📚 IGCSE Edexcel Chemistry: A Guide to Experimental Techniques | IGCSE Edexcel 化学：实验操作指南
Mastering experimental techniques is essential for success in IGCSE Edexcel Chemistry. This guide covers the key practical skills you need, from safety and measurement to advanced procedures like titration and chromatography. Each section provides clear explanations paired with bilingual content to help you understand and apply the methods confidently in the lab and in your exams.
掌握实验操作对于在 IGCSE Edexcel 化学中取得成功至关重要。本指南涵盖你所需的关键实践技能，从安全、测量到滴定和色谱等高级操作。每个部分都提供清晰的解释，并配有双语内容，帮助你在实验室和考试中自信地理解和应用这些方法。
1. Laboratory Safety | 实验室安全
Always wear safety goggles, a lab coat, and closed shoes to protect against chemical splashes and spills. Know the location of the fire extinguisher, fire blanket, eyewash station, and emergency exits. Never taste chemicals or return unused reagents to stock bottles.
始终佩戴护目镜、实验服和封闭式鞋，以防化学物质飞溅和溢出。了解灭火器、灭火毯、洗眼器和紧急出口的位置。切勿品尝化学品或将未使用的试剂倒回原瓶。
Handle concentrated acids and alkalis with extra care, using a fume cupboard when dealing with volatile or toxic substances. Always add acid to water slowly when diluting, not the reverse, to avoid violent splashing. Wash skin immediately with plenty of water if any chemical contact occurs.
处理浓酸和浓碱时要格外小心，处理挥发性或有毒物质时应在通风橱中进行。稀释时总是将酸缓慢加入水中，而不是相反，以避免剧烈飞溅。如果皮肤接触到任何化学品，应立即用大量清水冲洗。
When heating substances, point the mouth of the test tube away from yourself and others. Use a Bunsen burner correctly: adjust the air hole to obtain a blue flame for heating, and never leave a lit burner unattended. Report all accidents and breakages to your teacher immediately.
加热物质时，试管口应远离自己和他人。正确使用本生灯：调节空气孔以获得用于加热的蓝色火焰，切勿让点燃的本生灯无人看管。所有事故和破损应立即向老师报告。
2. Measurements and Apparatus | 测量与仪器
Accurate measurement is vital in chemistry experiments. Use a digital balance (read to 0.01 g or 0.001 g) to measure mass. Record the mass of substances directly or by difference. A measuring cylinder typically measures volumes to the nearest 0.5 cm³, while a pipette delivers a fixed volume (e.g., 25.0 cm³) with high precision.
精确测量在化学实验中至关重要。使用电子天平（读数可至 0.01 g 或 0.001 g）称量质量。直接记录物质质量或采用差量法。量筒通常可量取体积至最接近的 0.5 cm³，而移液管可高精度地移取固定体积（如 25.0 cm³）。
For preparing solutions, a volumetric flask (e.g., 250.0 cm³) is used to achieve a known concentration. Burettes deliver variable volumes and can be read to 0.05 cm³. Always read the bottom of the meniscus at eye level for transparent liquids, and use the upper meniscus for coloured liquids like potassium permanganate.
配制溶液时，使用容量瓶（如 250.0 cm³）来获得已知浓度。滴定管可放出可变体积并可读数至 0.05 cm³。对于透明液体，始终在视线水平处读取凹液面的底部；对于像高锰酸钾这样的有色液体，则读取凹液面的顶部。
Time is measured using a stopwatch or digital timer to the nearest second. For temperature, a thermometer with a range of -10 to 110 °C (read to 0.5 °C or 0.1 °C) is commonly used. Always clamp the thermometer securely when measuring boiling points or during distillations.
时间使用秒表或数字计时器测量，精确到秒。测温时常用的温度计量程为 -10 至 110 °C（读数可至 0.5 °C 或 0.1 °C）。在测量沸点或蒸馏过程中，始终牢固地固定温度计。
3. Heating Methods | 加热技术
The Bunsen burner is the most common heating device. A non-luminous blue flame (air hole open) provides higher temperature and less soot, suitable for rapid heating. The safety flame (air hole closed) is yellow and visible, used when not actively heating. Always use a tripod and wire gauze to support glassware when heating with a Bunsen burner.
