📚 IB WJEC Chemistry: A Guide to Experimental Techniques | IB WJEC 化学：实验操作指南
Mastering practical skills is essential for success in both IB and WJEC Chemistry. This guide covers core experimental techniques, from accurate measurements to common pitfalls, helping you build confidence in the lab and in written practical assessments. Whether you are following the IB internal assessment or WJEC specified practical work, understanding the principles behind each technique will sharpen your scientific thinking and boost your grades.
掌握实验技能是 IB 和 WJEC 化学成功的关键。本指南涵盖从准确测量到常见误区的核心实验技术，帮助你在实验室和书面实验评估中建立信心。无论你正在进行 IB 内部评估还是 WJEC 规定的实验任务，理解每项技术背后的原理都能提升你的科学思维并提高成绩。
1. Safety in the Laboratory | 实验室安全
Always wear safety goggles and a lab coat to protect your eyes and skin from chemical splashes. Tie back long hair and avoid loose clothing or jewellery that may catch fire or dip into reagents.
始终佩戴护目镜和实验服，保护眼睛和皮肤免受化学品飞溅伤害。长发应束起，避免穿着宽松衣物或佩戴首饰，以防着火或浸入试剂。
Familiarise yourself with the location of safety equipment, including the eyewash station, fire extinguisher, and emergency shower. When heating flammable liquids, never use an open flame unless directed by your teacher; use a water bath or heating mantle instead.
熟悉安全设备的位置，包括洗眼器、灭火器和紧急淋浴器。加热易燃液体时，除非老师指导，否则切勿使用明火；应使用水浴或加热套。
Chemicals should never be tasted, and vapours should be wafted gently towards your nose rather than inhaled directly. Always read hazard symbols and risk phrases on reagent bottles before handling.
化学品绝不可尝，闻气体时应用手轻轻将蒸气扇向鼻子，不可直接吸入。处理试剂前务必阅读瓶身危险标志和风险说明。
2. Measuring Mass and Volume | 称量与体积测量
Use an electronic balance with a precision of at least 0.01 g for quantitative work. Always place a weighing boat or paper on the pan and tare (zero) the balance before adding the sample. Record the mass to the precision allowed by the instrument.
定量实验需使用精度至少为 0.01 g 的电子天平。称量前在秤盘上放一张称量纸或称量舟，并归零（去皮）。按仪器允许的精度记录质量。
For volume measurement, graduated cylinders are suitable for approximate volumes, but for precise work use a pipette (e.g., 25.0 cm³) and a burette (read to 0.05 cm³). When reading the meniscus, align your eye horizontally with the liquid level; for transparent liquids, read the bottom of the meniscus.
测量体积时，量筒适用于粗略体积，但精密工作需使用移液管（如 25.0 cm³）和滴定管（读数至 0.05 cm³）。读取弯月面时，视线应与液面保持水平；透明液体读取弯月面底部。
sk is used to prepare standard solutions, typically with an error of ±0.1 cm³ at the mark.
使用前需用待测液润洗玻璃器皿，以防稀释误差。容量瓶用于配制标准溶液，其刻度线处的典型误差为 ±0.1 cm³。
3. Heating Techniques | 加热技术
Use a Bunsen burner with a blue flame (non-luminous) for strong heating, but ensure the air hole is fully open. For gentle or even heating, use a water bath, which maintains a steady temperature up to 100 °C. Never heat a closed system as pressure build-up can cause an explosion.
需强热时可用本生灯的蓝色火焰（非发光焰），但应确保气孔全开。如需温和或均匀加热，可使用水浴，它能维持最高 100 °C 的稳定温度。切勿加热密闭系统，压力积聚可能引发爆炸。
When heating a test tube, point the mouth away from yourself and others, and move the tube continuously through the flame to avoid sudden boiling. A sand bath or oil bath can be used for temperatures above 100 °C in WJEC required practicals.
加热试管时，管口应朝向无人处，并不断在火焰中移动试管，防止暴沸。WJEC 指定实验中，温度超过 100 °C 可使用沙浴或油浴。
To prevent 'bumping', add anti-bumping granules to liquids before heating. In IB experiments, always consider how the heating method might affect the rate and equilibrium of a reaction, and record the temperature accurately.
