Year 12 CIE Chemistry: Practical Examination Skills | 12年级CIE化学：实验考核要点

📚 Year 12 CIE Chemistry: Practical Examination Skills | 12年级CIE化学：实验考核要点

The practical assessment in CIE AS Level Chemistry (Paper 3) tests your ability to handle apparatus, make accurate measurements, record data, and analyze results. This guide consolidates the key techniques and common pitfalls to help you excel in the practical examination.

CIE AS 化学（试卷3）的实验考核测试你操作仪器、准确测量、记录数据和分析结果的能力。本指南汇总了关键技巧和常见失误，助你在实验考试中脱颖而出。

---

1. Safety First and Core Apparatus | 安全第一与核心仪器

Before any experiment, ensure you wear safety goggles and a lab coat. Tie back long hair and avoid loose clothing. Know the location of the safety shower, eyewash station, and fire extinguisher.

在任何实验前，务必佩戴护目镜和实验服。扎起长发，避免穿着宽松衣物。熟悉紧急淋浴器、洗眼器和灭火器的位置。

Basic glassware includes beakers, conical flasks, test tubes, and measuring cylinders. When heating, use heat-resistant borosilicate glass and always check for cracks beforehand. Crucibles, evaporating dishes, and tripods with gauze are used for heating solids or solutions.

基本玻璃器皿包括烧杯、锥形瓶、试管和量筒。加热时使用耐热硼硅玻璃，并提前检查是否出现裂纹。坩埚、蒸发皿和三脚架配石棉网用于加热固体或溶液。

---

2. Mastering Mass Measurements | 掌握质量测量

Use an analytical balance that reads to 0.001 g or better. Place a weighing boat on the pan, tare (zero) the balance, then add the solid. Never place chemicals directly on the pan.

使用精确到 0.001 g 或更好的分析天平。将称量舟放在秤盘上，去皮归零后再加入固体。切勿将化学品直接放在秤盘上。

Record the mass immediately and check that the reading stabilises. Close the balance doors to avoid air currents. Consistent technique ensures reliable masses for preparing standard solutions or measuring mass loss.

立即记录质量并确认读数稳定。关闭天平罩门以防止气流干扰。一致的操作可确保标准溶液配制或质量损失测量的可靠性。

---

3. Precise Volume Measurements | 精确的体积测量

Use a volumetric pipette with a pipette filler to transfer an exact aliquot (e.g. 25.0 cm³). Rinse the pipette with the solution to be transferred before use. Allow the solution to drain, touching the tip to the side of the flask; do not blow out the last drop.

使用单标移液管配合吸耳球转移精确体积（如 25.0 cm³）。使用前用待转移溶液润洗移液管。让溶液自然流下，将管尖接触瓶壁；不要吹出最后一滴。

A burette delivers variable volumes to 0.05 cm³ resolution. Rinse the burette with the titrant, fill past the zero mark, and open the tap to remove air bubbles in the tip. Always read the bottom of the meniscus with your eye at the same level as the liquid surface.

滴定管可准确读取至 0.05 cm³。用滴定液润洗，加液至零刻度以上，打开旋塞排出尖嘴处的气泡。视线与液面齐平，读取弯月面底部。

Volumetric flasks are used to prepare solutions of known concentration. Dissolve the weighed solid in a beaker, transfer all washes to the flask, and fill to the graduation mark. Invert the stoppered flask several times to mix thoroughly.

容量瓶用于配制已知浓度的溶液。在烧杯中溶解称量的固体，将所有洗涤液转移至容量瓶，加水至刻度线。盖紧瓶塞，反复颠倒充分混匀。

---

4. The Art of Titration | 滴定艺术

A titration requires a standard solution and an indicator. Choose an indicator whose pH range matches the equivalence point: phenolphthalein for a strong base–strong acid or weak acid–strong base titration; methyl orange for a strong acid–weak base.

滴定需要标准溶液和指示剂。所选指示剂的 pH 变色范围应与等当点匹配：强碱–强酸或弱酸–强碱滴定用酚酞；强酸–弱碱用甲基橙。

Swirl the conical flask constantly while adding titrant from the burette. As the end point approaches, add the titrant dropwise. The end point is when the indicator colour changes permanently (e.g. phenolphthalein from pink to colourless).

滴定管放液时持续摇荡锥形瓶。接近终点时逐滴加入滴定液。终点时指示剂发生永久颜色变化（如酚酞由粉红变为无色）。

NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

Record the initial and final burette readings for each trial. Repeat the titration until two concordant results are obtained (volumes within 0.10 cm³ of each other). Calculate the mean titre from concordant values.

记录每次初读数和终读数。重复滴定直至获得两组精密度在 0.10 cm³ 以内的读数，取其平均值作为滴定剂用量。

---

5. Investigating Enthalpy Changes | 研究焓变

Use a polystyrene cup as a simple calorimeter, placed in a beaker for support. Measure a known volume of solution, record its initial temperature, and add a known mass of solid or another solution. Stir gently and record the maximum (or minimum) temperature reached.

用聚苯乙烯杯作为简易量热计，置于烧杯中固定。量取已知体积的溶液，记录初始温度，加入已知质量的固体或另一溶液。轻轻搅拌，记录达到的最高（或最低）温度。

Calculate the heat transferred using q = m c ΔT, where m is the total mass of solution (in g, assuming density ≈ 1 g cm⁻³), c is the specific heat capacity (usually 4.18 J g⁻¹ K⁻¹), and ΔT is the temperature change. Then find the enthalpy change per mole, ΔH = −q / n.

