氧化还原滴定全攻略 | Redox Titration: WJEC Eduqas A-level Chemistry Flashcards

📚 Redox Titration — WJEC Eduqas Chemistry A-level 核心考点 | WJEC Eduqas A-Level Chemistry Core Topic

引言 / Introduction

氧化还原滴定（Redox Titration）是 WJEC Eduqas A-level 化学考试中的高频题型，尤其在 SP PI1.2a 模块中，要求学生掌握从实验设计到数据处理的完整流程。本文基于 PMT Education 官方 Flashcards，拆解核心概念与解题技巧。

Redox titration is a high-frequency topic in the WJEC Eduqas A-level Chemistry specification, particularly in Module SP PI1.2a. Students are expected to master the full workflow from experimental design to data analysis. This guide is based on PMT Education’s official flashcards, breaking down core concepts and exam techniques.

知识点 / Key Points

1️⃣ 什么是氧化还原反应？What is a redox reaction?

氧化还原反应是指氧化和还原同时发生的化学反应——电子在化学物种之间转移，导致氧化态发生变化。记住 OIL RIG：Oxidation Is Loss（失电子），Reduction Is Gain（得电子）。

A redox reaction is one where both oxidation and reduction occur simultaneously — electrons are transferred between chemical species, causing a change in oxidation states. Mnemonic: OIL RIG — Oxidation Is Loss, Reduction Is Gain of electrons.

2️⃣ 如何用简单氧化还原滴定测定铁(II)盐的相对分子质量？Determining Mr of an iron(II) salt

步骤：①将铁(II)盐配制成标准溶液；②用已知浓度的高锰酸钾(KMnO₄)滴定；③MnO₄⁻ 将 Fe²⁺ 氧化为 Fe³⁺；④记录所用 KMnO₄ 体积 → 结合反应方程式计算摩尔数 → 求出相对分子质量。

Steps: (i) Prepare a standard solution of the iron(II) salt; (ii) Titrate with a known concentration of potassium manganate(VII); (iii) MnO₄⁻ oxidises Fe²⁺ to Fe³⁺; (iv) Use the titre volume and the overall reaction equation to calculate moles of the iron(II) salt, then determine its relative molecular mass.

3️⃣ MnO₄⁻ / Fe²⁺ 反应中哪个被氧化？哪个被还原？Which species is oxidised/reduced?

高锰酸钾(KMnO₄) 被还原（它充当氧化剂）—— Mn 从 +7 降到 +2。
铁(II)盐 被氧化—— Fe 从 +2 升到 +3。

Potassium manganate(VII) is reduced (acts as the oxidising agent) — Mn goes from +7 to +2. The iron(II) salt is oxidised — Fe goes from +2 to +3.

4️⃣ 半反应方程 / Half Equations

还原半反应 (Reduction): MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O
氧化半反应 (Oxidation): Fe²⁺ → Fe³⁺ + e⁻
总离子方程: MnO₄⁻ + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O

5️⃣ 实验中为什么不需要外加指示剂？Why no indicator is needed?

KMnO₄ 自身呈深紫色，Mn²⁺ 近乎无色——滴定终点时，过量的第一滴 KMnO₄ 使溶液呈现持久粉红色，即为自指示剂 (self-indicator)。这一特性极大简化了实验操作。

KMnO₄ is deep purple while Mn²⁺ is almost colourless — at the endpoint, the first excess drop of KMnO₄ turns the solution a persistent pale pink. KMnO₄ acts as its own indicator (self-indicator), greatly simplifying the procedure.

学习建议 / Study Tips

• 🔁 反复练习 半反应配平（酸性条件下 O 用 H₂O 补，H 用 H⁺ 补）
• 📐 掌握摩尔比计算：1 mol MnO₄⁻ ↔ 5 mol Fe²⁺
• 📝 刷题时重点关注 AQA & WJEC 近五年真题中的滴定计算题
• 🧪 理解实验操作细节：酸化的必要性（避免 MnO₂ 沉淀）、弯月面读数

— Practice balancing half-equations in acidic conditions; master the 1:5 MnO₄⁻ to Fe²⁺ ratio; focus on recent past paper titration calculations from AQA & WJEC; understand why acidification is essential (prevents MnO₂ precipitate).

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