📚 CH01-INS January 2023: Enthalpy of Neutralisation Practical Walkthrough | CH01-INS 2023年1月：中和焓实验操作详解
The January 2023 International AS Chemistry Unit 1 Insert (CH01-INS) guided students through the classic enthalpy change of neutralisation experiment. This article breaks down the practical steps, data handling and exam pitfalls using the actual insert format. Whether you are preparing for a lab session or revising for your exam, mastering every detail of this procedure is essential for top marks.
2023年1月国际AS化学单元1插入材料（CH01-INS）指导学生完成经典的中和焓变实验。本文依据真实的插入材料格式，拆解实验操作、数据处理和考试陷阱。无论你是在准备实验课还是备考复习，彻底掌握这个操作的每一个细节都是拿高分的关键。
1. Introduction to the Insert | 插入材料简介
The insert titled ‘Determination of the enthalpy change of neutralisation between hydrochloric acid and sodium hydroxide’ provides a list of apparatus, reagents, a step‑by‑step method and a blank results table. Students are expected to follow it precisely, record temperatures, plot a graph and calculate ΔHneut. This article mirrors that structure while adding the theory and common examiner comments.
这份插入材料题为“测定盐酸与氢氧化钠中和反应的焓变”，提供了一份仪器和试剂清单、分步操作说明以及一张空白结果记录表。学生需要严格遵循步骤，记录温度，绘制图像并计算中和焓（ΔHneut）。本文复现该结构，同时补充理论解释和考官常见点评。
2. Apparatus and Chemicals Listed | 所列仪器与化学品
The insert specifies: a polystyrene cup (calorimeter) with lid, a 100 cm³ measuring cylinder, a thermometer (0–50 °C, ±0.1 °C), a stopwatch, 2.0 mol dm⁻³ hydrochloric acid, 2.0 mol dm⁻³ sodium hydroxide solution, and wash bottles. No beaker or conical flask is used as the reaction vessel – the expanded polystyrene cup minimises heat exchange with the surroundings.
插入材料列出的仪器包括：带盖的聚苯乙烯杯（量热计）、100 cm³量筒、温度计（0–50 °C，精度±0.1 °C）、秒表、2.0 mol dm⁻³盐酸、2.0 mol dm⁻³氢氧化钠溶液和洗瓶。反应容器不使用烧杯或锥形瓶——发泡聚苯乙烯杯可以最大限度减少与周围环境的热交换。
3. Understanding the Principle | 理解实验原理
Strong acid–strong base neutralisation is essentially a reaction between H⁺(aq) and OH⁻(aq) forming H₂O(l). At constant pressure, the heat released (q) equals the mass of the solution × specific heat capacity × temperature rise. By dividing q by the amount of water formed (in moles), we obtain ΔHneut, which for HCl–NaOH should be close to −57.1 kJ mol⁻¹.
强酸与强碱的中和在本质上是 H⁺(aq) 与 OH⁻(aq) 结合生成 H₂O(l) 的反应。在恒压条件下，放出的热量（q）等于溶液质量 × 比热容 × 温度升高值。用 q 除以生成水的物质的量，即可得到 ΔHneut，对于 HCl 与 NaOH 反应，该值应接近 −57.1 kJ mol⁻¹。
4. Step‑by‑Step Procedure | 分步操作流程
Step 1: Measure exactly 50.0 cm³ of 2.0 mol dm⁻³ HCl using the measuring cylinder and pour it into the polystyrene cup. Record its initial temperature every 30 seconds for 2 minutes to establish a steady baseline.
Step 2: Measure 50.0 cm³ of 2.0 mol dm⁻³ NaOH. Rinse the thermometer and, at exactly the 3‑minute mark, quickly add the NaOH to the acid, stir gently with the thermometer and start the stopwatch.
Step 3: Continue recording the temperature every 30 seconds for a further 8–10 minutes until a clear cooling trend is visible.
