CIE A Level Chemistry Coursebook Experimental Techniques | CIE A Level 化学教科书实验操作

📚 CIE A Level Chemistry Coursebook Experimental Techniques | CIE A Level 化学教科书实验操作

This article summarises the essential experimental techniques featured in the CIE A Level Chemistry coursebook, from titrations and calorimetry to organic synthesis and chromatography. Each section pairs practical guidance with the underlying principles, helping you master the core skills required for Paper 3 and Paper 5.

本文总结了CIE A Level化学教材中核心的实验操作技能，涵盖滴定、量热法、有机合成与色谱等技术。每个小节将操作指导与原理配对，助你扎实掌握Paper 3和Paper 5所需的实验技能。

1. Acid-Base Titration Techniques | 酸碱滴定技术

A burette must first be rinsed with the titrant solution to prevent dilution. The reading is taken from the bottom of the meniscus with the eye level at the mark, using a white tile behind the flask to make the colour change visible.

滴定管必须先用滴定液润洗以防稀释。读数时视线应与弯月面最低点水平，并可在锥形瓶后放置白瓷砖以便观察颜色变化。

A pipette should be rinsed with the solution it will deliver, not with water, and the conical flask may be rinsed with distilled water only, because the number of moles of the analyte is unchanged by the added water.

移液管需用待取溶液润洗，不可用水；锥形瓶则只可用蒸馏水冲洗，因为加入的水不会改变待测物质的物质的量。

The indicator is chosen so its pH colour change interval lies within the steep portion of the titration curve. For a strong acid–strong base titration, both methyl orange and phenolphthalein are suitable.

选择指示剂时，其变色pH范围应落在滴定曲线的突跃区间内。强酸强碱滴定中，甲基橙和酚酞均可使用。

Table 1: Common indicators and their pH ranges.

表1：常用指示剂及其变色范围。

Indicator (指示剂)	pH range	Colour change (颜色变化)
Methyl orange (甲基橙)	3.1–4.4	Red to yellow (红→黄)
Phenolphthalein (酚酞)	8.3–10.0	Colourless to pink (无色→粉红)

A ‘rough’ titration is performed first to estimate the end point, and then accurate titrations are repeated until concordant results (within 0.10 cm³) are obtained. The mean of the concordant titres is used in calculations.

先进行一次粗略滴定以估算终点，然后重复精确滴定，直到得到一致的结果（相差≤0.10 cm³）。计算时使用多次一致体积的平均值。

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2. Calorimetry and Enthalpy Determination | 量热法与焓变测定

A simple coffee-cup calorimeter consists of a polystyrene cup with a lid, a thermometer and a stirrer. The heat capacity of the cup is often assumed to be negligible, but for greater accuracy the apparatus should first be calibrated.

简易量热器由聚苯乙烯杯、杯盖、温度计和搅拌棒组成。杯子的热容通常忽略，但为提高准确性可先进行标定。

For a reaction in solution, the heat change is calculated using q = mcΔT, where m is the mass of the solution (approximated as the volume in cm³ for dilute aqueous solutions), c is the specific heat capacity (usually 4.18 J g⁻¹ °C⁻¹), and ΔT is the temperature change after extrapolation.

对溶液中的反应，热量变化用 q = mcΔT 计算，m 为溶液质量（对稀水溶液可近似等于体积cm³），c 为比热容（通常取4.18 J g⁻¹ °C⁻¹），ΔT 为外推校正后的温度变化。

ΔH = −mcΔT / n

The temperature change is determined by plotting temperature against time and extrapolating the cooling curve back to the time of mixing. This compensates for heat loss to the surroundings.

温度变化通过作温度-时间图并将冷却段直线外推至混合时刻求得。此法可补偿向环境的热量散失。

Main sources of error include heat loss to the cup and air, inaccuracy in thermometer readings, and incomplete reaction. For combustion reactions, a spirit burner must be shielded to minimise draughts.

