IGCSE Chemistry: Mastering Experimental Techniques | IGCSE化学：实验操作指南

📚 IGCSE Chemistry: Mastering Experimental Techniques | IGCSE化学：实验操作指南

Practical work lies at the heart of IGCSE Chemistry. A solid grasp of experimental techniques not only boosts your confidence in the laboratory but also sharpens your ability to analyse data and draw valid conclusions during exams. Whether you are measuring volumes, heating substances, or separating mixtures, each operation demands precision, safety awareness, and a clear understanding of the underlying principles.

实验操作是IGCSE化学的核心。牢固掌握实验技巧不仅能提升你在实验室中的信心，还能提高你分析数据并在考试中得出合理结论的能力。无论是量取体积、加热物质还是分离混合物，每一项操作都需要精准、安全意识以及对基本原理的清晰理解。

1. Safety in the Laboratory | 实验室安全

Before any experiment, you must identify potential hazards. Always wear safety goggles to protect your eyes from splashes, fumes, and flying objects. A laboratory coat shields your skin and clothing. When handling corrosive chemicals such as concentrated acids (e.g. HCl, H₂SO₄) or alkalis (e.g. NaOH), wear chemical-resistant gloves. Tie back long hair and avoid dangling jewellery. Work in a well-ventilated area or use a fume cupboard when dealing with toxic gases like chlorine (Cl₂) or sulfur dioxide (SO₂). Know the location of emergency equipment – eyewash station, safety shower, fire extinguisher, and first-aid kit. Never taste or directly inhale any chemical; instead, waft the vapour towards your nose.

在任何实验开始前，你必须识别潜在的危险源。始终佩戴护目镜，以保护眼睛免受飞溅物、气体和飞出物体的伤害。实验服可以保护皮肤和衣物。处理浓酸（如HCl, H₂SO₄）或浓碱（如NaOH）等腐蚀性化学品时，应戴上耐化学腐蚀的手套。扎好长发，避免佩戴悬垂的首饰。在处理有毒气体如氯气(Cl₂)或二氧化硫(SO₂)时，应在通风良好的环境或通风橱中操作。熟悉应急设备的位置——洗眼器、安全淋浴器、灭火器和急救箱。绝对不要品尝或直接闻任何化学品；应采用扇闻法，将蒸气扇向鼻孔。

2. Measuring Mass and Volume | 质量与体积的测量

The electronic balance is used to measure mass precisely, typically to 0.01 g or 0.001 g. Place a weighing boat or filter paper on the pan, tare (zero) the balance, and then add the substance. Record the mass directly. For approximate volumes, a measuring cylinder suffices; read the bottom of the meniscus at eye level. For accurate fixed volumes, especially in titrations, a volumetric flask and pipette are preferred. The volumetric flask (e.g. 250 cm³) prepares standard solutions: dissolve the solute, transfer quantitatively, and fill to the mark. A pipette (10 cm³, 25 cm³) delivers a precise aliquot; use a pipette filler, never your mouth. The burette (50 cm³) allows variable but highly accurate delivery; rinse with the solution before use and ensure the tip is filled.

电子天平用于精密测量质量，通常精确到0.01 g或0.001 g。将称量舟或滤纸放在称盘上，去皮（归零），然后加入物质，直接记录质量。粗略量取体积可用量筒；读取液面弯月面的最低点，视线与液面齐平。滴定等需要精确固定体积时，首选容量瓶和移液管。容量瓶（如250 cm³）用于配制标准溶液：溶解溶质，定量转移，然后定容至刻度线。移液管（10 cm³, 25 cm³）可移取精确等分溶液；需使用洗耳球，绝不能用嘴吸。滴定管（50 cm³）可进行可变的且高度精确的滴加；使用前用待装溶液润洗，并确保尖嘴部分充满溶液。

