📚 Mastering CAIE IGCSE Chemistry 0620 Alternative to Practical | CAIE IGCSE 化学 0620 实验替代卷高分指南
The Alternative to Practical paper is a written examination that replaces hands-on laboratory work for candidates who cannot access a full practical exam. It tests your ability to plan experiments, record and present data, identify sources of error and draw conclusions from chemical observations.
实验替代卷是一份书面考试，用来替代无法参加完整实验操作的考生所进行的动手实验考查。它考查你设计实验、记录与呈现数据、识别误差来源以及从化学现象中得出结论的能力。
1. Understanding the Paper 6 Format | 了解 Paper 6 考试形式
CAIE IGCSE Chemistry 0620 Paper 6 is a written paper lasting 1 hour and carrying 40 marks. You will not carry out any practical work, but every question is based on laboratory situations, data tables, diagrams of apparatus, or descriptions of procedures.
CAIE IGCSE 化学 0620 试卷 6 是一份时长 1 小时、总分 40 分的书面试卷。你不需要进行任何实际操作，但每一道题都基于实验室情境、数据表、仪器示意图或实验步骤描述。
Questions often ask you to complete a results table, plot a graph, calculate a quantity, suggest a piece of apparatus, describe a safe method, identify anomalies, state sources of error and propose improvements. Familiarity with standard practical skills is essential.
题目通常要求你补全结果表、绘制图表、计算某个量、指出所需仪器、描述安全方法、找出异常数据、说明误差来源并提出改进方案。熟悉标准实验技能至关重要。
Total marks = 40 | Time = 60 minutes | Written only
总分 = 40 分 | 时间 = 60 分钟 | 仅笔试
2. Common Laboratory Apparatus and Their Uses | 常见实验仪器及其用途
You must be able to identify common apparatus and state what each piece is used for. You should also know which instrument gives the most accurate or most suitable measurement in a given experiment.
你必须能够识别常见仪器并说明每种仪器的用途。你还应当知道在给定的实验中，哪种仪器能给出最准确或最合适的测量结果。
| Apparatus | Main use |
|---|---|
| Burette | Delivers variable volumes accurately, especially in titrations |
| Pipette | Delivers one fixed volume accurately, e.g. 25.0 cm³ |
| Measuring cylinder | Measures approximate volumes of liquids |
| Gas syringe | Collects and measures the volume of gas produced |
| Conical flask | Holds liquids during mixing or titration, reduces splashing |
| Beaker | Holds, mixes or heats liquids roughly |
| Thermometer | Measures temperature, usually to nearest 0.5 °C |
| Balance | Measures mass, usually to 0.01 g or 0.001 g |
| Stopwatch | Measures time intervals |
Burette reading: 0.05 cm³ | Pipette: 25.0 cm³ | Measuring cylinder: 0.5–1 cm³
滴定管读数：0.05 cm³ | 移液管：25.0 cm³ | 量筒：0.5–1 cm³
Always read the bottom of the meniscus at eye level. For coloured liquids, read the top of the meniscus. The chosen apparatus must match the required precision of the question.
读数时始终在眼睛水平高度读取弯月面底部。对于有色液体，读取弯月面顶部。所选仪器必须与题目要求的精确度相匹配。
3. Measuring and Recording Data | 测量与记录数据
A results table must have clear headings with the quantity and unit separated by a slash, for example "time / s" or "temperature / °C". Do not put units in the body of the table.
结果表必须有清晰的表头，用斜线分隔物理量和单位，例如 "time / s" 或 "temperature / °C"。不要在表格主体中写单位。
Record all raw data to the correct number of decimal places according to the measuring instrument used. If you repeat a measurement, calculate the average and exclude any obvious anomalous value before calculating the mean.
根据所用测量仪器，将所有原始数据记录到正确的小数位数。如果重复测量，计算平均值，并在求平均前排除明显异常的数据。
Mean = (value 1 + value 2 + value 3) ÷ number of values
平均值 = (数值 1 + 数值 2 + 数值 3) ÷ 数值个数
Consistency is important: if a balance reads to 0.01 g, write all masses as 5.00 g, 5.20 g, not 5 g or 5.2 g. This shows you understand precision.
一致性很重要：如果天平读到 0.01 g，那么所有质量都应写成 5.00 g、5.20 g，而不是 5 g 或 5.2 g。这表明你理解精确度的概念。
4. Experimental Design and Variables | 实验设计与变量控制
You need to identify three types of variables: independent variable, dependent variable, and control variables. A fair test keeps all variables constant except the independent variable.
