📚 Mastering CIE IGCSE Chemistry (0620) Alternative to Practical: Essential Practical Skills | CIE IGCSE化学替代实验考试必备实验技能
The CIE IGCSE Chemistry Alternative to Practical paper (Paper 6) tests your understanding of experimental procedures, data analysis, and chemical techniques without performing the actual experiments. Success relies on knowing the correct apparatus, step‑by‑step methods, and common sources of error. This guide covers every essential practical skill you need, from safely heating a substance to identifying ions and plotting accurate graphs.
CIE IGCSE化学替代实验考试（试卷6）考查你对实验步骤、数据分析和化学操作技能的理解，而不需要动手操作。要想取得好成绩，就必须熟知正确的仪器、操作流程和常见的误差来源。本指南涵盖了所有关键的实验技能，从安全加热物质到离子鉴定和准确绘图，助你从容应考。
1. Laboratory Safety and Basic Apparatus | 实验室安全与基本仪器
Never enter the laboratory without wearing safety goggles. Tie back long hair and avoid loose clothing. When heating a substance, always point the mouth of a test tube away from yourself and others. Do not taste or directly smell chemicals; instead, waft the vapour towards your nose with your hand. Familiarise yourself with the names and uses of common glassware: a beaker for holding or heating liquids, a conical flask for titrations, a measuring cylinder for approximate volumes, a pipette for transferring exact volumes, a burette for dispensing variable precise volumes, and a test tube for small‑scale reactions.
进入实验室必须佩戴护目镜，束好长发，不穿宽松衣物。加热物质时，试管口必须远离自己和他人。不要尝药品或直接闻气体，而应用手轻扇，将少量蒸气引向鼻子。熟悉常用玻璃仪器的名称和用途：烧杯用于盛放或加热液体，锥形瓶用于滴定，量筒用于量取大致体积，移液管用于精确移取固定体积，滴定管用于可变精确体积的加液，试管用于小规模反应。
An evaporating dish is used to concentrate a solution, often placed on a tripod and gauze above a Bunsen burner. A filter funnel and filter paper are essential for filtration. When a reaction produces harmful gases, carry it out in a fume cupboard or a well‑ventilated area. Always read reagent labels carefully, and report any spillages or breakages to your teacher immediately.
蒸发皿用于浓缩溶液，常置于三脚架和石棉网上方，用本生灯加热。漏斗和滤纸是过滤时必备的器材。若反应产生有害气体，应在通风橱或通风良好的地方进行。务必仔细阅读试剂标签，任何泼洒或破损都应立即报告老师。
2. Measuring Techniques and Accuracy | 测量技术与准确性
Accurate measurements are at the heart of reliable experimental results. When reading the volume of a liquid in a measuring cylinder or burette, your eye must be level with the bottom of the meniscus. For a liquid that wets glass, such as water, the meniscus curves downwards, and you read the lowest point. A pipette should be used with a pipette filler – never mouth pipette. Rinse the pipette with the solution to be measured before drawing the exact volume, so that residual water does not dilute the solution.
精确的量取是可靠实验结果的核心。读取量筒或滴定管中的液体体积时，视线必须与凹液面的最低点保持水平。对于浸润玻璃的液体（如水），凹液面向下弯曲，读取最低点。移液管必须配合洗耳球使用，严禁用嘴吸。移取液体前，应先用待测液润洗移液管，以免残留的水稀释溶液。
A burette can generally be read to the nearest 0.05 cm³, while a typical measuring cylinder is read to the nearest 0.5 cm³ or even 1 cm³, depending on its scale. To reduce random errors, repeat each measurement and calculate the mean; discard any readings that are obviously inconsistent. Additionally, ensure that the thermometer bulb is fully immersed in the liquid but not touching the container bottom when recording temperature. Digital thermometers or data‑loggers can improve precision.
滴定管的读数通常可读到 0.05 cm³，而普通量筒根据其刻度只能读到 0.5 cm³ 甚至 1 cm³。为了减小随机误差，需要重复测量并计算平均值，并剔除明显不一致的数据。另外，测量温度时温度计的感温泡应完全浸没在液体中，但不要碰到容器底部。使用数字温度计或数据采集器可提高精度。
3. Heating Techniques in the Laboratory | 实验室加热技术
Bunsen burners are the most common heat source. Adjust the air hole to obtain a blue, roaring flame for strong heating; a yellow safety flame is used when heating is not required or when you need to see the flame. Never leave a lit Bunsen burner unattended. Flammable liquids must never be heated directly over a flame; instead, use a water bath – a beaker of water heated on a tripod and gauze – to ensure gentle, indirect heating.
本生灯是最常用的加热工具。调节空气孔可获得蓝色强烈火焰，用于强热；黄色安全火焰则在不需要加热或需要观察火焰时使用。点燃的本生灯切勿无人看管。易燃液体绝不能用明火直接加热，而应使用水浴（放在三脚架和石棉网上加热的烧杯中的水）来间接温和加热。
When heating a liquid in a test tube, hold the tube with a test‑tube holder, keep it sloping, and move it in and out of the flame continuously to prevent bumping and sudden ejection of the hot liquid. The open end must point away from anyone. When heating a solid, such as hydrated copper(II) sulfate, place the test tube almost horizontally with a slight downward tilt to allow any water vapour to escape without condensing and running back onto the hot glass.