加热液体前加入沸石可防止暴沸。在 IB 实验中，始终要考虑加热方式如何影响反应速率和平衡，并准确记录温度。
4. Titration | 滴定
Titration is a quantitative technique used to determine the concentration of an unknown solution. Rinse the burette with the solution it will dispense, fill it past the zero mark, and run some solution through the tip to remove air bubbles. Record the initial burette reading to the nearest 0.05 cm³.
滴定是一种用于测定未知溶液浓度的定量技术。先用待装液润洗滴定管，加液至零刻度以上，然后从滴嘴放出少许溶液以排尽气泡。记录初始读数至 0.05 cm³。
Use a pipette filler to safely draw solution into a pipette up to the mark, then deliver it into a conical flask. Add a few drops of a suitable indicator. In IB, you are often expected to explain the choice of indicator based on the pH range of the equivalence point.
使用洗耳球将溶液吸至移液管刻度线，然后转移至锥形瓶中。加入几滴合适的指示剂。IB 常要求学生根据等当点的 pH 范围解释指示剂的选择。
During rough and accurate titres, swirl the flask gently and add titrant dropwise near the endpoint. The endpoint is reached when the indicator just changes colour permanently. Concordant titres should agree within 0.10 cm³. For WJEC, you may perform a redox titration using potassium manganate(VII), which acts as its own indicator.
在进行粗滴和精滴时，轻轻旋转摇动锥形瓶，接近终点时逐滴加入滴定剂。当指示剂颜色发生持久变化时即达终点。吻合的滴定体积应在 0.10 cm³ 以内。WJEC 可能使用高锰酸钾（VII）进行氧化还原滴定，它自身可作为指示剂。
concentration (mol dm⁻³) = (n × c × V) / Vsample or use c₁V₁ = c₂V₂ for monoprotic acids
浓度 (mol dm⁻³) = (n × c × V) / V样品 或 一元酸可用 c₁V₁ = c₂V₂
5. Filtration and Crystallisation | 过滤与结晶
Gravity filtration is used to separate an insoluble solid from a liquid. Fold filter paper into a cone, place it in a funnel, and wet it slightly with solvent. Pour the mixture slowly down a glass rod to prevent splashing and direct the liquid into the filtrate.
重力过滤用于分离不溶性固体和液体。将滤纸折叠成圆锥放入漏斗，用溶剂稍加润湿。沿玻璃棒缓慢倒入混合物，以防飞溅，并将滤液导入接收瓶。
Vacuum filtration, using a Büchner funnel and flask, is faster and dries the solid more effectively. For crystallisation, cool a saturated solution slowly to obtain large, pure crystals. Dry crystals between filter paper or in a low-temperature oven.
使用布氏漏斗和吸滤瓶的减压过滤速度更快，固体更干燥。结晶时，缓慢冷却饱和溶液可得到大而纯的晶体。在滤纸间或用低温烘箱干燥晶体。
When calculating percentage yield, the actual mass of dry crystals is divided by the theoretical mass and multiplied by 100. Both IB and WJEC require evaluation of yield losses, such as material left in the filter paper or lost during transfer.
计算产率时，将干燥晶体的实际质量除以理论质量再乘以 100%。IB 和 WJEC 都要求评估产率损失，例如留在滤纸上或转移中损失的物质。
6. Distillation and Reflux | 蒸馏与回流
Simple distillation separates a liquid from a solution of a non-volatile solute or from liquids with significantly different boiling points. The flask must include anti-bumping granules; the thermometer bulb should be positioned at the side arm of the still head to measure the vapour temperature accurately.
简单蒸馏可将液体与非挥发性溶质的溶液分开，或分离沸点差异大的液体。烧瓶需加入沸石；温度计水银球应置于蒸馏头支管口处，以准确测量蒸气温度。
Fractional distillation, used for mixtures with closer boiling points, employs a fractionating column packed with glass beads to provide a large surface area for repeated condensation and evaporation. This technique is central to WJEC’s organic practicals.
分馏用于沸点较接近的混合物，使用装有玻璃珠的分馏柱，提供大面积表面进行反复冷凝与蒸发。该技术是 WJEC 有机实验的核心。
Reflux involves heating a reaction mixture to boiling while continuously condensing the vapour back into the flask. It prevents loss of volatile reactants and products. Screw the condenser securely and remember to run cold water in at the bottom and out at the top. In IB, you may need to calculate the yield of an organic liquid after reflux and purification by separating funnel.
