📚 A-Level Chemistry Unit 3 Core Principles from Jan 2020 Exam Report | A-Level 化学 Unit 3 2020年1月考卷报告核心原理
The January 2020 Unit 3 examination report for International A-Level Chemistry offers a wealth of insight into the practical skills and core principles that examiners expect students to master. Unit 3 focuses on experimental techniques, data analysis, and the ability to evaluate procedures — skills that go far beyond theoretical recall. By studying the common errors and mark allocations detailed in the report, students can refine their approach and avoid costly mistakes. This article distils the key principles highlighted in the report, providing both explanation and exam-focused guidance.
2020年1月的国际A-Level化学Unit 3考试报告为考生提供了大量关于实验技能与核心原理的深刻洞见。Unit 3着重考查实验技术、数据分析以及评估方案的能力——这些技能远非单纯的理论记忆可比。通过研读报告中详述的常见错误与分值分布，学生可以优化解题思路，避免重大失分。本文提炼出报告中强调的核心原理，并配以解释和应试指导。
1. Accurate Measurement and Recording of Quantities | 准确测量与数据记录
A recurring theme in the January 2020 report is the need for precise measurement and the use of appropriate instruments. When measuring mass, a balance reading to at least 0.01 g is expected for small quantities; for larger masses, 0.1 g may be acceptable. The report criticises candidates who recorded masses to an inconsistent number of decimal places, which undermines the reliability of their results. Always record the full reading displayed on the balance, including trailing zeros.
2020年1月的报告反复强调精准测量与选用合适仪器的重要性。称量质量时，对于少量物质须使用读数至少到0.01 g的天平；对较大量，0.1 g也可接受。报告批评了那些记录质量时小数位数不一致的考生，这削弱了结果的可靠性。务必记录天平显示的全部读数，包括末尾的零。
Similarly, when measuring volumes with a pipette or burette, the report insisted that burette readings be recorded to ±0.05 cm³ (i.e., to 0.00 or 0.05 cm³) and not rounded incorrectly. A 25.0 cm³ pipette delivers 25.0 cm³, and students should state this as 25.0 cm³, not 25 cm³. Ignoring trailing zeros was a common fault, leading to a loss of marks for ‘appropriate degree of precision’.
同样地，使用移液管或滴定管测量体积时，报告要求滴定管读数记录到 ±0.05 cm³（即读到0.00或0.05 cm³），不得错误地四舍五入。一支25.0 cm³的移液管移取的体积是25.0 cm³，学生应写为25.0 cm³，而非25 cm³。忽略末尾的零是常见错误，会导致在“合适的精度”这一评分点上失分。
The use of a thermometer demands readings to the nearest 0.5 °C or 0.1 °C, depending on the scale; the report noted marks were lost when temperatures were recorded to whole degrees only, making it difficult to calculate a reliable mean for enthalpy changes.
温度计的使用要求读数准确到0.5 °C或0.1 °C（依刻度而定）；报告指出，当温度仅记到整数位时，难以计算出可靠的焓变平均值，遂致失分。
2. Mastering Titration Technique and Choosing the Right Indicator | 掌握滴定技巧与选择合适的指示剂
Titration skills are at the heart of Unit 3, and the January 2020 paper tested the ability to identify an appropriate indicator for a given reaction type. For a strong acid–strong base titration, methyl orange or phenolphthalein are both suitable; however, the report showed that many candidates failed to justify their choice with reference to the pH range over which the indicator changes colour. An answer that merely states ‘methyl orange’ without linking it to the equivalence point pH (approx. 7) was awarded only partial credit.
滴定技能是Unit 3的核心，2020年1月的试卷考查了针对特定反应类型选择合适指示剂的能力。对于强酸强碱滴定，甲基橙或酚酞均适用；然而报告显示，许多考生未能参照指示剂的变色pH范围来说明理由。仅回答“甲基橙”而未将其与等当点pH（约为7）关联起来的答案只能得部分分数。
Rinsing procedures were another weak area. A burette should be rinsed with the solution it will contain, not with water, to avoid dilution. The conical flask must not be rinsed with the solution being titrated, or the measured volume delivered from the burette would be larger than needed, leading to a systematic error. The report emphasised that ‘rinsing the conical flask with the solution to be titrated’ was a frequent error.
