CH05-INS: Mastering Experimental Operations for Unit 5 | CH05-INS: 掌握Unit 5实验操作

📚 CH05-INS: Mastering Experimental Operations for Unit 5 | CH05-INS: 掌握Unit 5实验操作

The CH05-INS insert for the International A Level Chemistry Unit 5 exam (January 2023) provides a detailed experimental procedure together with spectroscopic data. This article unpacks each step, highlighting the key techniques candidates must understand to successfully interpret and perform the practical work behind the paper.

2023年1月国际A Level化学第五单元考试中的CH05-INS资料提供了一份完整的实验步骤以及光谱数据。本文逐条解析每一步操作，重点阐述考生需要理解的关键技术，以便正确解读并完成试卷背后的实验工作。

1. Understanding the Insert and Safety First | 理解实验资料与安全第一

The insert begins by listing chemicals: for example, an aromatic carboxylic acid, an alcohol, concentrated sulfuric acid, sodium hydrogencarbonate solution, and anhydrous magnesium sulfate. Always read the entire insert before starting to answer any related question.

资料开头会列出所用化学品，例如一种芳香族羧酸、一种醇、浓硫酸、碳酸氢钠溶液和无水硫酸镁。在开始回答任何相关问题之前，务必通读整份资料。

Identify ALL hazard symbols and phrases. For instance, concentrated sulfuric acid is corrosive and causes severe burns, while the alcohol may be flammable and harmful if inhaled.

识别所有危险标志和短语。例如，浓硫酸具有腐蚀性，会造成严重灼伤；醇类可能易燃，吸入有害。

Personal protective equipment is non-negotiable: wear safety goggles, lab coat, and nitrile gloves. When handling volatile organic solvents or adding concentrated acid, always work in a fume hood.

个人防护装备必不可少：佩戴护目镜、实验服和丁腈手套。在处理挥发性有机溶剂或添加浓酸时，始终在通风橱内操作。

Familiarity with the COSHH (Control of Substances Hazardous to Health) assessment for each reagent is expected. You should know the location of eyewash stations and safety showers.

预计你熟悉每种试剂的健康危害控制评估（COSHH）。你应该知道洗眼器和安全喷淋装置的位置。

2. Setting Up Reflux for Reaction | 搭建回流装置进行反应

In many Unit 5 procedures, the synthesis involves heating a mixture under reflux to complete the reaction without losing volatile components. The insert typically describes ‘heat under reflux for 30 minutes’.

在许多第五单元的实验中，合成步骤包括加热回流混合物，以在不损失挥发性组分的情况下使反应完全。资料通常会写明“加热回流30分钟”。

Use a round-bottom flask not a conical flask, because the round bottom allows even heating and reduces bumping when combined with anti-bumping granules.

使用圆底烧瓶而不是锥形瓶，因为圆底可均匀受热，并能在加入沸石后减少暴沸。

Add two or three anti-bumping granules before heating to ensure smooth boiling. Never add them to a hot liquid, as this can cause violent eruption.

在加热前加入2–3粒沸石以确保平稳沸腾。切勿将沸石加入热液体中，否则可能引起剧烈喷溅。

Fit a condenser vertically on the flask, and secure the joints with plastic clips. Water should enter the condenser at the bottom and exit at the top to maintain efficient cooling.

在烧瓶上垂直安装冷凝管，并用塑料夹固定接口。冷却水应从下端进入、上端排出，以保持高效冷却。

Heat the flask using an electric heating mantle or a water bath set to the appropriate temperature, as an open flame could ignite flammable vapours.

使用电热套或设定至合适温度的水浴加热烧瓶，因为明火可能点燃可燃蒸气。

3. Isolation by Liquid-Liquid Extraction | 液-液萃取分离

After reflux, the mixture typically contains the ester product, unreacted starting materials, water, and acid catalyst. The insert will instruct you to ‘pour the mixture into a separating funnel and add sodium hydrogencarbonate solution’.

