📚 AQA A Level Chemistry Unit 4 Insert Jan20: Data Sheet and Exam Guide | AQA A Level 化学 Unit 4 Jan20 插页：数据表与考试指南
The AQA A Level Chemistry Unit 4 insert from January 2020 is a compact data booklet issued with the question paper. It contains the periodic table, key equations, and spectral reference data. This guide explains how to use every section accurately and avoid common mistakes under exam pressure.
AQA A Level 化学 Unit 4 2020 年 1 月考试的插页是一本随卷提供的紧凑数据手册，包含周期表、关键公式和光谱参考数据。本指南将讲解如何在考试压力下准确使用每一部分，并避免常见错误。
1. What the Insert Contains | 插页包含什么
The Jan20 Unit 4 insert is not a mark scheme. It gives reference values that help you answer calculations and spectroscopy questions. You still need to learn key definitions and methods, but you can look up constants, pKa values, equilibrium expressions, and spectral ranges during the exam.
Jan20 Unit 4 插页不是评分标准。它提供参考数值，帮助你完成计算和光谱题。你仍然需要掌握关键定义和方法，但考试中可以查阅常数、pKa 值、平衡表达式和光谱范围。
- Periodic table: atomic numbers, relative atomic masses, and element symbols.
- Useful formulae: pH, Kw, Ka, Kc, Kp, rate equations, and the Arrhenius equation.
- Spectroscopic data: proton NMR shifts, carbon-13 NMR shifts, and IR absorption ranges.
- Constants: R = 8.31 J K⁻¹ mol⁻¹, standard pressure = 100 kPa.
- 周期表：原子序数、相对原子质量和元素符号。
- 常用公式：pH、Kw、Ka、Kc、Kp、速率方程和阿伦尼乌斯方程。
- 光谱数据：质子 NMR 位移、碳-13 NMR 位移和红外吸收范围。
- 常数：R = 8.31 J K⁻¹ mol⁻¹，标准压力 = 100 kPa。
Use the insert as a checklist, not as a replacement for knowing how to set up a calculation. Before you begin a question, identify which table or constant is relevant and underline the unit given.
把插页当作检查清单，而不是替代你知道如何列出计算式的工具。开始做题前，先确定哪张表或哪个常数相关，并在给出的单位下划线。
2. Periodic Table and Relative Atomic Masses | 周期表与相对原子质量
tains C, H, O, and N, read C = 12.0, H = 1.0, O = 16.0, N = 14.0 directly from the insert.
插页中的周期表给出的相对原子质量保留一位小数。使用这些数值进行摩尔质量计算。例如，如果有机物含有 C、H、O、N，直接从插页读取 C = 12.0、H = 1.0、O = 16.0、N = 14.0。
Do not round too early. Keep at least three significant figures in intermediate steps, then round only the final answer to the precision shown in the question. If the insert gives an atomic mass of 35.5 for Cl, use 35.5, not 35 or 36.
不要过早四舍五入。中间步骤至少保留三位有效数字，最后才按题目要求保留精度。如果插页给出 Cl 的相对原子质量为 35.5，就使用 35.5，不是 35 或 36。
A common Unit 4 task is to convert mass to moles, then use an equation to find an equilibrium yield or reaction rate. Always show the molar mass calculation line so examiners can see you have used the insert correctly.
Unit 4 常见任务是先把质量换算成摩尔，再用方程式求平衡产率或反应速率。始终写出摩尔质量计算步骤，让阅卷老师看到你正确使用了插页。
3. Key Formulas and Constants | 关键公式与常数
The insert contains the main equation sheet for Unit 4. You must choose the correct form of each equation and convert units consistently. The table below summarises the most frequently used relationships.
插页包含 Unit 4 的主要公式表。你必须选择每个方程的正确形式，并统一换算单位。下表总结了最常用的关系式。
| Quantity | Equation | Notes |
|---|---|---|
| pH | pH = -log₁₀[H⁺] | [H⁺] in mol dm⁻³ |
| Ionic product of water | Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ mol² dm⁻⁶ at 298 K | Only at 298 K |
| pKa | pKa = -log₁₀Ka | Ka in mol dm⁻³ |
| Weak acid Ka expression | Ka = [H⁺][A⁻] / [HA] | For HA ⇌ H⁺ + A⁻ |
| Kc | Kc = [products] / [reactants] | Powers equal stoichiometric coefficients |
| Kp | Kp = partial pressures of products / reactants | Partial pressure = mole fraction × total pressure |
| Arrhenius equation | ln k = -Ea/(RT) + ln A | R = 8.31 J K⁻¹ mol⁻¹, T in K |
| Rate equation | rate = k[A]m[B]n | m and n come from experiment, not coefficients |
Always write the equation first, then substitute values with units. In equilibrium questions, the insert gives the form of Kc or Kp, but you must build the expression from the specific chemical equation.
始终先写公式，再代入带单位的数值。在平衡题中，插页给出了 Kc 或 Kp 的形式，但你必须根据具体化学方程式构建表达式。
4. pH and Buffer Calculations | pH 与缓冲溶液计算
equals the acid concentration, so pH = -log₁₀[H⁺]. For a weak acid, use the approximation [H⁺] = √Ka × [HA] when the acid is only slightly dissociated.
Unit 4 计算题大多依赖插页中的 pH 和缓冲公式。对于一元强酸，[H⁺] 等于酸浓度，因此 pH = -log₁₀[H⁺]。对于弱酸，当酸仅少量解离时，使用近似公式 [H⁺] = √Ka × [HA]。
For buffer solutions, the key equation is:
对于缓冲溶液，关键公式为：
[H⁺] = Ka × [HA] / [A⁻]
Work out moles of HA and A⁻ after any added acid or base has reacted, then divide by the total volume. Since volume cancels in the ratio, you can often use moles directly.
先计算加入酸或碱反应后 HA 和 A⁻ 的摩尔数，再除以总体积。由于体积在比值中抵消，通常可以直接使用摩尔数。
In alkaline solution, calculate [H⁺] by dividing Kw by [OH⁻]: [H⁺] = Kw / [OH⁻] ol² dm⁻⁶ at 298 K. If the question gives a different temperature, use the value provided in the insert or question.
在碱性溶液中，用 Kw 除以 [OH⁻] 计算 [H⁺]：[H⁺] = Kw / [OH⁻]。请记住 Kw 仅在 298 K 时为 1
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