📚 Essential Chemistry for Cambridge IGCSE: Experimental Techniques | 剑桥IGCSE化学基础：实验操作
Mastering experimental techniques is fundamental to success in Cambridge IGCSE Chemistry. These skills not only help you carry out practical investigations safely and accurately but also prepare you for the alternative-to-practical paper. Understanding laboratory apparatus, measurement, separation methods, and common procedures builds the confidence needed to interpret data and design experiments. This article covers the essential experimental operations you will encounter, from basic safety rules to advanced techniques like titration and chromatography.
掌握实验技术是剑桥 IGCSE 化学取得成功的基础。这些技能不仅能帮助你安全、准确地进行实验探究，也为参加实验替代考试做好准备。了解实验室仪器、测量方法、分离手段以及常见操作程序，可以建立解读数据和设计实验的信心。本文涵盖你将遇到的基本实验操作，从基本安全规则到滴定、色谱等高级技术。
1. Safety in the Laboratory | 实验室安全
Always wear a lab coat and safety goggles to protect your skin and eyes from chemical splashes. Tie back long hair and avoid wearing loose clothing that could catch fire or knock over apparatus. Closed shoes must be worn, never sandals.
务必穿着实验服并佩戴护目镜，以保护皮肤和眼睛免受化学品飞溅的伤害。长发应束起，避免穿着宽松衣物，以免着火或碰倒仪器。必须穿不露脚趾的鞋，禁止穿凉鞋。
When heating substances, always point the mouth of a test tube away from yourself and others. Use a water bath or sand bath for flammable liquids, never a direct flame. Know the location of the fire extinguisher, fire blanket, and eyewash station before starting any experiment.
加热物质时，试管口要远离自己和他人。易燃液体应使用水浴或沙浴加热，绝不可用明火直接加热。开始任何实验前，都应熟悉灭火器、灭火毯和洗眼器的位置。
Do not taste any chemicals, and avoid inhaling fumes directly. Always use a fume cupboard when handling toxic or volatile substances. Wash hands thoroughly after practical work, even if gloves were worn.
不要品尝任何化学品，避免直接吸入烟雾。处理有毒或挥发性物质时，务必使用通风橱。实验结束后即使戴了手套，也要彻底洗手。
2. Measuring Mass and Volume | 质量与体积的测量
An electronic balance is used to measure mass, typically with a precision of 0.01 g or 0.001 g. Place a weighing container or weighing paper on the pan and press 'tare' to zero the balance before adding the substance. Record the mass as soon as the reading stabilises.
电子天平用于测量质量，通常精度为 0.01 g 或 0.001 g。将称量容器或称量纸放在托盘上，按 '去皮' 键归零，再加入待称物质。待读数稳定后立即记录质量。
For measuring volumes, use a measuring cylinder for approximate work, a volumetric pipette for transferring a fixed volume accurately, and a burette for delivering variable volumes with high precision. Always read the bottom of the meniscus at eye level to avoid parallax error.
测量体积时，粗略实验用量筒，精确移取固定体积用移液管，高精度可变体积用滴定管。读数时要平视弯月面最低点，以避免视差错误。
| Apparatus | Typical uncertainty |
|---|---|
| 100 cm3 measuring cylinder | ±0.5 cm3 |
| 25 cm3 volumetric pipette | ±0.06 cm3 |
| 50 cm3 burette | ±0.05 cm3 |
Table: Common volumetric apparatus and their uncertainties
表：常见体积测量仪器及其不确定度
3. Heating Techniques | 加热技术
The Bunsen burner provides a clean, hot flame. Adjust the air hole to obtain a blue, non-luminous flame for strong heating, and a yellow, luminous flame for gentle heating or when visible flame is required. To heat a test tube, hold it with a test-tube holder and move it in and out of the flame at an angle, never heating just one spot.
本生灯提供清洁的高温火焰。调节气孔可获得强烈加热的蓝色非发光焰，以及温和加热或需要可见火焰时的黄色发光焰。加热试管时，使用试管夹夹持，以一定角度在火焰中移动加热，切勿只加热一处。
A water bath is used when a temperature not exceeding 100 °C is needed and for heating flammable liquids safely. Place the substance in a beaker and put the beaker into a larger container of water on a tripod and gauze. Stir the water to ensure even temperature distribution.
