📚 Mastering Experimental Techniques from AS Chemistry Unit 1 (June 2019) | 掌握AS化学单元1实验操作（2019年6月卷）
Experimental skills form the backbone of AS Chemistry Unit 1, and the June 2019 exam paper tested candidates on a range of practical procedures, from accurate measurement to data analysis. This article revisits the core experimental operations that appeared or were implied in that series, breaking down each technique into key steps, common pitfalls, and error reduction strategies. Whether you are preparing for your own practical assessment or tackling written questions on experimental design, mastering these techniques will boost both your confidence and your marks.
实验技能是 AS 化学单元1 的核心，2019 年 6 月试卷从精确量取到数据分析，全面考查了考生的动手能力。本文回顾该系列试卷中出现或隐含的基本实验操作，将每项技术分解为关键步骤、常见错误及减少误差的策略。无论你是在准备实际操作考核，还是在应对实验设计相关的笔试题目，掌握这些技术都能增强信心并提高分数。
1. Safety and Preparation | 安全与实验准备
Before any experiment, you must wear safety goggles and a lab coat. Long hair should be tied back, and any loose clothing should be secured. Check that the work area is clean, that you know the location of the nearest eyewash station and fire extinguisher, and that you have read the risk assessment for the chemicals involved.
进行任何实验前，必须佩戴护目镜和实验服。长发要束好，宽松的衣物需固定好。确保工作区域整洁，了解最近的洗眼器和灭火器的位置，并已阅读所用化学品的风险评估。
In the June 2019 context, typical experiments involved dilute acids, alkalis, and oxidising agents. Always add concentrated acid to water slowly while stirring, never the reverse. When heating flammable liquids, use a water bath or electric heater rather than an open flame. Label all test tubes and beakers clearly to avoid cross‑contamination.
在 2019 年 6 月的考试情境中，典型实验涉及稀酸、碱和氧化剂。务必在搅拌下将浓酸缓慢加入水中，切勿反向操作。加热易燃液体时，应使用水浴或电热板，避免明火。所有试管和烧杯都要清楚标注，以防交叉污染。
2. Measuring Mass and Using the Analytical Balance | 质量称量与分析天平的使用
An analytical balance is used to measure mass to 0.001 g or even 0.0001 g. The June 2019 paper likely included a magnesium ribbon or a solid reagent where precise mass was crucial. Before weighing, check that the balance is level and clean. Place a weighing boat on the pan, close the glass doors, and press ‘tare’ to zero the reading. Then add the substance and record the stable reading.
分析天平可精确到 0.001 g 甚至 0.0001 g。2019 年 6 月试卷很可能涉及镁带或其他固体试剂，精确称量至关重要。称量前，检查天平是否水平且清洁。将称量舟放在托盘上，关闭玻璃门，按 ‘tare’ 键归零。然后添加物质，待读数稳定后记录。
Avoid tapping the bench while mass readings are taken, and never weigh a hot object—cool it in a desiccator first. When weighing pre‑cut lengths of magnesium ribbon for a molar volume experiment, record the mass before they tarnish, and handle them with forceps to prevent moisture transfer from fingers.
读数时避免敲击实验台，切勿称量热的物体——应先在干燥器内冷却。在为摩尔体积实验称取预先剪好的镁带时，应在它们失去光泽前及时记录质量，并用量子夹取，防止手指传递水分。
3. Volume Measurement: Burettes, Pipettes and Volumetric Flasks | 体积量测：滴定管、移液管与容量瓶
5 cm³, while a volumetric pipette provides a fixed volume with high accuracy. In a typical June 2019 titration question, you would have rinsed the burette with distilled water and then with the solution it will contain. Fill the burette using a small funnel, remove the funnel, and open the tap briefly to fill the tip without air bubbles. Record the initial reading to the nearest 0.05 cm³, making sure your eye is level with the meniscus.