步骤1：用量筒准确量取 50.0 cm³ 2.0 mol dm⁻³ HCl，倒入聚苯乙烯杯中。在 2 分钟内每隔 30 秒记录一次初始温度，建立稳定基线。
步骤2：量取 50.0 cm³ 2.0 mol dm⁻³ NaOH。润洗温度计，在恰好 3 分钟时迅速将 NaOH 加入酸中，用温度计轻轻搅拌，同时启动秒表。
步骤3：继续每 30 秒记录一次温度，持续 8–10 分钟，直至观察到明显的降温趋势。
5. Recording Temperature Readings | 记录温度读数
The insert provides a table with columns for time/min and temperature/°C. Below is a typical set of results as you might collect in the lab. The first 2 minutes show a constant acid temperature, then a sharp jump at mixing, followed by gradual cooling.
插入材料提供的记录表包含时间/min 与温度/°C 两列。下面是你在实验中可能收集到的一组典型数据：前 2 分钟酸的温度保持恒定，混合时温度急剧上升，然后缓慢下降。
| Time / min | Temperature / °C |
|---|---|
| 0.0 | 21.0 |
| 0.5 | 21.0 |
| 1.0 | 21.0 |
| 1.5 | 21.0 |
| 2.0 | 21.0 |
| 2.5 | 21.0 |
| 3.0 (mix) | — |
| 3.5 | 33.5 |
| 4.0 | 33.4 |
| 4.5 | 33.2 |
| 5.0 | 33.0 |
| 6.0 | 32.5 |
| 7.0 | 32.0 |
| 8.0 | 31.6 |
6. Temperature Correction and Extrapolation | 温度校正与外推法
Because the temperature starts to drop immediately after mixing due to heat loss, the measured maximum (33.5 °C) is lower than the true theoretical temperature rise. The insert guides you to plot temperature against time and draw two best‑fit lines: one through the pre‑mixing points and another through the post‑mixing cooling points. By extrapolating the cooling line back to the mixing time (t = 3.0 min), you obtain a corrected maximum temperature of 33.7 °C. The corrected temperature rise ΔT = 33.7 – 21.0 = 12.7 °C.
由于热损失，混合后温度随即开始下降，实测最高温度（33.5 °C）低于真实理论温升。插入材料指导学生绘制温度–时间图，并画出两条最佳拟合直线：一条穿过混合前的数据点，另一条穿过混合后的冷却数据点。将冷却线外推回混合时刻（t = 3.0 min），得到校正最高温度 33.7 °C。校正温升 ΔT = 33.7 – 21.0 = 12.7 °C。
7. Calculating the Heat Released | 计算释放的热量
The total volume of solution is 50.0 cm³ + 50.0 cm³ = 100.0 cm³. Assuming the density of the dilute solution is 1.00 g cm⁻³, the mass m = 100.0 g. The specific heat capacity c of water (the solution is mostly water) is taken as 4.18 J g⁻¹ K⁻¹. Using q = m c ΔT:
溶液总体积为 50.0 cm³ + 50.0 cm³ = 100.0 cm³。假设稀溶液密度为 1.00 g cm⁻³，则质量 m = 100.0 g。水的比热容 c（溶液基本是水）取 4.18 J g⁻¹ K⁻¹。用公式 q = m c ΔT 计算：
q = 100.0 g × 4.18 J g⁻¹ K⁻¹ × 12.7 K = 5308.6 J ≈ 5.31 kJ
This is the heat released by the reaction, hence the enthalpy change will carry a negative sign because the reaction is exothermic.
这是反应放出的热量，因为反应放热，焓变数值将带有负号。
8. Determining Moles of Water Formed | 确定生成水的物质的量
Amount of HCl: n(HCl) = 2.0 mol dm⁻³ × 0.0500 dm³ = 0.100 mol.
Amount of NaOH: n(NaOH) = 2.0 mol dm⁻³ × 0.0500 dm³ = 0.100 mol.
The equation is HCl + NaOH → NaCl + H₂O. Both reactants are present in exactly equal moles, so the limiting reactant is either, and 0.100 mol of water is produced.
