📚 Basic Laboratory Techniques and Safety Operations | 化学考点：基本实验方法与安全操作
Chemistry is an experimental science, and every reliable result depends on correct technique and disciplined safety practice. Examiners frequently test not only the final colour change or precipitate, but also the reasoning behind each procedure: why a certain apparatus is chosen, why a reagent is added in a specific order, and what should be done if something goes wrong.
化学是一门实验科学，任何可靠的结果都依赖于正确的手法与严格的安全规范。考官不仅考查最终的颜色变化或沉淀现象，更频繁考查每个操作背后的原理：为何选择某种仪器、为何按特定顺序加入试剂，以及意外发生时应当如何处理。
1. Fundamental Principles of Safe Experimentation | 安全实验的基本原则
Before any practical work, a competent chemist forms a complete mental plan. This plan includes the purpose of the experiment, the hazards of each substance, the order of operations, and the correct treatment for potential accidents. Rushing into a procedure without preparation is the most common root of laboratory errors.
在开始任何实验之前，一名合格的化学家会先在脑海中形成完整的方案。该方案包括实验目的、每种物质的危险性、操作顺序以及潜在事故的正确处理方式。未经准备就匆忙操作，是实验室差错最常见的根源。
Read the entire procedure twice before touching any chemical; identify each hazard symbol and note any warning in the method.
在接触任何化学品之前通读两遍实验步骤；识别每个危险符号并留意方法中的警告事项。
Inspect all glassware for cracks, chips, or stars; damaged apparatus can shatter when heated or when placed under reduced pressure.
检查所有玻璃器皿是否有裂纹、缺口或星状破损；受损仪器在加热或减压时可能碎裂。
Keep the bench clear of bags, books, and loose clothing; a tidy workspace allows quick access to safety equipment.
保持台面整洁，不放书包、书本和松散衣物；干净的工作区便于快速取用安全设备。
Never eat, drink, or apply cosmetics in the laboratory; chemicals may be transferred from hands to food or lips without being noticed.
实验室内严禁饮食或化妆；化学品可能在不知不觉中从手转移到食物或嘴唇上。
Report every spill, breakage, and accident immediately, even if it appears minor; professional judgment begins with honest communication.
即使看起来微不足道，也要立即报告每次泄漏、破损和事故；专业素养始于诚实沟通。
2. Personal Protective Equipment | 个人防护装备
Personal protective equipment, or PPE, is the first line of defence between the chemist and the chemical. PPE must be worn correctly before the experiment begins and kept on until all apparatus is cleaned and all waste is stored. The correct selection of gloves and eye protection depends on the specific reagents being used.
个人防护装备（PPE）是化学家与化学品之间的第一道防线。必须在实验开始前正确穿戴 PPE，并一直保持到所有仪器清洗完毕、所有废料储存妥当为止。手套和眼部防护的选择取决于所使用的具体试剂。
Safety goggles protect the eyes from acid splash, flying glass, and corrosive powders; contact lenses do not provide this protection.
护目镜可保护眼睛免受酸液飞溅、碎玻璃和腐蚀性粉末的伤害；隐形眼镜不具备这种防护作用。
A full-length cotton or flame-retardant lab coat covers skin and ordinary clothing; synthetic fabrics may melt onto the skin in a fire.
全长棉质或阻燃实验服能遮盖皮肤和普通衣物；合成纤维在火灾中可能熔化并粘附在皮肤上。
Nitrile or vinyl gloves resist most dilute acids and alkalis; latex gloves are less resistant to organic solvents such as propanone.
丁腈或乙烯基手套能抵抗大多数稀酸和稀碱；乳胶手套对丙酮等有机溶剂的抵抗能力较弱。
Closed-toe shoes and tied-back hair prevent chemical spills and flames from reaching vulnerable areas of the body.
穿不露趾鞋并束起长发，可防止化学品泼溅和火焰接触身体易受伤部位。
3. Hazard Labels and Chemical Classification | 危险标识与化学品分类
The Globally Harmonized System, often abbreviated as GHS, uses a set of standard pictograms to communicate chemical hazards. A candidate must be able to interpret these symbols and link each one to the correct precaution. Misreading a hazard label is a direct source of accidents and lost marks.