滴定管可精确至 ±0.05 cm³，而容量移液管能提供高精度的固定体积。在 2019 年 6 月典型的滴定问题中，你需要先用蒸馏水、再用待装液润洗滴定管。用小漏斗灌装，然后移开漏斗，短暂打开活塞以充满尖端并排出气泡。读数时视线与弯月面相平，记录初始读数至 0.05 cm³。
A volumetric pipette is used to transfer a precise volume, e.g. 25.0 cm³ of sodium hydroxide solution, into a conical flask. Rinse it with the solution, use a pipette filler (never your mouth), allow the solution to drain freely, and touch the tip to the side of the flask to remove the last drop. Do not blow out the remaining liquid unless the pipette is marked ‘TD, blow‑out’. A volumetric flask is employed when you need to prepare a standard solution—dissolve the weighed solid in a beaker, transfer it quantitatively (with washings), then make up to the mark with the bottom of the meniscus touching the graduation line.
容量移液管用于转移精确体积，例如 25.0 cm³ 氢氧化钠溶液至锥形瓶。用该溶液润洗，使用洗耳球（切勿用嘴），让溶液自然流出，并将尖端轻触瓶壁以除去最后一滴。除非移液管标有 ‘TD, blow‑out’，否则不要吹出残留液。配制标准溶液时使用容量瓶——将称好的固体在烧杯中溶解，定量转移（连同洗液），然后加水至刻度，使弯月面底部与标线相切。
4. Titration Technique and End‑Point Determination | 滴定操作与终点判定
Titration is a high‑precision method for determining the concentration of an unknown solution. In the Jun 19 Unit 1 paper, an acid–base titration using phenolphthalein or methyl orange was probably featured. After pipetting the aliquot into a conical flask, add 2–3 drops of indicator. Place the flask on a white tile under the burette tip and swirl continuously while adding titrant. Slow down near the end point and add dropwise with thorough mixing.
滴定是测定未知溶液浓度的高精度方法。在 2019 年 6 月单元1 试卷中，很可能出现使用酚酞或甲基橙的酸碱滴定。将整分溶液移入锥形瓶后，加入 2–3 滴指示剂。将锥形瓶放在白色瓷砖上，置于滴定管尖端下方，边旋转边滴加。接近终点时放慢速度，逐滴加入并充分摇匀。
A concordant pair of titres means two readings within 0.10 cm³ of each other. If the rough titre is overshot, it is discarded. Always calculate the mean of the concordant values. To improve accuracy, rinse the inside walls of the flask with a small amount of distilled water during the titration—this does not change the number of moles of analyte but ensures all reagent reaches the solution.
若两次滴定读数相差不超过 0.10 cm³，则为吻合滴数。粗测的数值如果超过终点则应舍弃。始终取吻合值的平均值。为提高准确性，可在滴定过程中用少量蒸馏水冲洗锥形瓶内壁——这不会改变被分析物的物质的量，却可确保全部试剂都参与反应。
5. Gas Collection and Determining Molar Volume | 气体收集与摩尔体积测定
A classic AS experiment involves measuring the molar volume of hydrogen produced when a known mass of magnesium reacts with excess dilute hydrochloric acid. In the June 2019 practical‑context question, you might have been given a gas syringe or inverted measuring cylinder set‑up. Attach the reaction flask to a gas syringe, ensuring all connections are airtight. Add the acid, drop in the magnesium, immediately stopper the flask, and record the volume of gas at room temperature and pressure (r.t.p.).
经典的 AS 实验是让一定质量的镁与过量稀盐酸反应，收集产生的氢气并测定其摩尔体积。在 2019 年 6 月的实际操作情境题中，可能提供了气体注射器或倒置量筒的装置。将反应瓶连接到气体注射器，确保所有接口气密。加入酸液，投入镁，迅速塞紧瓶口，记录室温常压下的气体体积。
The collected volume must be converted to molar volume (24.0 dm³ at r.t.p. or 22.7 dm³ at STP) by applying the ideal gas equation if conditions differ. Common sources of error include gas leaking before the bung is inserted, some hydrogen dissolving in the water (in the water‑displacement method), and the reaction being too fast to capture the exact final volume. To reduce these, use a larger reaction flask, pre‑cut the magnesium to minimise the time the flask is open, and allow the apparatus to cool back to room temperature before taking the final reading.
