📚 Mastering Experimental Operations from A-Level Chemistry Unit 5 Jan 2019 Paper Insert | 掌握A-Level化学Unit 5 Jan 2019试卷插页中的实验操作
The January 2019 Edexcel IAL Chemistry Unit 5 (WCH05) paper insert provides a rich set of experimental data, tables and reaction schemes that directly test candidates' ability to interpret and design practical work. Understanding the experimental operations behind the insert is essential for mastering topics such as transition metal complex preparation, organic synthesis, spectroscopic analysis and volumetric titration. This article breaks down the key techniques and laboratory skills embedded in the insert, giving you the tools to confidently handle similar tasks in the examination.
2019年1月Edexcel IAL化学第五单元（WCH05）的试卷插页包含丰富的实验数据、表格和反应流程，直接考查考生解读与设计实验的能力。透彻理解插页背后的实验操作，是掌握过渡金属配合物制备、有机合成、光谱分析以及容量滴定等主题的关键。本文详细拆解插页中隐含的关键技术与实验技能，帮助你自信应对考试中的类似题目。
1. Preparation and Isolation of Transition Metal Complexes | 过渡金属配合物的制备与分离
Weigh approximately 4.0 g of copper(II) sulfate pentahydrate (CuSO₄·5H₂O) and dissolve it in 15 cm³ of warm distilled water in a 50 cm³ beaker. Stir the solution continuously with a glass rod until all crystals dissolve, forming a clear blue solution of [Cu(H₂O)₆]²⁺ ions.
称取约4.0 g五水硫酸铜（CuSO₄·5H₂O），在50 cm³烧杯中用15 cm³温热蒸馏水溶解。用玻璃棒持续搅拌，直至晶体全部溶解，得到含有[Cu(H₂O)₆]²⁺离子的清亮蓝色溶液。
In a fume cupboard, slowly add concentrated aqueous ammonia (NH₃, approximately 10 cm³) dropwise with constant stirring. A pale blue precipitate of copper(II) hydroxide, Cu(OH)₂, first appears. Upon further addition, the precipitate redissolves to yield a deep royal-blue solution containing the tetraamminecopper(II) complex, [Cu(NH₃)₄]²⁺. The balanced equation is:
在通风橱中，在持续搅拌下缓慢逐滴加入浓氨水（约10 cm³）。首先生成浅蓝色的氢氧化铜Cu(OH)₂沉淀。继续滴加氨水，沉淀复溶，得到深宝蓝色溶液，其中含有四氨合铜(II)配合物[Cu(NH₃)₄]²⁺。配平的离子方程式为：
Cu²⁺(aq) + 2NH₃(aq) + 2H₂O(l) → Cu(OH)₂(s) + 2NH₄⁺(aq)
Cu(OH)₂(s) + 4NH₃(aq) → [Cu(NH₃)₄]²⁺(aq) + 2OH⁻(aq)
Cool the mixture in an ice bath to promote crystallisation. Add an equal volume of ethanol slowly down the inside wall of the beaker to reduce the solubility of the complex. Deep blue needle-shaped crystals of [Cu(NH₃)₄]SO₄·H₂O will form. Filter the crystals using a Büchner funnel under reduced pressure, wash with a small amount of cold ethanol and then with a little diethyl ether. Transfer the product onto a watch glass and allow it to dry in a desiccator.
将混合物置于冰浴中冷却以促进结晶。沿烧杯内壁缓慢加入等体积的乙醇，降低配合物的溶解度。深度蓝色的针状晶体[Cu(NH₃)₄]SO₄·H₂O便会析出。使用布氏漏斗减压抽滤，先后用少量冷乙醇和少量乙醚洗涤晶体。将产品转移到表面皿上，放入干燥器中干燥。
2. Colour of Complex Solutions and Absorption Spectroscopy | 配合物溶液的颜色与吸收光谱
The deep blue colour of the tetraamminecopper(II) complex arises from d–d electron transitions within the partially filled 3d orbitals of the Cu²⁺ ion. In an octahedral field created by ammonia ligands, the energy gap (Δ) corresponds to the absorption of orange–yellow light, transmitting blue. The intensity of colour is directly proportional to the concentration of the absorbing species, as described by the Beer–Lambert law.
