AS Chemistry Insert 1 June 22: Making an Ester – Essential Experimental Techniques | AS化学实验操作（2022年6月材料一）：制备酯——核心技巧

📚 AS Chemistry Insert 1 June 22: Making an Ester – Essential Experimental Techniques | AS化学实验操作（2022年6月材料一）：制备酯——核心技巧

Insert 1 from the June 2022 AS Chemistry exam presents a step-by-step practical procedure for synthesising an ester, typically ethyl ethanoate, using alcohol and carboxylic acid with an acid catalyst. This article unpacks every experimental stage—reflux, separation, drying, distillation—linking each action to the underlying chemical principles and safety considerations that examiners expect you to understand.

2022年6月AS化学考试的材料一呈现了一个逐步合成酯（通常是乙酸乙酯）的实验流程，利用醇和羧酸在酸催化下反应。本文将拆解每个实验阶段——回流、分离、干燥、蒸馏——并将其与化学原理和安全考量相联系，帮助你掌握考官期望的知识点。

1. Safety First: Risk Assessment and Reagent Handling | 安全第一：风险评估与试剂处理

Concentrated sulfuric acid acts as the catalyst and is highly corrosive; ethanol and ethanoic acid are flammable and volatile. The procedure requires wearing chemical-splash goggles, a lab coat, and heat-resistant gloves when handling hot glassware. The reaction mixture must be heated gently in a water bath or electric heating mantle—never with a naked flame—to avoid ignition of vapour.

浓硫酸用作催化剂且具有强腐蚀性；乙醇和乙酸易燃且易挥发。实验要求佩戴防化学飞溅护目镜、实验服，并在接触热玻璃器皿时使用防热手套。反应混合物须在水浴或电热套中温和加热，严禁使用明火，以防蒸气着火。

2. Understanding the Reaction: Fischer Esterification | 理解反应：费歇尔酯化

The esterification between ethanol and ethanoic acid is a reversible condensation reaction, catalysed by H⁺ from sulfuric acid. The forward reaction forms ethyl ethanoate and water, while the reverse hydrolysis regenerates reactants. The equation, using structural formulae, is: CH₃COOH(l) + C₂H₅OH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l). To drive the equilibrium towards the ester, one reactant is used in excess or the water is removed.

乙醇与乙酸的酯化反应是可逆的缩合反应，由硫酸提供的H⁺催化。正向反应生成乙酸乙酯和水，逆向水解则使反应物再生。反应方程式（结构式）为：CH₃COOH(l) + C₂H₅OH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l)。为使平衡向酯方向移动，通常使一种反应物过量或除去生成的水。

3. Assembling the Reflux Apparatus | 搭建回流装置

A round-bottom flask containing the alcohol, acid, and a few anti-bumping granules is connected to a vertical water-cooled condenser. Water enters at the lower inlet and exits at the upper outlet to ensure efficient cooling. The condenser prevents volatile organic compounds from escaping while allowing the mixture to boil safely for the specified time.

圆底烧瓶中装入醇、酸和几粒防沸石，连接直立的水冷冷凝管。冷却水从下口进入、上口流出以确保充分冷却。冷凝管可防止挥发性有机物逸出，同时使混合物在规定时间内安全沸腾。

4. Heating Duration and Observation | 加热时间与观察

Heat the mixture under reflux for about 30–45 minutes. The vapour rises, condenses, and drips back into the flask. Anti-bumping granules promote smooth boiling. Avoid overheating; a gentle reflux ring should be visible about one-third of the way up the condenser. After heating, allow the apparatus to cool before dismantling.

回流加热约30–45分钟。蒸气上升、冷凝并滴回烧瓶。防沸石促进平稳沸腾。避免过热；应能看到冷凝管下三分之一处有轻柔的回流环。加热结束后，待装置冷却再拆卸。

5. Neutralising the Acid Catalyst | 中和酸催化剂

Once cooled, the mixture still contains concentrated sulfuric acid. The insert directs you to slowly pour the mixture into a beaker of cold water, then add sodium carbonate solution until fizzing stops. This neutralises the acid, forming CO₂ gas and soluble sulfate salts, which are later removed in the aqueous layer.

