📚 IB OCR Chemistry: A Guide to Laboratory Techniques | IB 与 OCR 化学实验操作指南
Mastering practical laboratory skills is essential for success in both IB and OCR Chemistry. From accurate measurement of mass and volume to precise control of reaction conditions, these techniques form the foundation of reliable experimental work. This guide covers the core procedures you will encounter in your internal assessments, practical endorsements, and examinations, helping you to work safely, confidently, and methodically.
掌握实验室实用技能对于 IB 和 OCR 化学的成功至关重要。从准确测量质量和体积到精确控制反应条件，这些技术构成了可靠实验工作的基础。本指南涵盖你在内部评估、实验认证和考试中会遇到的各项核心操作，帮助你安全、自信、有条不紊地进行实验。
1. Safety and Preparation | 安全与准备
Before any experiment, a thorough risk assessment must be carried out. Identify the hazards associated with each chemical (e.g. corrosive, flammable, toxic) and plan appropriate control measures such as using a fume cupboard, wearing gloves and goggles, and disposing of waste correctly. Always tie back long hair, remove loose jewellery, and wear a lab coat.
任何实验前都必须完成全面的风险评估。识别每种化学品相关的危害（如腐蚀性、易燃性、毒性），并规划适当的控制措施，例如使用通风橱、佩戴手套和护目镜，以及正确处理废液废渣。始终把长发扎起，取下松散的饰品，并穿着实验服。
2. Measuring Mass: The Analytical Balance | 测量质量：分析天平
An analytical balance reads to 0.001 g or 0.0001 g and is used when precise masses are required. Place a weighing boat on the pan, close the draft shield doors, and tare (zero) the balance. Add the substance using a spatula until the desired mass is approached, then add dropwise. Record the mass directly from the display. Never weigh chemicals directly on the balance pan.
分析天平可读至 0.001 g 或 0.0001 g，用于需要精确质量的场合。将称量舟放在秤盘上，关闭防尘罩门，去皮（归零）。用药匙添加物质，接近目标质量后逐粒加入。直接从显示屏记录质量。绝不能将化学品直接放置在秤盘上称量。
3. Measuring Volumes: Pipettes and Burettes | 测量体积：移液管和滴定管
A volumetric pipette delivers a fixed volume with high accuracy (e.g. 25.0 cm³). Rinse the pipette with the solution, fill it so the meniscus rests on the calibration mark, and allow it to drain freely. A burette is used to deliver variable volumes and is read to ±0.05 cm³. Rinse it with the titrant, fill through a funnel, and remove air bubbles from the jet. Read the bottom of the meniscus at eye level, with a white tile placed behind.
单标移液管可高准确度地移取固定体积（如 25.0 cm³）。先用溶液润洗移液管，装液至弯月面与刻度线相切，自由放液排出。滴定管用于变量体积的量取，读数可精确至 ±0.05 cm³。用滴定剂润洗，通过漏斗装液，排去管尖的气泡。在眼睛水平高度读取弯月面最低点，并放置白纸衬底。
4. Titration Techniques | 滴定技术
A titration determines the concentration of an unknown solution by reacting it with a standard solution. Add the standard acid or base to the burette. Pipette the analyte into a conical flask, add a few drops of indicator, and swirl. The end point is reached when a permanent colour change is observed. A rough titration first, followed by two or three concordant titres (within 0.10 cm³), ensures precision.
滴定法通过使未知溶液与标准溶液反应来确定其浓度。将标准酸或碱装至滴定管中。用移液管量取待测液放入锥形瓶，加入几滴指示剂，摇动。当观察到永久性颜色变化时即达到终点。先进行一次粗滴定，再完成两三次符合度在 0.10 cm³ 以内的平行滴定，可确保精密度。
5. Making a Standard Solution | 配制标准溶液
A standard solution has a precisely known concentration. Calculate the mass of solid needed, weigh it accurately, and transfer into a beaker with deionised water. Stir to dissolve, then pour the solution into a volumetric flask via a funnel. Rinse the beaker and funnel with deionised water and add the washings to the flask. Make up to the mark with deionised water, stopper, and invert several times to mix.
标准溶液具有准确已知的浓度。计算所需固体质量，准确称量后转移至烧杯中，加入去离子水。搅拌溶解，然后通过漏斗将溶液转移至容量瓶中。用去离子水冲洗烧杯和漏斗，洗液一并转入容量瓶。加去离子水定容至刻度线，盖塞，反复倒转混匀。
6. Heating and Temperature Control | 加热与温度控制
Controlled heating is critical for many reactions. A water bath provides steady temperatures up to 100 °C and is ideal for below-boiling-point reactions. An electric heating mantle or a Bunsen burner with a tripod and gauze can be used for higher temperatures, but direct flames must be avoided with flammable solvents. Temperatures are monitored using a thermometer or digital temperature probe, and the thermometer bulb must be fully immersed in the liquid without touching the vessel walls.
许多反应需要精确控温。水浴可提供最高 100 °C 的稳定温度，是沸腾点以下反应的理想选择。电热套或配有石棉网的铁架台及本生灯可用于更高温度，但易燃溶剂须避免明火直接加热。用温度计或数字温度探头监测温度，温度计的感温泡应完全浸没在液体中，且不接触容器壁。
7. Filtration and Recrystallisation | 过滤与重结晶
Gravity filtration separates an insoluble solid from a liquid. Fold filter paper into a cone, place in a funnel, and pour the mixture. Vacuum filtration using a Büchner flask and funnel speeds up the process and dries the solid. Recrystallisation purifies a solid: dissolve the impure solid in a minimum amount of hot solvent, filter if necessary, cool slowly to form pure crystals, then filter and dry. The melting point of the dried crystals confirms purity.
