📚 IB Edexcel Science: A Guide to Experimental Operations | IB Edexcel 科学：实验操作指南
Welcome to this comprehensive guide designed for both IB and Edexcel science students. Whether you are undertaking an internal assessment (IA) in the IB Diploma, or completing core practicals and controlled assessments for Edexcel, mastering experimental operations is crucial. This article provides step-by-step guidance on planning, executing, analysing, and evaluating science experiments, helping you build the practical competencies and scientific mindset examiners expect.
欢迎阅读这份为 IB 和 Edexcel 科学学生设计的综合指南。无论你是在完成 IB 文凭课程的内部评估（IA），还是 Edexcel 的核心实验与受控评估，掌握实验操作都至关重要。本文分步指导你如何规划、实施、分析和评估科学实验，帮助你建立考官所期望的实践能力和科学思维。
1. Planning and Designing Experiments | 实验规划与设计
Every successful experiment begins with a focused research question. It must be specific, measurable, and directly linked to a testable hypothesis.
每个成功的实验都始于一个聚焦的研究问题。它必须具体、可测量，并与一个可验证的假设直接相关。
Clearly define the independent variable (IV) — the factor you will deliberately change. The dependent variable (DV) is what you will measure, and controlled variables (CVs) are those that you must keep constant to ensure a fair test.
明确界定自变量（IV）—— 你将有意改变的因素。因变量（DV）是你将测量的结果，而控制变量（CV）是必须保持不变以确保公平测试的因素。
Write a detailed method before entering the lab. Include step-by-step instructions, quantities, equipment, and the range of IV values you will test. A pilot study can help refine your method.
进入实验室前写出详细的方法。包括分步操作指引、用量、仪器以及你要测试的自变量取值范围。预实验能帮助你改进方法。
Justify your choice of equipment and techniques. For IB IA, you also need to show personal engagement by explaining why you chose a particular approach.
解释你选择仪器和技术的理由。对于 IB 内部评估，你还需要通过说明为何选择某一方法来展现个人参与。
2. Variables, Controls, and Fair Testing | 变量、控制与公平测试
Independent variables should be varied systematically. Use at least five different values (e.g., five temperatures: 20 °C, 30 °C, 40 °C, 50 °C, 60 °C) to allow reliable analysis.
自变量应该系统地变化。至少使用五个不同数值（例如五个温度：20 °C、30 °C、40 °C、50 °C、60 °C），以便进行可靠的分析。
The dependent variable must be measured with an appropriate instrument, and the method of measurement must be consistent. Record the DV with its associated uncertainty.
因变量必须用合适的仪器测量，且测量方法要保持一致。记录因变量时连同其相关的不确定度。
Controlled variables need to be actively monitored. For example, if you are investigating enzyme activity, control pH and temperature. Specify how you will keep them constant and what you will do if they drift.
控制变量需要被主动监控。例如，若你研究酶活性，要控制 pH 和温度。说明你将如何保持它们恒定，以及如果发生漂移你会如何处理。
A fair test means that only the independent variable affects the dependent variable. Any other influence must be eliminated or minimised.
公平测试意味着只有自变量影响因变量。任何其他影响都必须被消除或最小化。
3. Selecting and Using Measuring Instruments | 选择与使用测量仪器
Choose instruments that give an appropriate resolution and accuracy for your measurements. The table below shows common instruments and their typical uncertainties.
选择能为你的测量提供合适分辨率和准确度的仪器。下表列出了常见仪器及其典型的不确定度。
| Instrument | Typical uncertainty |
|---|---|
| Metre ruler | ±1 mm |
| Vernier caliper | ±0.01 mm |
| Micrometer screw gauge | ±0.01 mm |
| Digital balance | ±0.01 g (or ±0.001 g) |
| Thermometer (liquid-in-glass) | ±0.5 °C |
| Digital thermometer | ±0.1 °C |
| Stopwatch | ±0.01 s (human reaction time introduces larger error) |
| Voltmeter (analogue) | ±0.1 V or half the smallest scale division |
| Measuring cylinder (100 cm³) | ±0.5 cm³ |
Always read a scale perpendicularly to avoid parallax error. For repeated readings, take the average and estimate the range or standard deviation.
始终垂直读取刻度以避免视差。对于重复读数，取平均值并估算范围或标准差。
When using digital instruments, the uncertainty is often taken as the smallest digit, e.g., ±0.01 g for a balance reading to 0.01 g, unless the manufacturer specifies otherwise.
使用数字仪器时，不确定度通常取最小数位，例如读数为 0.01 g 的天平，不确定度为 ±0.01 g，除非制造商另有说明。
4. Recording Data and Observations | 记录数据与观察
Record all raw data directly into a pre-prepared table. Use clear headings with units, e.g., ‘Temperature / °C’ or ‘Time / s’.
将所有原始数据直接记录在预先准备的表格中。使用清晰的标题及单位，例如 “Temperature / °C” 或 “Time / s”。
Quantitative data should be recorded to the appropriate number of decimal places, consistent with the instrument’s precision. Qualitative observations, such as colour changes or precipitation, must be noted alongside the readings.
