📚 Cambridge IGCSE Chemistry Practical Skills | 剑桥IGCSE化学实验操作
Practical work is at the heart of Cambridge IGCSE Chemistry. The course not only demands a clear understanding of chemical theory but also the ability to perform experiments safely, record observations accurately, and interpret results. This article covers the essential practical skills you need to master, from measuring volumes and heating substances to carrying out titrations and identifying ions. Each technique is explained with key points that examiners look for, helping you build confidence in the laboratory and perform well in the practical assessment.
实验操作是剑桥IGCSE化学课程的核心。这门课程不仅要求清晰理解化学理论，还要求有能力安全地完成实验、准确记录观察结果并解读数据。本文涵盖了你需要掌握的基本实验技能，从量取体积、加热物质，到进行滴定和离子鉴定。每一项技术都结合考官关注的关键要点加以说明，帮助你在实验室建立信心，并在实验考核中取得优异成绩。
1. Laboratory Safety | 实验室安全
Always wear safety goggles and a lab coat throughout the practical session. Tie back long hair and avoid loose clothing. Never eat, drink, or run in the laboratory. When heating a test tube, do not point its mouth towards yourself or others, and move the tube gently across the flame to prevent bumping. Acids and alkalis must be handled with care; if any chemical spills on the skin, wash immediately with plenty of water. Know the location of the eye wash station, safety shower, and fire extinguisher before starting any experiment. Always follow the instructions given by the teacher or the worksheet exactly, and never perform unauthorised experiments.
在整个实验过程中，始终佩戴护目镜和实验服。长发需束起，避免穿着宽松的衣物。不得在实验室里进食、饮水或奔跑。加热试管时，管口切勿朝向自己或他人，并且应在火焰上轻轻移动试管以防止暴沸。酸和碱必须小心处理；如果任何化学品溅到皮肤上，应立即用大量清水冲洗。在开始任何实验之前，要熟悉洗眼器、安全淋浴器和灭火器的位置。必须严格遵循教师或实验单上的指示，不得进行未经批准的实验操作。
2. Measuring Volumes of Liquids | 量取液体体积
ximate volumes, with the reading taken at eye level from the bottom of the meniscus. For more accurate work, use a burette (typically readable to ±0.05 cm³) or a volumetric pipette (e.g., 25.0 cm³) which delivers a fixed volume with high precision. When using a pipette, always use a pipette filler – lling, to avoid dilution. Record all readings to the appropriate number of decimal places.
量取液体体积会用到多种玻璃器皿，其精度各不相同。量筒适用于近似体积，读数时视线应与液面凹液面的最低处在同一水平线上。对于更精确的测量，可以使用滴定管（通常可读至 ±0.05 cm³）或移液管（如 25.0 cm³），后者能高精度地转移固定体积。使用移液管时，必须使用洗耳球——严禁用嘴吸取液体。在装液之前，要用待盛溶液润洗滴定管和移液管，以免稀释溶液。所有读数都应记录到合适的小数位数。
3. Measuring Mass and Temperature | 测量质量和温度
Mass is measured with a digital balance, usually recording to 0.01 g or 0.001 g. Place a weighing boat or piece of paper on the pan and press 'tare' before adding the substance, so that only the mass of the substance is recorded. For temperatures, a liquid-in-glass thermometer (alcohol or mercury) is typically used, with a scale reading every 0.5 °C or 1 °C. Thermometers should be placed so that the bulb is fully immersed in the substance but not touching the bottom of the container. When measuring melting or boiling points, allow the temperature to stabilise before reading. Digital probes can give quicker and more precise readings.
质量使用电子天平测量，通常记录至 0.01 g 或 0.001 g。将称量舟或称量纸放在托盘上，按“去皮”按钮后再加入物质，这样可以只记录物质本身的质量。温度通常使用液体-玻璃温度计（酒精或水银），刻度间隔为 0.5 °C 或 1 °C。放置温度计时，应使温度计球泡完全浸没在物质中，但不能接触容器底部。测量熔点或沸点时，要等温度稳定下来再读数。数字探头可以提供更快速、更精确的读数。
4. Heating Substances Safely | 安全加热物质
For gentle heating, a water bath is ideal, particularly when dealing with flammable organic liquids. A Bunsen burner gives a hotter flame; use the blue 'roaring' flame for strong heating and the yellow 'safety' flame when not actively heating. When boiling a liquid in a test tube, add anti‑bumping granules (small pieces of porous porcelain) to ensure smooth boiling and prevent sudden steam eruptions. Always heat the tube from the side, moving it back and forth. For heating solids, use a crucible on a pipe‑clay triangle, and for strongly heating solids in a combustion tube, tilt the tube slightly downwards to allow any condensation to run away from the hot zone.