润洗程序是另一个薄弱环节。滴定管应当用即将装入的溶液润洗，而非用水，以避免稀释。锥形瓶绝不可用待滴定溶液润洗，否则滴定管注入的溶液体积会比实际需要的大，造成系统误差。报告强调，“用待滴定溶液润洗锥形瓶”是一个常见错误。
During titration, swirling the flask continuously and using a white tile to detect the end-point colour change were both expected refinements. Adding the titrant dropwise near the end-point prevents overshooting. The report noted that candidates who described these steps scored well on the ‘method’ mark.
滴定过程中，不断摇动锥形瓶并使用白瓷板来观察终点颜色变化都是被期待的优化操作。接近终点时逐滴加入滴定剂可防止过量。报告指出，描述了这些步骤的考生在“方法”这一项上得分良好。
3. Enthalpy Change Experiments: Minimising Heat Loss | 焓变实验：最大限度减少热量损失
Enthalpy change determination, typically via calorimetry, was a major focus. The report highlighted that a simple polystyrene cup with a lid is an adequate calorimeter, yet many candidates omitted the lid when drawing or describing the apparatus. Heat loss to the surroundings is the principal source of error, and all reasonable measures — using a lid, stirring, and measuring the initial and final temperatures over a period of time to extrapolate the curve — should be included.
焓变测定（通常通过量热法）是一大重点。报告强调，一个带盖的简单聚苯乙烯杯足以作为量热计，但很多考生在画图或描述仪器时遗漏了杯盖。向环境散热是误差的主要来源，所有合理的措施——使用杯盖、搅拌、以及在升温曲线前中后测量温度以做外推——都应包含在内。
The report stressed the importance of a temperature correction graph: plotting temperature against time, drawing lines of best fit before and after mixing, and extrapolating to the time of mixing gives a more accurate ΔT. Candidates who simply subtracted the initial temperature from the maximum temperature were penalised because the maximum reading may be lower due to slow response of the thermometer and heat loss. The correct ΔT is obtained from the vertical distance between the two extrapolated lines at the mixing time.
报告强调了温度校正图的重要性：绘制温度—时间图，在混合前后各画最佳拟合线，外推至混合时间点，可获得更准确的ΔT。简单地将最高温度减去初始温度的考生会被扣分，因为温度计响应迟缓和热量损失会使最高读数偏低。正确的ΔT应从混合时刻两条外推线之间的垂直距离读取。
Calculations of ΔH require conversion of heat energy (q = mcΔT) to an enthalpy change per mole. The report exposed a common mistake: using the mass of the solid alone instead of the total mass of solution for m, or using the specific heat capacity of the solid rather than that of water (4.18 J g⁻¹ K⁻¹) for aqueous reactions. The correct unit for ΔH is kJ mol⁻¹, and sign conventions (negative for exothermic) must be retained.
计算ΔH需要将热能（q = mcΔT）换算为每摩尔的焓变。报告曝光了一个常见错误：用固体的质量而非溶液总质量作为m，或者用固体的比热容而非水的比热容（4.18 J g⁻¹ K⁻¹）用于水溶液反应。ΔH的正确单位是kJ mol⁻¹，且必须保留符号惯例（放热为负）。
4. Rate of Reaction: Continuous Monitoring and the Initial Rate Method | 反应速率：连续监测与初始速率法
The January 2020 Unit 3 paper expected candidates to describe methods for following the progress of a reaction. A popular context was the reaction between magnesium and an acid, where the volume of hydrogen gas evolved can be measured using a gas syringe or an inverted measuring cylinder over water. The report noted that candidates often confused the two methods, but the gas syringe was preferred because it can be used for gases soluble in water, and it reads directly without adjustment.
2020年1月的Unit 3试卷要求考生能描述跟踪反应进程的方法。常见的场景是镁与酸的反应，可用气体注射器或排水集气法测量放出的氢气体积。报告指出，考生经常混淆这两种方法，但气体注射器更受青睐，因为它可用于溶于水的气体，且可直接读数，无需校正。
For a colour change reaction, colorimetry or a visual timing method (clock reaction) can be used. The report emphasised that timing from the start of mixing until a cross disappears or a colour appears is acceptable, but the same observer and same viewing conditions must be used for all runs. The initial rate method, where the gradient of a concentration–time curve at t = 0 is taken, requires graphing data and drawing a tangent at the origin; too many candidates attempted to calculate rate by simply dividing concentration by time, which is only valid for zero-order reactions.