回流是将反应混合物加热至沸腾，同时将蒸气冷凝回流至烧瓶。它可防止挥发性反应物和产物的损失。固定好冷凝管，记住冷却水从下端进、上端出。在 IB 中，可能需要计算回流后通过分液漏斗纯化得到的有机液体产率。
7. Chromatography | 色谱法
Paper chromatography and thin-layer chromatography (TLC) separate components based on their relative affinity for a stationary phase and a mobile phase. Draw a pencil line about 1 cm from the bottom of the paper or plate, spot the sample, and allow it to dry.
纸色谱和薄层色谱（TLC）基于组分对固定相和流动相的相对亲和力进行分离。在纸或板底部约 1 cm 处用铅笔画线，点样，并使其干燥。
Place the chromatogram in a sealed container with a shallow layer of solvent below the pencil line. When the solvent front is near the top, remove and mark the front with a pencil. Locate colourless spots using a UV lamp or iodine vapour.
将色谱图放入密闭容器中，溶剂层应在铅笔线以下。当溶剂前沿接近顶部时取出，用铅笔标记前沿。无色斑点可用紫外灯或碘蒸气显色。
Calculate Rf values: Rf = distance moved by spot ÷ distance moved by solvent. In WJEC and IB, comparing Rf values with known substances helps identify amino acids or dyes. Always repeat spotting to ensure reliability.
计算 Rf 值：Rf = 斑点移动距离 ÷ 溶剂移动距离。在 WJEC 和 IB 中，比较 Rf 值与已知物质有助于鉴定氨基酸或染料。务必重复点样确保可靠性。
8. Gas Collection | 气体收集
Gases can be collected by downward displacement of air (for gases denser than air, e.g., CO₂, HCl), upward displacement (for gases less dense than air, e.g., H₂, NH₃), or over water. The method depends on the gas’s density and solubility.
气体可通过向下排空气法（密度大于空气，如 CO₂、HCl）、向上排空气法（密度小于空气，如 H₂、NH₃）或排水集气法收集。方法取决于气体的密度和溶解度。
When collecting over water, the first few bubbles of gas may contain displaced air and should be discarded. Using a gas syringe is a more precise method to measure the volume of a gas evolved over time, frequently required in IB kinetics experiments.
排水集气时，最初几个气泡可能含被排出的空气，应舍弃。使用气体注射器是更精确地测量随时间产生气体体积的方法，常出现在 IB 动力学实验中。
For gases that react with water (e.g., SO₂, Cl₂), use an air displacement method or a gas syringe. Check for leaks in gas collection set-ups by immersing connectors in water and looking for bubbles.
与水反应的气体（如 SO₂、Cl₂）需使用排空气法或气体注射器。检查气体收集装置是否漏气，可将接头浸入水中观察气泡。
9. pH Measurement and Indicators | pH 测量与指示剂
Universal indicator paper gives a rough pH range, but a pH meter provides precise digital readings. A pH meter must be calibrated using buffer solutions of known pH (e.g., pH 4.00, 7.00, 10.00) before use. Rinse the probe with distilled water between measurements.
通用指示剂试纸可给出粗略 pH 范围，但 pH 计能提供精确数字读数。使用前须用已知 pH 的缓冲溶液（如 pH 4.00、7.00、10.00）校准 pH 计。每次测量间用蒸馏水冲洗探针。
Indicators themselves are weak acids or bases, and their colour change depends on the H⁺ concentration. In an acid-base titration, choose an indicator with a pKa close to the equivalence point pH. For a strong acid – strong base titration, phenolphthalein or methyl orange can be used.
指示剂本身是弱酸或弱碱，其颜色变化取决于 H⁺ 浓度。在酸碱滴定中，选择 pKa 接近等当点 pH 的指示剂。强酸-强碱滴定可选用酚酞或甲基橙。
For biochemical systems, such as investigating enzyme activity in IB, use a pH buffer to maintain a constant pH. The effect of pH on rate can be graphed to find the optimum pH.