收集到的体积需根据条件折算为摩尔体积（常温常压下 24.0 dm³，标准状况下 22.7 dm³），如果温度压力不同，则可应用理想气体方程。常见误差来源包括塞子未塞紧前气体泄漏、排水集气法中部分氢气溶于水，以及反应太快无法捕捉到精确的最终体积。为减少误差，可使用较大的反应瓶，预先剪好镁带以缩短敞口时间，并在读取最终体积前使装置冷却回室温。
6. Calorimetry and Enthalpy Change Measurements | 量热法与焓变测定
Enthalpy changes, such as the standard enthalpy of neutralisation or the enthalpy of solution of an anhydrous salt, can be measured using a simple polystyrene cup calorimeter. In the Jun 19 paper, you might have calculated ΔH from temperature rise data. Measure the initial temperature of both solutions, mix them in the cup, stir continuously, and record the highest (or lowest) temperature reached. The polystyrene cup provides insulation, and a lid with a thermometer hole minimises heat loss.
测定焓变（如标准中和焓或无水盐的溶解焓）可使用简易的聚苯乙烯杯量热器。在 2019 年 6 月试卷中，你可能需要根据温升数据计算 ΔH。分别测量两种溶液的初始温度，在杯中混合，持续搅拌，记录达到的最高（或最低）温度。聚苯乙烯杯能隔热，配有温度计插孔的盖子可减少热损失。
Use the formula ΔH = − m c ΔT / n, where m is the mass of the solution (g), c is the specific heat capacity (4.18 J g⁻¹ K⁻¹), ΔT is the temperature change, and n is the number of moles of the limiting reactant. The most significant error is heat exchange with the surroundings; you can compensate by plotting a cooling‑correction graph and extrapolating back to the mixing time. For solid‑liquid reactions, make sure the solid dissolves completely before the temperature peak is recorded, and stir vigorously to ensure uniform temperature.
使用公式 ΔH = − m c ΔT / n，其中 m 为溶液质量（g），c 为比热容（4.18 J g⁻¹ K⁻¹），ΔT 为温度变化，n 为限量反应物的物质的量。最大的误差来自与环境的热交换；可通过绘制冷却校正图并外推至混合时间进行补偿。对于固–液反应，确保在记录温度峰值前固体完全溶解，并剧烈搅拌以确保温度均匀。
7. Investigating Rate of Reaction | 反应速率的探究
Rate experiments measure how fast a product forms or a reactant disappears. A likely June 2019 practical design involved the reaction between sodium thiosulfate and dilute hydrochloric acid, producing a yellow sulfur precipitate that makes the solution cloudy. You would place a conical flask over a cross drawn on paper, mix the reactants, start the stopwatch, and time until the cross is no longer visible.
速率实验测量产物生成或反应物消耗的快慢。2019 年 6 月可能涉及硫代硫酸钠与稀盐酸的反应，生成黄色硫沉淀使溶液变浑浊。你将锥形瓶放在画有十字的纸上，混合反应物，启动秒表，记录到十字消失的时间。
The initial rate is approximated as 1/time. To show the effect of concentration, the experiment is repeated with different dilutions of sodium thiosulfate while keeping the total volume and acid concentration constant. All runs must be carried out at the same temperature—even slight warming from hands can accelerate the reaction. The cross must be identical each time, and the person observing the disappearance must remain the same to ensure consistency.