对于颜色变化的反应，可使用比色法或视觉计时法（时钟反应）。报告强调，从混合开始计时到十字消失或颜色出现的方法是可以接受的，但所有实验必须由同一观察者在相同观察条件下进行。初始速率法需要在浓度—时间图上通过原点处的切线斜率求得；太多考生试图直接以浓度除以时间来计算速率，但此法仅对零级反应有效。
The report also pointed out that students should be able to suggest how to change the concentration of a reactant while keeping the total volume constant, e.g., by replacing portions of the reactant solution with distilled water. Describing this as ‘keeping other factors constant’ was insufficient unless the practical details were specified.
报告还指出，学生应当能够提出如何在保持总体积不变的情况下改变反应物浓度，例如，用蒸馏水代替部分反应物溶液。仅仅描述为“保持其他因素不变”是不够的，除非具体操作细节得以明确。
5. Organic Synthesis: Setting Up Reflux and Distillation Safely | 有机合成：安全搭建回流与蒸馏装置
The reflux setup is a staple of Unit 3, and the report was unforgiving about incomplete or unsafe diagrams. A vertical condenser must be shown with water entering at the bottom and leaving at the top, and the flask must be heated with a heating mantle or a water bath — never a direct Bunsen flame if flammable solvents are used. Anti-bumping granules must be added to the flask to ensure smooth boiling.
回流装置是Unit 3的基本内容，报告对不完整或不安全的图示毫不留情。必须画出竖直的冷凝管，并标明冷却水从下端进入、从上端流出，加热需使用加热套或水浴——若使用易燃溶剂，绝不可直接用本生灯加热。烧瓶中必须加入防暴沸颗粒以确保平稳沸腾。
The report noted that many candidates lost marks by drawing the condenser with water flowing from top to bottom, which would leave the condenser jacket only partially filled and reduce cooling efficiency. Connections between joints should be secure, and the system must be open to the atmosphere (not sealed) to prevent pressure build-up.
报告指出，许多考生将冷凝管画成水流自上而下，这会使得冷凝夹套只有部分充水，降低冷却效率，从而失分。各接合处必须稳固，系统须对大气敞开（不可密封），以防止压力积聚。
Distillation for product separation, particularly simple distillation to collect a pure liquid, requires a thermometer bulb placed exactly at the side arm of the still head to measure the vapour temperature of the distilling liquid. The report penalised diagrams where the thermometer bulb was placed too high or too low. Using a fractionating column for separating liquids with closer boiling points was also expected knowledge, though not always required by the context.
用于分离产物的蒸馏，尤其是简单蒸馏收集纯液体，要求温度计的水银球正好位于蒸馏头侧管口处，以测量蒸出的蒸汽温度。报告对温度计位置过高或过低的图示均予扣分。虽然不一定每次都要求使用分馏柱，但考生应知道当分离沸点相近的液体时需要使用分馏柱。
6. Purification and Yield Calculation: Filtration, Recrystallisation, and Drying | 纯化与产率计算：过滤、重结晶与干燥
Once an organic solid has been prepared, it usually needs purification by recrystallisation. The report stressed that the chosen solvent must dissolve the solid when hot but only sparingly when cold. Candidates were expected to state that the hot solution should be filtered while hot to remove insoluble impurities, then cooled slowly to allow crystals to form. Rapid cooling, e.g., in an ice bath, yields smaller crystals that trap impurities and reduce purity.
制得有机固体后，通常需通过重结晶进行纯化。报告强调，所选溶剂必须能在热时溶解固体，冷时仅微溶。考生应指出，热溶液应趁热过滤以去除不溶杂质，随后缓慢冷却以形成晶体。快速冷却，例如在冰浴中，会产生裹挟杂质的小晶体，降低纯度。
Suction (Büchner) filtration is used to isolate the crystals. The report pointed out that candidates rarely mentioned washing the crystals with a small volume of cold solvent to remove surface impurities, followed by drying between filter papers or in a desiccator. Oven drying is permissible only if the solid is thermally stable; otherwise, air-drying at room temperature is safer.
