📚 IGCSE CIE Chemistry: A Guide to Experimental Techniques | IGCSE CIE 化学：实验操作指南
Mastering experimental techniques is essential for success in the IGCSE CIE Chemistry course. The practical skills you learn in the laboratory are directly tested in Paper 6 (Alternative to Practical) and also help you understand key chemical concepts more deeply. This guide covers the most important procedures, from basic measurements to separation methods and gas handling, with clear instructions that align with the CIE syllabus.
掌握实验操作技巧是在 IGCSE CIE 化学课程中取得成功的关键。你在实验室学到的实践技能会通过 Paper 6（实验替代卷）直接进行考核，同时也能帮助你更深入地理解核心化学概念。本指南涵盖了从基本测量到分离方法及气体处理等最重要的操作流程，并提供了与 CIE 大纲要求相符的清晰说明。
1. Measuring Mass and Volume | 称量与量取体积
Always use an electronic balance placed on a flat, stable surface to measure mass. Before placing any substance on the pan, press the tare (zero) button to reset the display. If you are weighing a solid directly, place a clean weighing boat or piece of filter paper on the pan first, then tare again so the reading shows the mass of the substance only. For liquids, a dry beaker or conical flask should be tared before adding the liquid.
测量质量时应始终使用放置在平坦稳固台面上的电子天平。在把任何物质放在秤盘上之前，先按下归零键使显示屏复位。若直接称量固体，应先在秤盘上放置干净的称量舟或称量纸，然后再次归零，这样读数便仅显示物质的质量。对于液体，则需先对待用的干燥烧杯或锥形瓶进行归零，再倒入液体。
Volume of liquids can be measured using measuring cylinders, pipettes, or burettes depending on the required precision. A measuring cylinder is sufficient for approximate volumes to the nearest 0.5 cm³ or 1 cm³, but for more accurate work, a volumetric pipette (e.g. 25.0 cm³) delivers a fixed volume with high precision. When reading the meniscus for a transparent liquid, your eye must be level with the bottom of the curved surface to avoid parallax errors; read the scale at the lowest point of the meniscus.
液体的体积可用量筒、移液管或滴定管测量，具体取决于所需的精度。量筒适用于精确到 0.5 cm³ 或 1 cm³ 左右的粗略量取，而在要求更准确的工作中，容量移液管（例如 25.0 cm³）能够高精度地移取固定体积。读取透明液体的弯月面时，眼睛必须与曲面最低点保持水平，以避免视差；应在弯月面底部所处的位置读取刻度。
2. Heating and Cooling Techniques | 加热与冷却技术
For gentle heating of a liquid in a test tube, a Bunsen burner with a medium blue flame is used. The test tube should be held with a test‑tube holder and moved continuously through the flame, with the mouth pointing away from yourself and others. Never heat a test tube that is more than one‑third full, and never point the mouth directly at anyone. When heating a beaker of liquid, place a wire gauze on a tripod to support the beaker and spread the heat evenly.
对试管中的液体进行温和加热时，使用本生灯的中等蓝色火焰。应用试管夹夹住试管并持续在火焰中移动加热，试管口须指向远离自己和他人的方向。切勿加热装液量超过三分之一的试管，也决不可将管口直接对着任何人。加热烧杯中的液体时，应在三脚架上放置铁丝网用以承托烧杯并使热量均匀分布。
Cooling a very hot solid or liquid to room temperature is often needed before measuring its mass or volume. The apparatus should be left on a heat‑resistant mat until it is cool enough to touch. To cool a sample more rapidly, the container can be placed in a beaker of cold water, but thermal shock should be avoided for glass apparatus – never plunge hot glass directly into ice‑cold water as it may crack.
在测量质量或体积之前，通常需要将极热的固体或液体冷却至室温。应将器材放置在耐热垫上，直至其充分冷却至可触碰的程度。如需加速冷却，可将容器放入盛有冷水的烧杯中，但对玻璃器材要避免热冲击——绝不能把灼热的玻璃直接投入冰水中，否则可能炸裂。
3. Filtration and Evaporation | 过滤与蒸发
Filtration separates an insoluble solid from a liquid. Fold a filter paper into a cone that fits snugly inside a filter funnel, moisten it slightly with distilled water, and seat it firmly against the funnel walls. The mixture is poured down a glass rod into the funnel so that the liquid passes through without splashing. The solid, called the residue, stays on the filter paper, while the filtrate (the liquid that passes through) is collected in a beaker or conical flask.
