined. Table salt (NaCl) is a compound – sodium and chlorine atoms are chemically bonded. Key tip: an element has one kind of atom; a compound has two or more elements bonded; a mixture has different substances not bonded. [1 mark per correct classification]
答案与解析：金（Au）是元素——只含有一种原子。二氧化碳（CO₂）是化合物——含有通过化学键结合的碳原子和氧原子。空气是混合物——由不同的气体（主要是氮气、氧气）组成，它们彼此没有化学结合。食盐（NaCl）是化合物——钠原子和氯原子通过化学键结合。关键提示：元素只有一种原子；化合物含有两种或以上元素通过化学键结合；混合物含有不同物质但没有结合。[每正确分类一个得1分]
4. Question 4: Physical and Chemical Changes in the Kitchen | 问题4：厨房里的物理变化与化学变化
The question: Melting butter and toasting bread both happen in a kitchen. Explain which one is a physical change and which one is a chemical change. Give a reason for each answer. [4 marks]
题目：融化黄油和烤面包都发生在厨房里。解释哪一个是物理变化，哪一个是化学变化，并分别给出理由。[4分]
Answer & analysis: Melting butter is a physical change. The butter changes from solid to liquid, but no new substance is made; it is still butter. This change is easily reversed by cooling. Toasting bread is a chemical change. The bread turns brown and produces a new smell; new substances are formed (such as from the browning reactions). It cannot be easily reversed. Physical changes are reversible and no new substance forms; chemical changes produce new substances and are usually irreversible. [2 marks for each correct identification with reason]
答案与解析：融化黄油是物理变化。黄油从固体变为液体，但没有产生新物质，它仍然是黄油。这个过程通过冷却可以轻易逆转。烤面包是化学变化。面包变成褐色并产生新的气味；形成了新物质（如褐变反应的产物）。该过程不易逆转。物理变化可逆且不产生新物质；化学变化产生新物质且通常不可逆。[每个正确判断和理由得2分]
5. Question 5: Separation – Filtration | 问题5：分离——过滤
The question: A beaker contains a murky mixture of sand and water. Describe step by step how you would obtain clear water using filtration. Name all the apparatus you would use. [4 marks]
题目：一个烧杯中装有沙子和水的浑浊混合物。请逐步描述如何使用过滤法得到清澈的水，并命名所有使用的仪器。[4分]
Answer & analysis: Step 1: Fold a filter paper and place it inside a filter funnel. Step 2: Put the funnel into the neck of a conical flask or a clean beaker. Step 3: Carefully pour the sand-water mixture into the funnel. The insoluble sand particles (the residue) get trapped on the filter paper, while clear water (the filtrate) passes through and collects in the flask. Apparatus: beaker, filter funnel, filter paper, conical flask (or receiving beaker). Filtration works because the solid particles are too large to pass through the tiny holes in the filter paper. [1 mark for each step and apparatus]
答案与解析：步骤1：将滤纸折叠并放入过滤漏斗中。步骤2：将漏斗放在锥形瓶或干净烧杯的瓶口上。步骤3：小心地将沙水混合物倒入漏斗。不溶的沙粒（残渣）被截留在滤纸上，而清澈的水（滤液）通过滤纸收集在锥形瓶中。所用仪器：烧杯、过滤漏斗、滤纸、锥形瓶（或接收烧杯）。过滤的原理是固体颗粒太大，无法通过滤纸的微小孔隙。[步骤和仪器命名各得1分]
6. Question 6: Obtaining Pure Water – Distillation | 问题6：获得纯水——蒸馏
The question: A science club wants to obtain pure water from a sample of salty seawater. They have a Bunsen burner, a round-bottom flask, a condenser and a beaker. Suggest the best method and explain how it works. [3 marks]
题目：科学俱乐部想从一份咸海水样品中获得纯水。他们有本生灯、圆底烧瓶、冷凝管和一个烧杯。请提出最佳方法并解释其原理。[3分]
Answer & analysis: The best method is simple distillation. Heat the seawater in the round-bottom flask. Water evaporates and turns into steam (water vapour). The steam travels into the cold condenser, where it loses energy and condenses back into liquid pure water, which drips into the beaker. The salt remains in the flask because its boiling point is much higher than water's. Simple distillation separates a liquid from a dissolved solid by boiling and condensation. [1 mark for naming distillation, 1 for evaporation/condensation description, 1 for explaining salt is left behind]
答案与解析：最佳方法是简单蒸馏。用本生灯加热圆底烧瓶中的海水。水蒸发变成水蒸气。蒸气进入冷的冷凝管，失去能量并冷凝回液态纯水，滴入烧杯。盐留在烧瓶中，因为它的沸点远高于水。简单蒸馏通过蒸发和冷凝将液体与溶解的固体分离。[命名蒸馏得1分，描述蒸发/冷凝得1分，解释盐留下得1分]
7. Question 7: Acids and Alkalis – pH and Indicators | 问题7：酸和碱——pH 与指示剂
The question: A student tests cola with universal indicator solution. The colour changes to red-orange. Explain what this result indicates about the drink. Name the ion that makes solutions acidic. [2 marks]
题目：一名学生用通用指示剂溶液测试可乐，颜色变为红橙色。解释该结果表明饮料的什么性质，并说出使溶液呈酸性的离子名称。[2分]
Answer & analysis: The red-orange colour indicates that cola is acidic with a pH around 3–4. Universal indicator shows the whole pH scale: red means strong acid, green means neutral, purple means strong alkali. The ion responsible for acidity is the hydrogen ion (H⁺). Solutions with a higher concentration of H⁺ ions have a lower pH and are more acidic. [1 mark for acidic, 1 mark for H⁺]
答案与解析：红橙色表明可乐是酸性的，pH 值约为 3–4。通用指示剂可显示整个 pH 范围：红色表示强酸，绿色表示中性，紫色表示强碱。导致酸性的离子是氢离子（H⁺）。H⁺ 离子浓度越高的溶液 pH 越低，酸性越强。[答出酸性得1分，答出 H⁺ 得1分]
8. Question 8: Solubility and Saturated Solutions | 问题8：溶解度与饱和溶液
The question: At 25 °C, the solubility of sugar in
Published by TutorHao | Year 7 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