对于温和加热，水浴是理想的选择，特别是在处理易燃有机液体时。本生灯能提供更强的火焰；强加热时使用蓝色的“咆哮”火焰，非加热状态下可调成黄色的“安全”焰。在试管中煮沸液体时，要加入沸石（多孔瓷片）以确保平稳沸腾，防止暴沸喷溅。加热时要从侧面加热试管，并来回移动。加热固体时，可在泥三角上使用坩埚；在硬质玻璃管中强热固体时，管口略向下倾斜，以便让冷凝液流离热区。
5. Filtration and Evaporation | 过滤与蒸发
Filtration separates an insoluble solid from a liquid. Fold filter paper into a cone and place it in a filter funnel. Pour the mixture along a glass rod to guide the liquid into the funnel without splashing. The solid (residue) remains on the paper, while the liquid (filtrate) passes through. To remove a soluble solid from a solution, evaporation can be used: pour the solution into an evaporating dish and heat gently over a water bath or a low Bunsen flame. Stop heating when the solution is concentrated, and allow the remaining solvent to evaporate slowly at room temperature, or heat to dryness if the solid is stable. Never evaporate to dryness directly over a strong flame unless instructed.
过滤可分离不溶性固体与液体。将滤纸折叠成圆锥形，放入漏斗中。通过玻璃棒引流将混合物倒入漏斗，避免飞溅。固体（滤渣）留在滤纸上，而液体（滤液）穿过滤纸。要从溶液中提取可溶性固体，可使用蒸发法：将溶液倒入蒸发皿中，在水浴或小火上缓慢加热。当溶液浓缩后停止加热，让剩余溶剂在室温下慢慢蒸发，或者如果固体稳定的话可以蒸干。除非明确指示，否则不要直接在强火下蒸干。
6. Crystallisation | 结晶
Crystallisation is the preferred method to obtain pure, hydrated crystals of a soluble salt. After partially evaporating the solution until it is just saturated (crystals begin to appear at the edge), allow it to cool slowly. Slow cooling encourages the formation of large, regular crystals. Once crystallised, filter the crystals out, wash them with a little cold distilled water to remove any impurities, and dry them between pieces of filter paper or in a warm oven below 60 °C. Do not heat hydrated crystals too strongly, as they may lose their water of crystallisation and turn into an anhydrous powder.
结晶是获得可溶性盐的纯净含水晶体的首选方法。将溶液部分蒸发，直至刚好饱和（溶液边缘开始出现晶体），然后让其慢慢冷却。缓慢冷却有助于形成大而规则的晶体。结晶完成后，将晶体过滤出来，用少量冷蒸馏水洗涤以除去杂质，再用滤纸吸干或在低于 60 °C 的烘箱中干燥。不要过强地加热含水晶体，否则它们可能失去结晶水而变成无水粉末。
7. Simple Distillation and Fractional Distillation | 简单蒸馏与分馏
Simple distillation separates a pure solvent from a solution. The solution is heated in a distillation flask; the solvent boils, vapour rises, and then it condenses back to liquid in a condenser. The condenser must have a steady flow of cold water entering at the bottom and leaving at the top to maintain the correct temperature gradient. For separating a mixture of two or more miscible liquids, fractional distillation is used. A fractionating column packed with glass beads provides a large surface area for repeated evaporation and condensation, allowing the separation of substances with boiling points closer than about 25 °C. Record the temperature range over which each fraction is collected. The thermometer bulb should be placed at the opening to the condenser to measure the temperature of the vapour accurately.