四氨合铜(II)配合物的深蓝色源自Cu²⁺离子部分填充的3d轨道中的d–d电子跃迁。在氨配体产生的八面体场中，能量差（Δ）对应于橙黄色光的吸收，从而透射出蓝色。颜色的强度与吸收物种的浓度成正比，遵循比尔–朗伯定律。
A typical insert might provide absorbance data measured at a fixed wavelength (e.g., 600 nm) using a colorimeter or a UV–Visible spectrophotometer. The table below shows a representative calibration set for [Cu(NH₃)₄]²⁺ solutions. A candidate would be expected to plot absorbance against concentration, determine the gradient and use it to calculate the unknown concentration of the complex in a sample.
典型的试卷插页可能会提供在固定波长（如600 nm）下使用比色计或紫外–可见分光光度计测得的吸光度数据。下表展示了[Cu(NH₃)₄]²⁺溶液的一组代表性校准数据。考生需要以吸光度对浓度作图，确定斜率，并由此计算样品中配合物的未知浓度。
| Concentration / mol dm⁻³ | Absorbance at 600 nm |
|---|---|
| 0.020 | 0.218 |
| 0.040 | 0.435 |
| 0.060 | 0.648 |
| 0.080 | 0.871 |
| 0.100 | 1.085 |
Accurate dilution technique is vital: use a volumetric pipette (e.g., 25.0 cm³) and a volumetric flask (e.g., 250.0 cm³) to prepare standard solutions. Always rinse the pipette with the stock solution before use and fill the flask to the graduation mark, ensuring the bottom of the meniscus touches the line.
精确的稀释技术至关重要：使用移液管（如25.0 cm³）和容量瓶（如250.0 cm³）配制标准溶液。使用前务必用储备液润洗移液管，并将容量瓶加液至刻度线，确保弯月面底部与刻度线相切。
3. Separating and Washing Organic Liquid Mixtures using a Separating Funnel | 有机液体混合物的分液与洗涤
The insert frequently features organic reaction mixtures that require work-up in a separating funnel, for example after esterification or nitration. First, pour the reaction mixture into the funnel and add an appropriate washing solution, such as saturated sodium hydrogencarbonate solution to neutralise excess acid. Place the stopper, invert the funnel and immediately open the tap to vent any CO₂ pressure.
试卷插页经常出现需要借助分液漏斗进行后处理的有机混合物，例如酯化或硝化后的反应液。首先，将反应混合物倒入分液漏斗，加入合适的洗涤液，如饱和碳酸氢钠溶液以中和过量酸。盖上瓶塞，倒置漏斗并立即打开活塞放出CO₂气体以泄压。
Shake the funnel gently while venting periodically. Allow the layers to separate completely. The denser aqueous layer (usually the lower layer) is run off carefully into a beaker. The organic layer remains in the funnel. Repeat the washing with water or brine as directed. Finally, pour the organic layer from the top of the funnel into a clean, dry conical flask and add a suitable drying agent, such as anhydrous magnesium sulfate or sodium sulfate. Swirl until the liquid becomes clear and the drying agent no longer clumps.
轻轻振摇漏斗，不时排放气体。静置，待两相彻底分层。密度较大的水层（通常为下层）小心放入烧杯中。有机层留在漏斗内。按指引依次用水或饱和食盐水重复洗涤。最后，将有机层从漏斗上口倒入干净干燥的锥形瓶中，加入适量干燥剂，如无水硫酸镁或无水硫酸钠。旋摇至液体澄清且干燥剂不再结块。
Gravity filtration or decantation removes the drying agent before further purification, such as distillation. Keeping the separating funnel operations methodical prevents emulsions and loss of yield.
在进一步纯化（如蒸馏）之前，通过重力过滤或倾析分离干燥剂。有条不紊地完成分液漏斗操作，能防止形成乳浊液，避免产率损失。
4. Reflux, Distillation and Boiling Point Determination | 回流、蒸馏与沸点测定
Many organic syntheses in the Unit 5 insert require heating under reflux to complete a reaction without loss of volatile components. Assemble a reflux apparatus with a round-bottom flask, a condenser mounted vertically and a heating mantle or water bath. Add anti-bumping granules to ensure smooth boiling. Heat the mixture so that the solvent vapours condense and drip back continually.