抽滤（布氏漏斗）用于分离晶体。报告指出，考生很少提及用少量冷溶剂洗涤晶体以除去表面杂质，随后在滤纸之间或干燥器中干燥。若固体热稳定，方可使用烘箱干燥；否则，室温风干更为安全。
Percentage yield calculations often appeared, and the report warned against using the mass of reactant before purification directly as the theoretical yield without using the stoichiometric mole ratio. Some candidates incorrectly used the mass of the limiting reagent instead of moles, leading to nonsensical yields over 100%. Yields should be given to an appropriate number of significant figures, reflecting the precision of the balance used.
试卷中常出现百分产率计算，报告警告考生不可不经化学计量比换算，直接将纯化前的反应物质量当作理论产量。有些考生错误地用限制试剂的质量代替物质的量，得出大于100%的荒谬产率。产率应以适当有效数字给出，反映所用天平的精度。
7. Qualitative Analysis: Recognising Functional Groups Correctly | 定性分析：正确识别官能团
The January 2020 paper tested tests for alkenes, alcohols, aldehydes, carboxylic acids, and halogenoalkanes. For alkenes, the decolorisation of bromine water is standard; however, the report noted that many candidates forgot to state that the test should be carried out in the dark to avoid interference from free-radical substitution if alkanes are present. Simply writing ‘bromine water turns from orange to colourless’ without specifying ‘in the absence of UV light’ was sometimes not enough for full marks.
2020年1月的试卷考查了烯烃、醇、醛、羧酸和卤代烷的检验。对烯烃，溴水褪色是标准方法；但报告指出，许多考生忘记说明实验应在黑暗中进行，以免存在烷烃时受自由基取代干扰。仅写“溴水由橙色变为无色”，而未说明“在无紫外光条件下”，有时不足以拿满分。
Tests for primary and secondary alcohols using acidified potassium dichromate(VI) were widely understood, but the distinction between aldehydes and ketones using Fehling’s or Benedict’s solution and Tollens’ reagent was less secure. Candidates frequently stated that aldehydes produce a silver mirror with Tollens’ reagent, but they omitted that the test tube must be warmed in a water bath, and the reagent must be freshly prepared to avoid explosive silver fulminate formation.
用酸化重铬酸钾(VI)检验伯醇和仲醇的知识普遍掌握，但使用斐林试剂或班氏试剂、托伦试剂区分醛和酮的认知则不够牢固。考生常答道醛与托伦试剂产生银镜，但遗漏了试管须在水浴中温热，且试剂必须新制，以免形成爆炸性的雷酸银。
For halogenoalkanes, the silver nitrate test following nucleophilic substitution with ethanol and aqueous sodium hydroxide, then acidification with nitric acid, was required. The report flagged that many candidates added silver nitrate directly without prior acidification, leading to the precipitation of silver oxide (brown) and masking the halide results. The sequence — NaOH(aq), warm, cool, add HNO₃, then AgNO₃ — is essential and must be memorised.
对卤代烷，要求先与乙醇和氢氧化钠水溶液进行亲核取代，再加硝酸酸化，然后加入硝酸银检验。报告警示，许多考生未预先酸化就直接加入硝酸银，导致氧化银（棕色）沉淀，掩盖了卤离子的检验结果。操作顺序——NaOH水溶液、温热、冷却、加HNO₃、再加AgNO₃——至关重要，务必牢记。
8. Data Handling: Precision, Graphs, and Standard Deviation | 数据处理：精密度、图表与标准偏差
Data analysis questions in Unit 3 demand careful attention to significant figures and the plotting of graphs. The report consistently marked down candidates who used an inappropriate scale for graphs, making it impossible to read values accurately. A common instruction is to ‘use scales such that the plotted points occupy more than half the graph paper in both directions’. The line of best fit should be drawn with equal numbers of points on each side, ignoring anomalous points.
Unit 3的数据分析题要求关注有效数字和图表的绘制。报告一致性地给那些使用不当坐标刻度的考生扣分，因为这样的刻度让人无法准确读取数值。常见的指导是“选择标度，使所有绘制点在两个方向上都占据半幅以上坐标纸”。应当画出最佳拟合线，使点均匀分布在两侧，并忽视异常点。
Calculating a gradient requires selecting two points on the line of best fit, not data points, and using them to compute Δy/Δx. The report cited instances where students simply averaged a set of inconsistent gradients, which is not valid. The y-intercept can be read directly or calculated using the equation of a straight line, y = mx + c.
