IGCSE Science: Experimental Operations Guide | IGCSE 科学：实验操作指南

📚 IGCSE Science: Experimental Operations Guide | IGCSE 科学：实验操作指南

Experimental skills are the backbone of success in IGCSE Science. This guide brings together key practical techniques from Biology, Chemistry, and Physics, helping you understand common procedures, handle apparatus correctly, collect reliable data, and stay safe in the laboratory. Whether you are preparing for coursework or the written alternative-to-practical paper, mastering these operations will build your confidence and accuracy.

实验技能是 IGCSE 科学取得成功的基石。本指南整合了生物、化学和物理中的关键实践技术，帮助你理解常见操作、正确使用仪器、收集可靠数据，并确保实验室安全。无论你是在准备课程作业还是笔试中的实验替代题，掌握这些操作都将提升你的信心与准确性。

1. Safety in the Laboratory | 实验室安全

Always wear safety goggles and a lab coat before starting any experiment. Long hair must be tied back, and loose clothing should be secured. Never eat, drink, or run in the laboratory. Know the location of the fire extinguisher, eyewash station, and emergency exits. Read reagent labels carefully and never return unused chemicals to their original containers.

开始任何实验前务必佩戴护目镜和实验服。长发应束起，宽松衣物需固定。严禁在实验室饮食或奔跑。要熟知灭火器、洗眼器和紧急出口的位置。仔细阅读试剂标签，剩余化学品绝不可倒回原瓶。

When heating flammable liquids, use a water bath rather than a direct flame. If you smell gas, immediately turn off the supply and open windows. Always use a fume cupboard when handling volatile or toxic substances. Report all accidents, however small, to your teacher instantly.

加热易燃液体时，应使用水浴而非明火。若闻到燃气气味，立即关闭气源并开窗。处理挥发性或有毒物质时，始终使用通风橱。任何意外，无论多轻微，都要立即报告老师。

2. Common Equipment and Measurement | 常用器材与测量

A graduated cylinder is suitable for measuring approximate volumes, while a volumetric pipette and burette deliver precise volumes for quantitative work. Always read the bottom of the meniscus at eye level to avoid parallax errors. Use a chemical balance to measure mass to the nearest 0.01 g, and record the value with the correct unit.

量筒适用于量取近似体积，而定量工作中需使用移液管和滴定管以获取精确体积。始终在视线水平处读取弯月面的最低点，以避免视差。使用分析天平测量质量，精确到 0.01 g，并记录正确单位。

A thermometer should not touch the sides of the container when measuring the temperature of a liquid. For time measurements, a stopwatch reading to 0.1 s is adequate for most IGCSE experiments. When using a measuring cylinder, note the uncertainty: for a 100 cm³ cylinder, the uncertainty is typically ±0.5 cm³, so record the volume as, for example, 20.0 ± 0.5 cm³.

使用温度计测量液体温度时，感温泡不应接触容器壁。计时方面，大多数 IGCSE 实验使用精确到 0.1 s 的秒表即可。使用量筒时需注意不确定度：对于 100 cm³ 的量筒，不确定度通常为 ±0.5 cm³，因此体积应记录为，例如，20.0 ± 0.5 cm³。

3. Heating and Cooling Techniques | 加热与冷却技术

For gentle heating that maintains a constant temperature, use a thermostatically controlled water bath. A Bunsen burner provides a range of flame types: use a roaring blue flame for strong heating and a yellow safety flame when the burner is not in direct use. When heating a test tube, point its mouth away from yourself and others, and move the tube continuously through the flame to avoid bumping.

需要温和且恒温的加热时，可使用恒温水浴锅。本生灯能产生多种火焰：强加热时用蓝色无光焰，不直接加热时用黄色安全焰。加热试管时，试管口朝向无人处，并在火焰中持续移动试管以防止暴沸。

To cool a substance quickly, immerse the container in an ice-water bath. For crystallisation experiments, allow the hot saturated solution to cool slowly at room temperature to form large, well-defined crystals. Rapid cooling produces smaller crystals, which may be desirable in certain solubility investigations.

