📚 AS Chemistry Paper 1 January 2018: Experimental Operations | AS化学卷一2018年1月：实验操作
The January 2018 AS Chemistry Paper 1 placed a strong emphasis on core practical techniques. Students were expected to demonstrate a thorough understanding of laboratory operations ranging from solution preparation and titration to gas handling and organic product purification. This article revisits the most important experimental operations that underpin the examination, offering step-by-step explanations, common pitfalls, and tips for accurate practical work.
2018年1月的AS化学卷一重点考查了核心实验技能。考生需要熟练掌握从溶液配制、滴定操作到气体处理和有机产物纯化等一系列实验操作。本文重温了该试卷中涉及的最重要的实验操作，提供逐步解释、常见错误以及精准实践工作的技巧。
1. Preparing Standard Solutions | 标准溶液的配制
t-shaped filter paper and tare the balance before adding the solid. Record the mass to at least ±0.001 g to meet AS-level precision requirements.
准确的标准溶液始于在分析天平上精确称量基准物质。使用干净、干燥的称量舟或舟形滤纸，添加固体前将天平去皮。记录质量至少精确到±0.001 g，以满足AS级别的精度要求。
Transfer the solid completely to a beaker containing about 50 cm³ of distilled water. Use a wash bottle to rinse the weighing boat and transfer all rinsings into the beaker. This quantitative transfer is essential to avoid loss that would lower the final concentration. After dissolving, pour the solution into a 250 cm³ volumetric flask via a funnel, rinse the beaker and funnel several times, and add all washings to the flask. Finally, make up to the graduation mark with distilled water using a dropping pipette for the last few drops. Stopper and invert the flask 10–15 times to homogenise.
将固体完全转移到一个盛有约50 cm³蒸馏水的烧杯中。用洗瓶冲洗称量舟，并将所有冲洗液转入烧杯。这种定量转移对于避免损失从而降低最终浓度至关重要。溶解后，通过漏斗将溶液倒入250 cm³容量瓶中，冲洗烧杯和漏斗数次，并将所有洗涤液加入容量瓶。最后，用滴管滴加蒸馏水至刻度线，盖紧瓶塞并反复倒置振荡10–15次以混合均匀。
2. Acid-Base Titration Technique | 酸碱滴定操作
tte above the 0.00 cm³ mark and allow some solution to run out through the jet to remove air bubbles— reading to the nearest ±0.05 cm³, reading the bottom of the concave meniscus at eye level.
用滴定剂（如0.100 mol dm⁻³ HCl或NaOH）润洗滴定管两次，以去除会稀释溶液的残留水分。将滴定管装液至0.00 cm³刻度以上，放出少量溶液以排出尖嘴中的气泡——这确保尖端完全充满。记录初始读数，精确到±0.05 cm³，在视线水平处读取凹液面底部。
Add exactly 25.0 cm³ of the solution to be titrated (measured by pipette) into a clean conical flask. Add only 2–3 drops of a suitable indicator: methyl orange for strong acid–strong base titrations, phenolphthalein for strong base–acid. Avoid excess indicator, as it is itself a weak acid or base that could consume a tiny amount of titrant. Swirl the flask constantly while adding titrant. Near the endpoint, add drops with swirling back and forth; one extra drop should cause a permanent colour change. Repeat until concordant titres (within 0.10 cm³) are obtained.
用移液管准确量取25.0 cm³待滴定溶液，放入干净的锥形瓶中。仅加入2–3滴合适的指示剂：强酸强碱滴定使用甲基橙，强碱弱酸滴定使用酚酞。避免指示剂过量，因为它本身是一种弱酸或弱碱，可能消耗微量滴定剂。不断旋摇锥形瓶的同时滴加滴定剂。接近终点时，逐滴加入并来回旋摇；最后一滴应引起永久性颜色变化。重复滴定至获得一致的结果（体积相差在0.10 cm³以内）。
3. Gas Collection Over Water | 排水集气法
When a gas is evolved in a reaction, it can be collected over water if it is insoluble or only slightly soluble, for example H₂, O₂, CH₄. Completely fill a large measuring cylinder or gas jar with water and invert it, mouth-downwards, in a trough of water. Insert the delivery tube below the mouth of the cylinder so that gas bubbles rise and displace the water. Ensure no air bubbles enter the cylinder at the start.