当需要不超过 100 °C 的温度以及安全加热易燃液体时，使用水浴。将待加热物置于烧杯中，再把烧杯放入搁在三角架和铁网上的大水浴容器里。搅拌水以确保温度均匀。
Direct heating of solids in a crucible requires a pipe-clay triangle on a tripod. Heat gently at first, then strongly. Allow the crucible to cool in a desiccator before weighing.
在坩埚中直接加热固体时，需在三角架上放置泥三角。先缓慢加热，再强热。坩埚冷却须在干燥器中进行，再称量。
4. Filtration, Evaporation and Crystallisation | 过滤、蒸发与结晶
Filtration separates an insoluble solid from a liquid. Fold a filter paper into a cone, place it in a filter funnel, and pour the mixture down a glass rod to prevent splashing. The residue stays on the paper, and the filtrate passes through.
过滤用于分离不溶性固体与液体。将滤纸折叠成锥形，放入漏斗中，把混合物沿玻璃棒倒入以防止飞溅。残渣留在滤纸上，滤液通过。
To obtain a soluble solid from a solution, evaporate the solvent. Use an evaporating dish on a water bath or gently heat with a Bunsen burner. Stop heating when crystals begin to form or when a saturated solution remains; allow it to cool slowly so large crystals can grow. Then filter and dry between sheets of filter paper.
要从溶液中获得可溶性固体，蒸发溶剂。将蒸发皿放在水浴上或用本生灯缓缓加热。当开始出现晶体或剩下饱和溶液时停止加热；让其缓慢冷却，以便生长出大晶体。然后过滤并在滤纸间压干。
Crystallisation is preferred over complete evaporation when producing pure, well-defined crystals. Rapid evaporation yields small, impure crystals, while slow cooling gives larger, purer ones.
制备纯净、规则的晶体时，结晶优于完全蒸干。快速蒸发得到的晶体小而纯度低，缓慢冷却则可获得更大、更纯的晶体。
5. Simple and Fractional Distillation | 简单蒸馏与分馏
Simple distillation separates a solvent from a solution, for example obtaining pure water from seawater. The solution is heated in a distillation flask; the vapour passes through a condenser where it is cooled and collected as a liquid. A thermometer measures the boiling point of the vapour.
简单蒸馏用于从溶液中分离溶剂，例如从海水得到纯水。溶液在蒸馏烧瓶中加热，蒸气通过冷凝器冷却并收集为液体。温度计测量蒸气的沸点。
Fractional distillation separates a mixture of miscible liquids with different boiling points, such as ethanol and water. A fractionating column packed with glass beads provides a large surface area for repeated condensation and vaporisation, improving separation. The liquid with the lower boiling point is collected first at a temperature near its boiling point.
分馏用于分离沸点不同且互溶的液体混合物，如乙醇和水。分馏柱中填充玻璃珠，提供较大的表面积进行反复冷凝和蒸发，从而提高分离效果。沸点较低的液体在先接近其沸点的温度下被收集。
When measuring boiling points, ensure the thermometer bulb is positioned just below the side arm of the distillation flask and the heating rate is steady. Record the constant temperature when distillation is occurring rather than the initial reading.
测量沸点时，确保温度计水银球位于蒸馏烧瓶支管口略下方，并保持加热速率稳定。记录蒸馏过程中恒定的温度，而非初始读数。
6. Chromatography | 色谱法
Paper chromatography separates small amounts of dissolved substances, such as food colourings or inks. Apply a tiny spot of the mixture on a pencil line drawn near the bottom of a chromatography paper. Place the paper in a beaker with solvent so the solvent level is below the pencil line. The solvent rises by capillary action, carrying the components at different rates.