回流后，混合物通常含有酯产物、未反应的原料、水和酸催化剂。资料会指示“将混合物倒入分液漏斗，加入碳酸氢钠溶液”。

Sodium hydrogencarbonate reacts with any remaining acid to produce CO₂ gas, which helps remove the acid layer. Shake the funnel gently with the stopper in place, and frequently invert it to release pressure by opening the tap.

碳酸氢钠与残留的酸反应产生CO₂气体，有助于去除酸层。塞好塞子后轻轻振摇漏斗，并经常倒转漏斗，打开活塞放气以释放压力。

Allow the layers to separate completely. The less dense organic layer usually forms the upper phase, but this depends on the identity of the organic product and the density of the aqueous layer.

让两相完全分层。密度较小的有机相通常在上方，但这取决于有机产物的种类以及水相的密度。

Run off the lower layer cautiously into a beaker. If the product is the bottom layer, drain it into a clean conical flask; if it is the top layer, drain the lower layer, then pour the top layer out of the top of the funnel to avoid contamination.

小心地将下层液体放入烧杯中。如果产物为下层，则排入干净的锥形瓶；如果产物为上层，则先放出下层，再从漏斗上口倒出上层液体，以避免交叉污染。

Repeat the extraction with a fresh portion of sodium hydrogencarbonate solution, and then wash once with distilled water to remove any remaining inorganic salts.

用新鲜的碳酸氢钠溶液重复萃取一次，然后用蒸馏水洗涤一次，以去除残留的无机盐。

4. Drying the Organic Product | 干燥有机产物

The washed organic layer contains traces of water, which must be removed before purification. The insert says ‘add anhydrous magnesium sulfate and swirl until the liquid becomes clear’.

洗涤后的有机层含有痕量水，必须在纯化前去除。资料会写明“加入无水硫酸镁，旋摇至液体变澄清”。

Anhydrous magnesium sulfate (MgSO₄) is a commonly used drying agent because it has a high capacity for water, absorbs quickly, and is easily removed by filtration.

无水硫酸镁（MgSO₄）是一种常用的干燥剂，因为它吸水容量大、速度快，并且容易通过过滤除去。

Add small amounts of the drying agent at a time, and observe the solid initially clumping together. Continue adding until the solid settles as freely moving powder, indicating that the liquid is dry.

每次加入少量干燥剂，观察固体最初结块。继续加入直到固体呈自由流动的粉末状，表明液体已干燥。

Alternatively, anhydrous sodium sulfate or calcium chloride can be used, but the choice depends on compatibility with the organic compound.

也可使用无水硫酸钠或氯化钙，但选择取决于干燥剂与有机物的相容性。

After drying, the liquid is decanted or filtered through a fluted filter paper under gravity—never apply heat to speed up the filtration if the solvent is flammable.

干燥后，通过倾析或使用扇形滤纸在重力下过滤——如果溶剂易燃，切勿加热以加速过滤。

5. Purification by Distillation or Recrystallisation | 通过蒸馏或重结晶纯化

The insert might describe either simple distillation, fractional distillation, or recrystallisation, depending on whether the product is a liquid or a solid.

资料可能描述简单蒸馏、分馏或重结晶，取决于产物是液体还是固体。

Product State	Purification Method	Key Apparatus / Principle
Liquid (e.g. ester)	Fractional distillation	Fractionating column, temperature control, collect the fraction boiling over a narrow range
Solid (e.g. substituted benzoic acid)	Recrystallisation	Hot solvent, hot filtration, slow cooling, suction filtration with Buchner funnel

For fractional distillation, set up a fractionating column packed with glass beads, and insulate it with aluminium foil or cotton wool. Record the boiling range at which the pure product distils over.

对于分馏，安装填充玻璃珠的分馏柱，并用铝箔或棉花保温。记录纯产物蒸馏时的沸点范围。

In recrystallisation, dissolve the crude solid in a minimum volume of hot solvent, carry out a hot filtration to remove insoluble impurities, and then allow the solution to cool slowly to obtain well-formed crystals.