本生灯是最常用的加热设备。非发光的蓝色火焰（空气孔打开）温度更高、烟灰更少，适用于快速加热。安全火焰（空气孔关闭）呈黄色且能见度高，用于不进行加热时。用本生灯加热时，始终使用三脚架和石棉网来支撑玻璃器皿。
For gentle and controllable heating, a water bath (beaker of water on a tripod) can be used to heat substances indirectly. This is particularly useful for heating flammable organic liquids or maintaining a constant temperature. An electric heating mantle provides even heating without an open flame and is preferred for distillation of flammable solvents.
对于温和且可控的加热，可使用水浴（置于三脚架上的烧杯装水）间接加热物质。这对于加热易燃有机液体或保持恒温特别有用。电热套可在无明火的情况下提供均匀加热，是蒸馏易燃溶剂的首选。
When heating a solid in a test tube, hold the tube with a test tube holder, tilt it slightly, and move it back and forth through the flame to avoid local overheating. Never heat a closed system as pressure build-up can cause explosions.
在试管中加热固体时，用试管夹夹持，略微倾斜，并在火焰中来回移动以避免局部过热。切勿加热密闭系统，因为压力积聚可能导致爆炸。
4. Separating Mixtures | 分离混合物
Filtration separates an insoluble solid from a liquid. Folded filter paper placed in a funnel is wetted to stick to the funnel. The mixture is poured along a glass rod into the funnel; the solid residue remains on the paper, while the filtrate collects in the beaker below. Common examples include separating sand from saltwater or purifying a crude product.
过滤用于分离不溶性固体和液体。将折叠好的滤纸放在漏斗中，润湿使之紧贴漏斗。混合物沿玻璃棒倒入漏斗；固体残渣留在滤纸上，而滤液收集在下方的烧杯中。常见的例子包括从盐水中分离沙子或提纯粗产品。
Crystallisation obtains a pure solid from a solution. The solution is heated to evaporate some of the solvent until saturation, then allowed to cool slowly. Crystals form as solubility decreases with temperature. The crystals are then filtered, washed with a small amount of cold solvent, and dried on filter paper or in a warm oven.
结晶用于从溶液中获得纯净固体。将溶液加热蒸发部分溶剂直至饱和，然后让其缓慢冷却。随着温度降低溶解度下降，晶体析出。然后过滤晶体，用少量冷溶剂洗涤，并在滤纸上干燥或在温暖烘箱中干燥。
Simple distillation is used to separate a liquid from a soluble solid or two liquids with widely different boiling points. The mixture is heated, the vapour condenses in a water-cooled condenser, and the pure distillate is collected. Fractional distillation, with a fractionating column packed with glass beads, separates miscible liquids with closer boiling points, such as ethanol and water.
简单蒸馏用于从可溶性固体中分离液体，或分离沸点相差很大的两种液体。加热混合物，蒸汽在水冷冷凝器中冷凝，收集到纯馏出液。分馏则使用装有玻璃珠的分馏柱，用于分离沸点相近的互溶液体，如乙醇和水。
Chromatography separates small amounts of dissolved substances based on their affinity for the stationary and mobile phases. A spot of mixture is placed on paper or a thin layer of silica, and the solvent front moves up. The components travel different distances, giving Rf values. This technique identifies food colours, amino acids, or metal ions.
色谱法根据物质对固定相和流动相的亲和力来分离少量溶解物质。将混合物点样在纸上或薄层硅胶上，溶剂前沿向上移动。各组分移动距离不同，从而得到比移值 Rf。该技术可鉴定食用色素、氨基酸或金属离子。
5. Preparing and Collecting Gases | 制备与收集气体
Gases like hydrogen, oxygen, carbon dioxide, and ammonia are commonly prepared in the lab. The choice of apparatus depends on the reaction and the properties of the gas. For example, hydrogen is prepared by reacting zinc with dilute hydrochloric acid. Carbon dioxide is obtained from calcium carbonate and dilute HCl.