要快速冷却物质，可将容器浸入冰水浴中。在结晶实验中，让热的饱和溶液在室温下缓慢冷却，以形成大而规则的晶体。快速冷却则产生小晶体，这在某些溶解度探究实验中可能更符合需要。

4. Separation Techniques | 混合物分离技术

Filtration separates an insoluble solid from a liquid. Fold the filter paper properly, place it in a filter funnel, and pour the mixture down a glass rod gently. The solid, called the residue, stays on the paper, while the filtrate passes through. To obtain a soluble salt from a solution, use evaporation: heat the solution in an evaporating dish over a water bath until crystals start to form, then leave to cool.

过滤用于分离不溶性固体和液体。正确折叠滤纸，放入漏斗中，用玻璃棒引流混合液。残留在滤纸上的固体称为滤渣，流出的液体称为滤液。要从溶液中获得可溶性盐，可使用蒸发：在水浴上加热蒸发皿中的溶液，直至晶体开始析出，然后静置冷却。

Simple distillation can separate a solvent from a solution. The solution is heated in a distillation flask; the solvent vaporises, passes through a condenser where it is cooled back to liquid, and is collected as the distillate. Fractional distillation, fitted with a fractionating column, is needed to separate two miscible liquids with close boiling points, such as ethanol and water.

简单蒸馏可将溶剂从溶液中分离出来。溶液在蒸馏烧瓶中加热，溶剂气化后通过冷凝管冷凝为液体，以蒸馏液的形式被收集。分馏适用于分离沸点接近的两种互溶液体，如乙醇和水，需安装分馏柱。

5. Acid–Base Titration | 酸碱滴定

A titration is a quantitative technique used to determine the concentration of an unknown solution. Rinse the burette with the acid (or standard solution) first, then fill it, ensuring no air bubbles in the jet. Use a pipette filler to transfer exactly 25.0 cm³ of alkali into a conical flask and add a few drops of indicator, such as phenolphthalein or methyl orange.

滴定是一种用于测定未知溶液浓度的定量技术。先用酸（或标准溶液）润洗滴定管，再灌满并确保尖嘴内无气泡。用移液管吸取 25.0 cm³ 碱液至锥形瓶中，加入几滴指示剂，如酚酞或甲基橙。

Place the conical flask on a white tile under the burette. Add the acid drop by drop while swirling the flask. When the indicator just changes colour (the end point), record the final burette reading. Repeat until you obtain two concordant titres within 0.1 cm³. Use the average titre to calculate the unknown concentration using: cₐVₐ = c_bV_b (mole ratio 1:1), or adjust for the stoichiometric ratio from the balanced equation.

H⁺ (aq) + OH⁻ (aq) → H₂O (l)

将锥形瓶置于滴定管下方的白色瓷板上。边摇动锥形瓶边逐滴加入酸液，直至指示剂恰好变色（终点），记录滴定管最终读数。重复实验，直至获得两个相差不超过 0.1 cm³ 的吻合读数。平均滴定体积用于计算未知浓度：cₐVₐ = c_bV_b（物质的量比为 1:1），或根据配平方程式调整化学计量比。

将锥形瓶放在滴定管下的白瓷板上，边旋转边逐滴加酸。指示剂刚好变色时即达终点，记录最终体积。重复实验直到两次滴定体积之差不超过 0.1 cm³，取平均值。利用 cₐVₐ = c_bV_b 计算浓度（若计量比 1:1），或根据方程式调整。

6. Microscopy and Slide Preparation | 显微镜使用与标本制作

To observe cells clearly, you must prepare a thin, flat specimen. For an onion epidermal peel, remove a small piece of the inner layer using forceps, place it on a slide, add a drop of iodine solution (to stain nuclei and cell walls), and gently lower a cover slip at an angle to avoid trapping air bubbles. For cheek cells, gently scrape the inside of your cheek with a cotton swab, smear onto a slide, and stain with methylene blue.

要清晰地观察细胞，需制备薄而平整的标本。制作洋葱表皮临时装片：用镊子撕取一小块内表皮，置于载玻片上，滴加一滴碘液（使细胞核与细胞壁着色），然后以一定角度轻轻放下盖玻片以避免气泡。用于观察口腔细胞时，用棉签轻刮口腔内壁，涂于载玻片上，用亚甲蓝染色。

When using a light microscope, start with the lowest-power objective lens. Use the coarse focus knob to bring the stage close to the lens while watching from the side, then look through the eyepiece and focus away until the image appears. Switch to higher power and use only the fine focus. Total magnification = eyepiece lens magnification × objective lens magnification.

