Basic Chemistry Laboratory Operations: Exam Points and Common Mistakes | 化学基本实验操作：考点与易错点

📚 Basic Chemistry Laboratory Operations: Exam Points and Common Mistakes | 化学基本实验操作：考点与易错点

Mastering basic laboratory operations is a fundamental requirement in chemistry practical examinations. From handling apparatus correctly to executing procedures safely, these skills are frequently assessed in both written and practical components of A-level chemistry exams. This article systematically reviews the core operations, highlights common errors, and provides strategies to avoid them.

掌握化学基本实验操作是化学实验考试的基本要求。从正确使用仪器到安全执行操作步骤，这些技能在 A-level 化学笔试和实验考试中都是高频考点。本文系统梳理核心操作、剖析常见错误，并提供规避策略。

1. Apparatus Identification and Correct Usage | 仪器识别与正确使用

The first step to laboratory competence is recognising each piece of apparatus and understanding its specific function. Examiners often ask students to name equipment shown in diagrams and state its purpose.

实验能力的首步是识别每种仪器并理解其特定功能。考官经常要求学生写出图中仪器的名称并说明其用途。

Volumetric flask is used to prepare accurate solutions of known concentration. It has a single calibration mark on the neck and must not be used for heating or storing solutions.

容量瓶用于配制准确浓度的溶液。瓶颈上只有一个刻度线，不可加热或长期储存溶液。

Burette is graduated from zero at the top to 50 cm³ at the bottom, enabling precise delivery of variable volumes during titrations. The smallest scale division is 0.1 cm³, and readings should be estimated to 0.05 cm³.

滴定管自上而下刻度从 0 到 50 cm³，可在滴定中精确放出不同体积的液体。最小分度值为 0.1 cm³，读数需估读到 0.05 cm³。

Pipette delivers a fixed volume, commonly 25.0 cm³, with high accuracy. The last drop must be allowed to drain naturally; blowing it out is a serious error.

移液管用于准确移取固定体积的液体，常见规格为 25.0 cm³。最后一滴应自然流尽，用吸球吹出是严重错误。

Measuring cylinder is less precise than a pipette or burette and is suitable only for approximate volume measurements.

量筒的精密度低于移液管和滴定管，仅适用于粗略量取体积。

2. Heating Operations | 加热操作

Heating is one of the most common operations in chemistry, yet it presents many hazards and opportunities for error. Correct technique depends on the type of apparatus and substance being heated.

加热是化学中最常见的操作之一，但也伴随诸多危险和出错机会。正确的操作技巧取决于仪器类型和所加热物质的性质。

When heating a test tube, hold it with a test tube holder at an angle of about 45°, pointing the mouth away from yourself and others. The liquid should not exceed one-third of the tube’s volume, and the tube should be moved gently through the flame to ensure even heating.

加热试管时，用试管夹夹持，试管与水平面约成 45° 角，管口切勿朝向自己或他人。液体的量不应超过试管容积的三分之一，且应在火焰中缓慢移动试管使其均匀受热。

Use a Bunsen burner with the air hole closed to produce a luminous safety flame when not in use, and open the air hole fully for a hot blue flame during heating. Always light the flame with the air hole closed first.

使用本生灯时，不使用时关闭空气孔以产生明亮的黄色安全火焰；加热时完全打开空气孔以获得高温蓝色火焰。点燃时务必先关闭空气孔。

Evaporating dishes and crucibles can withstand high temperatures but should be handled with crucible tongs. Never place a hot crucible on a cold surface, as thermal shock may cause it to crack.

蒸发皿和坩埚可承受高温，但必须用坩埚钳夹取。切勿将炽热的坩埚放置在冷的表面上，热冲击会导致其破裂。

When heating with a water bath, flammable or volatile substances such as ethanol and ether must never be heated directly over a flame. In such cases, use a water bath or electric heater.

使用水浴加热时，易燃或挥发性物质如乙醇和乙醚绝不可直接在火焰上加热，应使用水浴或电加热器。

酒精灯使用要点：不能用燃着的酒精灯去点燃另一盏酒精灯；熄灭时不能用嘴吹，必须用灯帽盖灭。

Alcohol burner rules: never ignite one burner from another; never blow out the flame — always use the cap.

3. Measuring and Transferring Liquids | 液体量取与转移

Accurate measurement of liquid volumes is essential for quantitative experiments. Each measuring device has unique reading rules and precautions.

