📚 IGCSE Chemistry Practical Skills: Experimental Operations | IGCSE 化学实验操作：剑桥课程教材核心技能
Mastering practical skills is essential for success in Cambridge IGCSE Chemistry. The coursebook guides students through a series of experiments that develop fundamental techniques such as measuring, heating, separating mixtures, and identifying substances. This article summarises the key experimental operations you need to know, with step-by-step explanations and safety precautions.
掌握实验技能对于剑桥 IGCSE 化学取得成功至关重要。课程教材引导学生通过一系列实验，培养基本技术，如测量、加热、分离混合物和鉴定物质。本文总结了你需要掌握的关键实验操作，并提供逐步说明和安全注意事项。
1. Using Measuring Instruments | 使用测量仪器
When measuring the volume of a liquid with a measuring cylinder, always place the cylinder on a flat surface and read the bottom of the meniscus at eye level. For more precise work, use a pipette to transfer a fixed volume (e.g. 25.0 cm³) or a burette to deliver variable volumes during a titration. A digital balance should be tared before weighing to zero out the container mass, and the reading must be recorded to the appropriate number of decimal places.
使用量筒测量液体体积时，务必将量筒放在平整表面上，视线与凹液面的底部齐平读数。若需要更高精度，使用移液管移取固定体积（如 25.0 cm³），或使用滴定管在滴定过程中释放可变体积。使用电子天平称量前必须先去皮（调零），以扣除容器质量，并正确记录小数点后的有效位数。
Thermometers must be handled carefully: when measuring the temperature of a liquid, keep the bulb fully immersed and read the temperature while the thermometer is still in the liquid. Never use a thermometer as a stirrer. Always select an appropriate range – a standard alcohol or digital thermometer covers −10 °C to 110 °C for most school experiments.
必须小心使用温度计：测量液体温度时，将感温泡完全浸没，并保持温度计在液体中读数。切勿将温度计当作搅拌棒使用。应根据实验选择合适量程——学校常规实验通常使用 −10 ℃ 至 110 ℃ 的酒精温度计或数字温度计。
2. Heating Substances Safely | 安全加热
When heating a liquid in a test tube, use a boiling tube rather than a narrow test tube, and add anti-bumping granules to ensure smooth boiling. Point the mouth of the tube away from yourself and others, and heat gently by moving the tube in and out of a Bunsen burner flame. Never look down the tube while heating.
在试管中加热液体时，应选用较粗的沸腾管而非细试管，并加入防暴沸颗粒以保证平稳沸腾。试管口不要对着自己和他人，将试管在本生灯火焰中温和地移动加热。加热时切勿俯视试管口。
For heating solids, place the solid in a hard-glass test tube and hold it in a nearly horizontal position, but with the mouth slightly lower than the base. This prevents condensed water droplets from flowing back onto the hot glass, which could cause the tube to crack. Use a test-tube holder or tongs, and always heat a solid gently at first. When using a Bunsen burner, adjust the air hole to obtain a roaring blue flame for strong heating, and place a heat-proof mat under all apparatus.
加热固体时，将固体置于硬质试管中，水平持握但让管口略低于管底。这样可防止冷凝的水滴倒流到灼热的玻璃上引起炸裂。使用试管夹或坩埚钳，并始终先温和加热。当使用本生灯时，调节空气孔以获得强热的蓝色呼啸焰，且所有装置下方均应放置隔热垫。
3. Filtration and Evaporation | 过滤与蒸发
To separate an insoluble solid from a liquid, fold a filter paper into a cone, place it snugly inside a filter funnel, and moisten it with distilled water so that it adheres to the glass. Pour the mixture slowly into the funnel; the insoluble residue collects on the paper, while the filtrate passes through and is collected in a beaker or conical flask. This technique is commonly used to remove sand from a salt solution.
为分离不溶性固体与液体，将滤纸折成圆锥形，使其紧密贴合漏斗内壁，用蒸馏水润湿令其贴紧玻璃。将混合物缓慢倒入漏斗，不溶性残渣留在滤纸上，滤液通过并收集在烧杯或锥形瓶中。此方法常用于去除砂粒从盐溶液中。
To obtain a soluble solid from the filtrate, transfer the filtrate to an evaporating basin and heat it over a water bath or gently on a tripod and gauze. As water evaporates, the solution becomes more concentrated and crystals start to form. Do not evaporate to complete dryness too rapidly, as splashing may occur. Instead, stop heating when small crystals appear and allow the remaining solvent to evaporate slowly at room temperature to yield larger, purer crystals.
要从滤液中获得可溶性固体，将滤液转移到蒸发皿中，在水浴上或用三脚架和石棉网缓慢加热蒸发。随着水蒸发，溶液浓缩并开始析出晶体。不要迅速完全蒸干，以免液体飞溅。应等到出现小晶体时停止加热，让剩余溶剂在室温下缓慢蒸发，可得到更大更纯的晶体。
4. Crystallisation | 结晶
Crystallisation is used to purify a soluble solid. First, prepare a saturated solution by dissolving the impure solid in a minimum volume of hot solvent (usually distilled water). Filter while hot to remove any insoluble impurities. Then allow the filtrate to cool slowly; solubility decreases on cooling, and pure crystals form gradually. Slow cooling encourages the formation of larger, well-defined crystals. If necessary, a seed crystal can be added to initiate crystallisation.
结晶用于提纯可溶性固体。首先，将不纯固体溶于尽量少的热溶剂（通常为蒸馏水）中制成饱和溶液。趁热过滤以除去不溶性杂质。然后将滤液缓慢冷却；溶解度随冷却而降低，纯晶体逐渐析出。缓慢冷却有利于形成大而完整的晶体。必要时可加入晶种来诱导结晶。
After crystallisation, the crystals are separated by filtration, washed with a little cold solvent to remove any adhering impurities, and finally dried between sheets of filter paper or in a low-temperature oven. The purity can be assessed by checking a sharp melting point.