常压过滤用于分离不溶性固体与液体。将滤纸折叠成锥形，放入漏斗，倾倒混合物。使用布氏漏斗和抽滤瓶进行减压过滤可加速过程并干燥固体。重结晶用于纯化固体：用最少量热溶剂溶解不纯固体，必要时热过滤，缓慢冷却析出纯净晶体，然后过滤干燥。干燥晶体的熔点可确认纯度。
8. Distillation and Reflux | 蒸馏与回流
Simple distillation separates a liquid from a non-volatile solute. The mixture is heated, vapour rises, passes through a condenser, and the distillate is collected. Reflux involves continuously boiling a reaction mixture and condensing the vapour back into the flask, allowing prolonged heating without loss of volatile components. An anti-bumping granule ensures smooth boiling. The water supply to the condenser must flow against gravity (in at the bottom, out at the top) for efficient cooling.
简单蒸馏可将液体与不挥发溶质分离。加热混合物，蒸气上升经过冷凝管，冷凝液被收集。回流操作让反应混合物持续沸腾，并将蒸气冷凝回烧瓶，可实现长时间加热而不损失挥发性组分。加入沸石可防止暴沸。冷凝管的水流方向应与重力相反（下进上出）以保证冷却效率。
9. Chromatography: Thin Layer and Paper | 色谱法：薄层与纸色谱
Thin-layer chromatography (TLC) and paper chromatography separate components of a mixture based on their relative affinities for a stationary and a mobile phase. Apply a small spot of the mixture and suitable references onto a baseline drawn in pencil. Place the plate or paper in a developing tank with a shallow layer of solvent below the baseline. When the solvent front has nearly reached the top, remove and mark the front immediately. Visualise spots using UV light or a locating agent, and calculate Rf values: Rf = distance moved by component ÷ distance moved by solvent front.
薄层色谱和纸色谱根据混合物中各组分对固定相和流动相的相对亲和力实现分离。在铅笔画的基线上点加少量样品及合适的参比物。将薄板或滤纸放入展开缸，溶剂液面须低于基线。当溶剂前沿接近顶端时取出，立即标记前沿位置。使用紫外灯或显色剂显现斑点，并计算 Rf 值：Rf = 组分移动距离 ÷ 溶剂前沿移动距离。
10. Measuring Rates of Reaction | 测量反应速率
The rate of a chemical reaction can be followed by monitoring the volume of gas evolved in a given time, the change in mass when a gas escapes, the appearance of a precipitate, or the change in colour or pH. For gas collection, a gas syringe or an inverted measuring cylinder over water is used. Ensure the apparatus is airtight and begin timing as soon as the reactants are mixed. Plot gas volume against time; the initial rate is given by the steepest tangent at t = 0.
化学反应速率可通过监测给定时间内产生的气体体积、气体逸出导致的质量变化、沉淀的出现或颜色、pH 的变化来追踪。集气可使用气体注射器或排水集气法。确保装置气密性良好，反应物一混合立即开始计时。绘制气体体积-时间曲线；初始速率由 t = 0 处最陡的切线给出。
11. pH Measurement and Acid-Base Indicators | pH 测量与酸碱指示剂
A pH meter provides a direct reading of hydrogen ion concentration after calibration with buffers of known pH (e.g. pH 4, 7, and 10). Rinse the electrode with deionised water between measurements. Acid-base indicators are weak acids with distinct colours in their protonated and deprotonated forms; choose an indicator whose pH range falls within the steep part of the titration curve. Universal indicator gives an approximate pH over a broad range.
pH 计经已知 pH 的缓冲溶液（如 pH 4、7、10）校准后可直读氢离子浓度。每次测量间需用去离子水冲洗电极。酸碱指示剂是弱酸，在质子化和去质子化形态下呈现不同颜色；应选择 pH 变色范围落在滴定曲线陡峭部分的指示剂。广用指示剂可在宽范围内给出近似 pH 值。
12. Gas Collection and Handling | 气体收集与处理
Gases such as hydrogen, oxygen, carbon dioxide, and ammonia can be prepared and collected in the laboratory. Downward delivery (for denser gases like CO₂) and upward delivery (for lighter gases like H₂ or NH₃) involve passing the gas through a delivery tube into an upright or inverted collection vessel. Gases can also be collected over water if they are insoluble or only slightly soluble. In quantitative work, a gas syringe minimises dissolution losses. Drying agents such as concentrated sulfuric acid, calcium chloride, or silica gel are used to obtain dry gases.
氢气、氧气、二氧化碳和氨气等可在实验室中制备和收集。向上排空气法（用于较轻气体如 H₂ 或 NH₃）和向下排空气法（用于较重气体如 CO₂）均通过导气管将气体通入倒立或直立的集气瓶中。对于难溶或微溶气体，可用排水集气法收集。定量实验中，气体注射器可减少溶解损失。浓硫酸、氯化钙或硅胶等干燥剂可用来获得干燥气体。
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