📚 Experimental Techniques for International AS Chemistry (Unit 2) | 国际AS化学（第二单元）实验操作
Mastering experimental techniques is the foundation of success in International AS Chemistry. This article concentrates on the core practical skills tested in Unit 2 (CH02), covering apparatus handling, measurement, organic synthesis, qualitative analysis, and data processing. A thorough grasp of these methods not only helps you answer exam questions accurately but also builds safe and precise laboratory habits.
掌握实验技术是学好国际AS化学的基础。本文聚焦于第二单元 (CH02) 考查的核心实验技能，涵盖仪器使用、测量、有机合成、定性分析和数据处理。透彻理解这些方法不仅有助于精准答题，也能养成安全、严谨的实验习惯。
1. Laboratory Safety and Good Practice | 实验室安全与良好规范
Always wear safety goggles and a lab coat throughout the experiment. Tie back long hair and ensure the work area is free of clutter.
实验过程中必须始终佩戴护目镜和实验服。长发应束起，工作区须保持整洁。
When handling volatile or toxic substances, use a fume cupboard. Never point the mouth of a test tube towards anyone while heating.
处理挥发性或有毒物质时，应在通风橱内操作。加热试管时，切勿将管口朝向任何人。
Dispose of chemical waste in the designated containers. Rinse glassware with distilled water before and after use to avoid cross-contamination.
化学废液应倒入指定容器。使用前后均需用蒸馏水润洗玻璃仪器，防止交叉污染。
2. Handling and Measurement of Liquids | 液体的处理与测量
Choose the appropriate apparatus based on the required precision. A measuring cylinder is suitable for approximate volumes, while a pipette and burette give high accuracy in volumetric analysis.
根据所需精密度选择适当的仪器。量筒适用于近似体积，而移液管和滴定管在容量分析中能提供高准确度。
| Apparatus | Typical volume / cm³ | Precision / ± cm³ |
|---|---|---|
| Measuring cylinder | 25 | 0.5 |
| Volumetric pipette | 25 | 0.06 |
| Burette | 50 | 0.05 |
When reading the meniscus of a transparent liquid, align your eye with the bottom of the meniscus. For coloured solutions, read the top of the liquid level.
读取透明液体的弯月面时，视线应与弯月面底部平齐。对于有色溶液，则读取液面顶端。
A volumetric pipette must be rinsed with the solution it will deliver before use. A burette is rinsed with the titrant solution and the tip must be filled with no air bubbles.
移液管使用前需用待移取的溶液润洗。滴定管须用滴定剂润洗，且管尖应充满溶液、无气泡。
3. Titration and Volumetric Analysis | 滴定与容量分析
A titration determines the concentration of an unknown solution by reacting it with a standard solution. An indicator, such as phenolphthalein or methyl orange, signals the end point by a sharp colour change.
滴定通过使未知溶液与标准溶液反应来测定其浓度。指示剂（如酚酞或甲基橙）在终点发生敏锐的颜色变化。
Carry out a rough titration first to find the approximate titre, then perform several accurate titrations until two consecutive readings agree within 0.10 cm³.
先进行一次粗略滴定以估计体积，随后进行多次精确滴定，直到连续两次读数之差在0.10 cm³ 以内。
A typical acid– O(l) + CO₂(g). The conical flask should be swirled continuously to ensure thorough mixing.
典型的酸碱滴定：Na₂CO₃(aq) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g)。滴定过程中应不断旋摇锥形瓶，使溶液充分混合。
Record burette readings to the nearest 0.05 cm³ and calculate the mean titre from the consistent values. Systematic errors can arise if the pipette or burette is not rinsed correctly.
读取滴定管刻度至0.05 cm³，用一致的滴定值计算平均体积。若移液管或滴定管未正确润洗，会引入系统误差。
4. Heating Methods: Bunsen Burner to Reflux | 加热方法：从本生灯到回流
A Bunsen burner can provide rapid heating, but a water bath (up to 100 °C) or an electric heating mantle gives more controlled heat, essential for flammable organic liquids.
