📚 Mastering Experimental Techniques in the January 2023 AS Chemistry Unit 1 Exam | 掌握2023年1月AS化学单元1考试中的实验技术
The January 2023 AS Chemistry Unit 1 paper requires students not only to recall theoretical knowledge but also to apply precise experimental techniques. Questions frequently probe the candidate’s understanding of how to set up apparatus, minimise errors, and interpret data collected in the laboratory. Mastering these practical skills is essential for achieving high marks in the calculations and evaluation sections.
2023年1月的AS化学单元1试卷不仅要求学生回忆理论知识，还要求运用精确的实验操作。考题经常考察考生对如何搭建装置、减少误差以及分析实验中采集数据的理解。掌握这些实践技能对于在计算和评估部分拿到高分至关重要。
1. Preparing a Standard Solution | 配制标准溶液
Begin by calculating the mass of pure solid required to make a solution of known concentration. Use a balance with at least 0.01 g precision and a clean, dry weighing boat.
首先计算配制已知浓度溶液所需纯固体的质量。使用精度至少为0.01 g的天平和干净干燥的称量舟。
Weigh the empty boat, tare the balance, then add the solid and record the mass precisely. Transfer the solid into a beaker, rinse any remaining solid from the boat with distilled water, and stir to dissolve.
称量空舟，去皮，然后加入固体并准确记录质量。将固体转移至烧杯中，用蒸馏水冲洗称量舟上残留的固体，搅拌至溶解。
Transfer the solution completely into a volumetric flask of the appropriate size using a funnel. Rinse the beaker and funnel several times, adding all washings to the flask.
使用漏斗将溶液完全转移至合适容量的容量瓶中。冲洗烧杯和漏斗几次，将所有洗涤液都转移到容量瓶中。
Make up to the mark with distilled water, using a dropper to add the last few drops until the bottom of the meniscus just touches the calibration line. Stopper and invert several times to mix thoroughly.
用蒸馏水定容至刻度线，使用滴管加入最后几滴，直到弯月面的底部刚好触及标线。塞紧瓶塞并反复颠倒几次以彻底混合。
2. Acid-Base Titration Technique | 酸碱滴定技术
Rinse the burette with the titrant solution first to avoid dilution. Fill the burette, check for air bubbles in the tip, and record the initial reading to ±0.05 cm³.
先用滴定剂溶液润洗滴定管以避免稀释。装满滴定管，检查尖端是否有气泡，并记录初始读数至±0.05 cm³。
Use a pipette and pipette filler to transfer exactly 25.0 cm³ of the analyte into a clean conical flask. Do not blow out the last drop remaining in the pipette tip.
使用移液管和洗耳球吸取恰好25.0 cm³的待测液到干净的锥形瓶中。不要吹出留在移液管尖端的最后一滴。
Add a few drops of suitable indicator and swirl constantly while running the titrant from the burette. Add the titrant dropwise near the end point, washing down the walls of the flask if needed.
加入几滴合适的指示剂，不断摇动锥形瓶并从滴定管加入滴定剂。接近终点时逐滴滴加，必要时冲洗瓶壁。
Record the final burette reading when a permanent colour change indicates the end point. Repeat until two concordant titres are obtained, differing by no more than 0.10 cm³.
当出现持久的颜色变化即表明到达终点时，记录滴定管最终读数。重复直至得到两次相差不超过0.10 cm³的吻合滴定体积。
c₁V₁ = c₂V₂
c₁V₁ = c₂V₂
3. Back Titration Calculations | 返滴定计算
When a solid is impure or reacts incompletely, a known excess of standard acid is added. The unreacted acid is then titrated with a standard base to determine how much acid was consumed by the sample.
当固体不纯或反应不完全时，加入已知过量的标准酸。然后用标准碱滴定未反应的酸，以确定样品消耗了多少酸。
Write balanced chemical equations for both the reaction with the solid and the titration reaction. Calculate the total moles of acid added, then subtract the moles titrated to find the moles that reacted with the sample.
写出固体反应和滴定反应的配平化学方程式。计算加入酸的总物质的量，然后减去被滴定的物质的量，得出与样品反应的物质的量。
Use the stoichiometric ratio to find the moles of the desired substance in the solid. Convert to mass and express as a percentage purity if required.
使用化学计量比求出固体中目标物质的物质的量。转化为质量，若需要则表示为纯度百分比。
Common pitfalls include forgetting to account for the dilution of the reaction mixture before titration and misinterpreting which indicator to use.
