Required Practical Activities: Exemplar Experiments | 必修实验活动：示范实验指南

📚 Required Practical Activities: Exemplar Experiments | 必修实验活动：示范实验指南

The AQA A-Level Chemistry specification requires students to complete twelve required practical activities (RPAs). These exemplar experiments are designed to develop the practical skills assessed in written examinations and to satisfy the Common Practical Assessment Criteria (CPAC) for the Practical Endorsement.

AQA A-Level 化学考纲要求学生完成十二项必修实验活动（RPAs）。这些示范实验旨在培养笔试中考查的实践技能，并满足实践认可（CPAC）的通用实践评估标准。

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1. Overview of the Twelve AQA Required Practicals | AQA十二项必修实验概览

Each required practical targets a specific skill set: volumetric analysis, enthalpy measurement, kinetics, qualitative analysis, organic synthesis, electrochemistry, pH measurement and chromatography.

每项必修实验针对一组特定技能：定量分析、焓变测量、动力学、定性分析、有机合成、电化学、pH测量和色谱法。

Practical	Title | 实验名称
RP 1	Make up a volumetric solution and carry out an acid–base titration | 配制体积溶液并进行酸碱滴定
RP 2	Measurement of an enthalpy change | 测量焓变
RP 3	Investigation of how rate changes with temperature | 研究温度对反应速率的影响
RP 4	Identification of cations and anions | 阳离子和阴离子的鉴别
RP 5	Distillation of a product from a reaction | 从反应产物中蒸馏
RP 6	Tests for alcohol, aldehyde, alkene and carboxylic acid | 醇、醛、烯烃和羧酸的检验
RP 7	Measuring rate by an initial rate method | 用初始速率法测量反应速率
RP 8	Measuring the EMF of an electrochemical cell | 测量电化学电池的电动势
RP 9	Investigating pH changes during a weak acid–strong base titration | 研究弱酸与强碱滴定过程中的pH变化
RP 10	Preparation of a pure organic solid and purity check | 制备纯有机固体并检验纯度
RP 11	Test-tube reactions for transition metal ions | 过渡金属离子的试管反应
RP 12	Separation by thin-layer chromatography | 薄层色谱分离

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2. RP 1 — Titration and Volumetric Analysis | RP1 滴定与定量分析

To make a standard solution, an accurately weighed mass of solute is dissolved in deionised water and made up to the mark in a volumetric flask. The key technique is swirling to ensure complete dissolution before the final dropwise addition of water.

配制标准溶液时，将准确称量的溶质溶于去离子水中，在容量瓶中定容至刻度线。关键技术是充分旋摇以确保完全溶解，然后逐滴加水至刻度线。

In the titration, a pipette transfers a precise volume of the analyte into a conical flask, and a burette delivers the titrant. Indicators such as phenolphthalein or methyl orange must be chosen so that the colour change coincides with the equivalence point.

滴定时，用移液管移取准确体积的待测液至锥形瓶，再用滴定管加入滴定剂。应选择酚酞或甲基橙等指示剂，使颜色变化恰好在等当点发生。

n = c × V
moles = concentration (mol dm⁻³) × volume (dm³)

Volumetric flasks, pipettes and burettes must be rinsed with the correct solution: the pipette with the analyte, the burette with the titrant, and the conical flask with deionised water only.

容量瓶、移液管和滴定管必须用正确溶液润洗：移液管用待测液、滴定管用滴定剂，而锥形瓶只用去离子水。

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3. RP 2 — Measuring an Enthalpy Change | RP2 测量焓变

This experiment measures the temperature change when a known mass of water absorbs heat released by a reaction, such as the neutralisation of HCl with NaOH or the dissolution of ammonium chloride.

本实验测量已知质量的水在吸收反应热量时的温度变化，例如HCl与NaOH的中和反应或氯化铵的溶解。

The temperature rise ΔT is recorded using a thermometer or datalogger. The heat change is calculated using q = mcΔT, where m is the mass of the solution, c is the specific heat capacity (4.18 J g⁻¹ K⁻¹) and ΔT is the temperature change in kelvin or degrees Celsius.

