📚 AQA 9620 CH03 2016 Mark Scheme Q2: Practical Analysis Made Simple | AQA 9620 CH03 2016 评分方案第 2 题：实验分析轻松拿分
Question 2 in the AQA 9620 CH03 2016 mark scheme is a classic practical-analysis question. It takes a student investigation and asks you to calculate results, comment on uncertainty, identify anomalies, and evaluate the method. This article breaks down the exact skills examiners rewarded so you can answer quickly and accurately.
在 AQA 9620 CH03 2016 年评分方案中，第 2 题是一道典型的实验分析题。题目给出学生的实验调查，要求你计算实验结果、讨论不确定度、识别异常值并评价实验方法。本文拆解阅卷老师给分的具体技能，帮助你快速、准确地作答。
1. What Q2 in CH03 2016 Tests | 第 2 题考查什么
In the AQA International A-Level Chemistry 9620, Unit 3 (CH03) focuses on practical and investigative skills. Question 2 in the 2016 mark scheme is usually a data-analysis and evaluation item. It often presents repeated measurements from a titration, calorimetry or rate experiment, then asks you to process the data and judge the quality of the procedure.
在 AQA 国际 A-Level 化学 9620 中，第 3 单元（CH03）侧重考查实验与探究技能。2016 年评分方案中的第 2 题通常属于数据分析与评价题。题目往往给出滴定、量热或速率实验中的多次测量数据，然后要求你处理数据并评价实验方案的质量。
Examiners look for precise calculations, correct significant figures, valid reasons for anomalies, and evaluation points that link to the method. Generic statements such as 'be more careful' do not score.
阅卷老师关注计算是否精确、有效数字是否正确、异常值的原因是否合理，以及评价是否与具体方法相关。像 "更小心操作" 这类空泛表述不得分。
2. Reading the Results Table Like an Examiner | 像考官一样阅读数据表
Before calculating, scan the table for anomalous values and rough trials. In the 2016 CH03 Q2, a common mark is given for identifying that the first run is a rough trial, or that two titres are not concordant because they differ by more than 0.10 cm³.
计算前先快速检查表格中的异常值和粗滴定。在 2016 年 CH03 第 2 题中，常见给分点是识别出第一次实验是粗滴定，或两次滴定体积相差超过 0.10 cm³ 因而不重合。
Always subtract the initial burette reading from the final burette reading. Check that all readings are given to two decimal places, as expected from a burette.
务必用滴定管末读数减去初读数。检查所有读数是否保留两位小数，因为滴定管读数通常要求记录到两位小数。
| Run | Final / cm³ | Initial / cm³ | Titre / cm³ | Comment |
| 1 | 25.10 | 0.00 | 25.10 | Rough trial - discard |
| 2 | 49.95 | 25.10 | 24.85 | Concordant |
| 3 | 24.90 | 0.05 | 24.85 | Concordant |
| 4 | 49.80 | 24.90 | 24.90 | Within 0.10 cm³ - use |
3. Titre Calculations: Final Minus Initial | 滴定体积计算：末读数减初读数
Every titre is a subtraction, and one arithmetic slip loses the rest of the question. Write the subtraction on the paper next to the table so the examiner can see your working.
每一个滴定体积都是一次减法，一处算错就会连带丢掉后面所有分。把减法过程写在表格旁边，让阅卷老师看得见你的思路。
Titre = final burette reading − initial burette reading
5 cm³. If your answer keeps one decimal place only, you have probably miscopied a reading.
上表第 2 次：49.95 − 25.10 = 24.85 cm³；第 3 次：24.90 − 0.05 = 24.85 cm³。如果你的答案只有一位小数，很可能是抄错读数了。
4. Choosing Concordant Results and the Mean Titre | 选取重合值并计算平均滴定体积
Concordant titres are those within 0.10 cm³ of each other. Only concordant values are averaged, and the rough trial is always excluded from the mean.