本生灯可快速加热，但水浴（最高100 °C）或电热套提供更均匀的控温，这对易燃有机液体至关重要。
Heating under reflux allows a reaction mixture to be boiled continuously without loss of volatile components. The vertical condenser returns vapours to the flask.
回流加热使反应混合物持续沸腾而不损失挥发性组分。垂直的冷凝管将蒸气冷凝返回烧瓶。
A typical reflux setup includes a round-bottom flask, a condenser clamped vertically, and anti-bumping granules to ensure smooth boiling. The water inlet should be at the bottom of the condenser jacket.
典型的回流装置包括圆底烧瓶、垂直固定的冷凝管，以及防止暴沸的沸石。冷凝管夹套的进水口应在下端。
Reflux is widely used for reactions such as the oxidation of ethanol to ethanoic acid with acidified K₂Cr₂O₇, or the preparation of halogenoalkanes from alcohols.
回流广泛用于乙醇被酸化重铬酸钾氧化为乙酸的反应，以及由醇制备卤代烷等反应。
5. Distillation and Separation | 蒸馏与分离
Simple distillation separates a liquid from a non-volatile impurity or separates liquids with boiling points differing by more than 40 °C. The thermometer bulb must be placed at the entrance to the condenser.
简单蒸馏用于分离液体与不挥发性杂质，或分离沸点相差超过40 °C的液体。温度计水银球应置于冷凝管入口处。
Fractional distillation uses a fractionating column to separate miscible liquids with close boiling points, such as ethanol and water. The column provides a large surface area for repeated condensation and vaporisation.
分馏使用分馏柱分离沸点相近的互溶液体，如乙醇和水。分馏柱提供大面积表面，实现多次冷凝和蒸发循环。
When collecting the distillate, use a clean, dry receiver and discard the first few drops of distillate if they may contain low-boiling impurities.
收集馏出液时，应使用洁净干燥的接收瓶，若前几滴可能含有低沸点杂质，则应弃去。
6. Filtration, Washing, and Drying of Solids | 过滤、洗涤与固体干燥
Gravity filtration through fluted filter paper is used to remove solid impurities from a hot solution. For collecting a crystalline product, vacuum filtration with a Büchner funnel is more efficient.
重力过滤使用折叠滤纸除去热溶液中的固体杂质。若收集晶体产物，使用布氏漏斗的减压过滤更高效。
Wash the solid with a small volume of ice‑cold solvent to remove soluble impurities without dissolving the product. An organic product may be washed with water and then with a drying agent.
用少量冰冷溶剂洗涤固体，以洗去可溶性杂质而不溶解产物。有机产物可先用水洗涤，再用干燥剂干燥。
Dry the purified solid in a low‑temperature oven or a desiccator. Check the melting point range to assess purity – a pure substance melts sharply within 1–2 °C.
纯化后的固体可在低温烘箱或干燥器中干燥。通过熔点范围来检验纯度——纯物质的熔距应在1–2 °C之内。
7. Preparation of an Organic Solid or Liquid | 有机固体或液体的制备
A typical synthesis, such as 1‑bromobutane from butan‑1‑ol, involves refluxing the alcohol with NaBr and excess concentrated H₂SO₄. The reaction mixture is then distilled to separate the crude product.
典型的合成（如由正丁醇制备1‑溴丁烷）包括将醇与溴化钠和过量浓硫酸加热回流，然后将反应混合物蒸馏以获得粗产物。
The distillate is transferred to a separating funnel. The organic layer is washed successively with water, NaHCO₃ solution to remove acid, and water again, then dried over anhydrous Na₂SO₄ or MgSO₄.
将馏出液转移至分液漏斗中，有机层依次用水、碳酸氢钠溶液（除去酸）和水洗涤，然后用无水硫酸钠或硫酸镁干燥。
Redistill the dried product and collect the fraction boiling over the expected temperature range (e.g. 99–103 °C for 1‑bromobutane). Calculate the percentage yield from the masses of reactant and product.