纸色谱法用于分离少量溶解的物质，如食用色素或墨水。在色谱纸靠近底部用铅笔画一条线，点上一小点混合物。将纸放入装有溶剂的烧杯中，溶剂液面低于铅笔线。溶剂因毛细作用上升，以不同速率带着各组分移动。
The Rf value identifies a substance under constant conditions. Calculate it using:
Rf = distance moved by substance ÷ distance moved by solvent front
Rf 值可用于在恒定条件下鉴定物质。计算式为：
Rf = 组分移动距离 ÷ 溶剂前沿移动距离
Ensure the spots are small to avoid overlapping. The lid must cover the beaker to prevent solvent evaporation and maintain a saturated environment. Allow the chromatogram to dry before measuring distances.
斑点要小，避免重叠。烧杯必须加盖以防止溶剂蒸发，维持饱和环境。待色谱图干燥后再测量距离。
7. Acid–Base Titration | 酸碱滴定
Titration is used to determine the concentration of an acid or alkali. A pipette is used to transfer a known volume of one solution into a conical flask. Add two to three drops of a suitable indicator, such as phenolphthalein for a strong acid–strong base titration. A burette is filled with the other solution, and the initial reading is recorded.
滴定用于测定酸或碱的浓度。用移液管量取已知体积的一种溶液，移入锥形瓶。加入两至三滴合适的指示剂，例如强酸强碱滴定用酚酞。滴定管中装入另一种溶液，记录初始读数。
Add the solution from the burette while swirling the flask continuously. Near the endpoint, add the solution drop by drop until the indicator changes colour. Record the final burette reading. Repeat the titration until two consecutive values agree within 0.10 cm3.
在持续旋摇锥形瓶的同时，从滴定管加入溶液。接近终点时，逐滴加入直至指示剂变色。记录最终读数。重复滴定，直到连续两次读数相差在 0.10 cm3 以内。
Concentration can be calculated using the formula:
cacidVacid / nacid = cbaseVbase / nbase
可用以下公式计算浓度：
c酸V酸 / n酸 = c碱V碱 / n碱
Wash the burette and pipette with the solutions they will contain before use to avoid dilution errors. Record readings to the nearest 0.05 cm3 from the bottom of the meniscus.
使用前用待装溶液润洗滴定管和移液管，以避免稀释误差。读数时从弯月面最低点读至 0.05 cm3 精度。
8. pH Measurement | pH 测量
Universal indicator solution or paper gives a quick estimate of acidity or alkalinity over the pH range 0–14. A few drops of universal indicator are added to the solution, and the colour is compared with a colour chart. The resulting colour provides an approximate pH, but cannot give a precise numerical value.
通用指示剂溶液或试纸可快速估计溶液酸碱度，覆盖 pH 0–14 范围。加入几滴通用指示剂，将颜色与色卡比对。所得颜色给出近似 pH，但无法提供精确数值。
A pH meter provides a more accurate reading. Rinse the electrode with distilled water and place it in the test solution. Wait for the reading to stabilise. The pH meter must be calibrated with buffer solutions of known pH before use.
pH 计提供更精确的读数。用蒸馏水冲洗电极，放入待测溶液。等待读数稳定。使用前必须用已知 pH 的缓冲液校准 pH 计。
When testing soil or solids, prepare a suspension in distilled water and test the clear liquid or use a dampened pH paper pressed against the solid. Never dip pH paper directly into the stock solution to avoid contamination.
检测土壤或固体时，用蒸馏水制成悬浊液，测试上层清液；或用湿润的 pH 试纸贴在固体表面。切勿将 pH 试纸直接浸入原瓶溶液，以免污染。
9. Collecting Gases | 气体收集
The method of collecting a gas depends on its density relative to air and its solubility in water. Upward delivery is used for gases less dense than air, such as hydrogen and ammonia. The gas is passed into an inverted collecting vessel, displacing air downwards.
收集气体的方法取决于其相对于空气的密度以及在水中的溶解度。向上排空气法用于密度小于空气的气体，如氢气和氨气。气体通入倒置的收集容器，向下排出空气。
Downward delivery is used for gases denser than air, like chlorine and sulfur dioxide. The gas is led to the bottom of a collecting jar, forcing air out upwards.
向下排空气法用于密度大于空气的气体，如氯气和二氧化硫。气体导入集气瓶底部，向上挤走空气。
Collection over water (downward displacement of water) is suitable for gases that are insoluble or only slightly soluble in water, such as hydrogen, oxygen, and carbon dioxide. The gas is bubbled into an inverted water-filled measuring cylinder or gas jar. This method also allows the volume of gas to be measured.
