AS Chemistry Unit 5 Practical Techniques from Jun19 Insert | AS化学单元5 Jun19插页实验操作

📚 AS Chemistry Unit 5 Practical Techniques from Jun19 Insert | AS化学单元5 Jun19插页实验操作

The June 2019 insert for AS Chemistry Unit 5 provides a detailed guide to essential practical operations that every candidate must master. This article unpacks those techniques, from accurate mass measurement to purification and yield calculation, reinforcing both theoretical understanding and hands-on competence.

2019年6月AS化学单元5的插页材料详细列出了每位考生必须掌握的关键实验操作。本文将逐一解析这些技术，从精确的质量测量到提纯与产率计算，强化理论理解和动手能力。

1. Safety in the Laboratory | 实验室安全

Before starting any procedure, you must identify the hazards associated with the chemicals and equipment used. Always wear safety goggles and a lab coat, and handle concentrated acids, alkalis and flammable solvents inside a fume cupboard. The Jun19 insert often labels substances with GHS hazard pictograms — make sure you can interpret them and state appropriate control measures such as ‘keep away from naked flames’ or ‘use gloves’.

开始任何操作前，必须识别所用化学品和仪器的危险性。务必佩戴护目镜和实验服，并在通风橱内处理浓酸、浓碱和易燃溶剂。Jun19插页通常会标有GHS危险象形图——确保你能解读这些符号，并说明适当的控制措施，例如“远离明火”或“戴手套”。

2. Measuring Mass and Volume | 测量质量与体积

A digital balance reading to ±0.01 g or ±0.001 g is used to weigh solids. Record masses immediately and to the full precision of the instrument. For volumes, use a volumetric pipette for fixed volumes (tolerance ±0.06 cm³ for a 25 cm³ pipette) or a burette for variable, accurate delivery. The Jun19 insert reminds you to rinse glassware with the solution it will contain before use.

使用可读至±0.01 g或±0.001 g的电子天平称量固体。立即记录质量，并保留仪器的全部精度。量取体积时，使用移液管量取固定体积（25 cm³移液管的允差为±0.06 cm³），或用滴定管进行可变的精确滴加。Jun19插页提醒你在使用前用待装溶液润洗玻璃器皿。

3. Heating Methods and Reflux | 加热方法与回流

Direct heating with a Bunsen burner is rarely used in organic preparations because many reagents are flammable. Instead, the insert describes heating a reaction mixture in a round-bottom flask fitted with a condenser, using either a water bath, an oil bath or an electric heating mantle. Refluxing allows the reaction to proceed at the boiling point of the solvent without loss of volatile material; the condenser’s water flow should enter at the bottom and exit at the top for efficient cooling.

由于很多试剂易燃，有机制备中很少用本生灯直接加热。插页介绍的是将反应混合物置于装有冷凝管的圆底烧瓶中，用水浴、油浴或电热套加热。回流可使反应在溶剂沸点温度进行而不损失挥发性物质；冷凝管的水流应从下端进入、上端排出，以达到高效冷却。

4. Distillation Techniques | 蒸馏技术

Simple distillation is used to separate a pure liquid from a non-volatile solute, while fractional distillation separates miscible liquids with close boiling points. The Jun19 insert may show a diagram of a fractionating column packed with glass beads; these provide a large surface area for repeated condensation–vaporisation cycles. The thermometer bulb must be placed exactly at the junction to the condenser to record the boiling point of the distilling vapour.

简单蒸馏用于从非挥发性溶质中分离纯液体，而分馏则用于分离沸点相近的互溶液体。Jun19插页可能展示一根填充玻璃珠的分馏柱；玻璃珠提供大量的表面积，实现反复的冷凝–蒸发循环。温度计水银球必须恰好放在与冷凝管连接处，以记录蒸出蒸气的沸点。

5. Filtration and Drying | 过滤与干燥

After crystallisation or precipitation, solid product is collected by vacuum filtration using a Büchner funnel and flask. The Jun19 insert emphasises washing the crude solid with a small amount of ice‑cold solvent to remove soluble impurities without dissolving the product. Moist product is then dried in a desiccator, a low‑temperature oven or by pressing between pieces of filter paper. Ensure you record the mass of an empty watch glass before weighing the dried solid.

结晶或沉淀后，使用布氏漏斗和吸滤瓶进行减压过滤以收集固体产品。Jun19插页强调用少量冰冷的溶剂洗涤粗产物，以除去可溶性杂质而不会溶解产品。湿的产品随后放入干燥器、低温烘箱中干燥，或在滤纸间挤压干燥。确保先记录空表面皿的质量，再称量干燥后的固体。

6. Recrystallisation | 重结晶

Recrystallisation is the primary method for purifying an impure organic solid. Dissolve the crude solid in the minimum volume of hot solvent, filter while hot to remove insoluble debris, then allow the solution to cool slowly. Pure crystals form, leaving soluble impurities in the mother liquor. The Jun19 insert notes that seed crystals, scratching the flask with a glass rod or cooling in an ice bath can induce crystallisation if it does not occur spontaneously.