准确量取液体体积是定量实验的核心。每种量器都有其独特的读数规则和注意事项。

Reading the meniscus: For colourless solutions, read the bottom of the meniscus at eye level. For deeply coloured liquids such as potassium permanganate, read the upper meniscus.

读凹液面：对于无色溶液，视线应与凹液面最低处齐平。对于高锰酸钾等深色液体，则应读取凸液面的上方。

Pipette technique: Rinse the pipette with the solution to be used, not with water, to avoid dilution. Use a pipette filler, never mouth pipetting. The transfer should occur with the tip touching the wall of the receiving vessel.

移液管操作：需用待取溶液润洗移液管而非用水润洗，以免稀释。必须使用吸耳球，严禁用嘴吸取。放液时管尖应接触接受器内壁。

Burette preparation: Before use, rinse the burette with deionised water and then with the titrant. Ensure the jet tip is filled with liquid and contains no air bubbles — an air bubble in the tip will invalidate the volume reading.

滴定管准备：使用前先用去离子水润洗，再用滴定液润洗。确保尖嘴部分充满液体且无气泡——尖嘴中的气泡会使体积读数失效。

Measuring cylinders should be placed on a level surface and viewed at eye level. Do not use them for precise quantitative analysis.

量筒应放置在水平台面上，视线与刻度齐平。不可用于精确的定量分析。

4. Filtration and Separation Techniques | 过滤与分离操作

Separation of mixtures is a classic exam topic, covering filtration, evaporation, crystallisation, distillation and solvent extraction.

混合物分离是经典考点，涵盖过滤、蒸发、结晶、蒸馏和萃取操作。

Filtration uses filter paper folded into a cone shape and placed in a glass funnel. The paper should be slightly smaller than the funnel, and the top edge should be below the rim of the funnel. After filtration, the solid residue is the “residue” and the liquid passing through is the “filtrate”.

过滤时需将滤纸折叠成锥形放入玻璃漏斗中。滤纸应略小于漏斗，且边缘应低于漏斗口。过滤后，留在滤纸上的固体称为”残渣”，透过滤液的液体称为”滤液”。

Use the technique of “pouring along a glass rod” to prevent splashing. The liquid should be poured gently along the rod, with the rod tip touching the filter paper below its top edge.

采用“沿玻璃棒引流”的方法防止液体飞溅。液体应沿玻璃棒缓缓倒入，玻璃棒尖端应接触滤纸三层一侧的下方。

Crystallisation: To obtain crystals from a solution, evaporate the solvent until a saturated solution forms at high temperature, then allow slow cooling. Rapid cooling produces small crystals; slow cooling produces larger, purer crystals.

结晶：要从溶液中获得晶体，先蒸发溶剂至高温饱和状态，再缓慢冷却。快速冷却得到小晶体，缓慢冷却则得到较大且更纯的晶体。

Distillation is used to separate a liquid from a solution or a mixture of miscible liquids. The thermometer bulb must be positioned at the side arm of the flask to measure the vapour temperature accurately. Anti-bumping granules are added to ensure smooth boiling.

蒸馏用于从溶液或互溶液体混合物中分离液体。温度计水银球必须置于蒸馏烧瓶支管口处，以准确测量蒸气温度。需加入沸石防止暴沸。

5. Titration Procedures | 滴定操作

Titration is arguably the most important quantitative technique in A-level chemistry practical exams. Accuracy and attention to detail are paramount.

滴定可以说是 A-level 化学实验考试中最重要的定量操作，精确性和对细节的关注至关重要。

Standard procedure: Using a pipette, transfer a known volume of the solution being analysed into a conical flask. Add 2–3 drops of the appropriate indicator. Then titrate from the burette while swirling the flask continuously.

标准流程：用移液管准确移取一定体积的待测溶液至锥形瓶中，加入 2–3 滴合适的指示剂，然后从滴定管中滴加滴定液，同时持续摇动锥形瓶。

End-point detection: The end point is reached when a single drop causes a permanent colour change. Near the end point, add drops very slowly, even half-drops, by partially opening the stopcock.

终点判断：当最后一滴溶液引起颜色持久变化时即为终点。接近终点时，应放慢滴加速度，可通过部分打开活塞实现半滴滴加。

Titration results: Repeat the titration until two concordant results are obtained (within 0.10 cm³ of each other). Discard the first rough titration and average the concordant ones.