当反应产生气体，若该气体不溶或微溶于水（如H₂、O₂、CH₄），可用排水集气法收集。将一个大刻度量筒或集气瓶装满水，倒置在盛有水的水槽中。将导气管伸入量筒口下方，使气泡上升、置换水。开始时必须确保量筒内无空气泡。
Once collection is complete, read the volume of gas at atmospheric pressure; however, the gas contains saturated water vapour. For accurate calculations, subtract the vapour pressure of water at the recorded temperature from the atmospheric pressure, using Dalton's law of partial pressures. Also adjust the volume to standard conditions if required by the question.
收集完毕后，读取大气压下的气体体积；但该气体含有饱和水蒸气。为精确计算，需根据道尔顿分压定律，从大气压中减去该温度下的水蒸气压。如有需要，还应将体积校正至标准状况。
4. Measuring Gas Volume Using a Gas Syringe | 用气体注射器测量气体体积
For reactions that produce gases which react with water or are soluble (e.g., CO₂, SO₂, NH₃), a gas syringe is preferred. Connect the syringe tightly to the reaction vessel via a rubber bung, and ensure the plunger moves smoothly without sticking. Start the timer and record the gas volume at regular time intervals, e.g., every 10 seconds, to obtain a rate curve.
对于产生能与水反应或可溶于水的气体（如CO₂、SO₂、NH₃）的反应，最好使用气体注射器。通过橡胶塞将注射器紧密连接到反应容器，并确保活塞顺畅移动、无卡滞。启动秒表，每隔一定时间（如每10秒）记录一次气体体积，以获得速率曲线。
Handle the syringe carefully; the plunger must be returned to the zero mark before each run. Keep the syringe horizontal and read the scale at the inner edge of the plunger seal. Avoid over-pressurisation by ensuring the system is not sealed completely if rapid gas evolution occurs—though keep tight enough to prevent leakage.
小心操作注射器；每次实验前活塞需归零。保持注射器水平，读取活塞密封内缘对应的刻度。避免因气体产生过快导致过压，但需确保系统密封性以防泄漏。
5. Heating Substances Safely | 安全加热物质
For direct heating with a Bunsen burner, place the crucible on a pipe-clay triangle on a tripod. For solids, heat gently at first to prevent spitting, then increase the flame. When heating an organic liquid, always use a water bath for temperatures below 100°C or an oil bath/sand bath for higher temperatures. Never heat flammable liquids with a naked flame.
使用本生灯直接加热时，将坩埚放在泥三角上，置于三脚架上。加热固体时应先小火预热以防迸溅，再加大火焰。加热有机液体时，温度低于100°C始终使用水浴，更高温度使用油浴或沙浴；严禁用明火加热易燃液体。
Safe heating of a test tube requires pointing the mouth away from everyone and moving the tube gently in and out of the flame. Use a test tube holder. For prolonged, even heating, employ a heating mantle or hot plate. Always wear safety spectacles and have appropriate cooling measures ready.
安全加热试管时，试管口须远离人群，用试管夹夹住并在火焰上来回移动。长时间均匀加热可使用加热套或电热板。始终佩戴护目镜，并准备好适当的冷却措施。
6. Filtration and Washing Precipitates | 过滤与洗涤沉淀
Gravimetric analysis requires quantitative separation of a precipitate. Set up a Buchner funnel with a filter paper that fits snugly onto the perforated plate, connect to a side-arm flask, and apply suction from a water pump or vacuum line. Wet the filter paper with a small amount of the same solvent to make it adhere firmly.
重量分析需要沉淀的定量分离。安装布氏漏斗，放置一张紧密贴合垫板的滤纸，连接到抽滤瓶，用水泵或真空管抽吸。用少许相同溶剂润湿滤纸使其紧贴。
Pour the suspension slowly down a glass rod into the centre of the funnel. Rinse the beaker with cold washing solvent and pour the rinsings through the precipitate. Once filtration is complete, wash the precipitate with small portions of cold solvent (e.g., cold deionised water or ethanol) to remove adsorbed impurities without dissolving the precipitate. Continue suction until the solid is as dry as possible before transfer for drying in an oven.
沿玻璃棒将悬浮液缓慢倒入漏斗中央。用冷洗涤溶剂冲洗烧杯，并将洗液倒入沉淀层。过滤结束后，用少量冷溶剂（如冷去离子水或乙醇）分次洗涤沉淀以去除吸附的杂质，同时不溶解沉淀。继续抽吸直至固体尽量干燥，然后转移至烘箱干燥。
7. Using a Separating Funnel | 使用分液漏斗
Place the heterogeneous mixture of organic and aqueous layers in a separating funnel supported on a ring. Allow the layers to separate clearly. Place a labelled conical flask under the stopcock. Remove the stopper, then open the stopcock to slowly run off the lower (usually aqueous) layer, closing it just as the interface reaches the tap. The remaining organic layer is drained into a different flask.