简单蒸馏可将纯溶剂从溶液中分离出来。溶液在蒸馏烧瓶中加热；溶剂沸腾，蒸气上升，然后在冷凝管中冷凝回液体。冷凝管必须有自下而上流动的稳定冷水，以保持正确的温度梯度。对于两种或多种可互溶液体混合物的分离，则使用分馏。装有玻璃珠的分馏柱提供了巨大的表面积，用于反复蒸发和冷凝，使沸点差在约 25 °C 以内的物质得以分离。记录每个馏分被收集时的温度范围。温度计球泡应放置在通向冷凝管的开口处，以准确测量蒸气的温度。
8. Paper Chromatography | 纸色谱法
Paper chromatography is used to separate and identify coloured substances, such as dyes, inks, and plant pigments. A pencil line is drawn near the bottom of the chromatography paper – never use ink. A small spot of the sample is placed on the line. The paper is then suspended in a beaker with the solvent level below the pencil line, and the beaker is covered to maintain a saturated atmosphere. As the solvent front moves up, the components separate. The paper is removed when the solvent front is near the top, and the solvent front is immediately marked with pencil. The Rf value (retardation factor) for each spot is calculated as: Rf = distance moved by substance ÷ distance moved by solvent front. Rf values are compared with known values to identify substances.
纸色谱法用于分离和鉴定有色物质，如染料、墨水和植物色素。在色谱纸底部用铅笔画一条线——绝不要使用墨水。在线上点上少量样品点。然后将纸悬挂在烧杯中，溶剂液面低于铅笔线，盖上烧杯以保持饱和氛围。随着溶剂前沿上移，各组分得以分离。当溶剂前沿接近纸的顶部时取出纸，并立即用铅笔标记溶剂前沿的位置。每个斑点的 Rf 值（比移值）计算如下：Rf = 物质移动的距离 ÷ 溶剂前沿移动的距离。将 Rf 值与已知值进行比较，以鉴定物质。
9. Titration | 滴定
An acid‑base titration determines the unknown concentration of an acid or alkali. A pipette is used to measure a fixed volume (e.g., 25.0 cm³) of one solution into a conical flask. A few drops of indicator (e.g., phenolphthalein or methyl orange) are added. The burette is filled with the other solution, ensuring the jet is completely filled and no air bubbles remain. The initial burette reading is noted. The tap is opened to add the solution in small volumes while constantly swirling the flask. Near the end point, add the solution drop by drop until the indicator just changes colour. Record the final burette reading. Repeat the titration until two consecutive results agree within 0.1 cm³, and take the average of these concordant titres. All results must be recorded in a clearly drawn table.
酸碱滴定用于测定酸或碱的未知浓度。用移液管量取固定体积（如 25.0 cm³）的一种溶液，移入锥形瓶中。加入几滴指示剂（如酚酞或甲基橙）。将另一种溶液装入滴定管，确保管尖完全充满液体且无气泡。记下滴定管的初始读数。打开旋塞，少量多次地加入溶液，同时不停旋转锥形瓶。接近终点时，逐滴加入直至指示剂恰好变色。记录滴定管最终读数。重复滴定，直到连续两次结果相差在 0.1 cm³ 以内，并取这些相符的滴定体积的平均值。所有结果必须记录在清晰的表格中。
10. Rate of Reaction Experiments | 反应速率实验
The rate of a reaction can be followed by measuring the volume of gas evolved over time, or by monitoring the change in mass or colour. A common setup involves a conical flask containing the reactants, connected to a gas syringe or an inverted measuring cylinder in a trough of water. For the reaction between marble chips and dilute hydrochloric acid, gas volume is recorded every 30 seconds. A typical equation is: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). The gradient of the graph of volume against time represents the rate. Investigating the effect of concentration, temperature, or surface area requires changing only one variable at a time and keeping all others constant. Always state the independent, dependent, and control variables clearly.
反应速率可以通过测量随时间产生的气体体积，或通过监测质量或颜色的变化来跟踪。常见的装置包括一个装有反应物的锥形瓶，连接到气体注射器或置于水槽中的倒置量筒。对于大理石碎片与稀盐酸的反应，每隔 30 秒记录一次气体体积。典型的反应方程式为：CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)。气体体积对时间作图的曲线斜率代表反应速率。研究浓度、温度或表面积的影响时，每次只改变一个变量，并保持其他所有变量不变。务必清楚陈述自变量、因变量和控制变量。
11. Gas Collection and Identification | 气体收集与鉴定
Gases are collected by upward or downward delivery, over water, or using a gas syringe, depending upon their density and solubility. Hydrogen (H₂), being less dense than air, is collected by upward delivery; carbon dioxide (CO₂) and chlorine (Cl₂), being denser, are collected by downward delivery. Gases that are only slightly soluble in water (such as O₂ and H₂) can be collected over water. To identify gases, use simple tests: a lit splint ‘pops’ with hydrogen; a glowing splint relights with oxygen; carbon dioxide turns limewater milky; ammonia turns damp red litmus paper blue; and chlorine bleaches damp litmus paper. Always record the procedure and the final observation clearly.
