📚 IGCSE Science Practical Skills: Key Experiments | IGCSE科学实验考点梳理
The IGCSE Science practical component (Physics, Chemistry, Biology) is not just about memorising procedures — it assesses your ability to plan, observe, record, analyse, and evaluate experiments. This article consolidates the core experiments and skills you must master for both Paper 5 (Practical Test) and Paper 6 (Alternative to Practical).
IGCSE科学实验部分（物理、化学、生物）不仅仅考查背诵实验步骤，更评估你计划、观察、记录、分析和评估实验的能力。本文为你整合了在Paper 5（实验考试）和Paper 6（实验替代卷）中必须掌握的核心实验与技能。
1. Experimental Design: Variables & Control | 实验设计：变量与控制
In any IGCSE practical question, you must identify the independent variable (the one you change), the dependent variable (the one you measure), and the controlled variables (the ones you keep constant). For example, in a reaction rate experiment, temperature, concentration, surface area, or a catalyst could be chosen as the independent variable.
在任何IGCSE实验题中，你必须识别自变量（你改变的量）、因变量（你测量的量）和控制变量（你保持不变的量）。例如，在反应速率实验中，温度、浓度、表面积或催化剂都可以作为自变量。
Independent variable: the factor deliberately changed, e.g., concentration of acid (mol/dm³).
自变量：刻意改变的因素，例如酸浓度（mol/dm³）。
Dependent variable: the factor measured, e.g., volume of gas produced per minute (cm³/min).
因变量：被测定的因素，例如每分钟产生的气体体积（cm³/min）。
Controlled variables: factors kept constant, e.g., temperature, mass of solid, total volume.
控制变量：保持恒定的因素，例如温度、固体质量、总体积。
Controlling variables is the key to a valid experiment → 控制变量是实验有效性的关键
2. Measurements & Instruments | 测量与仪器使用
You must know the precision of common lab instruments and choose the right one for each measurement. A measuring cylinder (accuracy ±0.5 cm³) is not suitable for precise volumes; a burette (±0.05 cm³) or pipette (±0.06 cm³) is better. A thermometer (±0.5°C) is used for temperature, while a stopwatch (±0.1 s) for time.
你必须了解常见实验室仪器的精度，并为每次测量选择合适的仪器。量筒（精度±0.5 cm³）不适合精密体积；滴定管（±0.05 cm³）或移液管（±0.06 cm³）更佳。温度计（±0.5°C）用于温度，秒表（±0.1 s）用于时间。
Burette readings: record to two decimal places ending in 0 or 5, e.g., 24.00 cm³, 24.25 cm³.
滴定管读数：记录至两位小数，末位为0或5，例如24.00 cm³、24.25 cm³。
Measuring cylinder: read at eye level from the bottom of the meniscus.
量筒：平视，读取凹液面底部。
Thermometer: avoid touching the container wall when reading.
温度计：读数时避免接触容器壁。
Ruler: measure from the zero mark; estimate to half a millimetre.
刻度尺：从零刻度开始测量；估读至半毫米。
| Instrument | Use | Precision |
| Burette | Titration volume | ±0.05 cm³ |
| Pipette | Fixed volume | ±0.06 cm³ |
| Measuring cylinder | Approx volume | ±0.5 cm³ |
| Thermometer | Temperature | ±0.5°C |
3. Physics Experiments: Density, Motion & Optics | 物理实验：密度、运动与光学
Physics practicals often involve measurements and graphical analysis. The density experiment requires measuring mass with a balance and volume using a measuring cylinder (regular solids via dimensions; irregular solids via displacement). Motion experiments use a ticker timer or motion sensor.
物理实验通常涉及测量和图形分析。密度实验需要用天平测质量，用量筒测体积（规则固体通过尺寸计算；不规则固体通过排水法）。运动实验使用打点计时器或运动传感器。
Density of a liquid: measure mass of empty cylinder, then mass of cylinder + liquid. Density = mass ÷ volume.
液体密度：测量空量筒质量，再测量量筒+液体质量。密度=质量÷体积。
Resistance experiment: use an ammeter in series and a voltmeter in parallel. R = V/I. Plot V against I; the gradient is R.
