📚 Experimental Techniques in Cambridge IGCSE™ Chemistry | 剑桥IGCSE化学实验操作
Practical work is at the heart of the Cambridge IGCSE Chemistry course. The ability to handle apparatus, record observations accurately, and analyse experimental data is assessed through Paper 5 (Practical Test) or Paper 6 (Alternative to Practical). Mastering these techniques not only builds confidence in the laboratory but also deepens understanding of chemical concepts covered in the Coursebook. This article revisits the key experimental operations that every IGCSE Chemistry candidate should practise, from basic measurements to the preparation of gases and the use of titration.
实验操作是剑桥IGCSE化学课程的核心。处理仪器、准确记录观察结果和分析实验数据的能力通过试卷5（实验操作考试）或试卷6（替代实验考试）进行评估。掌握这些技术不仅能增强在实验室中的信心，还能加深对教材中化学概念的理解。本文回顾了每位IGCSE化学考生都应练习的关键实验操作，从基本测量到气体制备以及滴定操作。
1. Handling Measurements and Recording Data | 测量与数据记录
Accurate measurement is the first essential skill. When using a measuring cylinder, read the bottom of the meniscus at eye level to avoid parallax error. For burettes and pipettes, always rinse them with the solution to be used before filling. Thermometers should be immersed in the liquid without touching the container, and readings must be taken only when the reading is steady. Record all measurements in a clearly labelled table, with units in the header row, and repeat readings where appropriate to calculate an average.
准确的测量是第一项必备技能。使用量筒时，要在与眼睛平齐的高度读取弯月面的最低点，以避免视差误差。对于滴定管和移液管，装液前必须用待取溶液润洗。温度计应浸入液体中但不能触碰容器壁，并且只有在读数稳定后才能记录。将所有测量数据记录在带清晰标题的表格中，表头注明单位，并酌情进行重复测量以计算平均值。
Time measurements deserve special care. For reactions that are faster than one minute, a stopwatch should be started at the moment of mixing and stopped when a distinct change, such as a colour change or the appearance of a precipitate, occurs. Always record time to the nearest second and note any difficulty in judging the endpoint. When constructing a results table for a rate experiment, include columns for time, volume of gas collected, and temperature if relevant.
时间测量需要特别注意。对于快于一分钟的反应，应在混合瞬间启动秒表，并在发生明显变化（如颜色改变或沉淀出现）时停止。记录时间要精确到秒，并注明判断终点的任何困难。在为速率实验构建结果表格时，应包括时间、收集气体体积以及相关温度的列。
2. Filtration and Evaporation | 过滤与蒸发
Filtration is used to separate an insoluble solid from a liquid. Fold a filter paper into a cone, place it in a filter funnel, and moisten it with distilled water so it sticks to the glass. Pour the mixture slowly along a glass rod directed into the funnel, ensuring the mixture does not rise above the edge of the paper. The residue stays on the paper, while the filtrate passes through. To obtain a dry sample of the insoluble solid, wash the residue with a small amount of distilled water and then dry it between pieces of filter paper or in a warm oven.
过滤用于分离不溶性固体与液体。将滤纸折叠成圆锥形放入漏斗，用蒸馏水湿润使其紧贴玻璃。将混合物沿玻璃棒缓慢引流到漏斗中，确保液面不高于滤纸边缘。滤渣留在纸上，滤液则通过。要获得干燥的不溶性固体样品，需用少量蒸馏水洗涤滤渣，然后在滤纸之间或烘箱中烘干。
Evaporation is employed to obtain a soluble solid from a solution. Pour the solution into an evaporating basin and heat it gently over a water bath or a low Bunsen flame. Stop heating when crystals just begin to form at the edges or when the volume has reduced by about half, then leave the basin to cool. Large, pure crystals form as the solution cools and evaporates further. For solids that decompose on strong heating, a water bath is safer than direct flame.
蒸发用于从溶液中获取可溶性固体。将溶液倒入蒸发皿，在水浴或小火上缓缓加热。当边缘开始出现晶体或体积减少约一半时停止加热，然后让其冷却。溶液冷却并进一步蒸发时会析出大而纯净的晶体。对强热易分解的固体，使用水浴比直接加热更安全。
3. Simple Distillation | 简单蒸馏
Simple distillation allows the separation of a solvent from a solution, for example obtaining pure water from salt water. The apparatus consists of a distillation flask with a thermometer positioned at the side arm, a condenser with a water jacket, and a receiving flask. Water enters the condenser at the bottom and exits at the top to ensure efficient cooling. Heat the solution until it boils steadily; the thermometer reading will remain constant at the boiling point of the solvent. The vapour condenses in the Liebig condenser and the pure distillate is collected.