过滤可将不溶性固体从液体中分离出来。将滤纸折叠成能紧贴漏斗的圆锥形，用蒸馏水稍加润湿，使其牢固地贴附在漏斗内壁上。把混合物沿着玻璃棒倒入漏斗，使液体顺利流下而不溅出。固体，即残渣，被留在滤纸上，而穿过滤纸的液体（滤液）则收集在烧杯或锥形瓶中。
Evaporation is used to remove the solvent from a solution, leaving the solute behind. The solution is poured into an evaporating basin and heated gently over a steam bath or a very small Bunsen flame. To avoid spitting of the solid, do not heat to complete dryness while still over the flame; instead, remove the basin when a small amount of liquid remains, and leave the rest of the solvent to evaporate naturally. This technique is often the first step in obtaining a crystalline solid before recrystallisation.
蒸发用于除去溶液中的溶剂，留下溶质。将溶液倒入蒸发皿，并在水浴或极小的本生灯火上温和加热。为避免固体飞溅，不要直接在火焰上加热至完全干涸；应当在还剩少量液体时取下蒸发皿，让剩余溶剂自然蒸发。这一操作通常是获得晶体固体之前再进行重结晶的第一步。
4. Crystallisation | 结晶
Crystallisation is a method of obtaining a pure crystalline solid from a saturated solution. After evaporation has been carried out until the solution is saturated (indicated by the first appearance of crystals on a cold glass rod dipped into the solution), the mixture is allowed to cool slowly. Slow cooling promotes the formation of larger, purer crystals. The crystals are then collected by filtration, washed with a small amount of cold distilled water, and dried between sheets of filter paper.
结晶是从饱和溶液中得到纯净晶体固体的一种方法。先将溶液蒸发至饱和状态（用冷的玻璃棒蘸取溶液时，棒上首次析出晶体即为饱和标志），然后让混合物缓慢冷却。缓慢降温有利于生成较大且较纯净的晶体。随后将晶体通过过滤收集，用少量冷的蒸馏水洗涤，最后夹在滤纸层之间干燥。
Impurities can be removed effectively by recrystallisation. The crude solid is dissolved in the minimum amount of hot solvent, the hot solution is filtered while hot to remove any insoluble impurities, and then it is left to cool and crystallise. Soluble impurities stay in the mother liquor. This process may be repeated to increase purity.
通过重结晶可有效去除杂质。将粗品固体溶解在尽可能少的热溶剂中，趁热过滤除去不溶性杂质，然后将滤液静置冷却、结晶。可溶性杂质则留在母液中。可重复进行该过程以进一步提高纯度。
5. Distillation | 蒸馏
Simple distillation is used to separate a liquid from a soluble solid or to separate two liquids with widely different boiling points. The mixture is heated in a distillation flask fitted with a thermometer (bulb placed level with the side arm) and a condenser. Cold water enters the condenser jacket at the lower end and exits at the upper end, ensuring efficient cooling. The vapour of the more volatile substance rises, enters the condenser, condenses back to a liquid, and drips into a receiving flask as the distillate.
简单蒸馏用于从可溶性固体中分离出液体，或分离沸点相差很大的两种液体。混合物在装有温度计（水银球与支管口齐平）和冷凝管的蒸馏烧瓶中加热。冷却水从冷凝管外套的下端进入、上端流出，以确保高效冷却。低沸点组分蒸气上升，进入冷凝管后冷凝回液体，并滴入接收瓶成为馏出液。
Fractional distillation is required for separating a mixture of miscible liquids with closer boiling points, such as ethanol and water. A fractionating column packed with glass beads is attached between the flask and the condenser. The beads provide a large surface area for repeated condensation and vaporisation cycles, effectively separating the components by their boiling points. The liquid with the lower boiling point is collected first.
若要分离沸点相差不大的互溶液体混合物（如乙醇和水），则需要使用分馏。在烧瓶与冷凝管之间加装一个填有玻璃珠的分馏柱。玻璃珠提供了较大的表面积以实现反复的冷凝和气化循环，从而依据各组分的沸点有效分离它们。沸点较低的液体首先被收集。
6. Chromatography | 色谱法
Paper chromatography is a technique used to separate and identify small amounts of coloured substances, such as dyes or food colourings. A concentrated spot of the mixture is placed on a pencil‑drawn baseline near one end of the chromatographic paper. The paper is suspended in a sealed container with the baseline above the solvent level. As the solvent moves up the paper, it carries the components at different rates, producing separated spots. The Rf value (retention factor) is calculated as:
Rf = distance moved by substance ÷ distance moved by solvent front
Rf values are used for identification when compared with known standards run under identical conditions.
纸上色谱法是用于分离和鉴定少量有色物质（如染料或食用色素）的技术。在靠近色谱纸一端的铅笔基线上点上一滴浓斑点混合物。将纸条悬挂在密封容器中，使基线保持在溶剂液面之上。随着溶剂沿纸上升，各组分以不同速率被携带移动，形成分开的斑点。比移值 Rf 的计算式为：
Rf = 物质移动距离 ÷ 溶剂前沿移动距离
将待测物的 Rf 值在与已知标准样在相同条件下得到的数值对比，即可用于鉴定。
To obtain reliable results, draw the baseline in pencil – never in ink, as ink may dissolve in the solvent. Use a capillary tube to apply a tiny, concentrated spot, and allow the spot to dry before placing the paper into the solvent. The chromatogram may be viewed under UV light or sprayed with a locating agent if the spots are colourless.