用试管加热液体时，用试管夹夹住，使试管倾斜，并不断在火焰中移动，以防止暴沸和热液体突然喷出。管口必须远离任何人。加热固体（如五水合硫酸铜）时，应将试管近乎水平放置并略向下倾斜，使水蒸气散逸而不致冷凝回流到热的玻璃上，避免试管炸裂。
4. Separation: Filtration, Evaporation and Crystallisation | 分离技术：过滤、蒸发与结晶
Filtration separates an insoluble solid from a liquid. Fold the filter paper into a cone and place it in the funnel, moistening it with water so that it sticks to the glass. Pour the mixture down a glass rod directed into the filter paper to prevent splashing. The residue (solid) stays on the paper, while the filtrate (solution) passes through. This technique is used, for example, to separate unreacted copper(II) oxide from the reaction mixture when preparing copper(II) sulfate.
过滤用于分离不溶性固体和液体。将滤纸折成锥形放入漏斗中，用水润湿使其紧贴玻璃。用玻璃棒引流，将混合物倒入滤纸中，以防飞溅。固体残渣留在滤纸上，滤液则通过滤纸。在制备硫酸铜时，就用此法分离未反应的氧化铜。
Evaporation is used to concentrate a solution by boiling off much of the solvent. Pour the solution into an evaporating dish and heat it gently, often over a water bath to avoid overheating. Crystallisation yields pure solid crystals from a solution. Heat the solution until saturated (a crust of crystals appears), allow it to cool slowly, and then filter the crystals, washing them with a little cold distilled water and drying them between pieces of filter paper. Never evaporate to complete dryness if you want well‑shaped crystals.
蒸发通过煮沸溶剂来浓缩溶液。将溶液倒入蒸发皿，缓缓加热，常借水浴进行以免过度受热。结晶能从溶液中析出纯净的固体。将溶液加热至饱和（出现晶膜），再让它缓慢冷却，然后过滤出晶体，用少量冷蒸馏水洗涤，再用滤纸压干。若要得到外形完好的晶体，绝不能彻底蒸干。
5. Separation: Simple Distillation and Chromatography | 分离技术：简单蒸馏与色谱
Simple distillation is used to recover a pure liquid from a solution (e.g. pure water from salt water) or to separate liquids with very different boiling points. The solution is heated in a distillation flask fitted with a thermometer whose bulb is level with the side arm. Vapour passes through the condenser, which has cold water flowing in at the inlet at the bottom and out at the top to ensure efficient condensation. The distillate is collected in a receiving flask.
简单蒸馏用于从溶液中回收纯液体（如从食盐水中得到纯水），或分离沸点差异很大的液体。溶液在蒸馏烧瓶中加热，插有温度计，其水银球应与支管口平齐。蒸气通过冷凝管；冷凝管的进水口在下端，出水口在上端，以保证充分冷凝。馏出液收集在接收瓶中。
Paper chromatography separates mixtures of soluble substances. Draw a baseline in pencil (not ink, as it would dissolve) on chromatography paper. Place a small spot of the sample on the line, and suspend the paper in a solvent so that the baseline is above the solvent surface. As the solvent rises, it carries the components different distances. The Rf value is calculated as: distance moved by substance ÷ distance moved by solvent front. Rf values are used to identify components by comparison with known substances.
纸色谱法分离可溶性混合物质。在色谱纸上用铅笔（不用墨水，因其会溶解）画一条基线，在线上点一小滴样品，将纸悬挂于溶剂中，基线要高于溶剂液面。溶剂上升时，将各组分带离不同距离。Rf 值公式为：溶质移动距离 ÷ 溶剂前沿移动距离。对比已知物质的 Rf 值可鉴定组分。
6. Gas Collection and Preparation | 气体的收集与制备
Common gases in the IGCSE syllabus (hydrogen, oxygen, carbon dioxide, ammonia, chlorine) are often generated by adding an acid to a solid or heating a solid. The preparation setup usually consists of a reaction flask (or boiling tube) with a delivery tube leading to a collecting vessel. For example, zinc granules and dilute sulfuric acid produce hydrogen, and marble chips (calcium carbonate) with dilute hydrochloric acid produce carbon dioxide.
IGCSE 大纲中常见气体（氢气、氧气、二氧化碳、氨气、氯气）大多由酸与固体反应或加热固体制得。制备装置一般包括反应瓶（或硬质试管）和导入收集容器的导管。例如，锌粒与稀硫酸反应产生氢气，大理石（碳酸钙）与稀盐酸反应产生二氧化碳。
Gases are collected by one of three methods: upward delivery for gases heavier than air (e.g. CO₂, Cl₂, HCl), downward delivery for gases lighter than air (e.g. H₂, NH₃), and collection over water for gases that are insoluble or only slightly soluble in water (e.g. H₂, O₂, CO₂). If a dry gas is required, it must be passed through a drying agent: concentrated sulfuric acid for acidic gases, calcium oxide for alkaline gases, and fused calcium chloride for most neutral gases. Always check textbooks for compatible drying agents.