滴定结果处理：重复滴定直至获得两次平行结果（相差不超过 0.10 cm³）。舍去首次粗糙滴定结果，取平行结果的平均值。

Indicator choice: Phenolphthalein (colourless → pink) is used for strong acid–strong base and strong base–weak acid titrations; methyl orange (red → yellow) is suitable for strong acid–weak base titrations.

指示剂选择：酚酞（无色→粉红）适用于强酸强碱及强碱滴定弱酸；甲基橙（红→黄）适用于强酸滴定弱碱。

锥形瓶用蒸馏水润洗即可，绝不能用待测液润洗；而滴定管和移液管必须用相应溶液润洗。

The conical flask should be rinsed only with distilled water, never with the analyte; however, the burette and pipette must be rinsed with the relevant solutions.

6. Gas Collection and Testing | 气体收集与检验

Gas preparation and identification are common in both theory and practical papers. Students must understand the appropriate collection method for each gas.

气体的制备与检验在理论和实验试卷中都十分常见。学生必须了解每种气体适用的收集方法。

Upward displacement of air (delivery tube pointing upward) is used for gases denser than air, such as CO₂ and Cl₂. Downward displacement of air is used for gases less dense than air, such as H₂ and NH₃.

向上排空气法（导管口向上）适用于密度大于空气的气体，如 CO₂ 和 Cl₂。向下排空气法适用于密度小于空气的气体，如 H₂ 和 NH₃。

Over water collection (downward displacement of water) is suitable for gases that are sparingly soluble in water, such as O₂, H₂ and NO. It is not suitable for highly soluble gases like HCl or NH₃.

排水集气法适用于难溶于水的气体，如 O₂、H₂ 和 NO。不适用于 HCl、NH₃ 等极易溶于水的气体。

Gas testing: Oxygen relights a glowing splint. Hydrogen produces a squeaky pop with a lighted splint. Carbon dioxide turns limewater milky. Ammonia turns damp red litmus paper blue. Chlorine bleaches damp litmus paper.

气体检验：氧气使带火星的木条复燃；氢气遇点燃的木条发出尖锐爆鸣声；二氧化碳使澄清石灰水变浑浊；氨气使湿润的红色石蕊试纸变蓝；氯气使湿润的石蕊试纸褪色。

7. Solution Preparation and Dilution | 溶液配制与稀释

Preparing a standard solution is a compulsory skill. The procedure follows a strict sequence that students must memorise precisely.

配制标准溶液是一项必备技能。操作步骤有严格的顺序，学生必须准确记忆。

Steps: (1) Weigh the required mass of solid accurately using a balance; (2) transfer the solid into a beaker containing about half the required volume of deionised water and stir to dissolve completely; (3) transfer the solution quantitatively into a volumetric flask using a glass rod and repeated rinsing; (4) add deionised water to the calibration mark; (5) stopper and invert the flask 10–15 times to mix thoroughly.

步骤：(1) 用天平准确称量所需固体质量；(2) 将固体转移至盛有约一半所需体积去离子水的烧杯中搅拌至完全溶解；(3) 用玻璃棒引流将溶液定量转移至容量瓶，并用去离子水多次洗涤烧杯和玻璃棒；(4) 加去离子水至刻度线；(5) 盖紧瓶塞，上下颠倒 10–15 次使溶液混合均匀。

Dilution calculation: The key equation for dilution is C₁V₁ = C₂V₂, where C₁ and V₁ are the concentration and volume of the stock solution, and C₂ and V₂ are those of the diluted solution.

稀释计算：稀释的核心公式为 C₁V₁ = C₂V₂，其中 C₁、V₁ 为浓溶液的浓度和体积，C₂、V₂ 为稀释后溶液的浓度和体积。

浓硫酸稀释：必须将浓硫酸沿器壁缓缓注入水中，并不断搅拌；切不可将水倒入浓硫酸中。

Diluting concentrated sulfuric acid: always add the acid slowly down the wall of the vessel into water with constant stirring — never pour water into concentrated acid.

8. Common Mistakes in Practical Examinations | 实验考试中的常见错误

Examining past mark schemes reveals recurring errors that cause students to lose significant marks. Avoiding these pitfalls can dramatically improve scores.