将干燥后的产物再次蒸馏，收集预计沸点范围内的馏分（如1‑溴丁烷为99–103 °C）。通过反应物与产物的质量计算产率。
Percentage yield = (actual yield / theoretical yield) × 100%
产率 = (实际产量 / 理论产量) × 100%
8. Testing for Functional Groups and Ions | 官能团和离子的检验
Halide ions are detected by adding dilute nitric acid and silver nitrate solution. A precipitate of AgCl (white), AgBr (cream) or AgI (yellow) forms. Adding aqueous ammonia helps to confirm: AgCl dissolves in dilute NH₃, AgBr in concentrated NH₃, AgI is insoluble.
卤离子通过加入稀硝酸和硝酸银溶液来检验。生成白色AgCl、奶油色AgBr或黄色AgI沉淀。加入氨水可进一步确认：AgCl溶于稀NH₃，AgBr溶于浓NH₃，AgI不溶。
Primary and secondary alcohols are oxidised by acidified K₂Cr₂O₇, turning the solution from orange to green. Tertiary alcohols do not react. Aldehydes give a red precipitate with Fehling’s solution and a silver mirror with Tollens’ reagent.
伯醇和仲醇被酸化重铬酸钾氧化，溶液由橙色变为绿色；叔醇不反应。醛与斐林试剂共热生成红色沉淀，与托伦试剂产生银镜。
Alkenes decolourise bromine water (orange to colourless). Unsaturation can be tested by this addition reaction.
烯烃能使溴水褪色（由橙变无色），可用该加成反应检验不饱和度。
9. Chromatography: TLC and Paper | 色谱法：薄层色谱与纸色谱
Chromatography separates components of a mixture based on their differential adsorption between a stationary phase and a mobile phase. In paper chromatography, the paper is the stationary phase; in TLC, it is a thin layer of silica on a plate.
色谱法根据混合物各组分在固定相和流动相中吸附力的差异进行分离。纸色谱中滤纸为固定相；薄层色谱中，固定相是涂在板上的硅胶薄层。
Apply a small spot of the mixture on the baseline drawn in pencil. Place the plate in a developing tank with the solvent below the baseline. Allow the solvent front to rise close to the top, then mark it immediately.
在铅笔画的基线上点少量混合物样品。将板放入展开缸，溶剂液面应低于基线。待溶剂前沿升至接近顶端时，立即取出并标记前沿位置。
/ distance moved by solvent front. Compare Rf values with known standards to identify components. Colourless spots can be visualised under UV light or with a locating agent.
计算Rf = 斑点移动距离 / 溶剂前沿移动距离，与已知标准品的Rf值比对以鉴定组分。无色斑点可在紫外灯下观察或用显色剂显色。
10. Errors, Precision, and Improving Accuracy | 误差、精密度与提高准确度
Random errors cause readings to be scattered around the true value and can be reduced by repeating measurements and calculating a mean. Repeating a titration until consistent titres are obtained minimises random error.
随机误差导致读数分散在真值周围，可通过重复测量并计算平均值来减小。滴定中重复操作至获得一致结果可最小化随机误差。
Systematic errors shift all readings in the same direction, for example a burette with a faulty scale. These cannot be reduced by averaging; the apparatus must be calibrated or the procedure corrected.
系统误差使所有读数朝同一方向偏移，例如滴定管刻度不准。这类误差无法通过取平均值减小，必须校准仪器或修正操作步骤。
Percentage uncertainty of a single reading = (absolute uncertainty / measured value) × 100% burette reading, absolute uncertainty is considered twice because two readings are taken.
单次读数的百分不确定度 = (绝对不确定度 / 测量值) × 100%。滴定管读数需考虑两次读数的绝对不确定度之和。
To improve accuracy, pre‑rinse apparatus with the relevant solutions, use fresh indicators, and ensure the balance is tared with a clean weighing boat. Recording all raw data immediately and clearly prevents transcription mistakes.
为提高准确度，应用相应溶液预洗仪器，使用新鲜指示剂，并确保天平用洁净称量舟去皮。立即清晰地记录原始数据，可避免转录错误。
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