Unit 5插页中的许多有机合成需要加热回流，以便在不损失挥发性组分的情况下完成反应。组装回流装置，包括圆底烧瓶、垂直安装的冷凝管和加热套或水浴。加入防暴沸颗粒以确保平稳沸腾。加热混合物，使溶剂蒸气持续冷凝并回流。
After the reaction, simple distillation is used to separate the desired product from the solvent and impurities. Set up a distillation apparatus with a thermometer bulb placed exactly at the side arm of the still head. Record the temperature when the first drop of distillate is collected (boiling point range). A pure liquid distils over a narrow range (typically 1–2 °C), whereas an impure sample shows a broader range. This boiling point determination directly tests the purity of the isolated compound.
反应结束后，使用简单蒸馏将目标产物与溶剂及杂质分离。搭建蒸馏装置，将温度计水银球准确置于蒸馏头支管口处。收集第一滴馏出液时记录温度（沸程）。纯液体在一个窄区间（通常1–2 °C）内馏出，而不纯样品的沸程较宽。沸点测定可直接检验分离化合物的纯度。
The insert may provide a boiling point temperature and ask for identification of the liquid by comparison with a data table. Always correct the observed boiling point for atmospheric pressure if necessary. A common error is heating too strongly, causing superheating and a false boiling point reading; control the heating rate so that distillate drips at about one drop per second.
插页可能给出沸点温度，要求通过与数据表对比来鉴定液体。必要时需对观测沸点进行大气压校正。常见错误是加热过猛，导致过热和沸点读数失真；应控制加热速率，使馏出液约每秒一滴。
5. Precise Titration Technique | 精确滴定的实验技术
Volumetric analysis appears frequently in the mark schemes linked to the insert. Begin by rinsing the burette with the standard solution (e.g., 0.100 mol dm⁻³ potassium manganate(VII)). Fill the burette, remove the air bubble below the tap and record the initial volume to the nearest 0.05 cm³. Pipette 25.0 cm³ of the analyte (e.g., iron(II) sulfate solution acidified with dilute sulfuric acid) into a clean conical flask.
容量分析常出现在与插页相关的评分方案中。先用标准溶液（如0.100 mol dm⁻³高锰酸钾溶液）润洗滴定管。加液，赶走活塞下方气泡，记录初始体积，精确到0.05 cm³。用移液管吸取25.0 cm³待测液（如酸化硫酸亚铁溶液）置于洁净锥形瓶中。
Add a few drops of an appropriate indicator if needed (e.g., for acid-base titrations). For redox titrations using KMnO₄, the reagent itself acts as the indicator, turning from colourless to a permanent pale pink at the end point. Titrate slowly, swirling the flask continuously. Approach the end point dropwise, and occasionally wash down the inside walls of the flask with distilled water to ensure all reactants are in the bulk solution.
必要时加几滴合适的指示剂（如酸碱滴定）。使用KMnO₄的氧化还原滴定中，试剂本身即可作为指示剂，终点时溶液由无色变为稳定的浅粉色。缓慢滴定，持续旋摇锥形瓶。接近终点时逐滴加入，不时用蒸馏水冲洗瓶壁，确保所有反应物都进入主体溶液。
ained. The mean titre is used for calculations. The insert might give a set of titre values and ask candidates to identify outliers, calculate the mean and determine the purity or concentration of the original sample using stoichiometry.
记录终点读数，重复滴定直至获得符合要求的平行结果（偏差在±0.10 cm³以内）。取平均滴定体积用于计算。插页可能提供一组滴定值，要求考生识别离群值、计算平均值，并运用化学计量关系确定原始样品的纯度或浓度。
6. Melting Point Determination and Purity Assessment | 熔点的测定与纯度判断
Determining the melting point of a solid product prepared in a synthesis is a key technique encountered in the insert. A small amount of the dry, powdered sample is packed into a capillary tube to a depth of about 2–3 mm. The capillary is placed in a melting point apparatus (e.g., electrically heated block or Thiele tube) alongside a calibrated thermometer.
测定合成所得固体产品的熔点，是插页涉及的关键技术。取少量干燥粉末样品，装入毛细管，填充高度约2–3 mm。将毛细管置于熔点测定仪（如电加热块或提勒管）中，与已校准的温度计并排。
Heat the apparatus slowly (1–2 °C per minute) near the expected melting point range. Observe the temperature at which the first drop of liquid appears and the temperature at which the entire sample becomes a clear liquid. This range provides information on purity: a pure compound typically melts sharply within a 1–2 °C range, whereas the presence of impurities both lowers and broadens the melting range.