简单蒸馏可以从溶液中分离出溶剂，例如从盐水中获得纯水。装置包括蒸馏烧瓶（温度计置于支管口处）、带水套的冷凝管和接收瓶。冷却水从冷凝管下端进入、上端流出以保证高效冷却。加热溶液至稳定沸腾；温度计读数将保持在溶剂的沸点。蒸汽在直形冷凝管中冷凝，收集到纯馏出液。
Anti-bumping granules must be added to the flask before heating to promote smooth boiling and prevent large bubbles that can cause splashing. The thermometer bulb should be placed exactly at the level of the side arm so that it measures the temperature of the vapour entering the condenser. In IGCSE exam situations, candidates are often asked to identify the direction of water flow in the condenser and the purpose of the boiling stones.
加热前必须在烧瓶中加入沸石，以促进平稳沸腾并防止产生可能引起喷溅的大气泡。温度计球部应恰好位于支管口处，使其测量的是进入冷凝管的蒸汽温度。在IGCSE考试场景中，考生经常需要判断冷凝管中水的流向以及沸石的用途。
4. Paper Chromatography | 纸色谱法
Paper chromatography separates small amounts of dissolved substances based on their different solubilities and affinities for the stationary and mobile phases. Draw a pencil baseline about 2 cm from the bottom of the chromatography paper—never use ink as it would run. Place a tiny spot of the mixture and separate spots of known reference compounds on the line. Dip the paper into a suitable solvent (the mobile phase) in a covered beaker, ensuring the spots are above the solvent level. The solvent rises through the paper, carrying the components to different heights.
纸色谱法利用溶解物质在固定相和流动相中不同的溶解度和亲和力来分离少量物质。在距色谱纸底部约2 cm处用铅笔画一条基线——切勿使用墨水，因为它会扩散。在线上点上微量混合物样品以及已知参比物的单独点。将纸张浸入装有适宜溶剂（流动相）的加盖烧杯中，确保样点高于液面。溶剂沿纸上升，将各组分带到不同高度。
Once the solvent front has nearly reached the top, remove the paper, mark the solvent front immediately, and let it dry. Locate the colourless spots if necessary by spraying with a locating agent or viewing under UV light. Measure the distance travelled by each spot and by the solvent front. The Rf value is calculated as Rf = distance moved by substance ÷ distance moved by solvent. Because distance is measured in the same units, Rf is a dimensionless number that can be compared with known values to identify components.
当溶剂前沿几乎到达顶端时，取出纸张，立刻标记溶剂前沿，然后晾干。必要时通过喷洒显色剂或在紫外灯下观察来确定无色斑点。测量每个斑点移动的距离和溶剂前沿移动的距离。Rf值计算为 Rf = 物质移动距离 ÷ 溶剂移动距离。由于距离单位相同，Rf是无量纲数，可与已知值比较以鉴别组分。
5. Acid-Base Titration | 酸碱滴定
Titration is a volumetric technique used to determine the concentration of an unknown acid or base by neutralising it with a standard solution. Rinse the burette with the known solution, then fill it, ensuring the tip is free of air bubbles and record the initial volume. Use a pipette and pipette filler to transfer a fixed volume of the unknown solution into a conical flask, and add two or three drops of a suitable indicator, such as phenolphthalein or methyl orange.
滴定是一种容量分析技术，用于通过与标准溶液中和来测定未知酸或碱的浓度。用已知溶液润洗滴定管，然后装液，确保尖端没有气泡，记录初始体积。使用移液管和吸耳球将一定体积的未知溶液移入锥形瓶，并加入两到三滴合适的指示剂，如酚酞或甲基橙。
Place the conical flask on a white tile and run the solution from the burette while swirling the flask continuously. When the indicator begins to change colour, add the solution dropwise until a permanent colour change is observed at the endpoint. Record the final burette reading. Repeat the titration until two concordant results (within 0.1 cm³) are obtained, and then calculate the average titre. Avoid washing the conical flask with the solution it will contain; it should be rinsed with distilled water only so that the number of moles of the unknown remains unchanged.
将锥形瓶置于白瓷板上，从滴定管中放出溶液，同时不断转动锥形瓶。当指示剂开始变色时，逐滴滴加溶液，直至在终点看到持久颜色变化。记录滴定管最终读数。重复滴定直到获得两次一致的结果（差值在0.1 cm³以内），然后计算平均滴定体积。不要用待盛溶液润洗锥形瓶；只应用蒸馏水冲洗，以使未知物的摩尔数保持不变。
6. Rate of Reaction – Gas Collection | 反应速率 – 收集气体
The rate of a reaction that produces a gas can be followed by measuring the volume of gas evolved at regular time intervals. A common setup uses a conical flask containing the reactants, connected via a delivery tube to an inverted measuring cylinder or gas syringe. If using an inverted measuring cylinder in a trough of water, the cylinder must be filled with water and clamped upside down, with the delivery tube directed into its mouth. The volume of gas is read directly from the graduation on the gas syringe or by the downward displacement of water.