实验室中常制备氢气、氧气、二氧化碳和氨气等气体。装置的选择取决于反应和气体的性质。例如，氢气通过锌与稀盐酸反应制备。二氧化碳则从碳酸钙与稀 HCl 反应获得。
Gases can be collected by several methods. Downward delivery (upward displacement of air) is used for gases denser than air, such as carbon dioxide and chlorine. Upward delivery (downward displacement of air) collects gases less dense than air, like hydrogen and ammonia. Collection over water is suitable for gases that are insoluble or slightly soluble in water, such as hydrogen, oxygen, and carbon dioxide.
气体可通过多种方法收集。向下排空气法用于比空气重的气体，如二氧化碳和氯气。向上排空气法收集比空气轻的气体，如氢气和氨气。排水集气法适用于不溶或微溶于水的气体，如氢气、氧气和二氧化碳。
After generation, the gas can be dried by passing it through a drying agent. Concentrated sulfuric acid dries acidic and neutral gases but not alkaline gases like ammonia. Calcium oxide or calcium chloride can be used for drying ammonia. Always check the gas with a test: a glowing splint relights in oxygen, a lighted splint gives a ‘pop’ with hydrogen, and limewater turns milky with carbon dioxide.
气体生成后，可使其通过干燥剂进行干燥。浓硫酸可干燥酸性和中性气体，但不能干燥氨气等碱性气体。氧化钙或氯化钙可用于干燥氨气。始终用测试检验气体：带火星的木条在氧气中复燃，点燃的木条遇氢气发出“噗”的一声，石灰水遇二氧化碳变浑浊。
6. Acid-Base Titration | 酸碱滴定
Titration is used to determine the concentration of an acid or alkali by neutralisation. A pipette is used to measure a fixed volume of the solution with unknown concentration into a conical flask. An indicator, usually phenolphthalein or methyl orange, is added. The other solution of known concentration is placed in a burette.
滴定用于通过中和反应确定酸或碱的浓度。用移液管量取固定体积的未知浓度溶液至锥形瓶中。加入指示剂，通常使用酚酞或甲基橙。将已知浓度的另一种溶液装入滴定管。
The burette reading is taken from the bottom of the meniscus. The solution from the burette is added slowly while swirling the flask. As the end point approaches (indicated by a colour change that takes longer to disappear), the addition is slowed to drop-by-drop. The indicator should change colour after adding one final drop – this is the end point.
从液面凹面底部读取滴定管读数。一边摇动锥形瓶一边缓慢滴加滴定管中的溶液。当接近终点时（表现为颜色变化消失得越来越慢），改为逐滴加入。加入最后一滴后指示剂应改变颜色——这就是终点。
A concordant result is obtained when two or three titre volumes are within 0.10 cm³ of each other. The average of concordant titres is used to calculate the unknown concentration using the formula: naMaVa = nbMbVb, where n is the number of moles, M the concentration, and V the volume.
当两到三次滴定体积彼此相差在 0.10 cm³ 以内时，即得到符合结果。利用符合滴定体积的平均值，用公式 naMaVa = nbMbVb 计算未知浓度，其中 n 为摩尔数，M 为浓度，V 为体积。
7. Investigating Reaction Rates | 实验探究反应速率
Reaction rate experiments focus on how changing concentration, temperature, surface area, or catalysts affects the speed of a reaction. Common systems include the reaction of magnesium with dilute acid, or the reaction between sodium thiosulfate and hydrochloric acid, which produces a precipitate of sulfur.
反应速率实验侧重于研究浓度、温度、表面积或催化剂的变化如何影响反应速度。常见体系包括镁与稀酸的反应，或硫代硫酸钠与盐酸的反应（该反应生成硫沉淀）。
To investigate the effect of concentration on the rate of reaction between sodium thiosulfate (Na2S2O3) and HCl, a cross is drawn on a piece of paper underneath the reaction flask. The time taken for the cross to disappear due to the formation of sulfur is measured. Varying the concentration of thiosulfate while keeping the acid constant provides data for a graph of 1/time against concentration.