结晶后，通过过滤分离晶体，用少量冷溶剂洗涤以除去表面附着的杂质，最后在滤纸间吸干或在低温烘箱中干燥。晶体纯度可以通过检查其是否具有明确的熔点来进行评估。
5. Simple Distillation | 简单蒸馏
Simple distillation separates a solvent from a solution, producing a pure distillate. The apparatus consists of a round-bottom flask containing the solution, connected to a condenser with a thermometer positioned at the junction to the condenser. The bulb of the thermometer must align with the side arm so that it measures the boiling point of the vapour. Anti-bumping granules are added to the flask to promote smooth boiling.
简单蒸馏用于从溶液中分离出溶剂，从而获得纯馏出液。装置由盛有溶液的圆底烧瓶、冷凝管以及置于烧瓶支管口处的温度计组成。温度计的感温泡必须与支管平齐，以准确测量蒸气的沸点。烧瓶中需加入防暴沸颗粒以确保平稳沸腾。
The solution is heated, and the vapour rises and passes into the water-cooled condenser. Cold water enters the condenser jacket at the bottom and exits at the top, ensuring efficient cooling. The vapour condenses back into a liquid and is collected as the distillate in a receiving flask. For example, simple distillation of salt water yields pure water, leaving the salt behind in the flask.
加热溶液，蒸气上升并进入水冷冷凝管。冷却水从冷凝管外套的下端进入、上端流出，以保证高效冷却。蒸气冷凝为液体，在接收瓶中收集为馏出液。例如，通过简单蒸馏盐水可得到纯水，而盐留在烧瓶中。
6. Paper Chromatography | 纸色谱
Paper chromatography separates a mixture of soluble substances, such as food colourings or plant pigments. Draw a starting line in pencil (never pen) approximately 2 cm from the bottom of a strip of chromatography paper. Use a fine capillary tube to place a small spot of the sample mixture onto the centre of the line. Allow the spot to dry and repeat to build up a concentrated but small spot.
纸色谱法用于分离可溶物质的混合物，例如食用色素或植物色素。在色谱纸距底边约 2 cm 处用铅笔（绝不可用钢笔）画一条起始线。用细毛细管在线的中央点上微量样品混合物。待斑点干燥后可重复点样，以得到集中但小范围的斑点。
Suspend the paper in a beaker containing a small depth of solvent, ensuring the starting line sits above the liquid surface. Cover the beaker with a lid or watch glass to maintain a saturated atmosphere. As the solvent rises up the paper, the different components migrate at different rates. When the solvent front has travelled near the top, remove the paper, immediately mark the solvent front in pencil, and let the chromatogram dry. Calculate the retention factor Rf for each spot:
将色谱纸悬挂在盛有少量溶剂的烧杯中，确保起始线在液面以上。用盖子或表面皿盖住烧杯，保持饱和气氛。溶剂沿纸上行时，各组分以不同速度移动。当溶剂前沿接近纸顶端时，取出纸，立即用铅笔标出溶剂前沿位置，晾干色谱图。计算每个斑点的比移值 Rf：
Rf = distance moved by spot ÷ distance moved by solvent front
Rf values can be compared with known reference values to help identify the components. Always use the same solvent and paper type for reliable comparisons.
Rf 值可以与已知参考值对比以帮助鉴定组分。为确保对比可靠，必须使用相同的溶剂和纸类型。
7. Acid-Base Titration | 酸碱滴定
Acid-base titration is an accurate volumetric technique used to find the concentration of an unknown acid or alkali. Rinse a clean burette with the acid solution, then fill it and record the initial volume to the nearest 0.05 cm³. Using a pipette filler, transfer a known volume of alkali (e.g. 25.0 cm³) into a conical flask and add a few drops of a suitable indicator, such as phenolphthalein or methyl orange.
酸碱滴定是一种精确的容量分析技术，用于测定未知酸或碱的浓度。用待测酸液润洗净的滴定管，然后加入酸液并记录初始体积，精确至 0.05 cm³。用吸耳球操作移液管，将已知体积（如 25.0 cm³）的碱液移入锥形瓶中，加入几滴合适的指示剂，如酚酞或甲基橙。
Place the conical flask on a white tile and run the acid from the burette while swirling the flask continuously. Slow down to drop-by-drop additions as the endpoint approaches, indicated by a permanent colour change (e.g. phenolphthalein from pink to colourless). Record the final burette reading. A rough titration is performed first to find the approximate endpoint, followed by two or more accurate titrations that should agree within 0.10 cm³.
将锥形瓶置于白色瓷砖上，边旋摇边从滴定管放出酸液。接近终点时改为逐滴加入，直至指示剂发生永久性颜色变化（例如酚酞由粉红变为无色）。记录滴定管的终读数。先进行一次粗略滴定以确定大致终点，随后再进行两次或更多次精密滴定，各次滴定体积差应控制在 0.10 cm³ 以内。
The average titre is used for calculation. For a reaction between a monoprotic acid and an alkali, the following relationship holds:
计算中使用平均滴定体积。对于一元酸与碱的反应，有以下关系：
cₐVₐ = c_bV_b
where c represents concentration (mol dm⁻³) and V is the volume (dm³). Always convert volumes from cm³ to dm³ by dividing by 1000 when substituting into formulas.
其中 c 代表浓度（mol dm⁻³），V 代表体积（dm³）。代入公式时始终记得将 cm³ 除以 1000 转换为 dm³。
8. Collecting and Testing Gases | 气体收集与检验
Several methods exist for collecting gases, depending on their solubility and density.
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