排水集气法（向下排水法）适用于不溶或微溶于水的气体，如氢气、氧气和二氧化碳。气体通入装满水并倒置的量筒或集气瓶。该方法还能测量气体的体积。
When collecting a dry sample, pass the gas through a drying agent like anhydrous calcium chloride or concentrated sulfuric acid before collection. Always use the minimum amount of gas and perform the experiment in a well-ventilated space.
若要收集干燥气体，收集前使气体通过干燥剂，如无水氯化钙或浓硫酸。始终使用最少量的气体，并在通风良好的地方操作。
10. Identifying Ions – Tests and Observations | 离子鉴定——检验与观察
Flame tests identify metal ions. Clean a nichrome wire loop with concentrated hydrochloric acid, dip it into the sample, and hold it in a blue Bunsen flame. Lithium gives a crimson red flame, sodium a bright yellow, potassium a lilac, calcium an orange-red, and copper a blue-green.
焰色反应可鉴定金属离子。用浓盐酸清洗镍铬丝圈，蘸取样品，置于本生灯蓝色火焰中。锂产生深红色火焰，钠为亮黄色，钾为淡紫色，钙为砖红色，铜为蓝绿色。
For cation identification in solution, add sodium hydroxide solution and observe the precipitate. White precipitate soluble in excess NaOH indicates Al3+ or Pb2+; white precipitate insoluble in excess suggests Ca2+; light blue precipitate gives Cu2+; green precipitate gives Fe2+; brown precipitate gives Fe3+. Ammonia gas released on heating indicates NH4+.
溶液中阳离子的鉴定可加入氢氧化钠溶液观察沉淀。白色沉淀且溶于过量 NaOH 的是 Al3+ 或 Pb2+；白色沉淀不溶于过量的为 Ca2+；浅蓝色沉淀是 Cu2+；绿色沉淀是 Fe2+；棕色沉淀是 Fe3+。加热产生氨气则表明 NH4+ 存在。
Common anion tests include: carbonate (CO32-) with acid producing CO2 which turns limewater milky; chloride (Cl-) with acidified silver nitrate giving a white precipitate soluble in dilute ammonia; sulfate (SO42-) with acidified barium chloride giving a white precipitate; and nitrate (NO3-) tested by adding aluminium and sodium hydroxide, warming, and detecting ammonia gas.
常见阴离子检验包括：碳酸根 (CO32-) 遇酸产生 CO2，使石灰水变浑浊；氯离子 (Cl-) 遇酸化硝酸银生成白色沉淀，可溶于稀氨水；硫酸根 (SO42-) 遇酸化氯化钡生成白色沉淀；以及硝酸根 (NO3-) 的检验：加入铝和氢氧化钠并加热，检测生成的氨气。
11. Experimental Errors and Uncertainty | 实验误差与不确定度
Random errors cause readings to be scattered around the true value. They can be reduced by taking multiple readings, calculating the mean, and working carefully. Examples include slight variations in reading a burette meniscus or timing a reaction.
随机误差导致读数在真值附近分散。可通过多次读数、计算平均值并小心操作来减小。例如读取滴定管弯月面或反应计时的微小差异。
Systematic errors shift all readings in one direction, often due to faulty apparatus or a consistent procedural flaw. An uncalibrated balance or a parallax error from reading above the meniscus can introduce systematic bias. Repeating readings does not eliminate systematic errors.
系统误差使所有读数朝同一方向偏移，常因仪器故障或一贯的操作缺陷所致。未校准的天平或从弯月面上方俯视读数都会引入系统偏差。重复读数无法消除系统误差。
Accuracy refers to closeness to the true value, while precision reflects the spread of repeated measurements. A set of data can be precise but not accurate if a systematic error is present. Always quote the uncertainty of apparatus and calculate percentage error where needed.
准确度指与真值的接近程度，精密度反映重复测量的离散程度。若存在系统误差，数据可能精密度高但不准确。务必注明仪器的不确定度，并在需要时计算百分误差。
Published by TutorHao | Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图