用温度计或数据记录仪记录温度升高ΔT。热量变化用q = mcΔT计算，其中m为溶液质量，c为比热容（4.18 J g⁻¹ K⁻¹），ΔT为温度变化（开尔文或摄氏度）。

q = mcΔT
ΔH = −q / n

Styrofoam or expanded polystyrene cups act as simple calorimeters to reduce heat loss. Stirring ensures uniform temperature distribution. For dissolving solids, the solid should be added quickly and the maximum or minimum temperature recorded.

泡沫聚苯乙烯杯可用作简易量热计以减少热量散失。搅拌确保温度均匀。对于固体溶解，应快速加入固体并记录最高或最低温度。

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4. RP 3 & 7 — Kinetics: Rate and Temperature | RP3与RP7 动力学：速率与温度

RP 3 typically uses the reaction between sodium thiosulfate and hydrochloric acid, where a precipitate of sulfur makes a cross drawn on paper disappear. The time taken is measured at different temperatures.

RP3通常使用硫代硫酸钠与盐酸的反应，生成的硫沉淀使纸上的十字标记消失。在不同温度下测量所需时间。

RP 7 uses an initial rate method: measuring the volume of gas released over time, the loss of mass, or quenching samples at timed intervals and titrating the remaining reactant.

RP7使用初始速率法：测量随时间释放的气体体积、质量损失，或每隔一定时间淬灭样品并滴定剩余反应物。

For the thiosulfate reaction, the rate is proportional to 1/time. Increasing temperature increases the frequency and energy of collisions, so the rate increases. Safety requires eye protection because HCl is corrosive and SO₂ is an irritant.

对于硫代硫酸盐反应，速率与1/时间成正比。升高温度会增加碰撞频率和能量，因此速率增大。安全方面需佩戴护目镜，因为HCl具有腐蚀性，SO₂具有刺激性。

The initial rate method is preferred when reactions are too fast to monitor continuously. Quenching stops the reaction by sudden cooling or adding a large excess of a reagent such as iced water.

当反应快得无法连续监测时，应优先采用初始速率法。淬灭通过骤冷或加入大量冰水等试剂来终止反应。

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5. RP 4 — Qualitative Ion Tests | RP4 离子定性检验

Cation tests include flame tests and precipitation with sodium hydroxide. Lithium gives a crimson flame, sodium yellow, potassium lilac, and copper(II) blue-green.

阳离子检验包括焰色反应和用氢氧化钠沉淀。锂呈绯红色火焰，钠呈黄色，钾呈淡紫色，铜(II)呈蓝绿色。

In the NaOH test, aluminium(III) and zinc ions dissolve in excess NaOH forming colourless solutions, while copper(II) gives a blue precipitate, iron(II) green and iron(III) brown.

在NaOH检验中，铝(III)和锌离子溶于过量NaOH形成无色溶液，而铜(II)生成蓝色沉淀，铁(II)生成绿色沉淀，铁(III)生成棕色沉淀。

Anion tests: carbonate ions release CO₂ when acid is added, which gives a white precipitate with limewater; sulfate ions give a white precipitate with BaCl₂ in acid; halide ions give precipitates with AgNO₃ — chloride white, bromide cream, iodide pale yellow.

阴离子检验：碳酸根离子遇酸释放CO₂，使石灰水变浑浊；硫酸根离子在酸性条件下与BaCl₂生成白色沉淀；卤离子与AgNO₃产生沉淀——氯化物为白色，溴化物为乳白色，碘化物为淡黄色。

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6. RP 5 & 10 — Organic Synthesis and Purification | RP5与RP10 有机合成与提纯

RP 5 involves distilling a liquid product from a reaction mixture, for example the dehydration of cyclohexanol to cyclohexene or the oxidation of ethanol to ethanal. Anti-bumping granules are added to ensure smooth boiling.

RP5涉及从反应混合物中蒸馏液态产物，例如环己醇脱水制备环己烯，或乙醇氧化制备乙醛。加入沸石以确保平稳沸腾。

RP 10 involves preparing a pure organic solid such as aspirin or azo dyes, then purifying it by recrystallisation and checking purity by melting point measurement.