重合值是指彼此相差不超过 0.10 cm³ 的滴定体积。只有重合值才用于取平均，而粗滴定永远不参与平均计算。
Mean titre = sum of concordant titres ÷ number of concordant titres
decimal places. Giving the mean to the same precision as the readings is a standard mark.
根据上表：（24.85 + 24.85 + 24.90）÷ 3 = 74.60 ÷ 3 = 24.87 cm³，保留两位小数。把平均值保留到与原始读数相同的小数位，是标准给分点。
5. Significant Figures and Units | 有效数字与单位
AQA expects the final answer to match the precision of the data, and units must always be stated. Titre volumes are in cm³, concentrations in mol dm⁻³, and enthalpy changes in kJ mol⁻¹.
AQA 要求最终答案与数据的精度相匹配，并且必须写出单位。滴定体积单位是 cm³，浓度单位是 mol dm⁻³，焓变单位是 kJ mol⁻¹。
00. Then moles = concentration × volume in dm³, and concentration = moles ÷ volume in dm³.
若要把 cm³ 换算成 dm³，需除以 1000。随后：物质的量 = 浓度 × 体积（dm³）；浓度 = 物质的量 ÷ 体积（dm³）。
n = c × V (dm³) ⇌ c = n ÷ V (dm³)
, for example H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O, so 1 mol of acid reacts with 2 mol of alkali.
遇到摩尔比步骤时，要依据配平方程式，例如 H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O，即 1 mol 酸与 2 mol 碱反应。
6. Handling Uncertainty and Percentage Error | 处理不确定度与百分误差
e is usually read to ± 0.05 cm³, and a two-reading titration therefore carries ± 0.10 cm³.
评分方案鼓励你写出仪器的不确定度。滴定管通常读到 ± 0.05 cm³，因此一次滴定包含两次读数，总不确定度为 ± 0.10 cm³。
Percentage uncertainty = (uncertainty ÷ measured value) × 100
For a mean titre of 24.87 cm³: (0.10 ÷ 24.87) × 100 = 0.40 % e percentage uncertainty, which is why examiners like the routine of repeating titrations.
以平均滴定体积 24.87 cm³ 为例：（0.10 ÷ 24.87）× 100 = 0.40 %，保留两位有效数字。滴定体积越小，百分不确定度越大，这正是考官推崇重复滴定的原因。
(± 0.5 °C) is far more damaging, because the temperature rise is often only a few degrees.
在量热实验中，温度计的不确定度（± 0.5 °C）影响更大，因为温度升高往往只有几摄氏度。
7. Spotting and Explaining Anomalies | 识别并解释异常值
An anomaly is a value that lies outside the concordant range and cannot be explained by random error alone. You must state it and then give a specific cause.
异常值是超出重合范围、且无法仅用随机误差解释的数据。你既要指出它是异常值，还要给出具体原因。
- An air bubble in the burette jet before the run, which escapes during titration.｜滴定前滴定管尖嘴内有气泡，滴定过程中气泡逸出。
- Overshooting the end-point so too much titrant was added.｜终点滴过，加入的滴定剂过量。
- Reading the burette from the wrong angle, causing parallax error.｜视线角度不对，产生视差误差。
- In calorimetry, heat lost because the lid was left off or the reaction was slow.｜量热时未盖盖子或反应过慢，导致热量损失。
'Human error' on its own is not an acceptable explanation. Name the error and say how it changes the value.
只写 "人为误差" 不能得分。必须点明误差名称，并说明它如何改变测量值。
8. Evaluation Points That Link to the Method | 与实验方法挂钩的评价要点
Evaluation marks depend on identifying a genuine limitation of the given procedure. Weak points in a titration include judging the colour change of the indicator, using a washed but not rinsed burette, and using too small a titre volume.