定量数据应记录到与仪器精度一致的小数位数。定性观察，如颜色变化或生成沉淀，必须与读数一同记录。
Avoid converting units during recording – do that later in processing. If you make a mistake, put a single line through the value and write the correct entry beside it; never use correction fluid.
记录时避免单位换算—— 留到后续数据处理时再做。如果出错，用单线划去错误数值，在旁边写正确值；切勿使用修正液。
Take repeated measurements at each IV value. Three replicates are a common minimum; more replicates improve reliability.
在每个自变量数值处进行重复测量。三次重复是常见的最低要求；更多重复可提高可靠性。
5. Processing Data: Calculations and Uncertainties | 数据处理：计算与不确定度
Show one example for each type of calculation. Common processing steps include calculating mean, percentage change, rate, or using a formula such as density = mass ÷ volume.
对每一种计算都要给出一个范例。常见的处理步骤包括计算平均值、百分比变化、速率，或使用如密度 = 质量 ÷ 体积的公式。
Absolute uncertainty for a single measurement is usually ± half the smallest scale division (analogue) or ± the least significant digit (digital). For a mean value, uncertainty can be estimated using half the range: (max − min) ÷ 2.
单次测量的绝对不确定度通常为 ± 最小刻度的一半（模拟仪器）或 ± 最低有效数位（数字仪器）。对于平均值，不确定度可以用范围的一半来估算：(最大值 − 最小值) ÷ 2。
Percentage uncertainty = (absolute uncertainty ÷ measured value) × 100%
百分比不确定度 = (绝对不确定度 ÷ 测量值) × 100%
When combining uncertainties, for addition/subtraction, add absolute uncertainties. For multiplication/division, add percentage uncertainties. Constants (e.g., number of moles) are treated as having no uncertainty.
组合不确定度时，加减法叠加绝对不确定度；乘除法叠加百分比不确定度。常数（如摩尔数）视为没有不确定度。
Propagation of uncertainties demonstrates the reliability of your results. IB Internal Assessment expects you to discuss significant figures and decimal places in processed data.
不确定度的传递证明了结果的可靠性。IB 内部评估期望你讨论处理后数据的有效数字和小数位数。
6. Graphical Representation of Data | 数据的图表表示
Plot a well-labelled graph with the independent variable on the x-axis and the dependent variable on the y-axis. Use appropriate scales so that your data occupies more than half of the graph area.
绘制一幅标注清晰的图表，自变量在 x 轴，因变量在 y 轴。使用合适的刻度，使数据占据图表面积的一半以上。
Include error bars to show uncertainties in the plotted data. For IB IA, you are often required to add both horizontal and vertical error bars if both variables have uncertainty.
添加误差线以展示图中数据的不确定度。对 IB 内部评估，通常要求 x 和 y 变量都存在不确定度时，同时添加水平和垂直误差线。
Draw a line of best fit. This is not necessarily a straight line; it can be a smooth curve that passes through or as close to as many points as possible, respecting error bars.
绘制最佳拟合线。它不一定是一条直线；可以是一条平滑曲线，尽可能穿过或接近最多数据点，并尊重误差线。
If the relationship appears linear, use a ruler to draw a trendline and determine the gradient and y-intercept. Calculate the gradient using two points far apart on the line, not directly from data points.
如果关系呈线性，用直尺画趋势线，并确定斜率和 y 截距。选择线上距离较远的两点计算斜率，而不要直接使用数据点。
Describe the trend: state whether the relationship is directly proportional, linear, curved, or inversely proportional. Use the gradient or intercept to derive physical quantities where appropriate.
描述变化趋势：说明是正比例、线性、曲线还是反比关系。适当的时候利用斜率或截距推导物理量。
7. Evaluating Experimental Results and Errors | 评估实验结果与误差
Identify systematic errors, which shift all readings in one direction (e.g., a miscalibrated thermometer). These affect accuracy but not precision.
识别系统误差，这类误差使所有读数向同一方向偏移（例如温度计未校准）。系统误差影响准确度，但不影响精密度。
Random errors cause scatter and affect precision. Examples include fluctuations in voltage or inconsistent timing. They can be reduced by taking more measurements.
随机误差导致数据分散，影响精密度。例如电压波动或计时不一致。可通过增加测量次数来减小随机误差。
Discuss the most significant sources of error and their impact on the results. Suggest realistic improvements, not vague statements like ‘be more careful’. For IB, this links to the Evaluation criterion.
讨论最显著的误差来源及其对结果的影响。提出切实可行的改进建议，而非 “更小心” 这类空泛表述。对 IB 而言，这与 Evaluation 评分标准相关。
Compare your conclusion with the accepted scientific theory. Calculate a percentage error where a literature value is known: (|experimental value − accepted value| ÷ accepted value) × 100%.
将你的结论与公认科学理论进行比较。当已知文献值时，计算百分比误差：(|实验值 − 公认值| ÷ 公认值) × 100%。
Consider the validity of your method: did you truly measure what you intended? Reflect on any anomalies and whether they should be excluded, providing justification.
