📚 AS Chemistry Insert 1 Jan 21: Essential Laboratory Operations | AS化学实验操作：2021年1月插入页1要点
The AS Chemistry Insert 1 from the January 2021 examination provides a detailed set of instructions for practical tasks commonly assessed in the laboratory. These operations cover fundamental techniques such as titration, solution preparation, purification, and data handling, all of which are essential for achieving reliable and reproducible results.
2021年1月AS化学考试插入页1为实验室中常见的实践任务提供了一套详细的操作指引。这些内容涵盖了滴定、溶液配制、提纯以及数据处理等基本技术，对于获得可靠且可重复的实验结果至关重要。
1. Reading the Insert: An Overview | 阅读插入页：总览
The insert typically begins with a list of required apparatus and chemicals, followed by step‑by‑step procedural notes. Candidates must read the entire insert before starting any practical work to anticipate key manipulations and safety warnings. Close attention to footnotes and highlighted values helps prevent common procedural mistakes.
插入页通常首先列出所需的仪器和化学品，随后给出分步操作说明。考生必须在开始任何实验操作之前通读全篇，以便预判关键的操作步骤和安全警告。仔细阅读脚注与高亮数值有助于避免常见的步骤性错误。
2. Using a Pipette and Burette | 使用移液管和滴定管
Rinse the pipette with the solution it will deliver, then use a pipette filler to draw the liquid above the graduation mark. Slowly release the liquid until the bottom of the meniscus sits exactly on the mark, allowing the solution to drain freely into the conical flask without blowing out the last drop.
用待吸取的溶液润洗移液管，再使用吸耳球将液体吸至刻度线上方。缓慢释放液体，直至弯月面底部正好对准刻度线，让溶液自由流入锥形瓶中，不要将管尖的最后一滴吹出。
For a burette, rinse it with the titrant, fill carefully above the zero mark, and open the tap briefly to remove air bubbles from the jet. Record the initial burette reading to the nearest 0.05 cm³, ensuring your eye is level with the meniscus. A white tile placed under the conical flask improves visibility of colour changes.
对于滴定管，先用滴定剂润洗，小心加液至零刻度线以上，然后快速打开活塞排出尖嘴中的气泡。记录初始读数时应精确至0.05 cm³，并保持视线与弯月面水平。在锥形瓶下放置白瓷板可以提高颜色变化的辨识度。
3. Weighing and Preparing Solutions | 称量及配制溶液
All mass measurements should be taken on a balance with at least ±0.01 g precision. Use a weighing boat or a piece of weighing paper and tape the reading to zero before adding the solid. For hygroscopic substances, weigh as quickly as possible to minimise moisture absorption.
所有质量测量应使用精度至少为±0.01 g的天平。使用称量舟或称量纸，并在加入固体前将读数归零。对于吸湿性物质，应尽快称量以减少吸潮。
To prepare a standard solution, dissolve the accurately weighed solid in a beaker with a small volume of deionised water, then transfer the solution quantitatively into a volumetric flask. Rinse the beaker, glass rod, and funnel several times and add the washings to the flask. Finally, make up to the graduation mark with deionised water, stopper, and invert several times to homogenise.
配制标准溶液时，将精确称量的固体在烧杯中用少量去离子水溶解，然后将溶液定量转移至容量瓶中。需冲洗烧杯、玻璃棒和漏斗数次，并将洗涤液一并转入容量瓶。最后用去离子水定容至刻度线，盖塞后反复颠倒摇匀。
4. Acid-Base Titration Procedure | 酸碱滴定步骤
A successful titration begins with a rough trial to estimate the endpoint volume. Add the titrant rapidly until a noticeable colour change, then repeat with fresh aliquots, adding the titrant dropwise near the expected endpoint. Swirl the flask continuously to ensure thorough mixing, and rinse the inner walls with deionised water if any splashes occur.
成功的滴定首先进行粗略试验以估算终点体积。快速加入滴定剂直至出现明显颜色变化，然后重新取液，在接近预期终点时逐滴加入滴定剂。持续旋转锥形瓶使溶液充分混合，若有飞溅可用去离子水冲洗瓶壁。
The following equation is often used to calculate the unknown concentration:
常用以下方程式计算未知浓度：
cₐVₐ / cₙVₙ = nₐ / nₙ
where cₐ and cₙ are the acid and base concentrations, Vₐ and Vₙ their volumes, and nₐ / nₙ the stoichiometric ratio. Concordant titres (within 0.10 cm³) should be obtained for reliable averaging.