气体的收集有三种方法：对于比空气重的气体（如 CO₂、Cl₂、HCl），用向上排空气法；比空气轻的气体（如 H₂、NH₃）用向下排空气法；不溶或微溶于水的气体（如 H₂、O₂、CO₂）可用排水集气法收集。如需干燥气体，应使其通过干燥剂：浓硫酸干燥酸性气体，氧化钙干燥碱性气体，熔融氯化钙干燥多数中性气体。注意根据教材选用相容的干燥剂。
| Gas | Test | Positive result |
|---|---|---|
| H₂ | Hold a lighted splint at the mouth of the tube. | Burns with a squeaky pop. |
| O₂ | Insert a glowing splint. | Splint relights. |
| CO₂ | Bubble through limewater. | Limewater turns milky. |
| NH₃ | Hold damp red litmus paper near the mouth. | Litmus turns blue. |
| Cl₂ | Hold damp blue litmus paper. | Turns red then bleaches white. |
表格总结了常见气体的检验方法：氢气遇点燃的木条有爆鸣声，氧气使带火星木条复燃，二氧化碳使石灰水变浑浊，氨气使湿润的红色石蕊试纸变蓝，氯气先使蓝色石蕊试纸变红后漂白。
7. Acid–Base Titration Techniques | 酸碱滴定技术
Acid‑base titration determines the concentration of an unknown solution. First, rinse the burette with the acid solution and the pipette with the alkali solution. Use the pipette to transfer exactly 25.0 cm³ of the alkali into a clean conical flask, then add two or three drops of a suitable indicator – phenolphthalein for a strong acid versus strong alkali is particularly clear (pink to colourless). Fill the burette with the acid, ensure the jet is filled with no air bubble, and record the initial reading.
酸碱滴定用于测定未知溶液的浓度。首先用酸液润洗滴定管，用碱液润洗移液管。用移液管准确移取 25.0 cm³ 碱液至洁净的锥形瓶中，加入 2–3 滴合适的指示剂——强酸强碱滴定时用酚酞效果清晰（由粉红变为无色）。将酸液注入滴定管，确保尖嘴部分充满液体无气泡，并记录初始读数。
Run the acid into the flask while swirling it continuously. As the endpoint approaches, the indicator colour change takes longer to disappear; at this point add the acid drop by drop. The endpoint is reached when the colour just changes permanently. A white tile placed under the flask makes the colour change easier to see. Repeat the titration until you obtain at least two concordant results (within 0.10 cm³ of each other). Calculate the mean titre and use the equation: moles = concentration × volume (in dm³) to find the unknown concentration.
一边旋转锥形瓶一边逐滴加入酸液。接近终点时，指示剂颜色消退变慢，此时应改为半滴半滴加入。当颜色发生永久性改变时即达终点。在锥形瓶下放置白瓷砖有助于观察颜色变化。重复滴定直至获得至少两个符合要求的结果（彼此相差不超过 0.10 cm³）。计算平均滴定体积，再利用 物质的量 = 浓度 × 体积（dm³）推算出未知浓度。
For monoprotic acids and alkalis reacting in a 1:1 ratio, you can use CₐVₐ = C_bV_b directly. Remember to convert cm³ to dm³ by dividing by 1000. In Paper 6 questions, you may also be asked to draw a table with initial and final burette readings and to calculate the average, excluding any rough titration.
对于一元酸与一元碱以 1∶1 反应的情况，可直接使用 CₐVₐ = C_bV_b。注意将 cm³ 转换为 dm³ 时除以 1000。试卷6常要求你绘制记录初读数和终读数的表格，并剔除粗略滴定的数据，再计算平均值。
8. Rate of Reaction Experiments | 反应速率实验
Two classic experiments investigate how concentration and temperature affect reaction rates. The first involves the reaction between marble chips (calcium carbonate) and dilute hydrochloric acid: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + CO₂(g) + H₂O(l). You can measure the volume of carbon dioxide produced in a gas syringe, or measure the loss in mass of the flask on a balance. Plot volume (or mass loss) against time; the gradient of the curve at any point equals the rate of reaction at that instant.
两个经典实验研究浓度和温度如何影响反应速率。第一个是大理石（碳酸钙）与稀盐酸的反应：CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + CO₂(g) + H₂O(l)。可用气体注射器测量产生的二氧化碳体积，或者用天平测量反应瓶的质量损失。绘出体积（或质量损失）对时间的曲线，曲线上任一点的切线斜率即代表该时刻的反应速率。
The second is the reaction between sodium thiosulfate solution and hydrochloric acid: a pale yellow precipitate of sulfur makes the solution cloudy. Place a conical flask over a cross drawn on paper and record the time taken for the cross to disappear. Change the concentration of sodium thiosulfate (keeping the total volume constant) or change the temperature, and observe how the time to obscure
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