Case Study: Practical Chemistry Exercises | 案例分析：化学实战演练

📚 Case Study: Practical Chemistry Exercises | 案例分析：化学实战演练

Welcome to a hands-on case study designed for Year 8 OCR Chemistry students. In this article, we follow Alex, a curious student, as he investigates everyday chemical mysteries using practical scientific methods. Each section presents a real-life problem and shows how core chemistry concepts—such as states of matter, separation techniques, chemical reactions, acids and alkalis, and material properties—can be applied to solve it. This exercise will not only reinforce your understanding but also develop your experimental reasoning skills.

欢迎参加为OCR八年级化学学生设计的实战案例分析。在本文中，我们将跟随好奇的学生阿历克斯，他运用实用的科学方法调查日常化学之谜。每个部分都呈现一个现实生活中的问题，并展示如何运用核心化学概念——例如物质状态、分离技术、化学反应、酸碱及材料性质——来解决问题。此练习不仅能巩固你的理解，还能培养你的实验推理能力。

1. Identifying the White Powder | 识别白色粉末

Alex finds an unlabelled jar containing a white crystalline powder at home. He wonders if it is table salt (sodium chloride), baking soda (sodium hydrogencarbonate), or sugar (sucrose). To identify it safely, he performs simple tests. First, he checks its solubility in water: all three dissolve, but baking soda dissolves more readily in warm water. He then adds a few drops of vinegar to a small sample. The powder fizzes and produces bubbles, suggesting it is baking soda, because acid reacts with hydrogencarbonate to release carbon dioxide gas. He confirms it is not salt or sugar, as they do not react with vinegar. Additionally, he tastes a tiny amount (safely) and finds it slightly salty and soapy, typical of baking soda.

阿历克斯在家中发现一个没有标签的罐子，里面装着白色结晶粉末。他想知道这是食盐（氯化钠）、小苏打（碳酸氢钠）还是糖（蔗糖）。为了安全地进行鉴别，他进行了简单的测试。首先，他检查了它们在水中的溶解性：三者都能溶解，但小苏打在温水中溶解得更快。接着，他往一小份样品中加入了几滴醋。粉末嘶嘶冒泡，表明这是小苏打，因为酸与碳酸氢盐反应会释放出二氧化碳气体。他确认这不是盐或糖，因为它们不会与醋发生反应。此外，他安全地尝了一点点，发现略带咸味和肥皂味，这是小苏打的典型味道。

The chemical reaction between baking soda and vinegar (acetic acid) can be represented by the word equation: sodium hydrogencarbonate + acetic acid → sodium acetate + water + carbon dioxide.

小苏打与醋（乙酸）之间的化学反应可以用文字方程式表示：碳酸氢钠 + 乙酸 → 乙酸钠 + 水 + 二氧化碳。

sodium hydrogencarbonate + acetic acid → sodium acetate + water + carbon dioxide

碳酸氢钠 + 乙酸 → 乙酸钠 + 水 + 二氧化碳

2. Separating Sand and Salt | 分离沙子和盐

Alex mixed sand and salt together accidentally. To recover the salt, he decides to use the difference in solubility. He adds water to the mixture and stirs. The salt dissolves, but the sand does not. He filters the mixture through filter paper; the sand remains on the paper as residue, while the salt solution passes through as filtrate. He then heats the filtrate gently to evaporate the water, leaving behind white salt crystals. This demonstrates the separation techniques of filtration and evaporation, which exploit physical properties such as solubility and boiling point.

阿历克斯不小心把沙子和盐混在了一起。为了回收盐，他决定利用溶解度的差异。他往混合物中加水并搅拌。盐溶解了，而沙子不溶。他用滤纸过滤混合物；沙子作为残渣留在滤纸上，而盐溶液则作为滤液通过。然后他轻轻加热滤液，蒸发掉水分，留下了白色的盐晶体。这演示了过滤和蒸发这两种分离技术，它们利用了溶解度和沸点等物理性质。

This process involves only physical changes because no new substances are formed. Salt dissolves and then crystallises again, which is reversible.

这个过程只涉及物理变化，因为没有生成新的物质。盐溶解后再结晶，是可逆的。

3. Analysing Ink with Chromatography | 用色谱分析墨水

Alex suspects that a black marker pen ink is actually a mixture of different coloured dyes. He uses paper chromatography to investigate. He draws a small dot of black ink near the bottom of a strip of filter paper and places the end in water. As water travels up the paper, it carries the ink components. Different dyes move at different speeds, separating into spots of blue, red, and yellow. This shows that black ink is a mixture, not a pure substance. The technique separates substances based on their solubility in the solvent and their attraction to the paper.

阿历克斯怀疑一支黑色马克笔的墨水实际上是不同颜色染料的混合物。他用纸色谱法来研究。他在滤纸条的一端靠近底部处画一个小黑点，并将这一端浸入水中。当水沿着纸上升时，会携带墨水成分。不同的染料以不同的速度移动，分离成蓝色、红色和黄色的斑点。这表明黑色墨水是一种混合物，而不是纯净物。该技术根据物质在溶剂中的溶解度以及它们对纸的吸引力来分离物质。

4. Bubbles from Baking Soda and Vinegar | 小苏打和醋的气泡

Alex mixes baking soda (sodium hydrogencarbonate) and vinegar (acetic acid solution) in a cup. The mixture fizzes vigorously, producing lots of bubbles. He tests the gas by holding a lit splint near the mouth of the cup – the flame goes out, confirming the gas is carbon dioxide. This is a chemical reaction that is irreversible. The signs of a chemical reaction observed include gas production, temperature change (the cup feels cooler), and the formation of new substances (sodium acetate, water, and carbon dioxide).

Published by TutorHao | Year 8 Chemistry Revision Series | aleveler.com

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