产生气体的反应速率可通过每隔一定时间测量释放的气体体积来跟踪。常用装置是：盛有反应物的锥形瓶通过导管连接到倒置的量筒或气体注射器。若使用水槽中倒置的量筒，量筒必须装满水并倒置夹稳，导管口伸入其下口。气体的体积直接从气体注射器的刻度读出，或通过排水法测量。
Start the reaction by adding the limiting reactant (e.g. marble chips to acid) and immediately seal the flask. Record the volume of gas every 30 seconds until the reaction is complete. Plot a graph of volume against time; the steepness of the curve at any point indicates the rate at that time. To investigate how concentration affects rate, repeat the experiment using acid of different molarities while keeping the mass of solid and the temperature constant. Always state the control variables: mass of solid, volume of acid, and temperature.
加入限制反应物（如将大理石碎片加入酸中）启动反应，并立即塞紧容器。每30秒记录一次气体体积，直至反应完成。绘制体积对时间的图形；曲线上任一点的斜率表示该时刻的反应速率。要探究浓度如何影响速率，可使用不同摩尔浓度的酸重复实验，同时保持固体质量和温度不变。务必说明控制变量：固体质量、酸的体积和温度。
7. Electrolysis of Aqueous Solutions | 水溶液的电解
Electrolysis experiments require a DC power supply, two electrodes (often graphite or inert metal), and an electrolyte solution in a beaker. For electrolysis of aqueous sodium chloride, place carbon electrodes in the solution, connect them to the supply, and observe bubbling at both electrodes. Test the gas at the anode with damp blue litmus paper—chlorine bleaches it white. The gas at the cathode is hydrogen, which burns with a squeaky pop. The solution near the cathode becomes alkaline due to the formation of sodium hydroxide, turning red litmus blue.
电解实验需要直流电源、两支电极（常用石墨或惰性金属）和盛在烧杯中的电解质溶液。电解氯化钠水溶液时，将碳电极插入溶液，接通电源，观察两极均有气泡冒出。用湿润的蓝色石蕊试纸检验阳极气体——氯气会将其漂白。阴极气体是氢气，燃烧时发出尖锐的爆鸣声。阴极附近溶液因生成氢氧化钠而呈碱性，使红色石蕊变蓝。
When electrolysing copper(II) sulfate solution with carbon electrodes, copper metal plates onto the cathode, turning from black to pinkish brown, and oxygen is formed at the anode. If copper electrodes are used instead, the anode copper dissolves into the solution as Cu²⁺ ions, and copper is simultaneously deposited on the cathode. This experiment illustrates that the products of electrolysis depend not only on the electrolyte but also on the electrode material. Make sure to note colour changes, gas tests, and mass changes of electrodes when recording observations.
用碳电极电解硫酸铜(II)溶液时，铜金属沉积在阴极，颜色由黑变为粉棕色，阳极生成氧气。若改用铜电极，阳极铜会溶解为Cu²⁺离子进入溶液，同时铜沉积在阴极。实验说明电解产物不仅取决于电解质，还取决于电极材料。记录观察结果时务必注意颜色变化、气体检验和电极质量变化。
8. Preparing and Testing Common Gases | 常见气体的制备与检验
Several gases can be prepared in the laboratory using simple apparatus. Hydrogen is made by reacting zinc granules with dilute hydrochloric or sulfuric acid in a flask fitted with a thistle funnel and delivery tube. Collect the gas over water as it is only slightly soluble. The squeaky-pop test with a lighted splint confirms hydrogen. Oxygen is produced by decomposing hydrogen peroxide with manganese(IV) oxide as a catalyst; it relights a glowing splint. Carbon dioxide is generated from marble chips and dilute hydrochloric acid, turning limewater milky.
几种气体可在实验室用简单装置制备。氢气可通过锌粒与稀盐酸或稀硫酸在配有蓟形漏斗和导管的烧瓶反应制得。由于氢气微溶于水，可用排水法收集。用点燃的木条进行爆鸣试验即可确认氢气。氧气由过氧化氢在二氧化锰催化剂作用下分解制得，它能使带火星的木条复燃。二氧化碳由大理石碎片和稀盐酸反应产生，它能使石灰水变浑浊。
Chlorine is prepared by oxidising concentrated hydrochloric acid with potassium manganate(VII) or by electrolysis of brine. It is toxic and must be handled in a fume cupboard. Chlorine has a sharp, choking smell and turns damp litmus paper red then bleaches it. For each gas, draw a labelled diagram of the assembly and recall the drying agent: concentrated sulfuric acid for hydrogen, chlorine, and carbon dioxide, but fused calcium chloride or calcium oxide for drying ammonia (which reacts with acid). The methods of collection—downward delivery, upward delivery, or over water—depend on the density and solubility of the gas.