电阻实验：电流表串联，电压表并联。R=V/I。绘制V-I图，斜率即为R。
Optics: measure angle of incidence and reflection using a ray box and protractor; verify Snell's law (sin i / sin r = n).
光学：用光具箱和量角器测量入射角和反射角；验证斯涅尔定律（sin i / sin r = n）。
Density = Mass / Volume → ρ = m/V
4. Chemistry: Acid-Base Titration | 化学：酸碱滴定
Titration is a core IGCSE practical. You use a pipette to transfer a fixed volume of alkali to a conical flask, add an indicator (e.g., methyl orange or phenolphthalein), then add acid from a burette until the endpoint. Repeat until concordant results (within ±0.10 cm³ of each other).
滴定是IGCSE核心实验。用移液管将固定体积的碱移入锥形瓶，加入指示剂（如甲基橙或酚酞），然后用滴定管加入酸至终点。重复实验，直到结果一致（相差不超过±0.10 cm³）。
Rinse the pipette with the alkali solution; rinse the burette with the acid solution.
用碱液润洗移液管；用酸液润洗滴定管。
Add the acid dropwise near the endpoint, swirling constantly.
接近终点时逐滴加入酸，持续摇动。
Record initial and final burette readings; calculate titre = final − initial.
记录初始和最终滴定管读数；计算滴定体积=最终−初始。
Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O （碳酸钠与盐酸反应）
5. Chemistry: Gas Collection & Rates of Reaction | 化学：气体收集与反应速率
To investigate factors affecting reaction rate, you can measure the volume of gas produced over time using an upside-down measuring cylinder (or gas syringe) in a water trough. Factors include concentration, temperature, surface area, and catalysts.
研究影响反应速率的因素时，可通过倒置量筒（或气体注射器）在水槽中收集气体，并测随时间产生的气体体积。因素包括浓度、温度、表面积和催化剂。
Draw a tangent to the curve at a given time to find the instantaneous rate.
在曲线上某点画切线，求出瞬时速率。
The steeper the gradient, the faster the reaction. As reactant is used up, the curve flattens.
斜率越大，反应越快。当反应物耗尽时，曲线变平。
To measure rate continuously: record gas volume every 10 seconds for 2 minutes.
连续测量速率：每10秒记录一次气体体积，持续2分钟。
Rate = volume of gas / time → 速率 = 气体体积 / 时间
6. Chemistry: Heating & Mass Changes | 化学：加热与质量变化
Heating experiments include dehydration of hydrated copper(II) sulfate and thermal decomposition of carbonates. You should observe colour changes and record mass before and after heating using a balance. In crucible experiments, heat to constant mass to ensure complete reaction.
加热实验包括硫酸铜结晶水的脱水和碳酸盐的热分解。你应观察颜色变化，并用天平记录加热前后的质量。在坩埚实验中，需加热至恒重以确保反应完全。
Hydrated copper(II) sulfate: blue → white when heated (loss of water).
硫酸铜晶体：加热时蓝色→白色（失去结晶水）。
Copper(II) carbonate: green → black, with CO₂ released (limewater turns milky).
碳酸铜：绿色→黑色，释放CO₂（石灰水变浑浊）。
Heat to constant mass: repeat heating and weighing until mass does not change.
加热至恒重：重复加热和称量，直到质量不再变化。
7. Biology: Food Tests | 生物：食物成分检测
Food tests are commonly assessed in Paper 6. You need to know the reagents, methods, and positive results for starch, reducing sugars, protein, and fats/lipids. Use control experiments for comparison.
食物检测是Paper 6常见考点。你需要掌握淀粉、还原糖、蛋白质和脂肪的试剂、方法及阳性结果。使用对照实验进行比较。
| Substance | Reagent | Positive result |
| Starch | Iodine solution | Blue-black |
| Reducing sugar | Benedict's solution (heat) | Green → yellow → brick-red |
| Protein | Biuret solution | Purple/violet |
| Fat | Ethanol + water | White emulsion |
8. Biology: Photosynthesis & Enzyme Experiments | 生物：光合作用与酶实验
Photosynthesis experiments often use pondweed (e.g., Elodea) to count oxygen bubbles or measure gas volume under different light intensities. Enzyme experiments typically investigate the effect of temperature or pH on reaction rate using amylase and iodine or catalase and hydrogen peroxide.