为探究浓度对 Na₂S₂O₃ 与 HCl 反应速率的影响，在反应瓶下方的纸上画一个十字。测量因生成硫沉淀而使十字消失所需的时间。在保持酸浓度不变的情况下改变硫代硫酸钠的浓度，可获得 1/时间 对浓度的关系图。
The rate of reaction when using marble chips (CaCO3) and dilute HCl can be followed by measuring the volume of carbon dioxide gas evolved over time using a gas syringe or by measuring the loss in mass of the flask on a balance. The gradient of a volume-time or mass-time graph initially gives the rate. The effect of surface area can be shown by comparing chips and powdered CaCO3.
使用大理石碎片 (CaCO₃) 和稀 HCl 时，可通过气体注射器测量一段时间内释放的二氧化碳体积，或通过天平测量烧瓶的质量损失，来跟踪反应速率。体积-时间或质量-时间图的初始斜率即为反应速率。通过比较块状和粉末状 CaCO₃ 可以展示表面积的影响。
Catalysts increase the rate without being used up. The decomposition of hydrogen peroxide (H2O2) using manganese(IV) oxide as a catalyst is a classic example. Oxygen produced can be collected and measured. The catalyst can be recovered unchanged at the end.
催化剂能加快反应速率而自身不被消耗。用过氧化氢 (H₂O₂) 在二氧化锰催化下的分解是一个经典例子。可收集并测量产生的氧气。催化剂在反应结束后可被回收，且不发生改变。
8. Chromatography | 色谱法
Paper chromatography separates coloured components according to their solubility in the solvent and their attraction to the paper. A small spot of the mixture is placed on a pencil base line near the bottom of a paper strip. The paper is dipped into a solvent, ensuring the spot is above the solvent level. The solvent moves up, carrying the components at different rates.
纸色谱法根据各组分在溶剂中的溶解度及其对纸张的吸引力来分离有色成分。将一小滴混合物点在靠近纸条底端的铅笔基线上。将纸条浸入溶剂中，确保点样处高于溶剂液面。溶剂向上移动，以不同速率带动各组分。
The Rf (retention factor) value for a component is calculated as: Rf = distance moved by substance / distance moved by solvent front. This value is characteristic for a given compound under fixed conditions and is used for identification. Colourless substances can be located using a locating agent (e.g., ninhydrin for amino acids) or by viewing under UV light.
组分的比移值 Rf 的计算公式为：Rf = 物质移动的距离 / 溶剂前沿移动的距离。该值在固定条件下是特定化合物的特征，可用于鉴定。无色物质可使用显色剂（例如用于氨基酸的茚三酮）或在紫外光下观察来定位。
In thin-layer chromatography (TLC), a glass or plastic plate coated with a thin layer of silica gel or alumina acts as the stationary phase. TLC provides better separation and is faster than paper chromatography. It is frequently used to monitor the progress of reactions or check the purity of a product.
在薄层色谱 (TLC) 中，涂有一薄层硅胶或氧化铝的玻璃或塑料板作为固定相。TLC 分离效果更好，且比纸色谱法更快。它常用于监测反应进程或检查产品的纯度。
9. Identification of Ions | 离子的鉴定
Chemical tests allow identification of cations and anions in unknown salts. Cation tests often involve adding sodium hydroxide solution. For example, Cu²⁺ gives a blue precipitate, Fe²⁺ a green precipitate turning brown in air, Fe³⁺ a rust-brown precipitate, and Ca²⁺ a white precipitate insoluble in excess NaOH. Ammonium ions (NH4⁺) release ammonia gas when warmed with NaOH, detected by damp red litmus turning blue.