常见的失误包括忘记考虑滴定前反应混合物的稀释以及误判应使用哪种指示剂。
4. Measuring Gas Volumes | 测量气体体积
Use a gas syringe or an inverted measuring cylinder over a trough of water to collect gas evolved from a reaction. Ensure all connections are airtight and the syringe barrel moves freely.
使用气体注射器或在水槽中倒扣的量筒来收集反应产生的气体。确保所有连接处不漏气，注射器管筒可以自由移动。
If collecting over water, correct for the vapour pressure of water when using the ideal gas equation. The measured pressure must account for the partial pressure of the dry gas.
如果是排水集气，在应用理想气体状态方程时要校正水的蒸气压。测量的压力必须考虑干气体的分压。
Record the volume at regular time intervals to monitor the rate of reaction. In the exam, you may be asked to plot a graph of volume against time and determine initial rate from the tangent at t = 0.
定期记录气体体积以监测反应速率。考试中可能要求绘制体积-时间图，并通过t = 0时的切线求初始速率。
pV = nRT
pV = nRT
5. Determining Relative Molecular Mass of a Volatile Liquid | 测定挥发性液体的相对分子质量
This classic experiment involves injecting a small volume of volatile liquid into a pre-weighed gas syringe heated in an oven. The liquid vaporises, and the syringe plunger moves to record the volume of gas produced at a known temperature and pressure.
这个经典实验是将少量挥发性液体注入预先称量的、在烘箱中加热的气体注射器中。液体气化，注射器活塞移动以记录在已知温度和压力下产生的气体体积。
Weigh the syringe before and after injection to obtain the mass of the liquid. Use the ideal gas equation to calculate the number of moles, then divide the mass by moles to obtain Mᵣ.
在注射前后称量注射器以获得液体的质量。使用理想气体状态方程计算物质的量，然后用质量除以物质的量得到相对分子质量Mᵣ。
Sources of error include liquid evaporating during the injection, temperature fluctuation in the oven, and incomplete vaporisation. Repeat measurements increase reliability.
误差来源包括注射过程中液体蒸发、烘箱温度波动以及气化不完全。重复测量可提高可靠性。
6. Enthalpy Change Measurement (Calorimetry) | 焓变测量（量热法）
Measure a known volume of solution into an expanded polystyrene cup and record its initial temperature. Add a known quantity of another reactant, stir, and note the highest or lowest temperature reached.
量取已知体积的溶液放入聚苯乙烯杯中，记录其初始温度。加入一定量的另一种反应物，搅拌，并记录达到的最高或最低温度。
Calculate the heat energy change using q = m c ΔT, where m is the total mass of the solution (assuming density 1 g cm⁻³), c is the specific heat capacity (4.18 J g⁻¹ K⁻¹ for water), and ΔT is the temperature change.
使用 q = m c ΔT 计算热量变化，其中 m 是溶液总质量（假设密度为1 g cm⁻³），c 是比热容（水的为4.18 J g⁻¹ K⁻¹），ΔT 是温度变化。
Convert q to kJ and divide by the moles of the limiting reactant to obtain ΔH in kJ mol⁻¹. Apply a sign: negative for exothermic, positive for endothermic.
将 q 转化为 kJ，除以限制反应物的物质的量，得到 ΔH（单位 kJ mol⁻¹）。加上符号：放热为负，吸热为正。
To reduce heat loss, use a lid, avoid touching the cup, and extrapolate the cooling curve if the temperature change is not instantaneous.
为了减少热损失，使用盖子，避免接触杯体，如果温度变化不是瞬间完成的，可以用冷却曲线外推法校正。
7. Finding the Formula of a Hydrated Salt | 确定水合盐的化学式
Weigh an empty crucible and lid, then add a known mass of hydrated salt. Heat gently at first, then strongly with a Bunsen burner, until the mass becomes constant, indicating all water of crystallisation has been driven off.
称量空坩埚和坩埚盖，然后加入已知质量的水合盐。先缓慢加热，然后用本生灯强热，直至质量恒定，表示所有结晶水已除去。
Cool in a desiccator to prevent re-absorption of moisture. Weigh again to find the mass of the anhydrous salt.
在干燥器中冷却以防止重新吸收水分。再次称量得到无水盐的质量。
Calculate the mass of water lost, convert both masses to moles, and find the simplest whole-number ratio x in salt·xH₂O.