RP10涉及制备纯有机固体如阿司匹林或偶氮染料，然后通过重结晶提纯并用熔点测量检验纯度。

A sharp melting point close to the literature value indicates high purity; a broad melting point below the literature range indicates impurities. The vacuum filtration apparatus uses a Buchner flask and Hirsch funnel to collect the crystals efficiently.

熔点尖锐且接近文献值表明纯度较高；熔点低于文献值且范围较宽则表明含有杂质。减压过滤装置使用布氏烧瓶和 Hirsch 漏斗高效收集晶体。

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7. RP 6 — Functional Group Tests | RP6 官能团检验

Six simple tests distinguish alcohols, aldehydes, alkenes and carboxylic acids. Bromine water decolourises in the presence of an alkene but not an alkane.

六种简单检验可用于区分醇、醛、烯烃和羧酸。溴水在烯烃存在下褪色，但在烷烃中不褪色。

Acidified potassium dichromate oxidises primary and secondary alcohols from orange to green, but does not oxidise carboxylic acids. Fehling’s or Tollens’ reagent distinguishes aldehydes from ketones.

酸化的重铬酸钾将伯醇和仲醇氧化，颜色从橙色变为绿色，但不氧化羧酸。斐林试剂或托伦斯试剂区分醛和酮。

Carboxylic acids turn blue litmus red and react with carbonates to release CO₂. The test for an acid is confirmed by effervescence with sodium carbonate and the formation of a white precipitate in limewater.

羧酸使蓝色石蕊变红，并与碳酸盐反应释放CO₂。酸类检验的确认依据是与碳酸钠反应产生气泡，且气体使石灰水变浑浊。

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8. RP 8 — Electrochemical Cells | RP8 电化学电池

Half-cells are connected by a salt bridge, which is a strip of filter paper soaked in an inert electrolyte such as KNO₃. Two metal electrodes in their own ion solutions generate a potential difference measured by a high-resistance voltmeter.

半电池通过盐桥连接，盐桥是浸有KNO₃等惰性电解质的滤纸条。两个金属电极置于各自离子溶液中，产生的高电动势用高电阻电压表测量。

In the zinc–copper cell, the zinc electrode is the negative terminal and dissolves as Zn → Zn²⁺ + 2e⁻. At the positive copper electrode, Cu²⁺ + 2e⁻ → Cu. The voltmeter reading is the cell EMF, typically close to +1.10 V under standard conditions.

在锌铜电池中，锌电极是负极，溶解为Zn → Zn²⁺ + 2e⁻。在正极铜电极处，Cu²⁺ + 2e⁻ → Cu。电压表读数即为电池电动势，标准条件下通常接近+1.10 V。

The salt bridge maintains electrical neutrality by allowing K⁺ to migrate into the cathodic half-cell and NO₃⁻ into the anodic half-cell. In exam answers, always state which electrode is positive and which half-cell reaction occurs at each electrode.

盐桥通过让K⁺迁移至阴极半电池、NO₃⁻迁移至阳极半电池来维持电中性。在考试作答中，务必说明哪个电极是正极，以及各电极发生的半反应。

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9. RP 9 — pH Titration Curves | RP9 pH滴定曲线

A pH meter or burette is used to add a strong base in small increments to a weak acid, recording pH after each addition. A graph of pH against volume added reveals the equivalence point and buffer region.

用pH计或滴定管将强碱少量分次加入弱酸中，每次加入后记录pH。以pH对加入体积作图，可显示等当点和缓冲区域。

For a weak acid–strong base titration, the equivalence point lies above pH 7, and a suitable indicator is phenolphthalein. The half-neutralisation point, where pH = pKₐ, occurs at half the equivalence volume.

对于弱酸-强碱滴定，等当点高于pH 7，适合的指示剂为酚酞。半中和点位于等当点体积的一半处，此时pH = pKₐ。

Suitable buffer regions appear where the curve is relatively flat. This experiment demonstrates the buffering action of the weak acid and its conjugate base, a concept frequently examined in AQA Paper 3.

