📚 AQA A-level Chemistry Insert 5 (Jan 2022): Standard Electrode Potentials and Data Booklet Skills | AQA A级化学2022年1月第五插入表：标准电极电势与数据手册技能
The January 2022 AQA A-level Chemistry data booklet includes an insert that many students underuse: Insert 5, which gives standard electrode potentials for a wide range of half-reactions. This page is not just a list of numbers — it is a powerful tool for predicting redox feasibility, calculating cell EMF, comparing oxidising and reducing agents, and justifying whether a reaction can occur under standard conditions.
2022年1月的AQA A级化学数据手册中包含一份许多学生没有充分利用的插入表：第五插入表给出了大量半反应的标准电极电势。这一页不仅仅是一串数字，它是预测氧化还原反应可行性、计算电池电动势、比较氧化剂和还原剂强弱以及判断反应在标准条件下能否发生的有力工具。
1. What Is Insert 5? | 什么是第五插入表？
In the January 2022 AQA A-level Chemistry examination series, Insert 5 is the section of the data booklet devoted to standard electrode potentials, E⦵. Each entry is a reduction half-reaction written with the oxidised form on the left, the reduced form on the right, and the standard electrode potential quoted in volts.
在2022年1月的AQA A级化学考试系列中，第五插入表是数据手册专门给出标准电极电势 E⦵ 的部分。每个条目都是一个还原半反应，左侧为氧化态，右侧为还原态，标准电极电势以伏特为单位列出。
For example, the half-reaction for zinc is written as:
例如，锌的半反应写作：
Zn²⁺ + 2e⁻ ⇌ Zn E⦵ = −0.76 V
The reduction direction is always used, even when the half-reaction acts as an oxidation in the cell. This convention is essential because all E⦵ values are measured relative to the standard hydrogen electrode.
即使半反应在电池中实际发生氧化，表格仍然使用还原方向。这一规则至关重要，因为所有 E⦵ 值都是以标准氢电极为参比测得的。
2. Standard Conditions and the E⦵ Symbol | 标准条件与 E⦵ 符号
The superscript ⦵ tells you that the value refers to standard conditions: a temperature of 298 K, a pressure of 100 kPa, and all ion solutions at a concentration of 1.00 mol dm⁻³. If conditions change, the measured potential also changes.
上标 ⦵ 表示该数值对应标准条件：温度 298 K、压强 100 kPa、所有离子溶液浓度均为 1.00 mol dm⁻³。如果条件改变，测得的电势也会改变。
Standard electrode potentials are measured against the standard hydrogen electrode, which is assigned a potential of 0.00 V. The hydrogen half-reaction is:
标准电极电势以标准氢电极为参比，其电势被规定为 0.00 V。氢的半反应为：
2H⁺ + 2e⁻ ⇌ H₂ E⦵ = 0.00 V
When you use Insert 5, assume that all species are in their standard states unless the question says otherwise.
使用第五插入表时，除非题目另有说明，默认所有物质都处于标准状态。
3. Reading the Table Correctly | 正确阅读表格
Every row in Insert 5 has the same layout: the oxidised form gains electrons to become the reduced form. The more positive the E⦵ value, the more readily the oxidised form is reduced — it is a stronger oxidising agent. The more negative the E⦵ value, the more readily the reduced form is oxidised — it is a stronger reducing agent.
第五插入表中每一行的结构相同：氧化态得到电子变成还原态。E⦵ 值越正，氧化态越容易被还原，即它是越强的氧化剂。E⦵ 值越负，还原态越容易被氧化，即它是越强的还原剂。
For instance, fluorine has a very positive E⦵ of +2.87 V, so F₂ is an extremely strong oxidising agent. Lithium has a very negative E⦵ of −3.04 V, so Li is a very strong reducing agent.
例如，氟的 E⦵ 为 +2.87 V，正值很大，因此 F₂ 是极强的氧化剂。锂的 E⦵ 为 −3.04 V，负值很大，因此 Li 是极强的还原剂。
4. The Electrochemical Series | 电化学序列
Arranging the half-reactions from the most negative E⦵ to the most positive E⦵ produces the electrochemical series. This series allows you to compare the relative strengths of oxidising and reducing agents without memorising individual values.
