📚 Year 10 Eduqas Chemistry: Case Study Practical Exercises | Year 10 Eduqas 化学：案例分析实战演练
In GCSE Chemistry, case study questions test your ability to apply theoretical knowledge to real or simulated laboratory scenarios. This article guides you through a detailed practical exercise focused on determining the purity of calcium carbonate in an antacid tablet using back titration. By working through each step, you will strengthen your skills in stoichiometric calculations, mole concepts, and evaluation of experimental methods.
在 GCSE 化学中，案例分析题考察你将理论知识应用于真实或模拟实验场景的能力。本文将带你详细完成一项实践练习——通过返滴定法测定抗酸药片中碳酸钙的纯度。逐步分析每一步，你将巩固化学计量计算、摩尔概念以及实验方法评价能力。
1. The Scenario: Analysing an Antacid Tablet | 案例场景：分析抗酸药片
A student is given a white antacid tablet labelled to contain calcium carbonate (CaCO₃) as the active ingredient. The task is to determine the percentage purity of CaCO₃ in the tablet. The student decides to use the back titration method: the tablet is reacted with a known excess of hydrochloric acid, and the leftover acid is titrated with standard sodium hydroxide solution.
一位学生拿到一片白色抗酸药片，标签标明有效成分为碳酸钙（CaCO₃）。任务是要测定药片中 CaCO₃ 的纯度百分比。学生决定采用返滴定法：让药片与已知过量的盐酸反应，然后用标准氢氧化钠溶液滴定剩余酸。
tion, the mixture is transferred to a 250 cm³ volumetric flask and made up to the mark with distilled water. A 25.0 cm³ portion of this solution is titrated against 0.100 mol dm⁻³ NaOH, using methyl orange as indicator. The average titre of NaOH is 17.00 cm³.
记录数据如下：药片质量 = 0.400 g；加入 1.00 mol dm⁻³ HCl 体积 = 25.0 cm³；反应后，混合物转移至 250 cm³ 容量瓶，用蒸馏水定容至刻度。取出 25.0 cm³ 该溶液，以甲基橙为指示剂，用 0.100 mol dm⁻³ NaOH 滴定。NaOH 平均消耗量为 17.00 cm³。
2. Why Use a Back Titration? | 为何使用返滴定？
Direct titration of CaCO₃ with acid is difficult because the solid sample may not dissolve completely or the reaction may be slow. By adding excess acid and then determining how much acid remains, we can calculate the exact amount that reacted with the carbonate. This indirect method improves accuracy and is widely used for insoluble or impure substances.
直接用酸滴定 CaCO₃ 比较困难，因为固体样品可能无法完全溶解或反应较慢。通过加入过量的酸，再测定剩余酸的量，就可以准确计算出与碳酸盐反应的酸量。这种间接方法提高了准确性，广泛用于不溶或不纯的物质。
3. Experimental Procedure Overview | 实验步骤概述
The key steps are: (1) Crush the tablet and weigh accurately. (2) Add the powder to a conical flask and pipette 25.0 cm³ of 1.00 mol dm⁻³ HCl. (3) Swirl until no more bubbles are seen, indicating complete reaction. (4) Transfer the solution and washings into a 250 cm³ volumetric flask, then fill to the calibration mark. (5) Pipette 25.0 cm³ of the diluted solution into a clean flask, add a
Published by TutorHao | Year 10 Chemistry Revision Series | aleveler.com
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