主要误差来源包括热量散失给杯子和空气、温度计读数不精确和反应不完全。燃烧反应中，酒精灯应加挡风罩以减少气流影响。

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3. Preparation and Collection of Gases | 气体的制备与收集

Gases can be collected by downward delivery, upward delivery, or over water, depending on their density and solubility. Before starting, the apparatus must always be checked for leaks.

根据气体的密度和溶解度，可用向下排空气法、向上排空气法或排水集气法收集气体。实验前务必检查装置气密性。

Oxygen is typically prepared by the catalytic decomposition of hydrogen peroxide: 2H₂O₂(aq) → 2H₂O(l) + O₂(g) using MnO₂ as a catalyst. It is collected over water because it is only slightly soluble.

通常用过氧化氢催化分解制氧气：2H₂O₂(aq) → 2H₂O(l) + O₂(g)，以MnO₂作催化剂。氧气微溶于水，可用排水法收集。

Carbon dioxide is made by reacting calcium carbonate with dilute hydrochloric acid: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). It is denser than air and collected by upward delivery, with the gas inlet extending to the bottom of the jar.

二氧化碳通过碳酸钙与稀盐酸反应制取：CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)。其密度大于空气，用向上排空气法收集，需将导管伸至瓶底。

Hydrogen, being less dense than air and insoluble in water, can be collected either over water or by downward delivery. It is often generated from zinc and dilute sulfuric acid.

氢气比空气轻且难溶于水，可用排水法或向下排空气法收集。通常用锌与稀硫酸反应制取。

Drying agents such as concentrated sulfuric acid, anhydrous calcium chloride, or silica gel may be used to remove water vapour from the gas stream, depending on the chemical inertness required.

根据化学惰性要求，可使用浓硫酸、无水氯化钙或硅胶等干燥剂去除气流中的水蒸气。

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4. Organic Synthesis and Purification | 有机合成与纯化

A typical synthesis, such as the preparation of ethyl ethanoate, involves heating a carboxylic acid and an alcohol under reflux with a few drops of concentrated sulfuric acid as a catalyst. The reflux condenser prevents volatile reactants from escaping.

典型的合成如制备乙酸乙酯，是将羧酸与醇在回流条件下加热，并加几滴浓硫酸作催化剂。回流冷凝管可防止挥发性反应物逸出。

After reflux, the mixture is distilled to collect the crude ester. The distillate is then washed with sodium carbonate solution in a separating funnel to remove unreacted acid, and the organic layer is dried over anhydrous sodium sulfate or magnesium sulfate.

回流结束后，蒸馏混合物收集粗酯。馏出液在分液漏斗中用碳酸钠溶液洗涤以除去未反应的酸，有机层再用无水硫酸钠或硫酸镁干燥。

For solid products, recrystallisation from a suitable solvent is used: the impure solid is dissolved in a minimum volume of hot solvent, filtered hot, and cooled slowly to allow pure crystals to form.

对固体产物，需用合适溶剂进行重结晶：将不纯固体溶于最小量热溶剂，趁热过滤，缓慢冷却使纯净晶体析出。

Purity is assessed by measuring the melting point range: a pure compound melts sharply within 1–2 °C, while an impure sample melts over a wide range and at a lower temperature. The yield is calculated as: % yield = (actual mass / theoretical mass) × 100%.

通过熔点范围评价纯度：纯物质熔程窄（1–2 °C），不纯物质熔程宽且熔点更低。产率计算：% 产率 = (实际质量 / 理论质量) × 100%。

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5. Investigating Reaction Rates | 反应速率探究

The reaction of sodium thiosulfate with hydrochloric acid is studied by measuring the time taken for a precipitate of sulfur to obscure a cross drawn on paper: Na₂S₂O₃(aq) + 2HCl(aq) → 2NaCl(aq) + SO₂(g) + S(s) + H₂O(l).

硫代硫酸钠与盐酸的反应可通过测量硫沉淀遮挡纸上十字所需的时间来研究：Na₂S₂O₃(aq) + 2HCl(aq) → 2NaCl(aq) + SO₂(g) + S(s) + H₂O(l)。

The rate is followed by recording the volume of gas evolved from a reaction, such as the decomposition of hydrogen peroxide, or by monitoring the loss in mass of the reaction flask when a gas is released.