HCl 的物质的量：n(HCl) = 2.0 mol dm⁻³ × 0.0500 dm³ = 0.100 mol。
NaOH 的物质的量：n(NaOH) = 2.0 mol dm⁻³ × 0.0500 dm³ = 0.100 mol。
反应方程式为 HCl + NaOH → NaCl + H₂O。两种反应物物质的量恰好相等，因此任一物质都是限制反应物，生成水的物质的量为 0.100 mol。
9. Calculating the Enthalpy Change | 计算焓变
ΔHneut = −q ÷ n(H₂O) = −5.31 kJ ÷ 0.100 mol = −53.1 kJ mol⁻¹. The accepted literature value is −57.1 kJ mol⁻¹. This 7 % discrepancy arises mainly from heat loss to the cup, the thermometer and the air, as well as from incomplete reaction and thermometer lag. Always express ΔH with a negative sign and the unit kJ mol⁻¹.
ΔHneut = −q ÷ n(H₂O) = −5.31 kJ ÷ 0.100 mol = −53.1 kJ mol⁻¹。文献参考值为 −57.1 kJ mol⁻¹。这约 7% 的偏差主要源于热量散失到杯子、温度计和空气中，以及反应不完全和温度计的滞后。书写 ΔH 时务必带负号，单位为 kJ mol⁻¹。
10. Sources of Error and Improvements | 误差来源与改进
Main systematic errors: heat loss; assuming the solution has the same density and specific heat capacity as pure water; thermometer precision; delay in reading the thermometer after mixing.
Improvements: use a lid with a stirrer and a digital temperature probe; calibrate the calorimeter by measuring its heat capacity; use a larger volume of solution to reduce percentage heat loss; repeat the experiment for consistency. The insert often asks you to suggest why the experimental value is less exothermic than the theoretical one.
主要系统误差：热交换损失；假设溶液密度和比热容与纯水相同；温度计精度限制；混合后读取温度的延迟。
改进方法：使用带搅拌器的密封盖和数字温度探头；通过测定量热计的热容进行校准；使用更大体积的溶液以减少热损失的百分比；多次重复实验以确保一致性。插入材料常要求解释为何实验值比理论值放热更少。
11. Exam‑Style Data Analysis | 考试题型数据分析
In the Unit 1 paper following this insert, candidates were required to plot the data, extrapolate to find ΔT, calculate q, convert to kJ, work out moles and compute ΔH. Some questions also tested understanding of the ionic equation: H⁺(aq) + OH⁻(aq) → H₂O(l) and why the enthalpy change for HCl–NaOH exactly matches that for HNO₃–NaOH but differs for weak acids like ethanoic acid. Below is a quick comparison.
在紧随这份插入材料的单元1考试中，考生需绘制数据图，外推求得 ΔT，计算 q，换算为 kJ，计算物质的量并求出 ΔH。部分题目还考查对离子方程式 H⁺(aq) + OH⁻(aq) → H₂O(l) 的理解，以及为何 HCl 与 NaOH 中和的焓变与 HNO₃ 和 NaOH 的完全一致，却不同于弱酸如乙酸。下表给出简要对比。
| System | ΔHneut / kJ mol⁻¹ | Reason |
|---|---|---|
| HCl + NaOH | −57.1 | Strong acid + strong base; net reaction always H⁺ + OH⁻ |
| HNO₃ + NaOH | −57.0 | Strong acid + strong base; value essentially the same |
| CH₃COOH + NaOH | −56.1 | Weak acid; some energy used to fully ionise CH₃COOH |
12. Key Takeaways from the Insert | 插入材料核心要点
The insert reinforces crucial practical skills: measuring volumes with the correct apparatus, using a stopwatch accurately, constructing a temperature‑time graph, applying extrapolation to correct for heat loss, and linking the experimental procedure to the underlying thermochemistry. Always show clearly how you correct the temperature, and never forget to convert joules to kilojoules before calculating ΔH.
插入材料强化了关键实验技能：使用正确仪器测量体积、准确使用秒表、构建温度‑时间图、应用外推法校正热损失、并将实验操作与热化学原理联系起来。务必清晰展示温度校正过程，并在计算 ΔH 前记住将焦耳换算为千焦。
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