你需要辨别三类变量：自变量、因变量和控制变量。公平实验除自变量外，所有其他变量都保持不变。
For example, when investigating the effect of acid concentration on reaction rate, concentration of acid is the independent variable, time or gas volume is the dependent variable, and temperature, mass of solid, volume of acid and surface area are control variables.
例如，在研究酸浓度对反应速率的影响时，酸浓度是自变量，时间或气体体积是因变量，而温度、固体质量、酸体积和表面积都是控制变量。
- Independent variable: the one you change deliberately.
- Dependent variable: the one you measure.
- Control variables: the ones you keep the same.
自变量：你主动改变的变量 | 因变量：你测量的变量 | 控制变量：保持不变的变量
A good plan should be written in numbered steps, using precise quantities and named apparatus. You should also include a safety precaution such as wearing goggles or using a fume cupboard when appropriate.
一份好的实验设计应采用编号步骤书写，写明具体数量和仪器名称。你还应写出安全措施，例如佩戴护目镜或在必要时使用通风橱。
5. Drawing Graphs and Interpreting Trends | 绘图与趋势分析
Graphs must have labelled axes with units, a sensible linear scale, and points plotted with small neat crosses. Use at least half of the graph paper and do not use awkward scales such as multiples of 3.
图表必须有带单位的坐标轴标签、合理的线性刻度，并用小而清晰的十字标记数据点。使用至少一半的图纸面积，避免使用如 3 的倍数等不便的刻度。
Draw a line or curve of best fit. Do not join points dot-to-dot. If a point is clearly anomalous, circle it and ignore it when drawing the best-fit line.
绘制最佳拟合直线或曲线。不要逐点连接。如果某个数据点明显异常，圈出该点，并在绘制最佳拟合线时忽略它。
Interpretation includes describing the relationship: directly proportional, inversely proportional, increasing, decreasing, levelling off. The gradient gives useful information, for example mass lost per unit time in a rate experiment.
解释包括描述关系：成正比、成反比、上升、下降、趋于平稳。斜率能提供有用信息，例如在速率实验中表示单位时间损失的质量。
Gradient = change in y ÷ change in x
斜率 = y 轴变化量 ÷ x 轴变化量
For a temperature–time graph, an extrapolated line can help you estimate the maximum temperature change after correcting for heat loss.
对于温度-时间图，外推直线有助于在校正热损失后估算最大温度变化。
6. Errors, Uncertainties and Improvements | 误差、不确定性与改进方法
Random errors cause readings to be scattered on either side of the true value. They can be reduced by repeating measurements and taking averages.
随机误差会使读数在真值两侧分散。可通过重复测量并取平均值来减小随机误差。
Systematic errors cause all readings to be shifted in one direction. Examples include a zero error on a balance, a faulty thermometer, or reading a burette from above the meniscus every time.
系统误差会使所有读数朝一个方向偏移。例子包括天平调零错误、温度计故障，或每次从弯月面上方读取滴定管读数。
| Source of error | Improvement |
|---|---|
| Heat loss to the surroundings | Use a polystyrene cup, lid, or insulation |
| Parallax error when reading volume | Read the meniscus at eye level |
| Gas escapes before collection begins | Fit the bung tightly and start the stopwatch immediately |
| Mass loss is too small to measure | Increase concentration or use a more precise balance |
| Reaction is too fast to time accurately | Dilute the solution or lower the temperature |
Uncertainty of a single reading = half the smallest scale division
单次读数的不确定度 = 最小分度值的一半
When suggesting improvements, always link the weakness to a specific action. Avoid vague answers such as "do it more carefully"; write "use a gas syringe instead of a measuring cylinder to reduce gas leakage".
提出改进建议时，始终将缺陷与具体操作联系起来。避免模糊回答，如“更仔细地操作”；应写“使用气体注射器代替量筒以减少气体泄漏”。
7. Separation and Purification Techniques | 分离与提纯技术
Paper 6 often asks you to describe how to separate a mixture. You must choose the correct technique based on differences in physical properties such as solubility, boiling point, particle size or magnetic attraction.
试卷 6 经常要求描述如何分离混合物。你必须根据溶解性、沸点、颗粒大小或磁性等物理性质的差异选择正确的分离方法。
- Filtration separates an insoluble solid from a liquid.
- Evaporation and crystallisation obtain a soluble solid from a solution.
- Simple distillation separates a solvent from a solution, e.g. water from salt water.
- Fractional distillation separates miscible liquids with close boiling points.
- Chromatography separates coloured or colourless substances in a solution.
