📚 AS Chemistry Unit 1 (January 2020) Experimental Techniques | AS化学单元1（2020年1月）实验操作
In the January 2020 AS Chemistry Unit 1 examination, experimental techniques are assessed both through theoretical questions and practical scenarios. Mastering common laboratory procedures, from accurate measurement to safe handling, is essential for success. This article reviews key experimental skills frequently tested in such papers, providing a comprehensive guide for revision.
在2020年1月的AS化学单元1考试中，实验操作通过理论问题和实际情景进行考核。掌握从精确测量到安全操作的常见实验室程序是取得好成绩的关键。本文回顾了此类试卷中常考的关键实验技能，为复习提供全面指南。
1. Safety in the Laboratory | 实验室安全
Always wear safety goggles and a lab coat when handling chemicals. Any spill on skin must be washed immediately with plenty of water.
处理化学品时必须佩戴护目镜和实验服。皮肤溅到化学品要立即用大量水冲洗。
When diluting concentrated sulfuric acid, always add acid to water slowly while stirring. Adding water to acid can cause violent splashing due to the exothermic reaction.
稀释浓硫酸时，必须将酸缓慢加入水中并搅拌。将水加入酸中会因放热反应引起剧烈飞溅。
Never pipette by mouth; always use a pipette filler. Dispose of chemical waste in designated containers, not down the sink unless instructed.
禁止用嘴吸移液管；务必使用洗耳球。化学品废液应倒入指定容器，除非有指示否则勿倒入水槽。
In titration, the burette should be filled using a small funnel, and the tip should be free of air bubbles before starting. If an accident occurs, report it immediately.
滴定中，应用小漏斗灌装滴定管，开始前确保尖嘴无气泡。如发生意外，立即报告。
2. Measuring Mass and Volume | 测量质量和体积
An analytical balance can measure mass to 0.001 g. Before weighing, ensure the balance is tared (zeroed) and use a weighing boat or paper to avoid contamination.
分析天平可称量至0.001 g。称量前确保天平调零，并使用称量舟或称量纸防止污染。
Volume of liquids is measured using graduated cylinders, volumetric pipettes, and burettes. A 25 cm³ pipette delivers exactly 25.0 cm³ with an uncertainty of ±0.06 cm³.
液体体积用量筒、移液管和滴定管测量。一支25 cm³移液管准确移取25.0 cm³，不确定度为±0.06 cm³。
When reading the meniscus, your eye must be level with the bottom of the meniscus to avoid parallax error. For burettes, read to the nearest 0.05 cm³.
读取弯月面时，视线应与弯月面底部水平以避免视差。滴定管读数精确到0.05 cm³。
A volumetric flask is used to prepare a solution of precise volume, e.g., 250.0 cm³. After dissolving solute, transfer carefully, rinse beaker, and make up to the mark.
容量瓶用于配制精确体积的溶液，如250.0 cm³。溶解溶质后，小心转移，洗涤烧杯，定容至刻度线。
3. Preparing Standard Solutions | 配制标准溶液
To prepare a standard solution of sodium carbonate, accurately weigh a known mass of anhydrous Na₂CO₃, dissolve in deionised water, transfer to a volumetric flask, and dilute to the mark.
配制碳酸钠标准溶液时，准确称取已知质量的无水Na₂CO₃，溶于去离子水，转移至容量瓶，稀释至刻度。
The solute must be completely transferred; rinse the beaker and stirring rod several times with deionised water and add the washings to the flask.
溶质必须完全转移；用去离子水冲洗烧杯和搅拌棒数次，洗涤液一并倒入容量瓶。
When filling to the mark, use a dropping pipette near the end to add water dropwise until the bottom of the meniscus just touches the line.
定容时，临近刻度线用滴管逐滴加水，直至弯月面底部刚好与刻度线相切。
Stopper the flask and invert several times to ensure uniform mixing. The concentration is calculated using:
盖好瓶塞，反复倒转数次，确保混合均匀。浓度计算公式为：
c = n / V = m / (M × V)
where m is mass of solute (g), M is molar mass (g mol⁻¹), and V is solution volume (dm³).
其中m为溶质质量(g)，M为摩尔质量(g mol⁻¹)，V为溶液体积(dm³)。
4. Titration Techniques | 滴定技术
Rinse the burette first with deionised water, then with the acid solution it will contain. Fill the burette, ensuring no air bubble remains in the tip.