气体的收集方式有向上排空气法、向下排空气法、排水集气法或使用气体注射器，具体取决于气体的密度和溶解度。氢气（H₂）比空气轻，采用向下排空气法收集；二氧化碳（CO₂）和氯气（Cl₂）比空气重，采用向上排空气法收集。在水中溶解度很小的气体（如 O₂ 和 H₂）可用排水集气法收集。鉴定气体时使用简单的测试：带火星的木条在氢气中“噗”地熄灭；带火星的木条在氧气中复燃；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；氯气使湿润的石蕊试纸褪色。始终清晰记录操作过程以及最终的观察结果。
12. Preparing a Soluble Salt | 制备可溶性盐
Soluble salts are often prepared by reacting an acid with an excess of a metal, metal oxide, or carbonate. For example, to prepare copper(II) sulfate crystals, add excess copper(II) oxide to warm dilute sulfuric acid while stirring, until no more solid dissolves. The excess solid is removed by filtration. The filtrate is then evaporated gently to concentrate it, and left to cool and crystallise. The crystals are filtered, washed with a little cold distilled water, and dried. A similar method works for any soluble salt where one reactant is an insoluble solid. Always name the starting materials and write the balanced equation, e.g.: CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l).
可溶性盐通常通过将酸与过量的金属、金属氧化物或碳酸盐反应来制备。例如，要制备硫酸铜晶体，可在温热的稀硫酸中加入过量的氧化铜，同时搅拌，直到不再有固体溶解。多余的不溶固体通过过滤除去。然后将滤液缓慢蒸发浓缩，静置冷却结晶。将晶体过滤出来，用少量冷蒸馏水洗涤，然后干燥。类似的方法适用于任何一种反应物为不溶性固体的可溶性盐的制备。务必列出起始原料并书写配平的方程式，例如：CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)。
13. Identifying Anions and Cations | 鉴定阴离子和阳离子
Qualitative analysis uses simple test‑tube reactions to identify ions. For anions: carbonate (CO₃²⁻) produces CO₂ when dilute acid is added, which turns limewater milky; chloride (Cl⁻), bromide (Br⁻), and iodide (I⁻) give coloured precipitates with silver nitrate solution followed by dilute/conc. ammonia tests; sulfate (SO₄²⁻) gives a white precipitate with barium chloride solution, insoluble in dilute HCl; nitrate (NO₃⁻) requires the brown ring test with iron(II) sulfate and concentrated sulfuric acid. For cations, flame tests give characteristic colours (e.g., sodium – yellow‑orange, potassium – lilac, calcium – brick red, copper – blue‑green). Adding sodium hydroxide solution produces coloured hydroxides: Cu²⁺ gives a blue precipitate, Fe²⁺ a green precipitate, Fe³⁺ a brown precipitate, and ammonium (NH₄⁺) produces ammonia gas on warming, which turns red litmus blue.
定性分析通过简单的试管反应来鉴定离子。阴离子方面：碳酸根（CO₃²⁻）遇稀酸产生 CO₂，使石灰水变浑浊；氯离子（Cl⁻）、溴离子（Br⁻）和碘离子（I⁻）与硝酸银溶液反应产生有色沉淀，随后可通过稀/浓氨水进一步区分；硫酸根（SO₄²⁻）与氯化钡溶液生成不溶于稀盐酸的白色沉淀；硝酸根（NO₃⁻）需要用硫酸亚铁和浓硫酸进行棕色环试验。阳离子方面，焰色反应给出特征颜色（例如：钠——橙黄色，钾——淡紫色，钙——砖红色，铜——蓝绿色）。加入氢氧化钠溶液会产生有色氢氧化物：Cu²⁺ 生成蓝色沉淀，Fe²⁺ 生成绿色沉淀，Fe³⁺ 生成棕色沉淀，而铵离子（NH₄⁺）在加热时放出氨气，使红色石蕊试纸变蓝。
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