在重结晶中，用最少量的热溶剂溶解粗固体，进行热过滤除去不溶性杂质，然后让溶液缓慢冷却以获得晶形良好的晶体。

Use a Buchner funnel and filter paper, moistened with a small amount of cold solvent, and apply suction filtration to collect the crystals. Wash with a little ice-cold solvent.

使用布氏漏斗和滤纸，用少量冷溶剂润湿滤纸，抽滤收集晶体。用少量冰冷溶剂洗涤。

6. Monitoring Reaction Progress with TLC | 用薄层色谱监测反应进程

Thin-layer chromatography (TLC) is frequently mentioned in Unit 5 inserts to check whether the reaction has gone to completion. Spots of the reaction mixture and a reference sample are applied to a silica plate.

薄层色谱法（TLC）在第五单元实验资料中经常出现，用于检查反应是否已完成。将反应混合物和对照样品的斑点点在硅胶板上。

Draw a pencil line about 1 cm from the base of the plate. Use a capillary tube to place a tiny spot of each solution, allowing the spots to dry between applications.

在距离板底约1 cm处画一条铅笔线。用毛细管点上每种溶液的小点，每加一次都要等斑点干燥。

Place the plate in a developing chamber containing a suitable solvent (mobile phase) so that the solvent level is below the pencil line. Cover the tank and allow the solvent to rise.

将板放入含有合适溶剂（流动相）的展开缸中，溶剂液面要低于铅笔线。盖好缸盖，让溶剂上升。

Once the solvent front has travelled most of the way up, remove the plate and mark the solvent front immediately with a pencil. View the spots under a UV lamp or use a locating agent.

当溶剂前沿上升至近顶端时，取出板并立即用铅笔标出溶剂前沿。在紫外灯下观察斑点或使用显色剂。

Calculate the Rf value using the formula:

计算Rf值采用下式：

Rf = distance travelled by the spot ÷ distance travelled by the solvent front

If the reaction mixture shows only one spot at the same Rf as the authentic product and no starting material spot, the conversion is complete.

如果反应混合物只显示一个与标准产物Rf相同的斑点，且没有原料斑点，说明反应转化完全。

7. Melting Point Determination | 熔点测定

For solid products, the insert often provides a literature melting point and asks you to compare it with the experimental value. A sharp melting range (1–2 °C) indicates high purity.

对于固体产物，资料通常会给出文献熔点，并要求你与实验值进行比较。熔程窄（1–2 °C）表明纯度高。

Prepare a capillary tube packed with 2–3 mm of finely powdered dry crystals. Tap the sealed end gently on the bench to compact the solid.

准备一根毛细管，装入2–3 mm高的精细粉末状干燥晶体。将密封端在工作台上轻轻敲击以夯实固体。

Place the capillary in a melting point apparatus (e.g. Thiele tube or electric melting point device), and heat the bath slowly (1–2 °C min⁻¹) near the expected melting point.

将毛细管放入熔点测定装置（如Thiele管或电熔点仪），在接近预期熔点温度时缓慢加热（每分钟1–2 °C）。

Record the temperature at which the first drop of liquid appears (the onset of melting) and the temperature at which the entire solid becomes a clear liquid.

记录第一滴液体出现时的温度（初熔）以及全部固体变成透明液体时的温度。

Impurities lower and broaden the melting range. If your experimental melting range is significantly lower and wider than the literature value, recrystallise again.

杂质会降低熔点并使熔程变宽。如果实验熔程明显低于文献值且较宽，应再次重结晶。

8. Interpreting Infrared Spectroscopy | 红外光谱解析

The insert supplies an IR spectrum of the product or an intermediate. You must be able to assign characteristic absorption bands to functional groups.

资料提供产物或中间体的红外光谱。你必须能够将特征吸收峰归属给官能团。

A broad peak around 2500–3300 cm⁻¹ indicates an O–H bond in carboxylic acids; for alcohols, the broad O–H stretch appears usually around 3200–3600 cm⁻¹.

在2500–3300 cm⁻¹附近的宽峰表明羧酸中的O–H键；对于醇，宽O–H伸缩振动峰通常在3200–3600 cm⁻¹附近出现。

A strong, sharp absorption at around 1680–1750 cm⁻¹ confirms a C=O group. Esters typically absorb at approximately 1735 cm⁻¹, while carboxylic acids are near 1700 cm⁻¹.