3. Heating Substances | 加热物质

Gentle heating is often done with a water bath, which keeps the temperature around 100 °C and avoids naked flames for flammable liquids like ethanol (C₂H₅OH). A Bunsen burner provides a naked flame: the non-luminous blue flame (air hole open) is hotter and quieter, ideal for strong heating; the luminous yellow flame (air hole closed) is safer for lighting the burner because it is visible. When heating a test tube containing a liquid, point the mouth away from yourself and others, and move the tube continuously to prevent bumping. Use a boiling chip or anti-bumping granules to ensure smooth boiling. For direct heating of solids, such as heating copper(II) sulfate crystals to remove water of crystallisation, a crucible with a lid placed on a pipeclay triangle is appropriate. Always allow hot apparatus to cool on a heat-resistant mat.

温和加热常用水浴，可使温度保持在约100 °C，避免明火接触可燃液体如乙醇(C₂H₅OH)。本生灯提供明火：蓝色的非发光火焰（空气孔打开）温度更高且安静，适合强热；黄色的发光火焰（空气孔关闭）点火时更安全，因为它易见。加热盛有液体的试管时，试管口应避开自己和他人，并不停移动试管以防暴沸。加入沸石或防暴沸颗粒可确保平稳沸腾。直接加热固体时，如加热五水合硫酸铜晶体以脱去结晶水，应使用带盖的坩埚，放置在泥三角上。务必让热的仪器在耐热垫上冷却。

4. Filtration | 过滤

Filtration separates an insoluble solid (residue) from a liquid (filtrate). Fold a filter paper into a cone, place it into a filter funnel, and moisten it with distilled water so it sticks to the funnel. Place the funnel in a conical flask or beaker. Pour the mixture down a glass rod to direct the stream into the centre of the filter paper, ensuring the liquid level never rises above the edge of the paper. The clear filtrate passes through, while the solid remains on the paper. To wash the residue, squirt a little distilled water around the filter paper. For faster filtration under reduced pressure, a Buchner funnel, side-arm flask, and vacuum pump can be used.

过滤用于分离不溶性固体（残渣）和液体（滤液）。将滤纸折成锥形，放入漏斗中，用蒸馏水润湿使其紧贴漏斗壁。将漏斗置于锥形瓶或烧杯上。把混合物沿玻璃棒倒在滤纸中央，确保液面永远不会超过滤纸边缘。澄清的滤液通过，而固体残留在滤纸上。要洗涤残渣，可用少量蒸馏水沿滤纸内壁冲洗。若需减压快速过滤，可使用布氏漏斗、抽滤瓶和真空泵。

5. Evaporation and Crystallisation | 蒸发与结晶

To obtain a soluble salt from its solution, evaporation and crystallisation are key. If you want to recover all the solute quickly, you can gently heat the solution in an evaporating dish on a water bath until the solvent evaporates completely, leaving dry crystals. However, this can cause impurities to be trapped, and some salts may decompose. A better method for purifying salts such as copper(II) sulfate is crystallisation. Gently heat the filtrate to concentrate it – heat until the solution is saturated (crystals appear on the edge of a glass rod dipped in the solution). Stop heating and allow it to cool slowly at room temperature. Large, pure crystals form. Filter the crystals, wash with a little cold distilled water, and dry between sheets of filter paper or in a desiccator.

从溶液中获得可溶性盐，蒸发和结晶是关键。若想快速回收所有溶质，可将溶液放在蒸发皿中水浴加热，直至溶剂完全蒸发，留下干燥晶体。但这样可能导致杂质被包夹，且某些盐可能会分解。纯化如硫酸铜等盐的更佳方法是结晶。温和加热滤液进行浓缩——加热直至溶液达到饱和（用玻棒蘸取溶液后在边缘析出晶体）。停止加热，让溶液在室温下缓慢冷却，就会形成大而纯净的晶体。过滤出晶体，用少量冷蒸馏水洗涤，然后在滤纸间压干或在干燥器中干燥。