将有机相与水相的非均相混合物放入固定在铁圈上的分液漏斗中。静置至清晰分层。将贴有标签的锥形瓶放在旋塞下方。取下瓶塞，然后打开旋塞，缓慢放出下层（通常是水层），在界面刚好到达旋塞时关闭。剩余有机层放入另一只锥形瓶。
If extracting a solute, add fresh solvent, stopper, and shake gently with occasional venting by opening the stopcock (pointed away from yourself) to release pressure. Repeat the draining procedure. Anhydrous drying agents like MgSO₄ or Na₂SO₄ can be added to the organic layer afterwards to absorb residual water.
若进行萃取，加入新鲜溶剂，塞好瓶塞，轻轻摇晃并时常通过打开旋塞（瓶口朝外）排放压力。重复排放步骤。随后可向有机层中加入无水干燥剂如MgSO₄或Na₂SO₄，以吸收残余水分。
8. Reflux and Distillation Setup | 回流与蒸馏装置
Reflux is used when a reaction requires prolonged heating at the boiling point of the solvent without loss of volatile substances. Attach a Liebig condenser vertically to a round-bottom flask containing the reaction mixture and a few anti-bumping granules. Water enters the condenser at the bottom and exits at the top to ensure the jacket is completely filled. Heat with a heating mantle, not a naked flame.
当反应需要在溶剂沸点长时间加热而又不损失挥发性物质时，使用回流。将直形冷凝管垂直安装在盛有反应混合物和几粒沸石的圆底烧瓶上。冷却水从冷凝管下端进入、上端流出，以确保夹套完全充满。使用加热套加热，禁用明火。
For simple distillation, the condenser is positioned at a downward slant so that the distillate can flow into a collection vessel. A thermometer bulb should be placed exactly at the side-arm opening to measure the vapour temperature of the condensing component. Adjust the heating rate so that distillation proceeds at about one drop per second. Collect fractions at specific temperature ranges to obtain pure substances.
简单蒸馏时，冷凝器呈向下的倾斜角度安装，使馏出液能流入接收容器。温度计球泡应准确放在支管口处，以测量冷凝组分的蒸气温度。调节加热速率，使蒸馏速度约为每秒一滴。在特定温度范围内收集馏分以获得纯物质。
9. Recrystallisation of Organic Solids | 有机固体的重结晶
This purification technique relies on the difference in solubility of the desired product and impurities in a hot solvent. Heat a minimal volume of the chosen solvent (often water, ethanol, or a mixture) to boiling in a water bath. Add the crude solid bit by bit until it just dissolves, then add a little extra solvent to keep it dissolved. Perform a hot filtration through a fluted filter paper in a pre-heated funnel to remove insoluble impurities.
这种纯化技术依赖于所需产物与杂质在热溶剂中的溶解度差异。在水浴中将所选溶剂（常用水、乙醇或混合溶剂）加热至沸腾。少量多次地加入粗产物直至恰好溶解，再加入少许溶剂以保持溶解状态。通过预热漏斗中的槽纹滤纸进行热过滤，以去除不溶性杂质。
Allow the filtrate to cool slowly at room temperature, which encourages the formation of well-shaped crystals rather than rapid precipitation. Further cooling in an ice bath maximises yield. Collect the crystals by suction filtration, wash with a small volume of cold solvent, and dry between sheets of filter paper or in a desiccator. Measure the melting point to assess purity: a sharp melting point close to the literature value indicates high purity.
将滤液于室温下缓慢冷却，这有助于形成良好晶形的晶体，而非快速析出。在冰水中进一步冷却可提高产率。通过抽滤收集晶体，用少量冷溶剂洗涤，并在滤纸之间压干或在干燥器中干燥。测定熔点以评估纯度：熔距短且接近文献值表明纯度高。
10. Recording and Processing Data | 记录与处理数据
All experimental data must be recorded in a well-structured table with appropriate units in the headings, e.g., volume / cm³, mass / g, temperature / °C. Record readings to the correct number of decimal places: burette readings to two decimal places (0.05 cm³), thermometer to the nearest 0.5°C, pipette volumes as 25.0 cm³. Ensure raw data is distinct from calculated values.