评价分取决于你能否指出给定方案中真实存在的局限。滴定的薄弱点包括：指示剂颜色变化难以判断、滴定管只洗涤未润洗、滴定体积过小等。
In a calorimetry question, typical limitations are heat loss to the surroundings, incomplete combustion in a spirit-burner experiment, and assuming the density and specific heat capacity of the solution are those of water.
在量热题中，典型局限是向环境散热、酒精灯燃烧不完全，以及假设溶液的密度与比热容等于水的值。
q = m × c × ΔT with c = 4.18 J g⁻¹ K⁻¹ for water
In a rate experiment, limitations include timing reactions by eye, temperature fluctuation of the water bath, and the subjective judgement of when a cross disappears.
在速率实验中，局限包括用肉眼计时、水浴温度波动，以及判断 "十字消失" 时带有主观性。
9. Improvements That Actually Earn Marks | 真正能得分的改进措施
An improvement only scores when it is a change to the method that directly removes the limitation you identified. Vague advice such as 'be more careful' or 'use better equipment' earns nothing.
改进措施只有在"针对你指出的局限、对方法作出具体改变"时才能得分。"更小心" 或 "用更好的仪器" 这类笼统建议不得分。
- Insulate the calorimeter with a lid and polystyrene cup to reduce heat loss.｜用盖子和聚苯乙烯杯隔热，减少热损失。
- Use a colorimeter instead of the naked eye to follow the cross-disappearing reaction.｜用比色计代替肉眼追踪十字消失反应。
- Rinse the burette with the titrant solution before use to avoid dilution.｜使用前用滴定剂润洗滴定管，避免稀释。
- Repeat and take a mean of concordant titres to reduce random error.｜重复实验并对重合值取平均，以减小随机误差。
- Use a larger mass of fuel or a larger volume of solution so ΔT is bigger.｜增大燃料质量或溶液体积，使 ΔT 更大。
10. Writing the Answer: Structure and Command Words | 答题结构与时态、指令词
Read the command word first. 'Calculate' means show the working and give units; 'suggest' means apply your chemistry knowledge to a new context; 'evaluate' means give strengths or weaknesses and support them with data.
先看清指令词。"Calculate" 要求写出过程并给出单位；"suggest" 要求把化学知识应用到新情境；"evaluate" 要求给出优点或缺点，并用数据支撑。
A short paragraph structure works well: state the point, quote a value from the table or the method, then explain the chemical reason. This gives you the mark even if the English is plain.
推荐使用简短段落结构：先陈述观点，再引用表格数值或方法细节，最后解释化学原理。即使语言朴素，也能拿到分数。
For calculations, always write the equation, substitute numbers, then state the answer with units and correct significant figures.
计算题一律先写公式，再代入数值，最后给出带单位且有效数字正确的答案。
11. Common Mistakes and a Final Checklist | 常见失分点与最终检查清单
The most frequent errors in CH03 Q2 answers are: including the rough titre in the mean, keeping too many decimal places, forgetting units, blaming 'human error', and suggesting improvements that do not match the stated limitation.
CH03 第 2 题最常见的失分点包括：把粗滴定计入平均值、小数位保留过多、漏写单位、把原因归结为 "人为误差"，以及改进措施与所述局限对不上。
- Have you excluded the rough trial and any value outside ± 0.10 cm³?｜是否排除了粗滴定以及超出 ± 0.10 cm³ 的数值？
- Does every answer carry a unit?｜每个答案是否都带单位？
- Have you quoted the uncertainty of the apparatus?｜是否写出仪器不确定度？
- Does each evaluation point link to a named limitation?｜每个评价点是否都对应一个具体局限？
Practise this question style with past CH03 papers, and time yourself writing the calculation, the anomaly judgement and the evaluation in under ten minutes. The skills are repetitive, so marks come from routine rather than luck.
用历年 CH03 真题反复练习这一题型，并限时在十分钟内完成计算、异常值判断与评价部分。这类技能高度重复，分数来自熟练度，而不是运气。
Published by TutorHao | AQA International A-Level Chemistry 9620 Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图