滴定管先用去离子水润洗，再用待装酸液润洗。灌装时确保尖嘴处无气泡残留。
Use a pipette and pipette filler to transfer 25.0 cm³ of alkali solution into a clean conical flask. Add 2–3 drops of methyl orange or phenolphthalein indicator.
用移液管和洗耳球准确量取25.0 cm³碱液至干净的锥形瓶中，加入2–3滴甲基橙或酚酞指示剂。
Record the initial burette reading. Titrate by adding acid from the burette while swirling the flask. Near the end-point, add acid dropwise.
记录初始读数。边摇动锥形瓶边由滴定管加入酸液。接近终点时，逐滴滴加。
The end-point is reached when the indicator colour changes permanently. For methyl orange, colour changes from yellow to red; for phenolphthalein, from pink to colourless. Record the final reading and calculate the titre.
当指示剂发生永久性颜色变化即达到终点。甲基橙由黄变红；酚酞由粉红变为无色。记录最终读数，计算滴定体积。
Repeat the titration until concordant titres (within 0.10 cm³) are obtained. Use the average of concordant results for calculation. For a quick check:
重复滴定至得到一致结果（差值不超过0.10 cm³）。取一致结果的平均值进行计算。快速检查公式：
c₁V₁ = c₂V₂
helps relate the unknown concentration to the standard.
可通过c₁V₁ = c₂V₂将未知浓度与标准浓度关联。
5. Heating and Cooling Methods | 加热与冷却方法
To dissolve a solid more quickly, heat the solution gently using a Bunsen burner or hot plate, never heat a volumetric flask directly.
为加速固体溶解，可用本生灯或电热板温和加热溶液，切勿直接加热容量瓶。
For determining melting point, pack a small amount of solid into a capillary tube and attach to a thermometer. Heat in an oil bath or melting point apparatus, observing the temperature at which melting occurs.
测定熔点时，将少量固体装入毛细管，固定在温度计上。在油浴或熔点仪中加热，观察熔化的温度。
After heating, objects must be allowed to cool in a desiccator to prevent absorption of moisture from the air before weighing.
加热后的物体需在干燥器中冷却，防止称量前吸收空气中的水分。
A water bath can be used to heat flammable liquids safely, maintaining a constant temperature below 100°C.
水浴可用于安全加热易燃液体，保持低于100°C的恒温。
6. Filtration and Drying | 过滤与干燥
Gravity filtration uses filter paper and a funnel to separate an insoluble solid from a liquid. Fold the filter paper to fit the funnel, and wet it with solvent before filtration.
常压过滤使用滤纸和漏斗分离不溶性固体与液体。折叠滤纸与漏斗贴合，过滤前先用溶剂润湿。
Vacuum filtration with a Büchner flask and funnel is faster and produces a drier solid. Place a moistened filter paper on the plate, apply suction, and pour the mixture.
使用布氏漏斗和抽滤瓶进行减压过滤更快，固体更干。在筛板上放置润湿的滤纸，开启抽气，倒入混合物。
Wash the solid residue with a small amount of cold solvent to remove soluble impurities. Then dry the product in an oven at a suitable temperature to constant mass.
用少量冷溶剂洗涤固体残渣，去除可溶性杂质。然后将产品在适宜温度的烘箱中干燥至恒重。
Check for complete drying by repeatedly heating, cooling, and weighing until the mass does not change by more than 0.02 g.
通过反复加热、冷却、称量直至质量变化不超过0.02 g，以检查是否完全干燥。
7. Testing for Gases | 气体检验
Oxygen gas relights a glowing splint. Hold a glowing wooden splint near the mouth of the test tube; it will burst into flame if oxygen is present.
氧气能使带火星的木条复燃。将带火星的木条靠近试管口，如有氧气，木条会燃起火焰。
Carbon dioxide turns limewater milky. Bubble the gas through calcium hydroxide solution; a white precipitate of calcium carbonate forms.
二氧化碳使石灰水变浑浊。将气体通入氢氧化钙溶液，形成碳酸钙白色沉淀。
Hydrogen gas gives a squeaky pop sound when a lit splint is introduced into the test tube containing the gas.
氢气遇燃着的木条会发出尖锐的爆鸣声。
Ammonia gas turns damp red litmus paper blue, as ammonia dissolves to form a basic solution.
氨气使湿润的红色石蕊试纸变蓝，因为氨溶于水形成碱性溶液。
Chlorine gas bleaches damp litmus paper; it first turns red due to acidity, then white due to bleaching.
氯气漂白湿润的石蕊试纸；先因酸性变红，后因漂白变白。
8. Flame Tests |
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