全球化学品统一分类和标签制度（常缩写为 GHS）使用一套标准象形图来传达化学品的危险性。考生必须能够解读这些符号，并将每种符号与正确的预防措施联系起来。误读危险标签既是事故的直接来源，也是失分的原因。
| Label | 标识 | Meaning | 含义 | Common Example | 常见实例 |
|---|---|---|
| Flame | 火焰 | Flammable; keep away from ignition sources | 易燃；远离火源 | Ethanol, propanone | 乙醇、丙酮 |
| Corrosion | 腐蚀 | Causes severe skin burns and eye damage | 导致严重皮肤灼伤和眼损伤 | Concentrated H₂SO₄, NaOH | 浓硫酸、氢氧化钠 |
| Skull and crossbones | 骷髅 | Acute toxicity; may be fatal if swallowed or inhaled | 急性毒性；吞入或吸入可能致命 | Methanol, potassium cyanide | 甲醇、氰化钾 |
| Flame over circle | 圆上火焰 | Oxidising; intensifies combustion | 氧化性；加剧燃烧 | KMnO₄, concentrated H₂O₂ | 高锰酸钾、浓过氧化氢 |
| Exclamation mark | 感叹号 | Irritant; can cause skin or respiratory inflammation | 刺激性；可引起皮肤或呼吸道炎症 | Dilute NH₃, bleach | 稀氨水、漂白剂 |
| Environment | 环境 | Hazardous to aquatic life | 对水生生物有害 | Copper(II) sulfate | 硫酸铜 |
4. Accurate Measurement of Liquids | 液体的精确测量
Volumetric accuracy separates a qualitative observation from a quantitative result. The volume of a liquid is read from the bottom of the meniscus at eye level so that parallax errors are eliminated. Different apparatus have different uncertainties, and the choice of apparatus should match the required precision of the experiment.
容积准确度决定了实验是定性观察还是定量结果。液体的体积应在视线水平上读取弯月面最低点，以消除视差误差。不同仪器的不确定度不同，仪器选择应与实验所需精度相匹配。
l uncertainty of ±0.05 cm³; readings are recorded to two decimal places, ending in 0 or 5.
滴定管的标称不确定度为 ±0.05 cm³；读数记录至两位小数，末位为 0 或 5。
A volumetric pipette delivers a fixed volume, such as 25.00 cm³, with high reproducibility; it is rinsed with the solution to be measured, not with distilled water.
移液管可转移固定体积（如 25.00 cm³），重现性高；应使用待测溶液润洗，而非蒸馏水。
for approximate volumes only; its uncertainty may be ±0.5 cm³ or larger depending on size.
量筒仅适合粗略量取体积；其不确定度可能为 ±0.5 cm³ 或更大，视规格而定。
A volumetric flask is used to prepare a solution of an exact concentration; the bottom of the meniscus must touch the calibration mark exactly.
容量瓶用于配制准确浓度的溶液；弯月面最低点必须恰好与刻度线相切。
percentage error = (uncertainty ÷ measured value) × 100%
百分比误差 =（不确定度 ÷ 测量值）× 100%
5. Heating and Flammable Substances | 加热与易燃物操作
Heating is one of the most dangerous operations in a school laboratory because it combines high temperature with volatile chemicals. The Bunsen burner must be adjusted correctly, and the heating method must match the flammability of the substances involved. A roaring blue flame is made by opening the air hole fully, while a yellow safety flame is produced when the air hole is closed.
加热是学校实验室中最危险的操作之一，因为它将高温与挥发性化学品结合在一起。必须正确调节本生灯，且加热方式必须与物质的易燃性相匹配。完全打开空气孔可得到嘶嘶作响的蓝色火焰，而关闭空气孔则产生黄色安全火焰。
Use an electric water bath or heating mantle for ethanol, propanone, and other flammable solvents; never heat them directly with a naked flame.
加热乙醇、丙酮及其他易燃溶剂时应使用电热水浴或加热套；切勿直接用明火加热。
When heating a liquid in a test tube, point the mouth of the tube away from yourself and your neighbours, and move the tube gently through the flame.
在试管中加热液体时，试管口不要朝向自己和他人，并应缓慢在火焰中移动试管。
Add anti-bumping granules or boiling chips to liquids before heating to ensure smooth boiling and prevent sudden violent ebullition.
加热前向液体中加入防暴沸颗粒或沸石，以保证平稳沸腾并防止突然暴沸。
Never heat a sealed container; the expansion of gas or vapour may cause the vessel to explode. Always leave an opening or a loose stopper.