在接近预期熔点范围时缓慢加热（每分钟升高1–2 °C）。观察样品出现第一滴液体时的温度以及全部样品变为清亮液体时的温度。这一熔程可提供纯度信息：纯化合物通常在1–2 °C的窄范围内熔融，杂质的存在则会降低熔点并拓宽熔程。
The insert may show a melting point determination procedure and ask students to evaluate the technique. Common sources of error include heating too rapidly (leading to erroneous readings), packing the capillary too tightly, or using a wet sample. Insert data might require comparison with literature values to identify the compound or assess if recrystallisation was successful.
插页可能呈现熔点测定的操作，要求学生评价该技术。常见错误包括加热过快（导致读数不准）、毛细管装填过紧或使用含水样品。插页数据可能需要与文献值比较，以鉴定化合物或判断重结晶是否成功。
7. Thin Layer Chromatography (TLC) | 薄层色谱法
Thin layer chromatography (TLC) is a rapid analytical technique to monitor the progress of a reaction or check the purity of an organic product. A pencil baseline is drawn about 1 cm from the bottom of a TLC plate coated with silica gel. A small drop of the dissolved sample is spotted gently using a capillary tube, and the spot is allowed to dry.
薄层色谱法（TLC）是一种快速分析技术，用于监测反应进程或检查有机产品纯度。在涂有硅胶的TLC薄板底端约1 cm处用铅笔画一条基线。用毛细管轻轻点加一小滴溶解的样品，晾干。
Place the plate in a developing chamber containing a suitable solvent (the eluent) to a depth no greater than 0.5 cm, ensuring the solvent level is below the baseline. Cover the chamber and allow the solvent front to ascend until it reaches about 1 cm from the top. Remove the plate, immediately mark the solvent front, and visualise the spots under UV light or by placing the plate in an iodine jar. Calculate the retention factor Rf for each spot (distance moved by spot ÷ distance moved by solvent front).
将薄板放入装有合适溶剂（展开剂）的展开缸中，液面深度不超过0.5 cm，并确保溶剂液面低于基线。盖上缸盖，让溶剂前沿上升，直至距顶端约1 cm。取出薄板，立即标记溶剂前沿，在紫外灯下或用碘缸显色。计算每个斑点的比移值Rf（斑点移动距离÷溶剂前沿移动距离）。
The insert might show a developed TLC plate with several spots and ask for identification of components by comparison with Rf values of known standards. Ensure that the pencil baseline is drawn lightly to avoid scratching the silica layer, and always use a fresh capillary for each sample to prevent cross-contamination.
插页可能展示一块已展开的TLC板，上面有多个斑点，要求通过与已知标准品的Rf值进行对比来识别组分。注意用铅笔轻轻画出基线，避免刮伤硅胶层；每种样品务必使用新的毛细管，防止交叉污染。
8. Experimental Data Analysis and Error Handling | 实验数据分析与误差处理
The Jan 2019 insert often includes a results table or graph that candidates must interpret. Systematic errors (e.g., a wrongly calibrated balance or a burette with a constant zero error) affect accuracy but not precision. Random errors (e.g., inconsistent reading of the meniscus) affect precision and can be reduced by performing replicates.
2019年1月的插页常包含一张结果表或图表，要求考生加以解读。系统误差（如天平未正确校准或滴定管存在固定零位误差）影响准确度但不影响精密度。随机误差（如弯月面读数不一致）影响精密度，可通过重复实验来减小。
percentage uncertainties by adding the percentage uncertainty of each measurement (e.g., a pipette uncertainty of ±0.06 cm³ on a 25.0 cm³ volume gives a percentage uncertainty of 0.24% overall uncertainty is used to assess whether the result falls within an acceptable range.
计算符合要求的滴定体积平均值，利用配平方程式中的化学计量比求出未知物的物质的量。通过将每个测量值的百分不确定度相加来传递误差（例如，25.0 cm³移液管的不确定度为±0.06 cm³，百分不确定度为0.24%）。总体不确定度用于评估结果是否在可接受范围之内。
When a graph is plotted, the uncertainty can also be represented by error bars. The gradient of the best-fit line and the steepest/shallowest acceptable lines provide the uncertainty in the gradient. Always state results with appropriate significant figures, reflecting the precision of the measuring instruments used.
绘制图形时，不确定度也可用误差棒表示。最佳拟合直线的斜率与最陡/最缓可接受直线的斜率之差，给出斜率的不确定度。始终以恰当的有效数字给出结果，反映所用测量仪器的精密度。
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