将半反应按 E⦵ 从最负到最正排列，就得到电化学序列。该序列可以让你在不逐条记忆数值的情况下比较氧化剂和还原剂的相对强弱。
A species on the left of a lower half-reaction can oxidise the species on the right of a higher half-reaction. In other words, the more positive oxidised form takes electrons from the more negative reduced form.
较低半反应左侧的物质可以氧化较高半反应右侧的物质。换句话说，E⦵ 较正的氧化态从 E⦵ 较负的还原态夺取电子。
This is the basis for predicting whether a redox reaction is feasible when the two half-reactions are combined.
这是将两个半反应组合后预测氧化还原反应是否可行的基础。
5. Calculating Cell EMF | 计算电池电动势
For a full cell, the standard cell potential is calculated using the formula:
对于完整电池，标准电池电动势使用以下公式计算：
E⦵(cell) = E⦵(reduced half-reaction) − E⦵(oxidised half-reaction)
The reduced half-reaction is the one with the more positive E⦵ value; it runs in the reduction direction at the cathode. The oxidised half-reaction is the one with the more negative E⦵ value; it runs in the oxidation direction at the anode.
还原半反应是 E⦵ 值较正的那个，在阴极按还原方向进行。氧化半反应是 E⦵ 值较负的那个，在阳极按氧化方向进行。
Always subtract the oxidation potential from the reduction potential. Do not add the two values unless you have already reversed the sign of the oxidation half-reaction.
始终用还原电势减去氧化电势。除非你已经将氧化半反应的符号取反，否则不要直接把两个数值相加。
6. Predicting Feasibility | 预测可行性
A redox reaction is thermodynamically feasible under standard conditions if the calculated E⦵(cell) is positive. If E⦵(cell) is negative, the reaction is not feasible in the forward direction, but the reverse reaction may be feasible.
在标准条件下，如果计算得到的 E⦵(cell) 为正，则氧化还原反应在热力学上可行。如果 E⦵(cell) 为负，则正方向反应不可行，但逆反应可能可行。
If E⦵(cell) is zero, the system is at equilibrium under standard conditions. In exam questions, you should state clearly which sign indicates feasibility and link it back to the direction written in the equation.
如果 E⦵(cell) 为零，则体系在标准条件下处于平衡状态。在考试题目中，应清楚说明哪个符号表示可行，并将其与方程式中书写方向联系起来。
7. Worked Example: The Zinc–Copper Cell | 示例：锌铜电池
Consider a cell made from Zn²⁺/Zn and Cu²⁺/Cu. From Insert 5:
考虑由 Zn²⁺/Zn 和 Cu²⁺/Cu 组成的电池。由第五插入表：
Zn²⁺ + 2e⁻ ⇌ Zn E⦵ = −0.76 V
Cu²⁺ + 2e⁻ ⇌ Cu E⦵ = +0.34 V
The copper half-reaction has the more positive E⦵, so it is the reduction at the cathode. The zinc half-reaction is reversed and becomes the oxidation at the anode. The cell potential is:
铜半反应的 E⦵ 较正，因此它在阴极发生还原。锌半反应被反转，在阳极发生氧化。电池电动势为：
E⦵(cell) = +0.34 − (−0.76) = +1.10 V
ue confirms that the reaction Zn + Cu²⁺ → Zn²⁺ + Cu is feasible under standard conditions.
正值证实了反应 Zn + Cu²⁺ → Zn²⁺ + Cu 在标准条件下可行。
8. Worked Example: Disproportionation of Cu(I) | 示例：Cu(I) 的歧化反应
Disproportionation occurs when the same species is both oxidised and reduced. Copper(I) is a classic example. Two relevant half-reactions appear in Insert 5:
当同一物质同时被氧化和被还原时，就发生歧化反应。铜(I) 是一个经典例子。第五插入表中给出了两个相关半反应：
Cu²⁺ + e⁻ ⇌ Cu⁺ E⦵ = +0.15 V
Cu⁺ + e⁻ ⇌ Cu E⦵ = +0.52 V
For disproportionation, the Cu⁺ ion on the right of the first half-reaction is oxidised to Cu²⁺, and the Cu⁺ ion on the left of the second half-reaction is reduced to Cu. Subtract the oxidation potential from the reduction potential:
对于歧化反应，第一个半反应右侧的 Cu⁺ 被氧化为 Cu²⁺，第二个半反应左侧的 Cu⁺ 被还原为 Cu。用还原电势减去氧化电势：
E⦵(cell) = +
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