📚 AQA A Level Chemistry Unit 4 June 2022 Mark Scheme: Examiner Insights | AQA A Level 化学第四单元 2022年6月评分方案：考官解析
The June 2022 AQA A Level Chemistry Unit 4 mark scheme is more than a list of answers; it is a map of exactly where candidates gain and lose marks. This article breaks down the key topics, common errors and examiner expectations so you can revise precisely.
2022年6月 AQA A Level 化学第四单元评分方案不仅仅是一份答案清单，更是一张精确标明考生得分与失分点的地图。本文剖析核心主题、常见错误与考官期望，帮助你精准复习。
1. Why the Mark Scheme Is Your Best Revision Tool | 为什么评分方案是你最好的复习工具
Many students complete past papers and check the final answer only. The June 2022 Unit 4 mark scheme reveals that within a 4-mark calculation, each step corresponds to a specific mark. If you miss a step, you lose a mark even if the final answer is close.
许多学生做完历年真题后只核对最终答案。2022年6月第四单元评分方案显示，在一道4分计算题中，每一步骤对应一个具体得分点。如果跳步，即使最终答案接近也会失分。
Use the mark scheme to build a 'mark by mark' habit: state the expression, convert to concentrations, substitute, calculate, and add units.
利用评分方案养成“逐分”习惯：写出表达式、换算为浓度、代入、计算并加上单位。
2. Command Words Decoded in Unit 4 | 第四单元指令词解析
AQA Unit 4 mark schemes are driven by command words. 'State' requires no working; 'explain' requires a scientific reason; 'calculate' requires full substitution; 'draw' requires accurate curly arrows and charges.
AQA 第四单元评分方案以指令词为核心。‘State’不需要过程；‘explain’需要科学原因；‘calculate’需要完整代入；‘draw’需要准确的弯箭头和电荷。
| Command word | What the mark scheme wants | Common error |
|---|---|---|
| State | A short factual answer, no justification | Wasting time on explanation |
| Explain | A scientific reason, often linked to collision theory or Le Chatelier | Giving a description without a reason |
| Calculate | Clear substitution into a formula and a final answer with units | Missing units or rounding too early |
| Draw | Accurate curly arrows, lone pairs and charges | Using single-headed arrows for pair movement |
3. Kinetics: Rate Equations and Orders | 动力学：速率方程与反应级数
In June 2022 Unit 4, rate questions typically ask you to use initial rates data to determine the order with respect to each reactant and write the rate equation. The mark scheme awards one mark for a clear comparison between two experiments, one mark for each correct order, and one mark for the rate constant with its units.
在2022年6月第四单元中，速率题通常要求利用初始速率数据确定各反应物的级数并写出速率方程式。评分方案为清晰的实验对比给1分，每个正确级数给1分，速率常数及其单位给1分。
For a reaction where A is first order and B is second order, the rate equation and units are shown below.
若反应中 A 为一级、B 为二级，则速率方程及单位如下所示。
rate = k[A][B]²
units of k = mol⁻² dm⁶ s⁻¹
Always compare experiments where only one concentration changes, so the effect on rate is isolated cleanly. The mark scheme does not give credit for guessing orders from a single experiment.
始终比较只改变一个浓度的实验组，这样才能干净地隔离对速率的影响。评分方案不会给从单个实验中猜测级数的做法任何分数。
4. Equilibrium: Kc and Kp | 平衡：Kc 与 Kp
Equilibrium questions in the Unit 4 mark scheme reward two things: the equilibrium expression and the use of equilibrium concentrations or partial pressures. A common mistake is to forget that Kp uses mole fractions multiplied by total pressure, not moles directly.
第四单元评分方案中的平衡题奖励两点：平衡表达式以及平衡浓度或分压的使用。常见错误是忘记 Kp 使用摩尔分数乘以总压，而不是直接使用摩尔数。
Kc is written as product concentrations multiplied together divided by reactant concentrations multiplied together, each raised to the power of its balancing number. Units for Kc depend on the change in the number of gas molecules.
Kc 写为生成物浓度相乘再除以反应物浓度相乘，每项浓度以其化学计量数为指数。Kc 的单位取决于气体分子数的变化。
pressure is given, the mark scheme usually gives one mark for calculating mole fractions and one mark for substituting into the Kp expression.
对于 Kp，使用分压 = 摩尔分数 × 总压。若给出总压，评分方案通常给计算摩尔分数1分，给代入 Kp 表达式1分。
5. Acids, Bases and Buffers | 酸、碱与缓冲溶液
Buffer questions are high-yield in Unit 4. The June 2022 mark scheme typically gives marks for identifying the weak acid and its conjugate base, writing the Ka expression, calculating [H⁺] using the acid-to-salt ratio,
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