初速率近似为 1/时间。为探究浓度的影响，实验中用不同稀释程度的硫代硫酸钠，保持总体积和酸浓度不变，重复进行。所有实验必须在相同温度下进行——手部的轻微升温都可能加速反应。每次使用的十字必须相同，观察者也要保持一致，以确保判断的一致性。
8. Preparing a Standard Solution | 标准溶液的配制
A standard solution is a solution of accurately known concentration, often used in titrations. In the Jun 19 paper, you may have been asked to describe how to prepare 250 cm³ of 0.100 mol dm⁻³ sodium carbonate solution. Weigh the required mass of anhydrous sodium carbonate in a weighing boat, transfer it to a beaker, and rinse the boat with distilled water into the beaker. Stir with a glass rod until dissolved.
标准溶液是浓度精确已知的溶液，常用于滴定。在 2019 年 6 月试卷中，可能要求你描述如何配制 250 cm³ 0.100 mol dm⁻³ 碳酸钠溶液。称取所需质量的无水碳酸钠于称量舟中，转移至烧杯，并用蒸馏水冲洗称量舟，洗液并入烧杯。用玻璃棒搅拌至溶解。
Then, use a funnel to pour the solution into a 250 cm³ volumetric flask. Rinse the beaker and glass rod several times with distilled water and add the washings to the flask. Finally, make up to the mark carefully using a dropping pipette until the bottom of the meniscus sits exactly on the line. Stopper the flask and invert it 10‑15 times to achieve homogeneity. If the solid is not anhydrous, or if it absorbs moisture from the air, the actual concentration will be lower than intended.
然后，通过漏斗将溶液转移至 250 cm³ 容量瓶。用蒸馏水多次清洗烧杯和玻璃棒，并将洗液全部转入容量瓶。最后，用胶头滴管小心定容至刻线，使弯月面底部刚好与线相切。塞紧瓶塞，倒转摇匀 10–15 次至均匀。若固体不是无水的，或易吸潮，则实际浓度会低于预期值。
9. Observing and Recording Data | 观察与数据记录
Good practical work requires systematic recording. In the 2019 exam, tables for titrations, temperature readings, or rate data had to be completed. Always label columns with the quantity measured (e.g. “Volume of HCl / cm³”) and include units. Record all raw data with the appropriate precision, and never rewrite a value that appears ‘wrong’—if it is an outlier, discard it during analysis with a reason.
良好的实验操作需要系统记录。2019 年考试中，需要填写滴定、温度读数或速率数据表格。务必将记录的量（如“盐酸体积 / cm³”）和单位标在表头。以合适的精度记录所有原始数据，切勿篡改看似“错误”的数值——若为离群值，则在分析时说明理由后剔除。
h quantity and unit, plot points as small crosses or dots with a circle, and draw the best‑fit line or smooth curve. For temperature‑ imum or minimum temperature. In rate graphs, the tangent at t = 0 can be difficult to draw—se using a transparent ruler and mirror method or drawing two tangents to see consistency.
绘制图表时，选择能占满一半以上图纸的标度，用量的名称和单位标注坐标轴，描点用细十字或圆点，并绘制最佳拟合线或平滑曲线。在量热法中的温度 – 时间图上，外推至混合时间以求得理论最高或最低温度。对于反应速率的初速率切线，可借助透明直尺和镜像法，或绘制两条切线以确认一致性。
10. Identifying Sources of Error and Suggesting Improvements | 误差来源分析与改进建议
Examiners love asking how an experiment could be modified to reduce uncertainty. For the magnesium–acid molar volume experiment, a significant error is losing hydrogen before the bung is inserted—using a side‑arm flask with the acid in the side arm and magnesium in the main flask, then mixing by tilting, can eliminate this loss. A thermostatically controlled water bath can minimise temperature fluctuations in rate experiments.
考官喜欢问如何改进实验以减小不确定度。对于镁与酸测定摩尔体积的实验，一个重大误差是塞入橡胶塞前的氢气损失——改用具侧臂的锥形瓶，将酸液置于侧臂内，镁置于主瓶中，倾斜即可混合，可避免这种损失。在速率实验中，恒温水浴可最大限度地减少温度波动。
Using a top‑pan balance to record mass changes for a reaction that produces a gas (e.g. marble chips with acid) is another common set‑up. Placing a cotton wool plug in the mouth of the flask prevents acid spray from escaping while allowing gas to leave. Always think about whether an error is systematic (e.g. faulty balance) or random (e.g. reading a burette incorrectly), and suggest specific changes such as calibrating the balance or using a burette with a narrower bore.