翻阅历年的评分标准可以发现，某些错误反复出现并导致大量失分。避免这些陷阱能显著提高分数。

常见错误 Common Mistake	正确操作 Correct Practice
用嘴吹灭酒精灯 Blowing out the alcohol burner	用灯帽盖灭 Cover with the cap
试管内液体超过容积的 1/3 Overfilling the test tube beyond 1/3	液体不超过 1/3，管口倾斜 45° Liquid volume ≤ 1/3, tilted at 45°
用量筒配制标准溶液 Using a measuring cylinder for standard solutions	用容量瓶配制 Use a volumetric flask
将水倒入浓硫酸 Pouring water into concentrated H₂SO₄	将酸缓慢加入水中 Add acid to water slowly
加热时管口朝向人 Directing the test tube mouth toward a person	管口不对人 Keep the mouth away from people
用待测液润洗锥形瓶 Rinsing the conical flask with the analyte	只用蒸馏水润洗 Rinse with distilled water only

9. Safety Rules and Emergency Responses | 安全守则与应急处理

Laboratory safety is not merely a formality — exam questions frequently test emergency response procedures and hazard identification.

实验室安全不仅仅是形式——考试题目经常考查应急处理程序和危险识别。

Eye protection: Safety goggles must be worn whenever heating, mixing chemicals or working with corrosive substances. If a chemical enters the eye, flood the eye with water for at least 15 minutes and seek medical attention.

眼部防护：凡涉及加热、混合化学药品或处理腐蚀性物质时，必须佩戴护目镜。若化学品溅入眼中，应立即用大量清水冲洗至少 15 分钟并及时就医。

Acid spills: Small acid spills can be neutralised with sodium hydrogencarbonate (baking soda) before wiping up. Alkali spills should be neutralised with a dilute acid such as acetic acid or treated with copious water.

酸液泄漏：少量酸液泄漏可先用碳酸氢钠（小苏打）中和再擦拭。碱液泄漏应用稀酸（如醋酸）中和或大量水冲洗。

Toxic gases: Experiments producing toxic gases such as Cl₂, H₂S, NO₂ or SO₂ must be performed in a fume cupboard. Never smell gases directly by bringing the container to the nose.

有毒气体：凡产生 Cl₂、H₂S、NO₂ 或 SO₂ 等有毒气体的实验必须在通风橱中进行。切勿将容器凑近鼻子直接闻气体。

Flammable materials: Keep flammable solvents away from open flames. If clothing catches fire, roll on the ground or use a fire blanket to smother the flames — never run.

易燃物：易燃溶剂应远离明火。若衣物着火，应就地打滚或用灭火毯灭火——切勿奔跑。

10. Exam Strategy and Final Tips | 应试策略与最终建议

Finally, developing strong practical awareness beyond memorising procedures is essential. Understand the principle behind each operation so you can answer “why” questions with confidence.

最后，在记忆操作流程之外，培养扎实的实践意识至关重要。理解每个操作背后的原理，才能自信地回答”为什么”类问题。

Read the question carefully: Identify whether the examiner requires the name of an apparatus, a reason for a procedure, or the observation at a specific step. Answers must match the command word.

仔细审题：判断考官要求的是仪器名称、操作原因还是某一步骤的现象描述，答案必须对应对指令词。

Use precise terminology: Write “place the test tube at a 45° angle” rather than “tilt the tube slightly”. Examiners award marks for specific quantitative descriptions.

使用精确术语：应写”将试管置于 45° 角”而非”稍微倾斜试管”。考官对具体的量化描述才给分。

Practise with mark schemes: Study how marks are allocated in past papers. A statement like “shake the flask” may earn a mark only if you specify “swirl continuously during titration”.

对照评分标准练习：研究往年试卷中的分数分配。”摇动锥形瓶”只有在写”滴定过程中持续旋转摇动”时才能得分。

Safety context: Whenever the question mentions heating, acids, flammable or toxic substances, always consider whether a safety point should be included in your answer.

安全语境：只要题目涉及加热、酸、易燃或有毒物质，就要考虑答案中是否需要包含安全要点。

Mastering these fundamental laboratory operations is not simply about memorising steps — it is about developing a systematic, safety-conscious and precise approach to practical chemistry. Regular practice, careful observation and reflection on errors will transform these skills into second nature.

掌握这些基本实验操作不仅仅是记忆步骤——而是培养一种系统化、安全意识强且精确的化学实践方法。勤加练习、仔细观察并反思错误，才能将这些技能转化为自然而然的素养。

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Basic Chemistry Laboratory Operations: Exam Points and Common Mistakes | 化学基本实验操作：考点与易错点