- A separating funnel separates immiscible liquids such as oil and water.
过滤：分离不溶性固体与液体 | 蒸发与结晶：从溶液中获得可溶性固体 | 简单蒸馏：分离溶剂与溶液 | 分馏：分离沸点相近的互溶液体 | 色谱法：分离溶液中的有色或无色物质 | 分液漏斗：分离油和水等不相溶液体
To prepare pure dry copper(II) sulfate crystals from copper(II) oxide and sulfuric acid, add excess black copper(II) oxide to warm acid, filter to remove unreacted solid, heat the filtrate to evaporate some water, then leave to cool and crystallise. Dry the crystals between filter paper.
要从氧化铜和硫酸制备纯净干燥的硫酸铜晶体，将过量的黑色氧化铜加入温热的酸中，过滤除去未反应的固体，加热滤液蒸发部分水分，然后冷却结晶。用滤纸将晶体干燥。
If a question asks why excess solid is used, the answer is to ensure all the acid is neutralised and fully reacted. The excess is then removed by filtration.
如果题目问为什么使用过量固体，答案是确保所有酸都被中和并完全反应。多余的固体随后通过过滤除去。
8. Tests for Gases and Ions | 气体与离子检验
Identification tests are highly examinable. You must know the reagent, the observed result, and sometimes the chemical name of the product that causes the observation.
鉴别检验是高频考点。你必须知道所用试剂、观察到的现象，有时还要知道引起该现象的产物化学名称。
| Gas | Test and positive result |
|---|---|
| Hydrogen, H₂ | Burning splint gives a squeaky pop |
| Oxygen, O₂ | Relights a glowing splint |
| Carbon dioxide, CO₂ | Turns limewater milky |
| Chlorine, Cl₂ | Damp blue litmus paper is bleached white |
| Ammonia, NH₃ | Turns damp red litmus paper blue |
For cations, sodium hydroxide solution is added to the unknown solution. A blue precipitate indicates Cu²⁺, a green precipitate Fe²⁺, and a brown precipitate Fe³⁺. Al³⁺ and Zn²⁺ both give white precipitates, but only the zinc hydroxide precipitate redissolves in excess ammonia solution.
对于阳离子，向未知溶液中加入氢氧化钠溶液。蓝色沉淀表示 Cu²⁺，绿色沉淀表示 Fe²⁺，棕色沉淀表示 Fe³⁺。Al³⁺ 和 Zn²⁺ 都会产生白色沉淀，但只有氢氧化锌沉淀能溶解在过量氨水中。
Flame tests are used for some metal ions: Li⁺ gives red, Na⁺ gives yellow, K⁺ gives lilac, Ca²⁺ gives orange-red, and Cu²⁺ gives blue-green.
焰色试验用于检验某些金属离子：Li⁺ 呈红色，Na⁺ 呈黄色，K⁺ 呈淡紫色，Ca²⁺ 呈橙红色，Cu²⁺ 呈蓝绿色。
For anions, carbonate ions react with dilute acid to release carbon dioxide. Chloride ions give a white precipitate with acidified silver nitrate; bromide gives cream, iodide gives yellow. Sulfate ions give a white precipitate with acidified barium chloride.
对于阴离子，碳酸根离子与稀酸反应放出二氧化碳。氯离子与酸化硝酸银溶液产生白色沉淀；溴离子产生奶油色沉淀，碘离子产生黄色沉淀。硫酸根离子与酸化氯化钡溶液产生白色沉淀。
9. Acids, Bases and Salt Preparation | 酸、碱与盐的制备
Salt preparation methods depend on solubility. Soluble salts of sodium, potassium and ammonium are usually made by titration. You must be able to describe the titration procedure and calculate concentration.
盐的制备方法取决于溶解性。钠、钾和铵的可溶性盐通常用滴定法制备。你必须能够描述滴定步骤并计算浓度。
For titration, a fixed volume of alkali is measured with a pipette and transferred to a conical flask. A few drops of indicator are added. Acid is added from a burette until the end point, then the volume of acid is recorded. The titration is repeated without indicator to obtain a pure salt solution.
滴定操作时，用移液管量取一定体积的碱液并转移到锥形瓶中。加入几滴指示剂。从滴定管中滴加酸直到终点，记录所用酸的体积。为了得到纯净的盐溶液，可在不加指示剂的情况下重复滴定。
n = c × V (V in dm³)
物质的量 = 浓度 × 体积 (体积单位 dm³)
To convert cm³ to dm³, divide by 1000. For example, 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide contains 0.00250 mol of NaOH. If it reacts with HCl in a 1:1 ratio, the same number of moles of HCl is required.