其中 cₐ 和 cₙ 代表酸和碱的浓度，Vₐ 和 Vₙ 为各自的体积，nₐ / nₙ 为化学计量比。为获得可靠的平均值，应取得一致滴定体积（相差不超过0.10 cm³）。
5. Collection and Measurement of Gases | 气体收集与测量
Gas volumes are often measured using a gas syringe or by downward displacement of water in an inverted measuring cylinder. Ensure all connections are airtight before starting the reaction. For reactions producing a known volume of gas, the ideal gas equation pV = nRT can be used to calculate the amount of substance, provided temperature and pressure are recorded.
气体体积通常使用气体注射器或通过排水集气法在倒置的量筒中测量。在反应开始前确保所有连接处气密。对于产生已知体积气体的反应，可使用理想气体状态方程 pV = nRT 计算物质的量，前提是记录温度和压力。
When collecting gas over water, correct for the saturated vapour pressure of water at the recorded temperature. The corrected pressure of the dry gas is P(dry gas) = P(atmospheric) − P(water vapour). Always read the volume at eye level with the lowest point of the meniscus if a gas syringe is used.
采用排水集气法时，应对记录温度下水蒸气的饱和蒸气压进行校正。干燥气体的校正压为 P(干燥气体) = P(大气压) − P(水蒸气)。若使用气体注射器，应在视线与弯月面最低点水平时读数。
6. Heating Under Reflux | 回流加热
Reflux allows a reaction mixture to be heated at its boiling point for an extended period without loss of volatile substances. Assemble the apparatus with a round‑bottom flask, a vertically mounted condenser, and a heating mantle or water bath. Always add anti‑bumping granules to promote smooth boiling and connect the water flow to the condenser from the bottom inlet to the top outlet.
回流加热可使反应混合物在其沸点下长时间受热而不损失挥发性物质。组装装置需使用圆底烧瓶、垂直安装的冷凝管以及加热套或水浴。务必加入防爆沸石以促进平稳沸腾，并将冷凝水从下至上接入冷凝管。
Monitor the reflux rate so that a steady ring of condensation is visible about one‑third of the way up the condenser. After heating, allow the apparatus to cool somewhat before disassembly to avoid pressure changes and vapour release. Never stopper a heated system, as this could cause an explosion.
控制回流速度，使得冷凝环稳定地保持在冷凝管三分之一高度处。加热结束后，让装置适当冷却再拆卸，以避免压力突变和蒸气释放。切勿堵塞正在加热的体系，否则可能引起爆炸。
7. Simple Distillation | 简单蒸馏
Simple distillation is employed to separate a pure liquid from a non‑volatile solute or to separate liquids with significantly different boiling points. Place the mixture in a round‑bottom flask, insert a thermometer so its bulb is level with the side arm of the still head, and attach a Liebig condenser sloping downwards. Heat gently and collect the distillate that boils within a narrow temperature range.
简单蒸馏用于从非挥发性溶质中分离纯液体，或分离沸点差异显著的液体混合物。将混合物装入圆底烧瓶，插入温度计使其水银球与蒸馏头支管口齐平，再连接向下倾斜的直型冷凝管。缓慢加热，收集在较窄温度范围内沸腾的馏分。
Record the boiling range of the collected fraction; a pure compound typically distils within a 1–2 °C span. Discard the first few drops of distillate (fore‑run) and never distil to dryness to avoid overheating and possible decomposition.
记录收集馏分的沸程；纯化合物通常在1–2 °C范围内蒸出。弃去最初几滴馏出液（初馏分），切勿蒸干，以免过热和可能分解。
8. Recrystallisation and Melting Point Determination | 重结晶与熔点测定
Recrystallisation purifies an impure solid by exploiting differences in solubility at high and low temperatures. Dissolve the crude solid in the minimum volume of hot solvent, filter the hot solution to remove insoluble impurities, then allow the filtrate to cool slowly. Impure crystals should be washed with a small amount of ice‑cold solvent and dried between filter papers.