光合作用实验常用金鱼藻（如伊乐藻）在不同光照强度下计数氧气气泡或测量气体体积。酶实验通常用淀粉酶与碘液，或过氧化氢酶与过氧化氢，探究温度或pH对反应速率的影响。
Variables for pondweed: independent = light intensity (distance from lamp); dependent = bubbles per minute.
金鱼藻变量：自变量=光照强度（距灯的距离）；因变量=每分钟气泡数。
Before starting, wait 2–3 minutes for the plant to equilibrate.
开始前等待2–3分钟，让植物平衡。
For enzyme pH: use buffer solutions to maintain a constant pH.
酶pH实验：使用缓冲液维持恒定pH。
9. Biology: Osmosis & Diffusion | 生物：渗透与扩散
A classic osmosis experiment uses potato strips or visking tubing (dialysis tubing) placed in different concentrations of sucrose solution. Measure length or mass change before and after to determine whether water entered or left the cells.
经典渗透实验用马铃薯条或玻璃纸袋（透析袋）置于不同浓度的蔗糖溶液中。测量前后长度或质量变化，以判断水进入或离开细胞。
Potato strips lose mass in concentrated solution and gain mass in dilute solution.
马铃薯条在浓溶液中失重，在稀溶液中增重。
Cut strips to equal length and size to control surface area.
将土豆条切成等长等大，以控制表面积。
Dry strips gently with paper towel before weighing to remove surface water.
称量前用纸巾轻轻吸干表面水分。
Percentage change = (final − initial) ÷ initial × 100% → 百分变化率
10. Data Recording & Tables | 数据记录与表格
Well-designed tables are part of the practical assessment. Headings must include quantity and unit, e.g., 'Volume / cm³' or 'Time / s'. Record raw data accurately, then show calculated values in separate columns. Repeat readings and include averages where appropriate.
设计良好的表格是实验评估的一部分。表头必须包含物理量和单位，例如“体积/cm³”或“时间/s”。准确记录原始数据，在单独列中显示计算值。适当进行重复读数并计算平均值。
Write units only in the column heading, not in every cell.
单位只写在列标题中，不要在每个单元格中重复。
Use a consistent number of decimal places for readings from the same instrument.
同一仪器的读数保持一致的小数位数。
Identify and discard anomalous results; explain why they are anomalous.
识别并剔除异常结果；解释异常原因。
11. Graphing Skills | 作图技能
Graphs are a critical part of IGCSE practical papers. Choose appropriate axes (independent variable on the x-axis, dependent on the y-axis), use a sharp pencil, label axes with units, and choose a scale that allows at least half of the graph paper to be used.
图表是IGCSE实验卷的关键部分。选择合适的坐标轴（自变量在x轴，因变量在y轴），用尖铅笔绘制，标注坐标轴和单位，选择至少使用一半坐标纸的刻度。
Precision: plot points with small crosses or dots, not large blobs.
精确性：用细叉号或小圆点标绘数据点，不要用大墨点。
Line of best fit: a single straight line or smooth curve passing between points, not necessarily through all.
最佳拟合线：一条直线或平滑曲线穿过各点之间，不一定经过所有点。
Gradient calculation: choose two points far apart on the line, use Δy/Δx, and include units.
斜率计算：在线上选择相距较远的两点，用Δy/Δx，并注明单位。
12. Evaluation: Errors, Limitations & Safety | 评估：误差、局限性与安全
Every real experiment has limitations. You should be able to suggest improvements, identify sources of error, and state whether results are reliable. If repeated readings are close, the experiment is repeatable; if concordant with the true value, it is accurate.
每个真实实验都有局限性。你应能提出改进建议、识别误差来源，并判断结果是否可靠。若重复读数接近，则实验可重复；若与真实值一致，则准确。
Random errors: parallax error, temperature fluctuation → reduce by repeating and averaging.
随机误差：视差、温度波动 → 通过重复和平均来减小。
Systematic errors: zero error, faulty instrument → fix or calibrate instrument.
系统误差：零误差、仪器故障 → 修正或校准仪器。
Safety: wear goggles, handle corrosive acids/careful with heat; state specific precautions.
安全：佩戴护目镜，小心处理腐蚀性酸/加热；指出具体注意事项。
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