在1680–1750 cm⁻¹附近的强而尖的吸收峰确认C=O基团。酯类通常在大约1735 cm⁻¹有吸收，而羧酸在1700 cm⁻¹附近。

Look for C–O stretches in esters and acids around 1000–1300 cm⁻¹, and for C=C aromatic stretches around 1450–1600 cm⁻¹ if an aromatic ring is present.

注意酯和酸中C–O伸缩振动峰在1000–1300 cm⁻¹附近，若存在芳环，则C=C芳环伸缩振动峰在1450–1600 cm⁻¹附近。

Absence of a broad O–H peak in the product spectrum when compared with the starting material spectrum often indicates successful conversion of a carboxylic acid to an ester.

与原料光谱相比，产物光谱中缺少宽O–H峰通常表明羧酸成功转化为酯。

9. Calculating Percentage Yield | 计算产率

The insert may provide the masses of reactants, the molecular formula of the product, and the actual mass collected. Determine the limiting reagent and calculate the theoretical yield.

资料可能给出反应物的质量、产物的分子式以及实际收集到的质量。确定限量试剂，计算理论产量。

Write a balanced equation for the reaction. For esterification: RCOOH + R’OH ⇌ RCOOR’ + H₂O. The stoichiometry is usually 1:1, so the reactant present in fewer moles is the limiting reagent.

写出反应的配平方程式。酯化反应：RCOOH + R’OH ⇌ RCOOR’ + H₂O。化学计量比通常为1:1，因此摩尔数较少的反应物为限量试剂。

The percentage yield is calculated as:

产率按下式计算：

Percentage yield = (actual mass ÷ theoretical mass) × 100%

Work systematically: convert masses to moles, identify the limiting reagent, calculate the expected moles of product, convert to mass, and then insert into the formula.

系统地进行计算：将质量转化为摩尔数，确定限量试剂，计算产物预期摩尔数，再转化为质量，最后代入公式。

A yield lower than 60% may indicate incomplete transfer, loss during washing, or incomplete reaction. If the yield exceeds 100%, the product likely contains impurities or solvent.

产率低于60%可能意味着转移不完全、洗涤时损失或反应不完全。如果产率超过100%，产物很可能含有杂质或溶剂。

10. Evaluating Errors and Improving Procedure | 评估误差与改进步骤

Every experimental procedure has inherent errors. Common sources of loss include transfer between vessels, incomplete extraction, and mechanical losses during filtration.

每个实验步骤都有固有误差。常见的损失来源包括容器间的转移、萃取不完全以及过滤时的机械损失。

To reduce these losses, rinse all glassware with small portions of a suitable solvent and add the rinsings to the main organic layer before drying.

为减少损失，用少量合适的溶剂淋洗所有玻璃仪器，并在干燥前将淋洗液并入主有机层。

If the yield is consistently low, consider whether the reaction equilibrium limited the conversion. Esterification is reversible; you could remove water using a Dean–Stark apparatus to drive the equilibrium forward.

如果产率持续偏低，考虑反应平衡是否限制了转化。酯化反应是可逆的；可以使用Dean–Stark装置除去水分，以推动平衡正移。

The insert may also contain a mass spectrum. Use molecular ion peaks to confirm the molar mass, and note that the presence of a peak at M+2 in a halogen-containing compound indicates the isotopic pattern.

资料也可能包含质谱图。利用分子离子峰确认摩尔质量，注意含卤化合物中出现M+2峰表明同位素模式。

Finally, contextualise the experiment within the Unit 5 syllabus: the techniques assessed here are directly transferable to any synthesis design question. Redraw the key steps as a flowchart in your revision.

最后，将实验置于第五单元课程背景下：这里考察的技术可直接迁移到任何合成设计题中。复习时将关键步骤重绘为流程图。

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CH05-INS: Mastering Experimental Operations for Unit 5 | CH05-INS: 掌握Unit 5实验操作