A-Level Chemistry: Reactivity of Metals & Displacement Reactions | 金属活动性与置换反应详解

Introduction | 引言

The reactivity series of metals is a cornerstone of A-Level Chemistry. Understanding why some metals displace others from their compounds — and how to investigate this experimentally — is essential for exam success. This guide walks you through the core concepts, experimental design, and key exam techniques.

金属活动性顺序是 A-Level 化学的基石。理解为什么某些金属能从化合物中置换出其他金属，以及如何通过实验探究这一现象，对考试成功至关重要。本文带你梳理核心概念、实验设计和关键答题技巧。

1. Understanding the Reactivity Series | 理解金属活动性顺序

The reactivity series ranks metals by their tendency to lose electrons and form positive ions. Key order for A-Level:

More reactive metals lose electrons more readily and can displace less reactive metals from their compounds. A classic investigation tests this by mixing metal powders with metal sulfate solutions and observing reactions.

越活泼的金属越容易失去电子，能从化合物中置换出较不活泼的金属。经典探究实验是将金属粉末与金属硫酸盐溶液混合，观察反应。

2. Experimental Design: Key Variables | 实验设计：关键变量

Exam tip: The dependent variable is what you measure or observe — in this case, whether a reaction occurred. The independent variable is what you change — the type of metal.

考试技巧：因变量是你测量或观察的内容——此处为是否发生反应。自变量是你改变的内容——金属种类。

3. Observations That Indicate a Reaction | 反应发生的观察指标

When zinc reacts with copper sulfate (Zn + CuSO₄ → ZnSO₄ + Cu), you can observe:

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• Colour change: Blue CuSO₄ solution fades as Cu²⁺ ions are reduced to copper metal.
• Solid deposit: A reddish-brown coating of copper metal forms on the zinc.
• Temperature change: The displacement reaction is exothermic — the solution warms up.

当锌与硫酸铜反应时（Zn + CuSO₄ → ZnSO₄ + Cu），可观察到：蓝色 CuSO₄ 溶液褪色（Cu²⁺ 被还原为铜金属）；锌表面出现红棕色铜金属沉积；置换反应放热，溶液温度升高。

4. Determining Reactivity Order from Results | 从实验结果确定活动性顺序

Using the student’s results table:

Rule: A metal can only displace a less reactive metal from its salt solution. From the table:

• Mg displaces Zn from ZnSO₄ → Mg > Zn
• Zn displaces Cu from CuSO₄ → Zn > Cu
• Therefore: Mg > Zn > Cu (Most reactive → Least reactive)

规则：金属只能从盐溶液中置换出活泼性低于自己的金属。从表中得出：Mg 从 ZnSO₄ 置换 Zn → Mg > Zn；Zn 从 CuSO₄ 置换 Cu → Zn > Cu；因此：Mg > Zn > Cu（最活泼 → 最不活泼）。

5. Safety: Why Not Use Sodium? | 安全：为什么不用钠？

Sodium is too reactive for this investigation:

• Sodium reacts violently with water (including water in solutions), producing hydrogen gas and heat.
• The reaction is dangerously fast and can cause splashing of hot, corrosive NaOH.
• Sodium must be stored under oil and handled with extreme caution — unsuitable for a standard bench investigation.
• Equation: 2Na + 2H₂O → 2NaOH + H₂ ↑

钠过于活泼不适合此实验：钠与水（包括溶液中的水）剧烈反应产生氢气和热量；反应速度极快可能导致灼热的苛性钠飞溅；钠必须在油中保存并极其小心地操作——不适合常规实验台实验。反应方程式：2Na + 2H₂O → 2NaOH + H₂ ↑

Study Tips | 学习建议

✅ Memorise the reactivity series — it’s fundamental to electrochemistry, extraction methods, and redox.
✅ Practice identifying independent, dependent, and control variables in any experimental design question.
✅ Learn the observable signs of a chemical reaction: colour change, gas production, temperature change, precipitate formation.
✅ Be ready to justify reactivity order from experimental data — this is a common data-analysis question.
✅ Always consider safety when selecting reagents — highly reactive metals like Group 1 elements are hazardous in aqueous investigations.

✅ 熟记金属活动性顺序——它是电化学、金属提取方法和氧化还原的基础。
✅ 练习在任何实验设计题中识别自变量、因变量和控制变量。
✅ 掌握化学反应的观察指标：颜色变化、气体产生、温度变化、沉淀生成。
✅ 准备好从实验数据推断活动性顺序——这是常见的数据分析题。
✅ 选择试剂时始终考虑安全——第一主族等高度活泼金属在水溶液实验中具有危险性。

Source: Reactivity-of-Metals-1-QP.pdf | Physics & Maths Tutor | A-Level Chemistry Past Paper

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