重结晶利用高温与低温下的溶解度差异提纯不纯固体。将粗产物溶解在尽可能少的热溶剂中，趁热过滤去除不溶性杂质，然后让滤液缓慢冷却。不纯的晶体应用少量冰冷溶剂洗涤，并在滤纸间压干。
The purity of the product can be assessed by its melting point. Use the apparatus below to measure the melting range:
产物的纯度可通过测定熔点来评估。使用下列装置测量熔程：
| Apparatus / 仪器 | Purpose / 用途 |
|---|---|
| Melting point tube (capillary) 熔点管 | Hold a small sample 装载少量样品 |
| Mel‑Temp or oil bath 熔点仪/油浴 | Provide slow, uniform heating 提供缓慢均匀加热 |
| Thermometer (0–300 °C) 温度计 | Monitor temperature 监测温度 |
A pure solid melts sharply within 1–2 °C, while impurities depress and broaden the melting range.
纯净固体在1–2 °C内敏锐熔融，而杂质会使熔点降低并拓宽熔程。
9. Chromatography Techniques | 色谱技术
Thin‑layer chromatography (TLC) is frequently used to monitor the progress of a reaction or to assess purity. Spot the sample on a TLC plate with a capillary tube, allow the spot to dry, and develop the plate in a sealed chamber containing a shallow layer of solvent. Ensure the baseline is above the solvent level.
薄层色谱 (TLC) 经常用于监测反应进程或评估纯度。用毛细管在薄层板上点样，待斑点干燥后，在含有浅层展开剂的密封层析缸中展开。确保基线高于溶剂液面。
When the solvent front has travelled approximately 1 cm from the top, remove the plate, mark the front, and visualise under UV light or with a locating agent. Calculate the Rf value for each spot using:
当溶剂前沿行进至距板顶约1 cm时取出薄层板，标记前沿，然后在紫外灯下或用显色剂显色。用下式计算每个斑点的 Rf 值：
Rf = distance moved by spot / distance moved by solvent front
Pure substances give a single well‑defined spot; additional spots indicate impurities or side products.
纯净物质呈现单一清晰的斑点；额外斑点表明存在杂质或副产物。
10. Recording Data and Estimating Uncertainty | 记录数据与估算不确定度
All measurements should be recorded using the appropriate number of significant figures, reflecting the precision of the instrument used. For example, a burette reading is recorded to two decimal places, while a 250 cm³ volumetric flask has an uncertainty of typically ±0.2 cm³.
所有测量数据应使用与仪器精度相符的有效数字位数记录。例如，滴定管读数记录至两位小数，而250 cm³容量瓶的典型不确定度为±0.2 cm³。
Typical instrumental uncertainties for common apparatus:
常见仪器的典型不确定度：
| Apparatus / 仪器 | Uncertainty / 不确定度 |
|---|---|
| 50 cm³ burette 滴定管 | ±0.10 cm³ |
| 25 cm³ pipette 移液管 | ±0.06 cm³ |
| 250 cm³ volumetric flask 容量瓶 | ±0.20 cm³ |
| 100 cm³ gas syringe 气体注射器 | ±1.0 cm³ |
| Thermometer (0–100 °C) 温度计 | ±0.5 °C |
To calculate the percentage uncertainty in a single measurement, divide the absolute uncertainty by the measured value and multiply by 100. When combining measurements, absolute uncertainties are added if quantities are added or subtracted; percentage uncertainties are added when quantities are multiplied or divided. This systematic approach is emphasised in the insert to help candidates critically evaluate their results.
计算单次测量的百分不确定度时，用绝对不确定度除以测量值再乘以100。当进行数据组合时，加减运算的绝对不确定度相加；乘除运算的百分不确定度相加。插入页强调这一系统方法，以帮助考生批判性地评估实验结果。
11. Key Safety Precautions | 主要安全预防措施
The insert highlights specific hazard warnings: wear chemical‑splash goggles and a lab coat at all times; use a fume hood when handling volatile or toxic reagents such as concentrated HCl or organic solvents; and never pipette by mouth. Heating flammable liquids must be carried out with a water bath or heating mantle rather than a direct Bunsen flame.
插入页明确标出了危险警告：随时佩戴防化学飞溅护目镜和实验服；处理浓盐酸或有机溶剂等挥发性、有毒试剂时需使用通风橱；严禁用嘴吸移液管。加热易燃液体必须使用水浴或加热套，不能直接使用本生灯火焰。
In the event of a chemical spill on skin, immediately rinse with copious amounts of running water for at least 15 minutes and report to the supervisor. All waste should be disposed of in the appropriately labelled containers, and it is essential to check the safety data sheets (SDS) before starting any procedure.
若皮肤接触化学品，立即用大量流水冲洗至少15分钟并向指导老师报告。所有废液应倒入相应标识的容器中，并且在开始任何操作前必须查阅安全数据表 (SDS)。
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