可通过记录反应中气体析出体积（如过氧化氢分解）或监测反应瓶因气体逸出导致的失重来跟踪反应速率。

In the ‘clock reaction’, the sudden appearance of a colour marks a fixed extent of reaction. Timing the colour change at different concentrations gives initial rates, from which the rate equation can be deduced.

在“时钟反应”中，颜色的突然出现标志着特定反应进度。测量不同浓度下颜色变化的时间可得出初始速率，进而推导速率方程。

A graph of concentration against time is plotted, and initial rate is obtained from the gradient of the tangent at t = 0. To determine the order with respect to a reactant, rates are compared for different initial concentrations.

绘制浓度-时间图，在t=0处切线的斜率即为初始速率。为确定某反应物的反应级数，需比较不同初始浓度下的速率。

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6. Electrochemical Cells and Electrode Potentials | 电化学电池与电极电势

A simple cell consists of two half-cells connected by a salt bridge and a high-resistance voltmeter. For example, a Zn²⁺/Zn half-cell and a Cu²⁺/Cu half-cell give a cell with Ecell ≈ +1.10 V under standard conditions.

简单电池由两个半电池经盐桥和高阻抗电压表连接而成。例如，Zn²⁺/Zn半电池与Cu²⁺/Cu半电池组成的电池在标准条件下电动势约为+1.10 V。

Each half-cell contains a metal electrode dipped into a solution containing its own ions, usually at a concentration of 1.0 mol dm⁻³. The salt bridge, often a strip of filter paper soaked in saturated KNO₃, completes the circuit by allowing ion migration without mixing the solutions.

每个半电池由金属电极浸入其自身离子的溶液中构成，离子浓度通常为1.0 mol dm⁻³。盐桥常为浸透饱和KNO₃的滤纸条，允许离子迁移而不使溶液混合。

The standard hydrogen electrode (SHE) is assigned an electrode potential of 0.00 V. It consists of a platinum electrode in 1 mol dm⁻³ H⁺ solution with H₂ gas bubbled through at 1 atm.

标准氢电极(SHE)的电极电势定为0.00 V。它由铂电极插在1 mol dm⁻³ H⁺溶液中，再以1 atm的H₂气流通入构成。

E°cell is calculated as E°cell = E°cathode − E°anode using standard reduction potentials. A positive E°cell indicates a spontaneous reaction.

利用标准还原电势计算标准电动势：E°cell = E°cathode − E°anode。E°cell为正值表示反应可自发进行。

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7. Determination of Equilibrium Constants | 平衡常数的测定

For the esterification reaction CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O, an equilibrium mixture is obtained by heating known amounts of acid and alcohol with an acid catalyst in a sealed flask at constant temperature. The mixture is then cooled rapidly in ice to ‘freeze’ the equilibrium.

对于酯化反应 CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O，将已知量的酸和醇与酸催化剂在密封烧瓶中恒温加热，达到平衡后迅速用冰水冷却以“冻结”平衡。

The amount of unreacted carboxylic acid is determined by titrating the cold mixture against standard sodium hydroxide solution, using phenolphthalein as indicator. From this, the equilibrium moles of all species are calculated.

用标准氢氧化钠溶液在低温下滴定混合物中的未反应羧酸，以酚酞为指示剂。由此可计算出所有物种在平衡时的物质的量。

Kc = [CH₃COOC₂H₅][H₂O] / [CH₃COOH][C₂H₅OH]

Since the volume cancels in the Kc expression for this reaction, concentrations can be replaced by moles. The experiment can be repeated at different temperatures to show that Kc varies with temperature.

该反应的Kc表达式中体积可消去，浓度直接以物质的量代替。可在不同温度下重复实验，证明Kc随温度变化。

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8. Chromatography Techniques | 色谱技术

In paper chromatography, a small spot of the mixture is placed on the baseline of the chromatography paper, which is then suspended in a suitable solvent so that the baseline is above the solvent level. The components separate as the solvent front moves up.