氯气可通过用高锰酸钾氧化浓盐酸或电解盐水制备。氯气有毒，必须在通风橱中操作。氯气有强烈刺激性气味，能使湿润的石蕊试纸先变红再漂白。对每种气体，画一幅标注装置图并记住干燥剂：氢气、氯气和二氧化碳用浓硫酸干燥，但干燥氨气需用熔融氯化钙或氧化钙（因为氨与酸反应）。收集方法——向下排气法、向上排气法或排水法——取决于气体的密度和溶解度。
9. Flame Tests and Ion Identification | 焰色反应与离子鉴别
Flame tests help identify certain metal cations based on the characteristic colour they impart to a non-luminous Bunsen flame. Clean a nichrome or platinum wire by dipping it in concentrated hydrochloric acid and heating it until no colour is observed. Moisten the wire with acid, dip it into the solid sample, and hold it in the edge of the roaring flame. Observe the colour immediately: lithium gives a red flame, sodium an intense yellow, potassium a lilac (often filtered through blue glass to mask sodium impurities), calcium a brick red, and copper a blue-green or green.
焰色反应根据某些金属阳离子在本生灯非明亮火焰中产生的特征颜色来鉴别它们。将镍铬丝或铂丝蘸浓盐酸后加热，直到火焰无颜色为止。用盐酸润湿金属丝，蘸取固体样品，置于强火焰边缘。立即观察颜色：锂呈红色，钠呈强烈黄色，钾呈淡紫色（常通过蓝色钴玻璃观察以滤去钠的干扰），钙呈砖红色，铜呈蓝绿色或绿色。
Anion tests require different wet chemistry. To test for carbonate ions, add dilute hydrochloric acid to the solid or solution; brisk effervescence of carbon dioxide turning limewater milky indicates CO₃²⁻. For sulfate ions, add dilute nitric acid followed by barium nitrate solution; a white precipitate of barium sulfate confirms SO₄²⁻. For chloride, bromide, and iodide ions, add dilute nitric acid then silver nitrate solution. The colours of the precipitates—white for AgCl, cream for AgBr, and yellow for AgI—and their solubility in ammonia solution can distinguish the halide ions.
阴离子检验需要不同的湿化学方法。检验碳酸根离子时，向固体或溶液中加入稀盐酸；产生使石灰水变浑浊的二氧化碳气泡证明有CO₃²⁻。检验硫酸根离子，先加稀硝酸，再加硝酸钡溶液；硫酸钡的白色沉淀证实SO₄²⁻。检验氯离子、溴离子和碘离子，先加稀硝酸，再加硝酸银溶液。沉淀的颜色——AgCl白色，AgBr奶油色，AgI黄色——以及它们在氨水中的溶解性可区分卤离子。
10. Determining Enthalpy Change in a Displacement Reaction | 测定置换反应的焓变
The enthalpy change of a reaction such as zinc displacing copper from copper(II) sulfate can be measured using a polystyrene cup calorimeter. Place a known volume and concentration of copper sulfate solution in the cup and record its initial temperature every minute for three minutes. Add an excess of zinc powder, stir with the thermometer, and record the temperature every half minute after mixing. Continue recording until the temperature stops rising and begins to fall, then plot temperature against time on a graph.
像锌从硫酸铜中置换铜这样的反应的焓变，可用聚苯乙烯杯量热计测定。将已知体积和浓度的硫酸铜溶液倒入杯内，每分钟记录一次初始温度，共三分钟。加入过量的锌粉，用温度计搅拌，混合后每半分钟记录一次温度。持续记录直到温度停止升高并开始下降，然后绘制温度对时间的图形。
Extrapolate the two linear portions of the graph to the time of mixing to obtain the maximum temperature change ΔT, which corrects for heat loss to the surroundings. Calculate the heat produced using Q = mCΔT, where m is the total mass of the solution (assume 1 cm³ of solution has a mass of 1 g) and C is the specific heat capacity of water, 4.2 J g⁻¹ °C⁻¹. Then find the number of moles of the limiting reactant and compute the molar enthalpy change ΔH = –Q/n (with the sign negative for exothermic reactions). Discuss sources of error, such as loss of heat to the air, the polystyrene cup, or incomplete reaction.
将图形上的两条线性部分外推至混合时刻，得到最大温度变化ΔT，这样可修正向环境的热损失。利用 Q = mCΔT 计算产生的热量，其中 m 是溶液总质量（假定1 cm³溶液质量为1 g），C 是水的比热容 4.2 J g⁻¹ °C⁻¹。然后求出限制反应物的摩尔数，计算摩尔焓变 ΔH = –Q/n（放热反应符号为负）。讨论误差来源，如热量散失到空气中、被聚苯乙烯杯吸收或反应不完全。
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