用 q = m c ΔT 计算热量，其中 m 为溶液总质量（g，假设密度约 1 g cm⁻³），c 是比热容（通常 4.18 J g⁻¹ K⁻¹），ΔT 为温度变化。再计算摩尔焓变，ΔH = −q / n。

To reduce heat loss, use a lid and insulate the sides. For a slow reaction, plot a temperature–time graph and extrapolate back to the time of mixing to obtain a corrected ΔT.

为减少热损失，可加盖并隔热。对于缓慢的反应，绘制温度–时间图，外推至混合时刻以校正 ΔT。

---

6. Following Reaction Rates | 追踪反应速率

To monitor the rate of a reaction, you can measure the volume of gas evolved (e.g. Mg + HCl → H₂), the loss in mass (e.g. CaCO₃ + HCl → CO₂), or the time taken for a precipitate to obscure a mark (the ‘disappearing cross’ with Na₂S₂O₃ and HCl).

监测反应速率时，可测量产生的气体体积（如 Mg + HCl → H₂）、质量的减少（如 CaCO₃ + HCl → CO₂），或沉淀遮蔽标记所需的时间（如 Na₂S₂O₃ 与 HCl 的“消失的十字”实验）。

In the gas volume method, use a gas syringe or inverted measuring cylinder in a trough of water. Ensure all connections are airtight. Record the volume at regular time intervals and plot a graph of volume against time.

在气体体积法中，使用气体注射器或在水槽中倒置量筒。确保所有连接气密。每隔固定时间记录体积，并绘制体积–时间图。

Na₂S₂O₃(aq) + 2HCl(aq) → 2NaCl(aq) + S(s) + SO₂(g) + H₂O(l)

The initial rate can be found by drawing a tangent at t = 0 on the concentration–time or volume–time curve. Compare rates under different conditions to deduce the effect of concentration or temperature.

通过在浓度–时间或体积–时间曲线上 t = 0 处作切线可求得初始速率。比较不同条件下的速率，可推断浓度或温度的影响。

---

7. Handling and Measuring Gases | 处理与测量气体

Gases are often collected over water in an inverted measuring cylinder. A delivery tube from the reaction vessel leads gas into the cylinder. The gas collected is saturated with water vapour, so correct the pressure accordingly if calculating the molar volume.

气体常用排水集气法在倒置量筒中收集。反应容器的导管将气体导入量筒。收集到的气体含水蒸气，若计算摩尔体积应考虑水蒸气压校正。

At room temperature and pressure (RTP: 20 °C, 1 atm), one mole of any gas occupies approximately 24 dm³ (24,000 cm³). Use the ideal gas equation pV = nRT only if conditions differ significantly from RTP.

在常温常压（RTP: 20 °C, 1 atm）下，1 摩尔任何气体的体积约为 24 dm³（24,000 cm³）。只有当实验条件明显偏离 RTP 时，才需使用理想气体状态方程 pV = nRT。

For a reaction producing hydrogen, measure the mass of the magnesium ribbon accurately, record the volume of H₂ collected, and calculate the moles of gas. Compare with the theoretical volume to assess the efficiency of the collection method.

对于产生氢气的反应，准确称量镁带质量，记录收集的 H₂ 体积，计算气体的摩尔数。与理论体积比较，可评估收集方法的效率。

---

8. Qualitative Analysis: Identifying Ions | 定性分析：鉴定离子

Qualitative tests allow you to identify cations, anions, and gases. Use small volumes of sample and reagents, and record all observations clearly (precipitate colour, solubility in excess, gas evolution, odour).

定性分析可鉴定阳离子、阴离子和气体。使用少量样品和试剂，清楚地记录所有现象（沉淀颜色、过量时的溶解性、气体放出、气味）。

Common cation tests with NaOH(aq) are summarised below. The presence of aluminium, zinc, or lead ions gives a white precipitate that dissolves in excess NaOH, whereas transition metals give characteristic coloured precipitates.

以下是使用 NaOH(aq) 检验常见阳离子的总结。铝、锌或铅离子产生白色沉淀并溶于过量 NaOH，而过渡金属则产生特征颜色沉淀。

Cation / 阳离子	Test with NaOH(aq) / 加NaOH	Observation / 现象
Cu²⁺	Add NaOH dropwise, then in excess / 逐滴加NaOH，再过量	Blue precipitate, insoluble in excess / 蓝色沉淀，过量不溶
Fe²⁺	Add NaOH, let stand in air / 加NaOH，在空气中放置	Green precipitate turns brown at surface / 绿色沉淀，表面变棕
Fe³⁺	Add NaOH / 加NaOH	Red-brown precipitate / 红棕色沉淀
Al³⁺ / Zn²⁺ / Pb²⁺	Add NaOH dropwise, then excess / 逐滴加NaOH，再过量	White precipitate, soluble in excess giving colourless solution / 白色沉淀，溶于过量得无色溶液
Ca²⁺	Add NaOH / 加NaOH	White precipitate (insoluble in excess) / 白色沉淀（过量不溶）

For anions, add dilute nitric acid to remove interfering carbonate ions, then test with specific reagents. Key tests include

Published by TutorHao | Year 12 Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）