为了获得可靠的结果，应用铅笔画基线——决不能使用钢笔，因为墨水会溶于溶剂。用毛细管点上一个微小而浓的斑点，并等斑点干燥后再把滤纸放入溶剂中。若斑点无色，可将色谱图放在紫外灯下观察或喷上显色剂来显色。
7. Titration | 滴定
Titration is a quantitative technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration. A pipette is used to transfer a known volume of one solution into a conical flask, and a suitable indicator (e.g. methyl orange or phenolphthalein) is added. The other solution is placed in a burette, and the initial volume is recorded to the nearest 0.05 cm³. The tap is opened to add the solution from the burette into the flask while swirling continuously.
滴定是一种定量技术，通过让未知浓度的溶液与已知浓度的溶液反应来确定其浓度。用移液管将一定体积的某溶液移入锥形瓶，并加入合适的指示剂（如甲基橙或酚酞）。另一种溶液装在滴定管内，记录初始读数，精确至 0.05 cm³。打开活栓并将滴定管中的溶液逐滴加入瓶中，同时不断摇动锥形瓶。
The end point is reached when the indicator just changes colour permanently. The final burette reading is recorded, and the titre (volume used) is calculated. A rough titration is performed first, followed by several accurate titrations until concordant results (within 0.10 cm³) are obtained. The average of the concordant titres is then used in calculations, often involving the formula:
amount of solute (mol) = concentration (mol dm⁻³) × volume (dm³)
当指示剂刚好发生永久性颜色改变时，即为滴定终点。记录滴定管终读数，并计算所用的标准溶液体积（滴定值）。先进行一次粗滴定，随后再进行数次精确滴定，直至获得贴合结果（偏差在 0.10 cm³ 以内）。然后将贴合滴定值的平均值代入计算，通常涉及公式：
溶质的物质的量 (mol) = 浓度 (mol dm⁻³) × 体积 (dm³)
During titration, the tip of the burette must be below the neck of the flask to avoid loss of solution. A white tile placed under the conical flask helps to see the colour change more clearly. Swirl the flask smoothly but take care not to splash.
滴定时，滴定管的尖嘴应处于锥形瓶瓶颈之下，以防溶液损失。瓶下放置白色瓷板有助于更清晰地观察颜色变化。平稳旋摇锥形瓶，但注意不要溅出。
8. Collection and Drying of Gases | 气体的收集与干燥
Gases can be collected by several methods depending on their density and solubility in water. Gases that are denser than air (e.g. CO₂, Cl₂, HCl) are collected by upward delivery using a gas jar with the delivery tube reaching the bottom of the jar. Gases less dense than air (e.g. H₂, NH₃) are collected by downward delivery with the jar inverted. For gases that are insoluble or only slightly soluble in water (e.g. O₂, H₂, CO₂), collection over water is convenient; the gas is bubbled into an inverted measuring cylinder full of water, forcing the water out.
气体的收集方法取决于其密度和在水中的溶解度。密度大于空气的气体（如 CO₂、Cl₂、HCl）使用向上排空气法收集，将导气管伸至集气瓶底部。密度小于空气的气体（如 H₂、NH₃）则用向下排空气法，集气瓶倒置。对于不溶或仅微溶于水的气体（如 O₂、H₂、CO₂），排水集气法较为方便；将气体通入装满水并倒置的量筒中，水被排出。
After collection, gases often need to be dried to remove water vapour. Common drying agents include concentrated sulfuric acid (for acidic and neutral gases like Cl₂, CO₂, SO₂, but not for NH₃), anhydrous calcium chloride (which can dry most gases except ammonia, with which it reacts), and quicklime, calcium oxide (used for ammonia and basic gases). The gas is passed through a U‑tube or a wash bottle containing the drying agent before collection.
收集后，气体通常需要干燥以除去水蒸气。常见的干燥剂有：浓硫酸（用于酸性及中性气体如 Cl₂、CO₂、SO₂，但不可用于 NH₃），无水氯化钙（可干燥除氨以外的大多数气体，因它会与氨反应），以及生石灰即氧化钙（用于氨等碱性气体）。气体在收集前需通过含有干燥剂的 U 形管或洗气瓶。
9. Testing for Common Gases | 常见气体的检验
CIE IGCSE requires you to know simple tests for hydrogen, oxygen, carbon dioxide, chlorine, ammonia, sulfur dioxide, and nitrogen dioxide. Each test provides a characteristic observation that confirms the identity of the gas. The table below summarises these tests.