使用托盘天平记录产生气体的反应（如大理石与酸）的质量变化，是另一种常见装置。在瓶口放置棉花塞可以防止酸雾逸出，同时允许气体通过。始终判断误差是系统性的（如天平不准）还是随机性的（如滴定管读数不准），并针对性地提出改进，例如校准天平或改用内径更窄的滴定管。
11. Applying June 2019 Paper Insights to Your Revision | 借鉴 2019 年 6 月试卷要点进行复习
The June 2019 Unit 1 paper reminded candidates that practical questions can appear in multiple sections—not only in the dedicated practical‑based question but also in the multiple‑choice and short‑answer sections. Revising the step‑by‑step calculation of titre, the conversion of gas volumes to moles, and the construction of enthalpy cycles from experimental ΔH is essential. It also tested how to interpret a temperature‑time graph when a solid dissolves and how to identify the end point in a weak acid–strong base titration without an indicator.
2019 年 6 月单元1 试卷提醒考生，实验相关题目可能出现在整卷的多个部分——不仅限于专门的实验设计题，选择题和简答题中也会涉及。复习时应重视滴度值的逐步计算、气体体积换算成物质的量、以及从实验 ΔH 构建焓变循环。试卷还测试了如何解读固体溶解时的温度 – 时间图，以及在弱酸–强碱滴定中不借助指示剂如何判定终点。
Work through past paper questions that ask you to identify the apparatus needed for heating under reflux, for distillation, or for collecting a gas over water. Be prepared to draw and label a quick sketch, because the June 2019 set required a labelled diagram for a simple calorimeter and a gas collection set‑up. Always use a sharp pencil in the exam, and label with simple, clear lines.
练习历年真题中要求你选择回流加热、蒸馏或排水集气装置的问题。准备好画出并标注简单的示意图，因为 2019 年 6 月要求绘制标有注释的简易量热器和气体收集装置。考试时务必使用削好的铅笔，并用简洁清晰的线条标注。
12. Summary and Final Tips | 总结与最后提示
Mastering experimental techniques for AS Chemistry Unit 1 is about precision, consistency, and an understanding of the underlying principles. From correctly reading a burette to planning a calorimetry run with proper cooling corrections, every detail can mean an extra mark on the paper. The June 2019 exam paper highlighted that theory and practical skill go hand in hand: you must not only know how to perform a titration but also be able to explain why concordant results are expected and how to treat anomalous data.
掌握 AS 化学单元1 的实验技术，在于精确、一致以及对基本原理的理解。从正确读取滴定管到规划带冷却校正的量热实验，每个细节都可能为你赢得宝贵的分数。2019 年 6 月试卷强调，理论与实践密不可分——你不仅要懂得如何完成滴定，还要能解释为什么期待得到吻合结果，以及如何处理异常数据。
As you revise, practise drawing apparatus set‑ups with all connections labelled, rehearse calculations for ΔH, molar volume, and concentrations, and always link an observation to a balanced equation. Keep a list of common errors (e.g. parallax error, heat loss, incomplete solubility) and the corresponding improvements. This reflective approach, combined with hands‑on practice, will ensure you are fully prepared for any experimental challenge Unit 1 throws at you.
复习时，练习绘制标注完整接口的装置图，反复演练 ΔH、摩尔体积和浓度的计算，并始终将观察结果与配平的化学方程式联系起来。整理一份常见错误（如视差、热损失、溶解不完全）及其改进措施的清单。这种反思性方法结合动手实践，将确保你充分准备好应对单元1 可能出现的任何实验挑战。
Published by TutorHao | Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图