计算失去的水的质量，将两种质量都转化为物质的量，并求出盐·xH₂O 中最简整数比 x。
Handle the hot crucible with tongs and safety goggles. Overheating may decompose the salt, leading to inaccurate results.
用坩埚钳夹取热坩埚并佩戴防护眼镜。过度加热可能会导致盐分解，带来不准确的结果。
8. Investigating Reaction Rate by Gas Collection | 通过气体收集研究反应速率
Set up a flask containing one reactant, connect it to a gas syringe, and quickly add the other reactant. Start the stopwatch immediately after mixing.
搭建一个装有某种反应物的烧瓶，连接到气体注射器上，然后迅速加入另一种反应物。混合后立即启动秒表。
Record the gas volume at 10–15 second intervals for several minutes. Plot volume against time, and draw tangents at different concentrations or temperatures to compare rates.
每隔10–15秒记录一次气体体积，持续几分钟。绘制体积-时间图，并在不同浓度或温度下画切线以比较速率。
The initial rate is found from the gradient of the tangent at t = 0. You can then deduce the order of reaction with respect to a particular reactant by changing its concentration.
初始速率由 t = 0 时切线的斜率求得。然后可以通过改变某一反应物的浓度推断出该反应物的反应级数。
Ensure the syringe plunger is frictionless and the apparatus is airtight. If the gas is soluble in water, avoid using the water-displacement method.
保证注射器活塞可自由滑动且装置气密。如果气体溶于水，应避免使用排水集气法。
9. Solvent Extraction and Simple Distillation | 溶剂萃取与简单蒸馏
If an organic product is in aqueous solution, a separating funnel is used with an immiscible organic solvent. Shake gently, venting frequently, then allow the layers to separate.
如果有机产物在水溶液中，使用分液漏斗和一种不混溶的有机溶剂。轻轻振荡，频繁排气，然后让液层分离。
Run off the lower aqueous layer, retaining the organic layer. Dry the organic layer with an anhydrous salt such as MgSO₄ or CaCl₂ before distillation.
放出下层水相，保留有机层。在蒸馏前用无水盐（如 MgSO₄ 或 CaCl₂）干燥有机层。
Set up a simple distillation apparatus with a thermometer positioned at the still-head to measure the boiling point of the distillate. Collect the fraction that boils at the expected temperature of the pure compound.
搭建简单蒸馏装置，温度计置于蒸馏头以测量馏出物的沸点。收集在纯化合物预期沸点下蒸出的馏分。
Use anti-bumping granules to prevent vigorous boiling. Distill slowly to obtain a purer product and avoid overheating.
使用止沸剂防止暴沸。缓慢蒸馏以获得更纯的产品并避免过热。
10. Common Errors and Improvements in Titration and Volumetric Analysis | 滴定与容量分析中的常见错误和改进
Parallax error when reading the meniscus – always align your eye at the same level as the mark and use the bottom of the concave meniscus for colourless solutions.
读取弯月面时的视差错误——始终将眼睛与标线保持同一水平，对于无色溶液读取凹液面底部。
Not rinsing the burette and pipette with their respective solutions causes dilution, leading to a systematically lower or higher titre. Rinse each apparatus 2–3 times with the solution it will contain.
未用相应溶液润洗滴定管和移液管会导致稀释，造成滴定体积系统性地偏低或偏高。每种仪器都要用待盛装溶液润洗2–3次。
Leaving the funnel in the top of the burette during titration can add extra drops, distorting the reading. Remove the funnel after filling.
滴定过程中将漏斗留在滴定管顶端可能会额外增加液滴，扭曲读数。加液后应将漏斗取下。
Using a dirty or wet conical flask for the analyte is acceptable as it does not change the number of moles of analyte, but adding excess deionised water can affect the indicator’s end point if the solution becomes too dilute.
使用不干净或湿润的锥形瓶盛装待测液是可接受的，因为这不会改变待测物的物质的量，但如果加入过量的去离子水使溶液过稀，可能会影响指示剂的终点。
For colorimetric indicators, the end point should be a single drop change. Practice identifying the point where the colour first remains for 10 seconds after swirling.
对于颜色指示剂，终点应为一滴之差。练习辨认在摇动后颜色首次持续10秒不变的点。
Systematic errors like faulty balance calibration can be identified by repeating with different equipment. Use both blank titrations and standardised solutions to improve accuracy.
像天平校准有误这类的系统误差可以通过更换设备重复实验来发现。使用空白滴定和经标定的溶液可提高准确度。
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