切勿加热密封容器；气体或蒸气的膨胀可能导致容器爆炸。务必留有开口或使用松的塞子。
6. Handling Acids, Bases and Corrosives | 酸碱及腐蚀品的处理
The dilution of concentrated acids is exothermic, which means it releases a significant amount of heat. The correct order is always to add acid to water, slowly and with stirring. Adding water to concentrated acid can cause the mixture to boil violently and splash corrosive droplets over the chemist.
浓酸的稀释是放热过程，意味着会释放大量热量。正确顺序永远是缓慢搅拌下将酸加入水中。若将水加入浓酸，混合液可能剧烈沸腾，并飞溅出腐蚀性液滴灼伤操作者。
H₂SO₄ + H₂O → H₃O⁺ + HSO₄⁻ (strongly exothermic)
H₂SO₄ + H₂O → H₃O⁺ + HSO₄⁻ （强烈放热）
For quantitative work, dilution calculations use the relationship between concentration and volume before and after dilution. This equation assumes that the amount of solute does not change when solvent is added.
定量工作中，稀释计算使用稀释前后浓度与体积的关系。该方程假设加入溶剂时溶质的物质的量不变。
C₁V₁ = C₂V₂
If concentrated acid is splashed onto the skin, flood the area with cold running water for at least 15 minutes and remove contaminated clothing; do not attempt to neutralise on the skin.
若浓酸溅到皮肤上，立即用冷自来水冲洗至少 15 分钟并脱去受污染衣物；切勿在皮肤上直接中和。
Spills of acid on the bench may be neutralised with sodium hydrogencarbonate, NaHCO₃, before being wiped up with absorbent material.
台面上的酸液泄漏可先用碳酸氢钠（NaHCO₃）中和，再用吸水材料擦拭。
When measuring a corrosive liquid, use a pipette filler or a syringe; never pipette by mouth.
量取腐蚀性液体时应使用洗耳球或注射器；切勿用嘴吸取。
7. Separation Techniques: Filtration and Crystallisation | 分离技术：过滤与结晶
Filtration separates an insoluble solid from a liquid. The filter paper is folded into a cone, placed in a funnel, and moistened with the solvent before the mixture is poured along a glass rod. The solid retained on the paper is called the residue, and the liquid that passes through is called the filtrate.
过滤用于分离不溶性固体与液体。将滤纸折叠成锥形放入漏斗，用溶剂润湿后，沿玻璃棒引流倒入混合物。滤纸上留存的固体称为滤渣，透过滤纸的液体称为滤液。
Hot filtration is used when the desired product is soluble and would crystallise out if the solution cooled during filtration.
当目标产物可溶，且若过滤时溶液冷却会析出晶体时，应采用热过滤。
Recrystallisation purifies a solid: dissolve the impure solid in the minimum volume of hot solvent, filter hot, then cool slowly to form pure crystals.
重结晶可提纯固体：用最少量的热溶剂溶解不纯固体，趁热过滤，再缓慢冷却以获得纯晶体。
After filtering, wash the crystals with a small portion of cold solvent and dry them between filter papers or in a warm desiccator.
过滤后，用少量冷溶剂洗涤晶体，并用滤纸吸干或在温热干燥器中干燥。
Slow cooling produces larger, purer crystals; rapid cooling traps impurities inside the crystal lattice.
缓慢冷却得到更大、更纯的晶体；快速冷却会将杂质裹入晶格内部。
8. Collection and Testing of Gases | 气体的收集与检验
Gas preparation requires matching the collection method to the properties of the gas, especially its solubility in water and its density relative to air. A gas that is insoluble in water may be collected over water; a gas that is denser or lighter than air may be collected by upward or downward delivery. Every gas also has a specific chemical test based on a distinctive reaction.
气体的制取需要根据气体性质选择收集方法，尤其是气体在水中的溶解度以及与空气的相对密度。不溶于水的气体可用排水集气法收集；比空气重或轻的气体可用向上或向下排空气法收集。每种气体也有基于特征反应的特定检验方法。
| Gas | 气体 | Test | 检验方法 | Observation | 现象 |
|---|---|---|
| H₂ | 氢气 | Lighted splint near the mouth of the tube | 将点燃的木条靠近管口 | Squeaky pop | 尖锐爆鸣声 |
| O₂ | 氧气 | Glowing splint is inserted into the gas | 将带火星木条伸入气体 | Splint relights | 木条复燃 |
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