使用光学显微镜时，先从低倍物镜开始。边从侧面观察边用粗准焦螺旋使载物台靠近物镜，然后从目镜观察并退焦，直至出现图像。转换到高倍镜后，仅使用细准焦螺旋。总放大倍数 = 目镜放大倍数 × 物镜放大倍数。

A biological drawing should be made with a sharp HB pencil, showing clear, continuous outlines without shading. Label all visible structures with straight, horizontal label lines, and include a title and magnification. If you calculate cell size, use: actual size = image size ÷ magnification, and express the result in appropriate units, such as µm.

生物学绘图应使用削尖的 HB 铅笔，绘制清晰连续的轮廓，不加阴影。所有可见结构用水平的直线标注，并写上标题和放大倍数。若需计算细胞实际大小，使用：实际尺寸 = 图像尺寸 ÷ 放大倍数，并以合适单位（如微米 µm）表示。

7. Food Tests | 食物测试

Food tests are qualitative experiments that reveal the presence of key nutrients. Always work with small samples and use water baths cautiously. The table below summarises the reagents and expected colour changes.

食物测试是揭示主要营养素的定性实验。始终使用少量样本并谨慎使用水浴。下表总结了所用试剂和预期的颜色变化。

Nutrient / 营养素	Reagent / 试剂	Positive result / 阳性结果
Starch (淀粉)	Iodine solution (碘液)	Orange-brown → blue-black (橙褐色 → 蓝黑色)
Reducing sugar (还原糖)	Benedict’s solution, heat (本尼迪克特试剂，加热)	Blue → green → yellow → brick-red ppt. (蓝色 → 绿色 → 黄色 → 砖红色沉淀)
Protein (蛋白质)	Biuret test (双缩脲试剂)	Blue → lilac / purple (蓝色 → 淡紫色)
Lipids (脂肪)	Ethanol emulsion test (乙醇乳化试验)	Cloudy white emulsion (白色乳浊液)

For Benedict’s test, place the test tube containing the food sample and Benedict’s solution in a boiling water bath for 2–5 minutes. Never heat the test tube directly, as the contents may spit. A gradual colour change from blue through green to orange/turbid red indicates a decreasing sugar concentration. For a fair comparison, keep the volume of the sample and the reagent constant across tests.

本尼迪克特测试中，将装有食物样本和本尼迪克特试剂的试管置于沸水浴中 2–5 分钟。切勿直接加热试管，以免暴溅。从蓝色渐变到绿色再到橙/浑浊红色，表明还原糖浓度由低到高。为公平比较，各测试中样本与试剂的体积应保持一致。

8. Electricity and Circuits | 电学与电路

When building a circuit, always connect the components with the power supply switched off. An ammeter is connected in series to measure current (I, unit A), while a voltmeter is connected in parallel to measure potential difference (V, unit V). Use the correct terminals: red for the positive side, black for the negative. For varied-resistance experiments, a rheostat or variable resistor can be included.

搭建电路时，务必在关闭电源的状态下连接元件。电流表串联以测量电流（I，单位 A），电压表并联以测量电势差（V，单位 V）。正确连接接线柱：红接正，黑接负。变阻器或可变电阻可用于改变电阻的实验。

When investigating Ohm’s law, take pairs of voltage and current readings, and plot a V–I graph. A straight line through the origin indicates that the conductor is ohmic. For a filament lamp, the graph curves as resistance increases with temperature. All readings should be repeated, and you should check for zero errors on the meters before starting.

探究欧姆定律时，记录成对的电压和电流值，并绘制 V–I 图像。一条过原点的直线表示导体是欧姆性的。对于白炽灯，其图像因电阻随温度升高而弯曲。所有数据应重复测量，并在开始前检查仪表是否有零误差。

The relationship between resistance, voltage and current is:

R = V / I

Use a standard resistor to verify that the calculated resistance matches the colour-band value. For circuits with resistors in series, total resistance R_total = R₁ + R₂; for resistors in parallel, 1/R_total = 1/R₁ + 1/R₂. Always disconnect the circuit before making changes.