将 cm³ 转换为 dm³ 时除以 1000。例如，25.0 cm³ 的 0.100 mol/dm³ 氢氧化钠溶液含有 0.00250 mol NaOH。如果它与 HCl 以 1:1 的比例反应，则所需 HCl 的物质的量相同。
Soluble salts of zinc, iron, copper and calcium are often prepared by reacting an excess insoluble base, metal or carbonate with a warm acid. Insoluble salts are made by precipitation: mix two soluble salts that contain the required ions, filter, wash and dry the precipitate.
锌、铁、铜和钙的可溶性盐通常通过过量不溶性碱、金属或碳酸盐与温热酸反应制备。不溶性盐通过沉淀法制备：混合两种含有目标离子的可溶性盐，过滤、洗涤并干燥沉淀。
10. Rate of Reaction Experiments | 反应速率实验
Rate of reaction can be followed by measuring the volume of gas produced at regular time intervals, recording the mass lost from a flask, or timing how long a precipitate takes to hide a cross under the reaction vessel.
反应速率可以通过以下方法跟踪：每隔固定时间测量产生气体的体积、记录烧瓶损失的质量，或记录沉淀物遮住反应容器下方十字标记所需的时间。
To investigate the effect of concentration, keep the mass and size of marble chips constant, keep the volume of acid constant, and change only the concentration of hydrochloric acid. Collect hydrogen or carbon dioxide gas and compare the gradients of the gas volume–time graphs.
研究浓度的影响时，保持大理石碎块的质量和大小不变、酸的体积不变，只改变盐酸的浓度。收集氢气或二氧化碳气体，并比较气体体积-时间图的斜率。
Average rate = total change in quantity ÷ total time taken
平均速率 = 总量的变化 ÷ 总时间
For a faster reaction, the graph rises more steeply at the start and reaches its final volume sooner, but the final volume of gas is the same if the same mass of limiting reactant is used.
对于较快的反应，曲线开始上升更陡，并且更快达到最终体积；但如果使用了相同质量的决定性反应物，最终气体体积相同。
Common control variables include temperature, total volume of solution, mass and surface area of the solid, and stirring rate. Surface area can be increased by crushing a solid into smaller pieces or powder.
常见的控制变量包括温度、溶液总体积、固体的质量和表面积以及搅拌速率。表面积可以通过将固体压碎成小块或粉末来增大。
11. Chromatography and Simple Analysis | 色谱法与简单分析
Paper chromatography is used to separate small amounts of dissolved substances, such as dyes in ink or food colourings. A baseline is drawn in pencil, not ink, because pencil does not dissolve in the solvent.
纸色谱法用于分离少量溶解物质，例如墨水或食用色素中的染料。基线用铅笔绘制，而不是用墨水，因为铅笔不溶于溶剂。
The chromatogram is placed in a closed container with a shallow layer of solvent below the baseline. The solvent moves up the paper and carries the dyes different distances according to their solubility and attraction to the paper.
将色谱纸放入密闭容器中，溶剂液面低于基线。溶剂沿纸上升，根据染料的溶解性和对纸的吸附力不同，将染料带到不同的高度。
Rf = distance moved by substance ÷ distance moved by solvent front
Rf = 物质移动距离 ÷ 溶剂前沿移动距离
Rf is always less than 1 and has no units. A pure substance shows one spot; an impure or mixed substance shows more than one spot. Locating agents are used to make colourless spots visible under ultraviolet light.
Rf 始终小于 1 且没有单位。纯物质只有一个斑点；不纯或混合物显示多个斑点。显色剂用于在紫外光下使无色的斑点显现出来。
If two spots have the same Rf value under the same conditions, they may be the same substance. To confirm identity, a known reference sample should be run alongside the unknown on the same chromatogram.
如果在相同条件下两个斑点的 Rf 值相同，它们可能是同一种物质。为确认物质身份，应在同一色谱纸上将已知参照样品与未知样品并排分离。
12. Thermal Chemistry and Energy Changes | 热化学与能量变化
Energy changes are measured in a simple calorimeter, usually a polystyrene cup placed inside a beaker. The cup reduces heat loss because polystyrene is a good insulator.
能量变化通常用简易量热计测量，一般是将聚苯乙烯杯放入烧杯中。聚苯乙烯是良好的绝热材料，因此杯子能减少热量损失。
To find the temperature change, record the initial temperature of the solution, add the other reactant, stir and record the highest or lowest temperature reached
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