在 IB 研究中如探究酶活性时，使用 pH 缓冲液维持恒定 pH。可绘制 pH 对速率影响图以找出最适 pH。
10. Data Recording and Uncertainty | 数据记录与不确定度
measurements must be recorded with the correct level of precision, matching the instrument' mallest division for analogue instruments or ± the smallest digit for digital instruments.
所有测量值必须按照仪器刻度分度记录的精确水平。在 IB 内部评估中，模拟仪器的不确定度估计为最小分度的一半，数字仪器则为最低位 ±1。
Perform replicate measurements and calculate a mean. Use the range or standard deviation to evaluate precision. In WJEC practical examinations, you are expected to identify anomalous results and either omit them or repeat the measurement.
进行重复测量并计算平均值。使用范围或标准偏差评估精密度。WJEC 实验考试中，需识别异常值并删去或重测。
ration ÷ Δ time) follows the rules of adding percentage uncertainties. Display raw data clearly in tables with headings including units and uncertainties, exactly as required by IB criteria.
合成数据中不确定度的传播（如速率 = Δ 浓度 ÷ Δ 时间）遵循百分比不确定度相加规则。原始数据应在表格中清晰展示，表头包括单位和不确定度，完全符合 IB 评价标准。
11. Common Mistakes and How to Avoid Them | 常见错误及避免方法
Failing to rinse a burette with titrant is a common systematic error, leading to a lower concentration reading because the first portion of acid/conjugate base is diluted. Avoid this by drying or rinsing all glassware with the solution it will contain.
未用滴定剂润洗滴定管是常见的系统误差，导致浓度读数偏低，因为初始的酸/共轭碱被稀释。应通过润洗或干燥所有玻璃器皿来避免。
In calorimetry, heat loss to surroundings causes a lower temperature change than theoretically expected. Use a lid, a well-insulated cup, and stir the solution continuously to minimise error. Plot a cooling curve to extrapolate the maximum temperature if necessary.
量热法中，热量散失到环境中导致温度变化低于理论值。使用盖子、良好隔热的量杯并持续搅拌溶液以减少误差。必要时绘制降温曲线外推最高温度。
During preparation of a standard solution, forgetting to reweigh the solute after transferring from a weighing boat leaves undissolved residue behind, giving a lower concentration. Wash the boat with solvent into the volumetric flask.
配制标准溶液时，转移称量舟中的溶质后忘了冲洗舟壁，会留下未溶解的残余物，导致浓度偏低。应用溶剂冲洗称量舟入容量瓶。
In organic synthesis, students often lose product when transferring between vessels or during washing in a separating funnel. Keep the stopper on when shaking, vent frequently, and collect all layers until you are certain which is the desired product.
有机合成中，学生经常在转移容器或分液漏斗洗涤时损失产物。震荡时塞住塞子，经常排气，并收集所有液体层直到确认所需的产物层。
12. Exam Tips for Practical Assessment | 实验评估考试技巧
Before starting any practical, read the full method and prepare a logical sequence of steps. Identify hazards and record precautions. Both IB and WJEC mark the ability to plan a method and design a results table independently.
开始任何实验前，通读整个方法并准备合理的步骤顺序。识别危险并记录预防措施。IB 和 WJEC 都考核独立策划方法和设计结果表格的能力。
Use precise scientific language, and always include units with numerical data. In WJEC, the quality of written communication is assessed, so write clearly and logically. For IB, a clear personal engagement and reflection on errors will strengthen your investigation report.
使用精确的科学语言，数值数据始终附带单位。WJEC 会评估书面沟通质量，因而要书写清晰且合逻辑。IB 中，清晰的个人投入和对误差的反思将加强你的探究报告。
Time management is crucial. Allocate time for repeat readings and for cleaning up. If you finish early, check for any incomplete data or inconsistent results and re-test if possible. Never leave a spirit burner or Bunsen burner unattended.
时间管理至关重要。为重复读数和清洁分配时间。若提前完成，检查是否有数据不全或结果矛盾，尽可能重测。无人看管时绝不可离开酒精灯或本生灯。
For graphical tasks, use a sharp pencil to plot points as small crosses, draw a best-fit line, and calculate gradients from large triangles. Describe the trend, not just the shape, and link it to underlying chemistry principles.
绘图任务中，用削尖铅笔将点画为小叉号，画出最佳拟合线，并从较大三角形计算梯度。描述趋势而非仅形状，并将其与背后的化学原理相联系。
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