6. Simple Distillation | 简单蒸馏

Simple distillation separates a liquid solvent from a solution by boiling the liquid and then condensing the vapour. The apparatus consists of a distillation flask (or a pear-shaped flask) attached to a condenser with a thermometer placed at the neck of the flask (bulb opposite the side arm). Cooling water enters the condenser at the bottom and exits at the top to ensure the jacket is full. Heat the flask gently; the pure solvent (e.g. water from saltwater) vaporises, rises, and passes into the condenser where it is cooled and collected as the distillate. The solute remains in the flask. The boiling point of the solvent can be read on the thermometer, confirming purity. Use anti-bumping granules to ensure smooth boiling. This technique is used to obtain pure water from seawater or to collect the solvent after a reaction.

简单蒸馏通过沸腾液体再冷凝蒸气，将液体溶剂从溶液中分离出来。装置由连接冷凝管的蒸馏烧瓶（或梨形瓶）组成，温度计置于烧瓶颈部（水银球对准支管口）。冷却水从冷凝管下端进入，上端流出，确保套管充满水。缓慢加热烧瓶；纯溶剂（如盐水中的水）汽化上升，进入冷凝管被冷却并收集为馏出液，溶质则留在烧瓶中。可在温度计上读出溶剂的沸点以确认纯度。加入防暴沸颗粒确保平稳沸腾。该技术用于从海水中获得纯水，或在反应后回收溶剂。

7. Fractional Distillation | 分馏

Fractional distillation separates miscible liquids with different boiling points, such as ethanol (bp 78 °C) and water (bp 100 °C). A fractionating column, packed with glass beads or a spiral, provides a large surface area for repeated condensation and re-evaporation. Mount the column vertically between the flask and the condenser. Heat the mixture slowly; the liquid with the lower boiling point boils first. Its vapour rises up the column, condenses on the cooler beads, and trickles back down while hotter vapour rises. This process gives a vapour increasingly rich in the more volatile component, which eventually reaches the top and enters the condenser. The thermometer reading stays steady at the boiling point of that component. Change the receiving flask as the temperature changes to collect different fractions. This method is essential in separating crude oil into its fractions.

分馏用于分离沸点不同的互溶液体，如乙醇（沸点78 °C）和水（沸点100 °C）。分馏柱内填充玻璃珠或螺旋形物，提供大的表面积进行反复冷凝和再蒸发。将分馏柱竖直安装在烧瓶与冷凝管之间。缓慢加热混合物；低沸点的液体首先沸腾。其蒸气上升进入分馏柱，在较冷的玻璃珠上冷凝，液体流回，而更热的蒸气继续上升。这个过程使得蒸气中挥发性更高的组分逐渐富集，最终到达顶端进入冷凝管。温度计读数在该组分的沸点保持稳定。当温度变化时更换接收瓶以收集不同馏分。该方法对于将原油分离成各种馏分至关重要。

8. Chromatography | 色谱法

Paper chromatography separates mixtures of soluble coloured substances, such as inks or food dyes. Draw a pencil baseline (not pen because ink would separate) about 2 cm from the bottom of chromatography paper. Place a small spot of the mixture on the line using a capillary tube; dry and re-spot to concentrate it. Suspend the paper in a beaker containing a suitable solvent (mobile phase) with the baseline above the solvent level, then cover with a lid. The solvent travels up the paper, carrying the components to different heights because they have different solubilities and degrees of adhesion to the paper. Once the solvent front nears the top, remove and mark the solvent front immediately with a pencil. Allow the paper to dry. Calculate the R_f value for each spot: R_f = distance moved by substance ÷ distance moved by solvent front. This value helps identify the components. Chromatography is also used for colourless substances by locating agents or UV light.