在纸色谱中，将混合物点在色谱纸基线上，然后将纸悬挂于合适溶剂中，确保基线在液面之上。组分随溶剂前沿上移而分离。

Each separated spot is identified by its Rf value, calculated as Rf = distance travelled by the spot / distance travelled by the solvent front. Rf values are compared with those of known substances run under identical conditions.

分离后的斑点用Rf值鉴别，Rf = 斑点移动距离 / 溶剂前沿移动距离。Rf值需与在相同条件下测得的标准品进行比较。

Thin-layer chromatography (TLC) uses a glass or plastic plate coated with silica gel. After development, spots can be visualised under UV light or with a locating agent such as iodine vapour.

薄层色谱(TLC)使用涂有硅胶的玻璃板或塑料片。展开后可用紫外灯或定位剂（如碘蒸气）显色以观察斑点。

For colourless components, a pencil is used to mark the baseline (never ink, as it would separate), and the chromatogram is removed as soon as the solvent front reaches the top line to prevent further diffusion.

对于无色组分，用铅笔标绘基线（不可用墨水，因墨水会分离），当溶剂前沿到达顶线时立即取出色谱纸或板，以防进一步扩散。

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9. Qualitative Analysis of Ions | 离子定性分析

Flame tests identify metal cations: Li⁺ gives a red flame, Na⁺ an intense yellow, K⁺ a lilac, Ca²⁺ a brick-red, and Cu²⁺ a blue-green flame. A nichrome wire dipped in concentrated HCl is used to clean the sample.

焰色试验可鉴别金属阳离子：Li⁺呈红色，Na⁺呈强烈黄色，K⁺呈淡紫色，Ca²⁺呈砖红色，Cu²⁺呈蓝绿色。用蘸浓盐酸的镍铬丝清洁试样。

Addition of sodium hydroxide solution produces characteristic precipitates: Cu²⁺ gives a pale blue precipitate, Fe²⁺ a green precipitate turning brown, Fe³⁺ a reddish-brown precipitate, and Zn²⁺ a white precipitate soluble in excess NaOH.

加入氢氧化钠溶液产生特征沉淀：Cu²⁺生成浅蓝色沉淀，Fe²⁺生成绿色沉淀而后变棕色，Fe³⁺生成红棕色沉淀，Zn²⁺生成白色沉淀且溶于过量NaOH。

Anions are tested by specific reagents: carbonate gives effervescence with dilute acid; sulfate gives a white precipitate with BaCl₂ acidified with HCl; halides give precipitates with AgNO₃ followed by dilute nitric acid – AgCl is white, AgBr cream, AgI yellow.

阴离子通过特征试剂检验：碳酸根遇稀酸产生气泡；硫酸根遇BaCl₂盐酸酸化生成白色沉淀；卤素离子加AgNO₃后加稀硝酸，生成AgCl白色、AgBr奶油色、AgI黄色沉淀。

Common gases are also tested: hydrogen gives a ‘squeaky pop’ with a lighted splint, oxygen relights a glowing splint, carbon dioxide turns limewater milky, and ammonia turns damp red litmus paper blue.

常见气体也需检验：氢气遇点燃的木条发出爆鸣声，氧气使带火星木条复燃，二氧化碳使石灰水变浑浊，氨气使湿润的红色石蕊试纸变蓝。

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10. Handling Liquids and Measurements | 液体操作与测量

A volumetric flask is used to prepare a solution of accurately known concentration. The solute is fully dissolved and the solution is made up to the graduation mark, with the bottom of the meniscus just touching the line.

容量瓶用于配制精确浓度的溶液。溶质完全溶解后，补加溶剂至刻度线，使弯月面最低点刚好与刻线相切。

Pipettes, usually of 10.0 or 25.0 cm³ capacity, deliver a fixed volume when the tip is touched against the glass wall after discharge. A pipette filler must be used; never pipette by mouth.

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