使用标准电阻验证计算出的阻值是否与其色环值一致。对于串联电阻，总电阻 R_total = R₁ + R₂；并联时，1/R_total = 1/R₁ + 1/R₂。修改电路前，务必先断开电源。

9. Gas Collection and Identification | 气体收集与鉴定

Collecting a gas depends on its density and solubility in water. Gases that are lighter than air and not very soluble, such as hydrogen (H₂) and ammonia (NH₃), can be collected by downward delivery (upward displacement of air). Gases heavier than air, like carbon dioxide (CO₂), chlorine (Cl₂) and sulphur dioxide (SO₂), are collected by upward delivery. Gases with low solubility, such as oxygen (O₂) and hydrogen, can also be collected over water (downward displacement of water).

气体收集方法取决于其密度和水溶性。比空气轻且不易溶的气体，如氢气 (H₂) 和氨气 (NH₃)，可用向下排空气法收集。比空气重的气体，如二氧化碳 (CO₂)、氯气 (Cl₂) 和二氧化硫 (SO₂)，采用向上排空气法。溶解度低的气体，如氧气 (O₂) 和氢气，也可用排水集气法收集。

The table below lists standard gas tests that can be performed in the laboratory.

Gas / 气体	Test / 检验方法	Positive observation / 阳性现象
Oxygen (O₂)	Glowing splint (带火星木条)	Splint relights (木条复燃)
Hydrogen (H₂)	Burning splint at mouth of test tube (点燃木条放在试管口)	Squeaky pop sound (发出尖锐爆鸣声)
Carbon dioxide (CO₂)	Bubble through limewater (通入石灰水)	Limewater turns milky (石灰水变浑浊)
Chlorine (Cl₂)	Place damp blue litmus paper in gas (将湿润蓝色石蕊试纸置于气体中)	Bleached white (先变红后漂白)
Ammonia (NH₃)	Damp red litmus paper (湿润红色石蕊试纸)	Turns blue (变蓝)

When preparing gases in the laboratory, always ensure the apparatus is airtight. If you are collecting a gas over water, the first few bubbles may contain air from the apparatus—discard them before collecting the sample. Always ventilate the room when handling toxic gases like chlorine.

实验室制备气体时，确保装置气密性。若用排水集气法，前几个气泡可能含有装置内的空气——先排掉再收集样品。处理氯气等有毒气体时，务必保持室内通风。

10. Data Handling and Lab Reports | 数据处理与实验报告

Record all raw data in a well-organised table before leaving the bench. The table should have clear headings with units, e.g. ‘Time / s’ and ‘Temperature / °C’. Record readings to the precision of the instrument used. If you suspect an anomalous result, repeat that measurement and mark the outlier in your table. Plot graphs with the independent variable on the x-axis and the dependent variable on the y-axis; use a sharp pencil to draw points as small crosses or encircled dots.

离开实验台前，将所有原始数据记录在条理清晰的表格中。表格应有带单位的明确表头，如“时间 / s”和“温度 / °C”。读数记录到仪器的最小分度值。若怀疑存在异常值，应重复该测量并在表中标记异常点。绘制图表时，自变量标在 x 轴，因变量标在 y 轴；用削尖铅笔以细小十字或带圈点标绘数据点。

Draw the best-fit line—either a straight line of best fit or a smooth curve—through the points, ignoring any outliers. If calculating the gradient of a straight line, pick two widely spaced points on the line (not necessarily data points) and use: slope = Δy / Δx. For a linear relationship, the equation of the line is y = mx + c, where m is the gradient and c is the y-intercept. Always title your graph and label axes clearly.

绘制最佳拟合线（直线或平滑曲线），忽略异常值。计算直线斜率时，在直线上选取两个间距较大的点（不一定是原始数据点），使用公式：斜率 = Δy / Δx。对于线性关系，直线方程为 y = mx + c，其中 m 为斜率，c 为 y-轴截距。图表必须有标题，坐标轴清晰标注。

A complete lab report should include: Title, Date, Aim, Apparatus, Method (written in the past impersonal tense), Results (table and graph), Conclusion, and Evaluation. In the evaluation, comment on the reliability of the data, identify sources of error (random or systematic), and suggest realistic improvements to the procedure.

一份完整的实验报告应包括：标题、日期、实验目的、器材、方法（用过去时第三人称叙述）、结果（表格和图表）、结论与评估。评估中应评论数据的可靠性，指出误差来源（随机误差或系统误差），并对步骤提出切实可行的改进建议。

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