冷却后的混合物仍含有浓硫酸。材料一要求将混合物缓慢倒入盛有冷水的烧杯中，然后加入碳酸钠溶液直至不再产生气泡。这一步中和了酸，生成CO₂气体和可溶性硫酸盐，随后在水层中分离出去。

6. Separating the Organic Layer | 分离有机层

Transfer the neutralised mixture to a separating funnel. The ester layer floats on top of the aqueous layer due to its lower density and immiscibility with water. Carefully run off the lower aqueous layer, retaining the ester-rich upper layer. This step removes water-soluble impurities and excess alcohol.

将中和后的混合物转移至分液漏斗中。酯层因密度较低且与水不混溶而浮在水层上方。小心地放出下层水层，保留富含酯的上层。该步骤除去了水溶性杂质和过量的醇。

7. Washing and Purification Steps | 洗涤与纯化步骤

Wash the crude ester sequentially: first with sodium carbonate solution to remove any residual acid, then with saturated calcium chloride solution (if required by the insert) to remove unreacted ethanol. Finally, wash with distilled water. After each wash, separate the layers, always retaining the upper ester layer.

依次洗涤粗酯：先用碳酸钠溶液除去残余的酸，而后按材料一可能要求用饱和氯化钙溶液除去未反应的乙醇，最后用蒸馏水洗涤。每次洗涤后分离液层，始终保留上层酯层。

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

Pour the ester into a clean, dry conical flask and add anhydrous magnesium sulfate (or another drying agent). Swirl and allow to stand until the liquid turns clear from cloudy. The drying agent absorbs water droplets, clumping as it does. If the solid becomes pasty, add more agent until free-flowing crystals remain.

将酯倒入洁净干燥的锥形瓶中，加入无水硫酸镁（或其他干燥剂）。旋摇并静置，直到液体由浑浊变澄清。干燥剂吸收水分后会结块。若固体呈糊状，则继续添加干燥剂，直至出现可自由流动的晶体。

9. Decanting and Simple Distillation | 倾析与简单蒸馏

Decant the clear ester liquid into a clean distilling flask, leaving behind the solid drying agent, and add fresh anti-bumping granules. Set up a simple distillation apparatus with a thermometer placed opposite the side arm. Heat gently; collect the fraction that distils at the boiling point of ethyl ethanoate (approximately 77°C). A narrow boiling range indicates high purity.

将澄清的酯液体倾析至洁净的蒸馏烧瓶中，留下固体干燥剂，并加入新的防沸石。搭建简单蒸馏装置，温度计置于支管对面。缓慢加热；收集在乙酸乙酯沸点（约77°C）附近蒸馏出的馏分。沸程窄表明纯度高。

10. Calculating Percentage Yield | 计算产率

Weigh the collected ester and record the mass. Using the moles of the limiting reactant (from the volumes and densities provided in the insert), calculate theoretical yield, then percentage yield = (actual mass ÷ theoretical mass) × 100. A yield below 100% is expected due to the reversible nature and losses during transfers.

称量收集到的酯并记录质量。利用限量反应物的物质的量（根据材料一中给出的体积和密度计算），算出理论产量，再计算产率 = (实际质量 ÷ 理论质量) × 100。反应可逆性和转移损失会导致产率低于100%。

11. Key Analytical Techniques | 关键分析技术

To confirm the identity and purity, a sample can be tested by measuring its boiling point; a pure ester gives a sharp boiling point. An infrared spectrum would show a C=O stretch around 1740 cm⁻¹ and C–O absorption in the 1000–1300 cm⁻¹ region, while the broad O–H signal of the starting acid or alcohol disappears.

为确认产物身份和纯度，可取样测量沸点；纯酯的沸点尖锐。红外光谱会在约1740 cm⁻¹处显示C=O伸缩振动吸收，并在1000–1300 cm⁻¹区域出现C–O吸收带，而起始酸或醇的宽O–H信号消失。

12. Common Errors and Examiner Tips | 常见错误与考官提示

Examiners frequently note mistakes such as using a flame for heating, forgetting anti-bumping granules, and shaking the separating funnel without venting. Inefficient drying leads to lower recorded yield. Always label glassware, and record observations. If the insert asks for a reason for thorough washing, link it to removing catalysts or side products that could contaminate the final distillate.

考官常发现的错误包括：用明火加热、忘记加防沸石、分液漏斗振荡后未放气。干燥不充分会导致记录的产率偏低。务必给玻璃器皿贴标签并记录观察现象。如果材料一要求解释彻底洗涤的理由，应将其与去除会污染最终馏分的催化剂或副产物联系起来。

Published by TutorHao | AS Chemistry Revision Series | aleveler.com

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