纸色谱法适用于分离可溶性颜色物质的混合物，如墨水或食品色素的分离。在距色谱纸底端约2 cm处用铅笔画基线（不能用笔，因为墨水会分离）。用毛细管在基线点上混合物的一个小斑点；吹干后再点，使其浓缩。将纸悬挂在盛有合适溶剂（流动相）的烧杯中，基线高于溶剂液面，然后盖上盖子。溶剂沿纸上行，携带各组分移动不同的高度，因为它们具有不同的溶解度和对纸的吸附程度。当溶剂前沿接近顶端时取出，立即用铅笔标记溶剂前沿，将纸晾干。计算每个斑点的R_f值：R_f = 物质移动的距离 ÷ 溶剂前沿移动的距离。此值有助于鉴定组分。对于无色物质，可通过显色剂或紫外灯显示。

9. Titration | 滴定

Acid-base titration determines the concentration of an unknown solution by reacting it with a standard solution of known concentration. Rinse a burette with the acid (or base), then fill it and record the initial reading. Rinse a pipette with the solution you wish to analyse and transfer a fixed volume (e.g. 25.0 cm³) into a conical flask. Add a few drops of a suitable indicator such as methyl orange (red in acid, yellow in alkali) or phenolphthalein (colourless in acid, pink in alkali). Place a white tile under the flask to see the colour change clearly. Add the solution from the burette slowly while swirling the flask until the indicator just changes colour (end point). Record the final burette reading. Repeat the titration to obtain consistent results within 0.1 cm³ (concordant titres). Calculate the average titre and use the formula: moles = concentration × volume (dm³) to find the unknown concentration. Rinse all apparatus thoroughly with distilled water after the experiment.

酸碱滴定通过让未知溶液与已知浓度的标准溶液反应，来测定其浓度。用酸（或碱）润洗滴定管，然后加满并记录初始读数。用待测溶液润洗移液管，然后移取固定体积（如25.0 cm³）至锥形瓶中。加入几滴合适的指示剂，如甲基橙（酸中红，碱中黄）或酚酞（酸中无色，碱中粉红）。在锥形瓶下放一张白瓷砖以便清晰观察颜色变化。缓慢加入滴定管中的溶液，同时不断摇动锥形瓶，直至指示剂刚好变色（终点）。记录滴定管最终读数。重复滴定，得到相差不超过0.1 cm³的结果（一致滴定值）。计算平均滴定值，再根据公式：摩尔数 = 浓度 × 体积(dm³) 求出未知浓度。实验结束后用蒸馏水彻底清洗所有仪器。

10. Collecting Gases | 收集气体

Several methods exist for collecting gases, chosen according to the gas’s density and solubility. Gases denser than air (e.g. carbon dioxide CO₂, chlorine Cl₂, sulfur dioxide SO₂) are collected by downward delivery – the delivery tube points downwards into a gas jar, and the heavier gas sinks and displaces air. Gases less dense than air (e.g. ammonia NH₃, hydrogen H₂) are collected by upward delivery – the tube points upwards. Gases that are slightly soluble or insoluble in water (e.g. oxygen O₂, hydrogen H₂, carbon dioxide CO₂, nitrogen N₂) can be collected over water. The gas is bubbled through water into an inverted measuring cylinder or gas jar filled with water. The gas displaces the water. To estimate the volume of gas produced, a gas syringe (100 cm³) is most accurate – the plunger moves as gas enters. Always check that the apparatus is airtight before beginning.

有多种收集气体的方法，可根据气体的密度和溶解度选择。密度比空气大的气体（如二氧化碳CO₂，氯气Cl₂，二氧化硫SO₂）用向下排空气法收集——导管向下送入集气瓶，较重的气体下沉并排出空气。密度比空气小的气体（如氨气NH₃，氢气H₂）用向上排空气法收集——导管向上。微溶或不溶于水的气体（如氧气O₂，氢气H₂，二氧化碳CO₂，氮气N₂）可用排水集气法。将气体通过水导入倒扣在水中充满水的量筒或集气瓶中，气体将水排出。若要测量产生气体的体积，使用气密注射器（100 cm³）最为精确——气体进入时柱塞移动。开始前务必检查装置气密性。