化学测试可用于鉴定未知盐中的阳离子和阴离子。阳离子测试常涉及加入氢氧化钠溶液。例如，Cu²⁺ 生成蓝色沉淀，Fe²⁺ 生成绿色沉淀（在空气中变为棕色），Fe³⁺ 生成铁锈色沉淀，Ca²⁺ 生成不溶于过量 NaOH 的白色沉淀。铵离子 (NH₄⁺) 与 NaOH 共热时会释放氨气，可用湿润的红色石蕊试纸变蓝来检测。
Flame tests are another way to identify certain metal ions: lithium (Li⁺) gives a red flame, sodium (Na⁺) a persistent yellow, potassium (K⁺) a lilac (often through cobalt blue glass), calcium (Ca²⁺) a brick red, and copper (Cu²⁺) a blue-green flame. Use a clean nichrome or platinum wire loop dipped in concentrated HCl before placing in the flame.
焰色反应是鉴定某些金属离子的另一种方法：锂 (Li⁺) 呈红色火焰，钠 (Na⁺) 呈持久的黄色，钾 (K⁺) 呈紫色（常通过钴蓝玻璃观察），钙 (Ca²⁺) 呈砖红色，铜 (Cu²⁺) 呈蓝绿色火焰。使用洁净的镍铬或铂丝环，蘸取浓 HCl 后置于火焰中。
Anion tests are specific. Carbonates (CO3²⁻) fizz with dilute acid and release CO₂, which turns limewater milky. Sulfates (SO4²⁻) give a white precipitate with barium chloride solution acidified with dilute HCl. Halide ions (Cl⁻, Br⁻, I⁻) give characteristic coloured precipitates with silver nitrate solution acidified with dilute nitric acid: white for chloride, cream for bromide, and yellow for iodide. The ammonia solubility test confirms the halide.
阴离子测试各有不同。碳酸盐 (CO₃²⁻) 与稀酸反应冒泡并放出 CO₂，使石灰水变浑浊。硫酸盐 (SO₄²⁻) 与用稀盐酸酸化的氯化钡溶液生成白色沉淀。卤离子 (Cl⁻, Br⁻, I⁻) 与用稀硝酸酸化的硝酸银溶液生成特征性有色沉淀：氯化物为白色，溴化物为淡黄色，碘化物为黄色。氨水溶解性试验可确认卤离子种类。
10. Experimental Design and Errors | 实验设计与误差
Good experimental design ensures reliable and reproducible results. A plan should include a clear aim, list of apparatus, step-by-step method, identification of variables (independent, dependent, and controlled), and a risk assessment. Always repeat measurements to obtain multiple readings and calculate a mean, discarding any anomalous results.
良好的实验设计可确保结果可靠且可重复。计划应包括明确的目的、仪器清单、分步方法、变量识别（自变量、因变量和控制变量）和风险评估。始终重复测量以获得多次读数并计算平均值，剔除任何异常结果。
Systematic errors affect all readings in the same direction and may be caused by faulty instruments, incorrect calibration, or wrongly read measurements. For instance, using a balance that always reads 0.5 g too low introduces a systematic error. These can often be reduced by careful technique and calibration.
系统误差使所有读数朝同一方向偏离，可能由仪器故障、校准不正确或读数错误引起。例如，使用一台始终偏低 0.5 g 的天平会引入系统误差。这些误差通常可通过仔细操作和校准来减少。
Random errors are unpredictable variations due to factors like environmental fluctuations or human judgement. Examples include reading a meniscus at slightly different angles or minor temperature changes during a reaction. They can be minimised by taking many readings, using the same apparatus, and averaging results.
随机误差是由环境波动或人为判断等因素引起的不可预测的变化。例如，从略微不同的角度读取凹液面或反应过程中微小的温度变化。通过多次读数、使用同一仪器以及求平均值可以最大程度地减少随机误差。
When presenting results, use tables with clear headings and units. Graphs should have labelled axes with units, scales that use more than half of the graph paper, and points plotted accurately with crosses or dots. A line of best fit (straight or smooth curve) should be drawn, avoiding the “join-the-dots” approach. Anomalous points should be identified and circled but not included in the line of best fit.
展示结果时，使用表格并附有清晰的标题和单位。图表应有带单位的坐标轴标签，刻度应超出方格纸的一半以上，点用叉号或圆点准确绘制。应画出最佳拟合线（直线或平滑曲线），避免“连点成线”。应识别并圈出异常点，但在绘制最佳拟合线时不予考虑。
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