重结晶是提纯不纯有机固体的主要方法。用最少量热溶剂溶解粗产物，趁热过滤除去不溶性杂质，然后让溶液缓慢冷却。纯晶体析出，可溶性杂质留在母液中。Jun19插页指出，若未能自发结晶，可用晶种、玻璃棒刮擦瓶壁或在冰浴中冷却来诱发结晶。

7. Melting Point Determination | 熔点测定

A pure organic solid melts sharply over a narrow range (typically 0.5–2.0 °C), whereas the presence of impurities lowers and broadens the melting range. Load a small amount of dry solid into a capillary tube, place it in an electric melting point apparatus or oil bath, and heat slowly near the expected temperature. Record the onset and clear point. The Jun19 insert expects you to compare the observed range with literature values and to comment on purity.

纯有机固体在一个狭窄范围内（通常0.5–2.0 °C）急剧熔化，而杂质的存在会降低并拓宽熔点范围。将少量干燥固体装入毛细管，放入电熔点仪或油浴中，在接近预期温度时缓慢加热。记录初熔温度和全熔温度。Jun19插页要求你将观察到的范围与文献值进行比较，并据此评价纯度。

8. Thin Layer Chromatography (TLC) | 薄层层析

TLC is used to monitor the progress of a reaction or to check the purity of a product. Use a pencil to draw a baseline on a silica‑coated plate; spot a dilute solution of sample and reference compounds. Develop the plate in a beaker containing a shallow layer of solvent, and ensure the spots are above the solvent level. Visualise spots under UV light or with iodine vapour. The Jun19 insert typically asks you to calculate the R_f value and to explain why the base line must be drawn in pencil, not ink.

薄层层析用于监测反应进程或检查产品纯度。用铅笔在硅胶薄板上划一条基线；点上样品和参比化合物的稀溶液。将薄板放入盛有浅层展开液的烧杯中展开，并确保样点高于液面。在紫外灯下或碘蒸气中显色。Jun19插页通常要求计算R_f值，并解释为什么基线要用铅笔而不用墨水绘制。

9. Titration and Yield Calculation | 滴定与产率计算

Acid–base or redox titrations are common in quantitative analysis. A burette should be rinsed with the titrant, and the tip must be free of air bubbles. The Jun19 insert may provide titre values; concordant results should be within 0.10 cm³. When preparing a product, you must calculate the percentage yield: % yield = (actual mass ÷ theoretical mass) × 100%. Always identify the limiting reagent first and show a fully balanced equation.

酸碱滴定或氧化还原滴定是定量分析中常见的操作。滴定管应用滴定剂润洗，且管尖不得有气泡。Jun19插页可能会提供滴定值；一致的结果应在0.10 cm³以内。制备产品时，必须计算产率：产率 = (实际质量 ÷ 理论质量) × 100%。务必先确定限量试剂，并写出完整的配平方程式。

10. Preparation of an Organic Solid: Aspirin | 有机固体制备：阿司匹林

A classic experiment featured in the Jun19 insert is the synthesis of aspirin (acetylsalicylic acid) from salicylic acid and ethanoic anhydride, with a few drops of concentrated phosphoric acid as catalyst. The mixture is warmed in a water bath, then cooled in ice; the crude aspirin is filtered, recrystallised from ethanol/water and its purity assessed by melting point or TLC. The insert provides the relevant chemical equation: C₇H₆O₃ + C₄H₆O₃ → C₉H₈O₄ + CH₃COOH.

Jun19插页中一个经典实验是用水杨酸和乙酸酐为原料，以几滴浓磷酸作催化剂合成阿司匹林（乙酰水杨酸）。混合物在水浴中温热，然后冰水冷却；粗阿司匹林过滤后，用乙醇/水重结晶，并通过熔点或TLC检验纯度。插页给出相应的化学方程式：C₇H₆O₃ + C₄H₆O₃ → C₉H₈O₄ + CH₃COOH。

11. Using a Separating Funnel | 分液漏斗的使用

When the product is a liquid immiscible with water, a separating funnel is employed to separate the organic layer. The Jun19 insert recommends adding a drying agent (e.g. anhydrous magnesium sulfate) to the organic layer and swirling until the liquid appears clear. Remember to remove the stopper before running out the lower layer, and to collect the upper layer separately through the top to avoid contamination.

当产物是与水不混溶的液体时，使用分液漏斗分离有机层。Jun19插页建议向有机层中加入干燥剂（如无水硫酸镁），并旋摇至液体变澄清。记住在放出下层液体之前取下玻璃塞，上层液体应从顶口倒出，以防交叉污染。

12. Drawing and Interpreting Graphs | 绘图与解释

The insert may involve plotting temperature–time cooling curves or concentration–time graphs. Use a sharp pencil, label axes with quantity and unit, choose sensible scales, and draw a line of best fit. For a cooling curve used to determine melting point, extrapolate the two linear portions — their intersection gives the freezing point. Always comment on any anomalous points and suggest improvements that reduce heat loss or improve temperature control.

插页可能涉及绘制温度–时间冷却曲线或浓度–时间图。用削尖的铅笔绘图，标注坐标轴所代表的量和单位，选择合适的标度，并画出最佳拟合线。对于用于确定熔点的冷却曲线，外推两条直线段——其交点即为凝固点。务必解释任何异常点，并提出减少热量损失或改善温度控制的改进措施。

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Published by TutorHao | Chemistry Revision Series | aleveler.com

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