CIE IGCSE 大纲要求你掌握氢气、氧气、二氧化碳、氯气、氨气、二氧化硫和二氧化氮的简易检验法。每种检验都会出现特征性现象，从而确证气体的身份。下表对这些检验方法作了总结。
| Gas / 气体 | Test / 检验方法 | Positive Result / 阳性结果 |
|---|---|---|
| Hydrogen (H₂) | Insert a lighted splint | Burns with a squeaky pop sound |
| Oxygen (O₂) | Place a glowing splint into the gas | The splint relights |
| Carbon dioxide (CO₂) | Bubble through limewater (calcium hydroxide solution) | Limewater turns milky (white precipitate of CaCO₃) |
| Chlorine (Cl₂) | Hold damp blue litmus paper or universal indicator paper in the gas | Damp blue litmus turns red then is bleached white; universal indicator is bleached |
| Ammonia (NH₃) | Hold damp red litmus paper near the gas | Turns blue |
| Sulfur dioxide (SO₂) | Pass through an acidified potassium dichromate(VI) solution | Orange solution turns green |
| Nitrogen dioxide (NO₂) | Observe colour and smell cautiously | Brown acidic gas with a pungent, choking smell |
For sulfur dioxide, an alternative test is to expose the gas to damp potassium manganate(VII) paper; it turns from purple to colourless. Always note the colour of the gas before applying a chemical test, as indicators like litmus may give additional information about acidity.
对于二氧化硫，另一种检验方法是将其接触湿润的高锰酸钾试纸；试纸会由紫色变为无色。在运用化学检验之前，始终应观察气体的颜色，因为像石蕊试纸这样的指示剂可能提供关于气体酸碱性的额外信息。
10. Recording Data and Uncertainties | 数据记录与不确定性
All observations should be recorded in ink, directly in a notebook or results table, as soon as they are noted. For titrations, burette readings must be written to two decimal places ending in .00 or .05, for example 24.55 cm³ or 23.40 cm³. When using a measuring cylinder, record the volume to the nearest half of the smallest scale division. Always state the resolution of the measuring instrument, as this indicates the precision of the measurement.
所有观察结果一旦注意到就应立即用墨水直接记录在笔记本或结果表格中。滴定实验中，滴定管读数必须记到小数点后两位，末位为 .00 或 .05，如 24.55 cm³ 或 23.40 cm³。使用量筒时，体积记录到最小刻度一半的精确度。要始终标明测量仪器的分辨率，因为这指示了测量的精密度。
In any measurement, there is an inherent uncertainty, typically taken as ± half of the smallest scale division for analogue instruments. For example, a thermometer with 1 °C divisions gives an uncertainty of ±0.5 °C. When two readings are subtracted to obtain a temperature change, the uncertainty in the difference is ±1 °C. These uncertainties should be considered when evaluating the reliability of the results.
任何测量都存在固有不确定度，对于模拟仪器通常取最小刻度的一半作为不确定度。例如，一支刻度间隔为 1 °C 的温度计，其不确定度为 ±0.5 °C。当两个读数相减得到温度变化时，温度差的不确定度为 ±1 °C。在评价结果的可靠性时，应将这些不确定度纳入考量。
11. Safety Precautions | 安全注意事项
Laboratory safety is paramount. Always wear safety goggles to protect your eyes. Tie long hair back and avoid loose clothing that could catch fire or knock over apparatus. When using a Bunsen burner, light the match before turning on the gas, and open the air hole only after the flame is established to prevent a strike‑back. Never leave a lit burner unattended.
实验室安全至关重要。始终佩戴护目镜以保护眼睛。长发应束好，避免穿着宽松衣物，以防着火或绊倒器材。使用本生灯时，先点火柴再开燃气，火焰建立后再打开气孔，以防回火。点燃的灯绝不能无人看管。
Handle chemicals with care, using spatulas or droppers rather than directly with fingers. When smelling a gas, waft the vapour gently towards your nose – never inhale deeply at the mouth of a test tube. Dilute acids and alkalis can cause skin irritation; wash any spills immediately with plenty of water. Dispose of all waste in the designated containers, never down the sink unless instructed. In the event of a minor burn, hold the affected area under cold running water for at least ten minutes.
小心处理化学品，使用药匙或滴管，切勿直接用手指接触。闻气体时，用手将蒸气轻轻扇向鼻子——决不要直接近口深闻试管口。稀酸稀碱也可能刺激皮肤；一旦溅到，立即用大量水冲洗。所有废弃物应倒入指定容器，未经指示不得倒入水槽。万一发生轻微灼伤，应将受伤部位在流动冷水下冲洗至少 10 分钟。
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