考虑方法的效度：你是否真正测量了想要测量的东西？反思任何异常值并说明是否应将其剔除，并给出理由。
8. Safety and Ethical Practice in the Lab | 实验室安全与伦理实践
Conduct a full risk assessment before any practical work. Identify hazards (e.g., corrosive chemicals, high voltage, hot surfaces) and the control measures you will employ.
进行任何实验操作前，完成全面的风险评估。识别危害（如腐蚀性化学品、高电压、灼热表面）以及你将采取的控制措施。
Always wear appropriate personal protective equipment (PPE) — safety goggles, lab coat, and in some cases, gloves. Tie back long hair and avoid loose clothing.
始终穿戴适当的个人防护装备（PPE）—— 护目镜、实验服，必要时戴手套。束起长发，避免宽松衣物。
Handle chemicals according to CLEAPSS or your institution’s guidelines. Dispose of waste safely: never pour organic solvents or heavy metals down the sink unless explicitly permitted.
按照 CLEAPSS 或学校指引处理化学品。安全处置废弃物：除非明确允许，否则绝不将有机溶剂或重金属倒入水槽。
In biology experiments, treat living organisms with respect. Follow ethical guidelines for handling plants, microorganisms, and animals. Ensure microbiology plates are sealed and sterilised after use.
在生物实验中，尊重活体生物。遵循处理植物、微生物和动物的伦理准则。确保微生物培养皿在使用后密封并灭菌。
For Edexcel core practicals, safety notes are explicitly required in your write-up. IB IA also expects you to mention safety and ethical considerations as part of the Exploration section.
对 Edexcel 核心实验，实验报告明确要求安全注意事项。IB 内部评估也期望你在 “探究” 部分提及安全与伦理考量。
9. Common Practical Techniques in Chemistry, Physics and Biology | 化学、物理与生物的常见实验技术
Titration (chemistry): Rinse the burette with the solution it will contain. Use a pipette filler, not your mouth. Record the initial and final burette readings to 0.05 cm³. Obtain concordant titres within 0.10 cm³.
滴定（化学）：用待装溶液润洗滴定管。使用洗耳球，切勿用嘴吸。记录滴定管初读数和终读数，精确至 0.05 cm³。确保几次滴定结果相差不超过 0.10 cm³，形成合数。
Microscopy (biology): Calibrate the eyepiece graticule using a stage micrometer. Draw biological specimens to scale, label visible structures, and include a magnification statement.
镜检（生物）：使用镜台测微尺标定目镜测微尺。按比例绘制生物标本，标注可见结构，并注明放大倍数。
Electrical circuits (physics): Check connections are tight and use appropriate ranges on ammeters and voltmeters. Connect the voltmeter in parallel and the ammeter in series. Record the polarity of connections when relevant.
电路（物理）：检查连接是否紧固，并在电流表和电压表上选择合适的量程。电压表并联，电流表串联。相关时记录连接的极性。
Heating and measuring temperature changes: Use a polystyrene cup for calorimetry to reduce heat loss. Stir continuously and record the maximum or minimum temperature reached.
加热与测量温度变化：使用聚苯乙烯杯进行量热实验以减少热量散失。持续搅拌并记录所达到的最高或最低温度。
Collecting gases: A gas syringe or inverted measuring cylinder over water can be used. Account for water vapour pressure if collecting over water. Check for leaks before starting.
收集气体：可使用气体注射器或排水集气法。若用排水法，需考虑水蒸气压。开始前检查气密性。
10. Writing a High-Quality Lab Report | 撰写高质量实验报告
Structure your report logically: Title, Research Question, Introduction, Method, Results, Analysis, Conclusion, Evaluation, and References. Both IB and Edexcel value clear and concise communication.
逻辑地组织你的报告：标题、研究问题、引言、方法、结果、分析、结论、评估和参考文献。IB 和 Edexcel 都重视清晰简洁的表达。
The Introduction should include background scientific theory and explain why the investigation is worth doing. State the hypothesis and how it was derived.
引言部分应包括背景科学理论，并解释为什么要进行这项研究。陈述假设及其推导过程。
Your Method section must be written in impersonal past tense (e.g., ‘The temperature was measured…’) and contain enough detail for someone else to replicate your work.
方法部分必须使用非人称的过去时态（如 “温度被测量……”），并包含足够的细节，让人能够复现你的工作。
Present Results in tables and graphs; processed data should be clearly distinguished from raw data. Use sample calculations and incorporate uncertainty analysis.
用表格和图表呈现结果；处理后的数据要与原始数据明确区分。展示示例计算并融入不确定度分析。
In the Evaluation, go beyond listing errors. Rank them by significance, explain their effect on the outcome, and propose specific, feasible improvements that could be made with available resources.
在评估中，不要只罗列误差。要按显著性排序，解释它们对结果的影响，并提出利用现有资源可实现的、具体可行的改进措施。
Reference all sources using a consistent style (such as APA or MLA). Cite any borrowed data, theoretical values, or methods to avoid plagiarism.
使用一致的引文格式（如 APA 或 MLA）引用所有来源。引用任何借鉴的数据、理论值或方法，以避免抄袭。
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