曲线较为平坦的区域即为缓冲区域。本实验展示了弱酸及其共轭碱的缓冲作用，这是AQA Paper 3中经常考查的概念。

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10. RP 11 — Transition Metal Ion Reactions | RP11 过渡金属离子反应

Small test-tube reactions identify transition metal ions by their colours in aqueous solution and their behaviour with NaOH and NH₃. Copper(II) solutions are blue; iron(II) pale green; iron(III) yellow-brown.

小试管反应通过水溶液颜色及与NaOH和NH₃的反应行为来鉴别过渡金属离子。铜(II)溶液呈蓝色；铁(II)呈浅绿色；铁(III)呈黄棕色。

Adding NaOH precipitates the metal hydroxide: Cu(OH)₂ is blue, Fe(OH)₂ green, Fe(OH)₃ brown. With excess NH₃, Cu(OH)₂ redissolves to give a deep blue solution of [Cu(NH₃)₄]²⁺.

加入NaOH生成金属氢氧化物沉淀：Cu(OH)₂为蓝色，Fe(OH)₂为绿色，Fe(OH)₃为棕色。加入过量NH₃时，Cu(OH)₂重新溶解，形成深蓝色[Cu(NH₃)₄]²⁺溶液。

Cobalt(II) gives a pink solution and a blue precipitate in NaOH, while chromium(III) gives a green solution and a grey-green precipitate. Memorising these colour changes is essential for identifying ions in unseen exam questions.

钴(II)溶液呈粉红色，与NaOH生成蓝色沉淀；铬(III)溶液呈绿色，生成灰绿色沉淀。熟记这些颜色变化对于在陌生考题中鉴别离子至关重要。

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11. RP 12 — Thin-Layer Chromatography | RP12 薄层色谱

A small spot of the mixture is placed on a silica or alumina TLC plate, which is then placed in a tank containing a small volume of developing solvent. The solvent rises by capillary action, separating the components according to their polarity.

将少量混合物样品点在硅胶或氧化铝薄层板上，然后将板放入装有少量展开剂的层析缸中。溶剂借毛细作用上升，根据极性差异分离各组分。

The retention factor is calculated as:

Rf = distance travelled by component ÷ distance travelled by solvent front

保留因子计算公式为：Rf = 组分移动距离 ÷ 溶剂前沿移动距离。

Non-polar components travel further and have higher Rf values. Comparison with a known standard run on the same plate allows identification. The solvent front must be marked before it evaporates.

非极性组分移动得更远，Rf值更高。在与同板已知标准品比较后即可鉴别。溶剂前沿必须在蒸发前标记好。

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12. Common Errors and Exam Advice | 常见误差与考试建议

The most frequent errors in practical exams include forgetting to rinse apparatus, reading the burette from the top of the meniscus, and failing to record units. Always quote final burette readings to two decimal places, ending in 0 or 5.

实操考试中最常见的错误包括忘记润洗仪器、从弯月面顶部读取滴定管刻度，以及忘记书写单位。滴定管最终读数应保留两位小数，以0或5结尾。

Heat loss corrections for enthalpy experiments are improved by plotting temperature against time and extrapolating back to the moment of mixing. In kinetics, use a graph to find the initial slope to avoid complications from falling concentrations.

焓变实验的热损失校正可通过绘制温度-时间图并外推回混合时刻来改进。动力学实验中，应使用图表求初始斜率，以避免浓度下降带来的复杂性。

For each required practical, AQA examiners expect you to describe the method, identify sources of error, suggest improvements, and state the significance of control variables. The Practical Endorsement also records your competence in five CPAC criteria, including following procedures, making accurate observations and working safely.

对于每项必修实验，AQA考官期望你能描述方法、指出误差来源、提出改进建议，并说明控制变量的意义。实践认可还考察你在五项CPAC标准中的能力，包括遵循操作步骤、准确观察和安全操作。

Finally, always read the question carefully: if it gives a mass in grams and asks for kJ mol⁻¹, convert using molar mass before calculating enthalpy change. Units are as important as numbers in A-level chemistry.

最后，务必仔细审题：若题目给出质量（克）并要求以kJ mol⁻¹作答，需先用摩尔质量换算再进行焓变计算。在A-level化学中，单位与数值同样重要。

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