计算斜率须在最佳拟合线上选取两点，而不是数据点，并用它们计算Δy/Δx。报告举例说明，有些学生简单地对一组不一致的斜率取平均值，这是无效的。y轴截距可以直接读取，或利用直线方程y = mx + c计算。
For repeated measurements, understanding the nature of random errors and the use of mean and range or standard deviation was tested. The report showed that many candidates could calculate a mean but could not interpret a large range as indicative of poor precision. When calculating standard deviation using the formula s = √[ Σ(x – x̄)² / (n – 1) ], errors often occurred in squaring the deviations or dividing by n instead of n-1. Candidates should show all steps clearly.
对于重复测量，考查了对随机误差本质的理解，以及平均值、极差或标准偏差的使用。报告显示，许多考生能计算平均值，但不能将由大极差推断为精密度差。使用公式 s = √[ Σ(x – x̄)² / (n – 1) ] 计算标准偏差时，常在计算偏差平方或除以n而非n-1时出错。考生应清晰展示所有步骤。
9. Identifying Sources of Error and Proposing Valid Improvements | 识别误差来源并提出有效的改进方案
The evaluation section of Unit 3 requires linking a specific source of error to a specific impact on the result, and then suggesting a practical improvement that directly addresses that source. The report found that many candidates were vague, saying ‘heat loss’ without explaining how it affects the final ΔH value (making it less negative) or how to reduce it. An improvement such as ‘use a lid’ or ‘insulate the beaker’ is acceptable, but ‘do the experiment in a closed room’ is not, because heat still escapes.
Unit 3的评价部分要求将特定的误差来源与其对结果的具体影响联系起来，然后提出针对该来源的切实改进方案。报告发现许多考生表述含糊，说“热量损失”却不解释它如何影响最终的ΔH值（使其负值偏小）或如何减少损失。像“加盖”或“隔热烧杯”这类改进是可接受的，但“在密闭房间中做实验”则不然，因为热量依然会散失。
For gas collection methods, a leak in the apparatus leads to a lower volume recorded. The improvement is to ensure all connections are airtight, using grease on ground-glass joints. The report warned that simply stating ‘be more careful’ is not a scientific improvement and will score no marks. Each improvement must be achievable with standard laboratory equipment and described with sufficient detail.
对于气体收集法，装置漏气会导致记录的体积偏低。改进方案是确保所有接口气密，可在磨口玻璃接头上涂抹凡士林。报告警告，仅仅说“更小心些”不是科学改进，无法得分。每一项改进方案都必须能用标准实验设备实现，并描述得足够详细。
Systematic errors, such as using a faulty thermometer that reads 2 °C higher across all readings, impact accuracy but not precision. The report advised that systematic errors are detected by calibrating instruments with a standard, and students should be able to propose a suitable calibration method.
系统误差，例如使用一只在所有读数上都偏高2 °C的故障温度计，影响准确度而不影响精密度。报告建议，通过用标准物校准仪器可以检测系统误差，学生应能提出合适的校准方法。
10. Designing Safe Procedures with Hazardous Chemicals | 危险化学品的安全操作设计
Safety is a recurrent theme, and the January 2020 paper included questions that required a risk assessment and justification of safety precautions. When using concentrated acids or alkalis, wearing gloves and eye protection is mandatory. The report penalised candidates who wrote ‘wear goggles’ alone, as goggles are not sufficient — safety spectacles or a face shield, plus a lab coat, were expected. For toxic or corrosive vapours, use of a fume cupboard must be specified.
安全是反复出现的主题，2020年1月的试卷中包含要求进行风险评估并说明安全预防措施理由的题目。使用浓酸或浓碱时，必须戴手套和护目装置。报告对仅写“戴护目镜”的考生予以扣分，因为仅护目镜是不够的——要求的是安全眼镜或面罩，外加实验服。对于有毒或腐蚀性蒸气，必须明确说明在通风橱操作。
When heating flammable liquids, an electric heating mantle or water bath must be used in place of a naked flame. Candidates who drew a Bunsen burner under a flask containing ethanol lost marks immediately. The report stressed that even if a precaution is obvious to a chemistry teacher, the examiner needs it stated explicitly in the answer.
加热易燃液体时，必须使用电热套或水浴来代替明火。在盛有乙醇的烧瓶下面画本生灯的考生立刻失分。报告强调，即使某些预防措施在化学教师看来是不言而喻的，考官仍需要考生在答案中明确说明。
Disposal of chemical waste was also examined: organic solvents should not be poured down the sink but collected in an organic waste bottle. Residues of toxic heavy-metal compounds require special disposal. The report appreciated candidates who mentioned ‘dispose of in accordance with local regulations’ and the use of labelled waste containers.