11. Testing for Gases and Ions | 气体与离子的检验

IGCSE Chemistry requires you to recall specific tests. For gases: hydrogen gas (H₂) gives a squeaky pop with a lit splint; oxygen (O₂) relights a glowing splint; carbon dioxide (CO₂) turns limewater milky (Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O); chlorine (Cl₂) bleaches damp litmus paper; ammonia (NH₃) turns damp red litmus paper blue. For cations: a flame test identifies lithium (Li⁺) crimson, sodium (Na⁺) yellow, potassium (K⁺) lilac, calcium (Ca²⁺) brick-red, and copper (Cu²⁺) blue-green. Adding aqueous sodium hydroxide precipitates metal hydroxides: Cu²⁺ gives a blue precipitate, Fe²⁺ green, Fe³⁺ reddish-brown. For anions: carbonate (CO₃²⁻) effervesces with dilute acid, producing CO₂; chloride (Cl⁻), bromide (Br⁻), and iodide (I⁻) give white, cream, and yellow precipitates respectively with silver nitrate, followed by ammonia solubility tests; sulfate (SO₄²⁻) gives a white precipitate with barium chloride in acidic medium.

IGCSE化学要求你记住特定的检验方法。气体检验：氢气(H₂)用点燃的木条检验，会产生轻微的爆鸣声；氧气(O₂)能使带火星的木条复燃；二氧化碳(CO₂)通入石灰水，石灰水变浑浊(Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O)；氯气(Cl₂)漂白湿润的石蕊试纸；氨气(NH₃)使湿润的红色石蕊试纸变蓝。阳离子检验：焰色反应中，锂(Li⁺)呈深红色，钠(Na⁺)黄色，钾(K⁺)淡紫色，钙(Ca²⁺)砖红色，铜(Cu²⁺)蓝绿色。加入氢氧化钠溶液会沉淀出金属氢氧化物：Cu²⁺产生蓝色沉淀，Fe²⁺绿色，Fe³⁺红褐色。阴离子检验：碳酸根(CO₃²⁻)遇稀酸起泡生成CO₂；氯离子(Cl⁻), 溴离子(Br⁻), 碘离子(I⁻)分别与硝酸银生成白色、奶油色、黄色沉淀，继以氨水溶解测试；硫酸根(SO₄²⁻)在酸性介质中与氯化钡生成白色沉淀。

12. Using Indicators and pH Measurements | 指示剂与pH测量

Indicators change colour depending on the pH of the solution. Litmus turns red in acid and blue in alkali, but does not distinguish strong from weak acid. Universal indicator, a mixture of several dyes, gives a range of colours from red (pH 1) through green (pH 7) to violet (pH 14). The pH of a solution can be estimated by adding a few drops of universal indicator solution or by dipping a universal indicator paper. For more accurate measurement, a pH meter with a probe is used; immerse the probe, allow the reading to stabilise, and record to one decimal place. The pH scale is logarithmic, so a change of one pH unit represents a ten-fold change in [H⁺]. Remember that acidic solutions have pH < 7, neutral pH = 7, alkaline pH > 7. To determine whether a substance is acidic, neutral, or alkaline without measuring exact pH, litmus paper is still a quick choice.

指示剂会因溶液pH而改变颜色。石蕊在酸中变红，在碱中变蓝，但不能区分强酸弱酸。通用指示剂由多种染料混合而成，呈现从红色(pH 1)经过绿色(pH 7)到紫色(pH 14)的渐变颜色。可滴加几滴通用指示剂溶液或用通用指示纸浸蘸来估测溶液的pH。若需更精确测量，则使用带探头的pH计；浸入探头，待读数稳定后记录到一位小数。pH值为对数标度，因此改变1个pH单位意味着[H⁺]改变10倍。记住酸性溶液pH<7，中性pH=7，碱性pH>7。若不需要精确pH值，仅需判断物质是酸性、中性还是碱性，石蕊试纸仍是快捷之选。

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IGCSE Chemistry: Mastering Experimental Techniques | IGCSE化学：实验操作指南