所有实验数据必须记录在结构清晰的表格中，表头标注适当单位，如体积/cm³、质量/g、温度/°C。读数记录到正确的小数位数：滴定管读数记录两位小数（0.05 cm³），温度计精确到0.5°C，移液管体积记为25.0 cm³。确保原始数据与计算值明确分开。
From titration data, discard any non-concordant titres (usually more than 0.10 cm³ apart) and calculate the mean of the closest values. Use the formula
mean titre = (T₁ + T₂ + T₃) / 3
if three values are concordant. Then convert to moles:n = c × V
where V is in dm³ (cm³ ÷ 1000). Express final answers to the appropriate number of significant figures, typically three.处理滴定数据时，剔除不平行结果（通常相差大于0.10 cm³），计算最接近值的平均值。若三个结果平行，使用平均滴定体积 = (T₁ + T₂ + T₃) / 3。然后换算为物质的量：n = c × V，其中V的单位为dm³（cm³ ÷ 1000）。最终答案保留适当有效数字，通常为三位。
11. Common Errors and Improvements | 常见错误与改进
A systematic error in titration is the inclusion of air bubbles in the burette jet. This causes the initial volume reading to be misrepresented. Always flush out air before taking the initial reading. Another common error is using too much phenolphthalein, which can lead to a premature pink colour from excess base being neutralised by the indicator itself. Stick to 2–3 drops.
滴定中的一个系统误差是滴定管尖嘴中存在气泡，这会导致初始体积读数失真。务必在读取初始读数前排除气泡。另一个常见错误是使用过多酚酞，过多的指示剂本身消耗碱，可能导致提前出现粉红色。应严格只用2–3滴。
In making a standard solution, losses during transfer due to splashing or incomplete rinsing lower the apparent concentration. Use a stirring rod to guide the liquid into the volumetric flask, rinse the beaker, rod and funnel thoroughly at least three times with distilled water, and add all washings. Parallax error when reading the meniscus can be avoided by placing the flask on a flat surface, bringing your eye to the level of the graduation mark, and ensuring the bottom of the meniscus touches the line.
配制标准溶液时，转移过程中的溅出或冲洗不充分会导致损失，使表观浓度偏低。使用玻璃棒引流液体至容量瓶，用蒸馏水彻底冲洗烧杯、玻璃棒和漏斗至少三次，并将所有洗液加入。读取弯月面时的视差可通过将容量瓶置于平面上、视线与刻度线齐平、确保弯月面最低点与刻度线相切来避免。
When measuring gas volumes, the dead volume in the connecting tubing can introduce a systematic error. Use the shortest possible tubing, and determine the volume of the apparatus by filling with water prior to the experiment. Also, fluctuating room temperature and pressure can affect readings; note the ambient conditions for later correction.
测量气体体积时，连接管路的死体积可引入系统误差。应使用尽可能短的管路，并在实验前用水填充法标定仪器体积。此外，室温和气压的波动也会影响读数；记录环境条件以便后续校正。
12. Safety Considerations in the Lab | 实验室安全注意事项
Always wear a lab coat, safety goggles, and if handling corrosive reagents, nitrile gloves. In the January 2018 paper, safe practices with concentrated acids (H₂SO₄, HCl) and alkalis (NaOH) were essential. Concentrated acids should be diluted by adding acid to water slowly while stirring, never the reverse, to prevent violent splashing.
始终穿着实验服、佩戴护目镜，处理腐蚀性试剂时还需戴上丁腈手套。在2018年1月的试卷中，正确处理浓酸（H₂SO₄、HCl）和强碱（NaOH）至关重要。稀释浓酸时应将酸缓慢加入水中并持续搅拌，切不可反向操作，以免剧烈飞溅。
Work in a fume cupboard when using volatile organic solvents (e.g., propanone, ethanol) or toxic gases (e.g., SO₂, NO₂). Keep flammable liquids away from ignition sources. Dispose of chemical waste in labelled containers—never down the sink unless specifically permitted. Report any spill immediately and know the location of the first-aid kit, eyewash station, and fire extinguisher.
使用挥发性有机溶剂（如丙酮、乙醇）或有毒气体（如SO₂、NO₂）时，需在通风橱中操作。易燃液体远离火源。将化学废液倒入贴有标签的废液桶，切勿直接倒入水槽，除非明确允许。发生溢洒立即报告，并熟知急救箱、洗眼器和灭火器的位置。
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