化学废物的处置也纳入考查：有机溶剂不应倒入水槽，而应收集在有机废液瓶中。有毒重金属化合物的残余物需要特殊处置。报告对提及“依照当地法规处置”及使用贴有标签的废物容器的考生表示赞赏。
11. Planning an Investigation: Variables and Control Experiments | 实验设计：变量与对照实验
Planning questions required candidates to identify independent, dependent, and control variables clearly. The report noted that many lost marks by stating a control variable without explaining how it would be controlled. For instance, ‘temperature’ must be controlled by using a thermostatted water bath, not just ‘monitored with a thermometer’. Quantifying the controlled variable, e.g., ‘maintain at 25.0 ± 0.5 °C’, adds precision that examiners reward.
实验设计题要求考生清晰识别自变量、因变量和控制变量。报告指出，许多人因只说出控制变量而未说明如何控制而失分。例如，“温度”必须通过恒温水浴来控制，而不是仅仅“用温度计监测”。对控制变量进行量化，例如“保持在25.0 ± 0.5 °C”，能增加精确度，从而获得考官的嘉许。
A well-constructed plan includes a clear stepwise sequence, enough repeats to assess reliability (at least three), and a statement of how the results will be used (plot a graph, calculate mean, etc.). The report encouraged candidates to state that any anomalous results will be identified and possibly excluded from the calculation of a mean, but only after repeating the measurement to check if it is truly anomalous.
一份完善的设计方案包括清晰的逐步操作顺序、足以评估可靠性的重复次数（至少三次），以及对结果处理方式的陈述（绘图、计算平均值等）。报告鼓励考生指出，任何异常值均会经识别，并可能从平均值计算中剔除，但须在重复测量确认其确属异常之后。
The concept of a control experiment — an experiment where one variable is omitted — was explored. For example, to confirm that the reaction of an alcohol with an oxidising agent is due to the alcohol and not the solvent water, a control using water alone under identical conditions must be performed. This notion was often poorly understood, with many candidates confusing a control variable with a control experiment.
试卷探讨了对照实验的概念——即省略一个变量的实验。例如，为证实某醇与氧化剂的反应是由醇而非溶剂水引起，须在相同条件下用纯水进行对照。这个概念常被理解得很差，许多考生混淆了控制变量与对照实验。
12. Interpreting Observations and Drawing Valid Conclusions | 解释观察结果并得出有效结论
The final section of Unit 3 often presents a novel experimental scenario and asks for an interpretation of results. The report stressed that any conclusion must be based solely on the evidence provided, not on prior knowledge about the substances. Candidates who stated that ‘the mixture turned blue-black, therefore starch is present’ earned the mark, but those who added ‘because starch reacts with iodine’ without being asked lost focus and time.
Unit 3的最后一节常给出一段新颖的实验情景，要求对结果进行解释。报告强调，任何结论都只能依据给出的证据，而不是根据事先对物质的了解。考生写道“混合物变为蓝黑色，因此存在淀粉”能得分，但那些未经要求而补充“因为淀粉与碘反应”的人失去了重点，还浪费了时间。
When a set of data shows an unexpected trend, students should be able to suggest a plausible chemical reason. For instance, a lower-than-expected enthalpy of neutralisation for a weak acid and strong base compared to a strong acid–strong base can be explained by the energy absorbed to ionise the weak acid completely. The January 2020 report rewarded such insights when they were linked directly to the observations.
当一组数据出现预料之外的趋势时，学生应能提出一个合理的化学原因。例如，弱酸与强碱的中和焓低于强酸强碱，可以解释为需要吸收能量使弱酸完全电离。2020年1月的报告对这类直接联系观察结果的见解给予加分。
Finally, the report reminded candidates that in evaluation, it is permissible to criticise the experimental method itself, provided the criticism is scientifically sound and not merely a matter of opinion. Phrases like ‘the method was fine, but I did it wrong’ are never acceptable; evaluation is about the method, not the individual.
最后，报告提醒考生，在评价中，只要批评在科学上是合理的，而不仅仅是个人意见，就可以批评实验方法本身。像“方法没问题，是我做错了”这样的说法永远不可接受；评价针对的是方法，而非个人。
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