Edexcel A-Level Combined Science 067: Quantitative Analysis – Moles, Titrations and Yield | 定量分析：摩尔、滴定与产率

📚 Edexcel A-Level Combined Science 067: Quantitative Analysis – Moles, Titrations and Yield | 定量分析：摩尔、滴定与产率

Quantitative analysis is a core skill in Edexcel A-Level Chemistry and Combined Science. It connects measurable laboratory data, such as mass and volume, with the amount of substance in moles. This article focuses on mole calculations, solution concentration, titration technique, and reaction yield.

定量分析是 Edexcel A-Level 化学及组合科学的核心技能。它将质量、体积等可测量的实验数据与物质的量联系起来。本文重点讲解摩尔计算、溶液浓度、滴定操作和反应产率。

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1. What Is Quantitative Analysis? | 什么是定量分析？

Quantitative analysis determines how much of a substance is present in a sample or how much product forms in a reaction. It relies on accurate measurements and the mole concept. In titration and gravimetric analysis, calculations convert experimental readings into chemical amounts.

定量分析用于测定样品中某物质的含量，或反应中生成多少产物。它依赖准确的测量和摩尔概念。在滴定和重量分析中，计算将实验读数转化为化学物质的量。

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2. The Mole and Avogadro Constant | 摩尔与阿伏伽德罗常数

One mole contains exactly 6.022 × 10²³ particles, which is the Avogadro constant. These particles can be atoms, molecules, ions, or electrons. The mole allows chemists to count particles by weighing macroscopic amounts.

1 摩尔包含 6.022 × 10²³ 个粒子，这就是阿伏伽德罗常数。这些粒子可以是原子、分子、离子或电子。摩尔使化学家能够通过称量宏观质量来计数粒子。

n = N / L

where N is the number of particles and L is the Avogadro constant.

其中 N 为粒子数，L 为阿伏伽德罗常数。

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3. Molar Mass and Mass-Mole Conversions | 摩尔质量与质量-摩尔换算

Molar mass M is the mass of one mole of a substance and has units g mol⁻¹. For elements and compounds, it equals the relative atomic or formula mass in grams. Use n = m / M to convert between mass and moles.

摩尔质量 M 是 1 摩尔物质的质量，单位为 g mol⁻¹。对于单质和化合物，它在数值上等于相对原子质量或相对式量。使用 n = m / M 进行质量与摩尔之间的换算。

n = m / M

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4. Empirical and Molecular Formulae | 实验式与分子式

The empirical formula gives the simplest whole-number ratio of atoms in a compound. The molecular formula gives the actual number of atoms in one molecule. To find an empirical formula, convert percentage composition to moles, then divide by the smallest value.

实验式给出化合物中原子的最简整数比。分子式给出一个分子中原子的实际数目。求实验式时，将元素百分含量换算为摩尔数，再除以最小值得到最简比。

• Step 1: Write the mass or percentage of each element.
• 步骤 1：写出各元素的质量或百分含量。
• Step 2: Divide each by its relative atomic mass to obtain moles.
• 步骤 2：将每个量除以对应相对原子质量，得到摩尔数。
• Step 3: Divide all moles by the smallest number of moles.
• 步骤 3：将全部摩尔数除以最小的摩尔数。

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5. Concentration and Molarity | 浓度与物质的量浓度

Concentration c is the amount of solute dissolved in 1 dm³ of solution: c = n / V. Its units are mol dm⁻³. In calculations, volume must be converted from cm³ to dm³ by dividing by 1000.

浓度 c 表示 1 dm³ 溶液中所含溶质的物质的量：c = n / V，单位为 mol dm⁻³。计算时，体积必须从 cm³ 换算为 dm³，即除以 1000。

c = n / V

For example, 25.0 cm³ of 0.100 mol dm⁻³ HCl contains n = 0.100 × 0.025 = 0.00250 mol.

例如，25.0 cm³ 的 0.100 mol dm⁻³ HCl 中含有 n = 0.100 × 0.025 = 0.00250 mol。

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6. Making Standard Solutions | 配制标准溶液

A standard solution has an accurately known concentration. Dissolve a weighed mass in a beaker, transfer it to a volumetric flask, rinse the beaker and add washings, then make up to the calibration mark. Invert several times to mix.

标准溶液是浓度准确已知的溶液。将称量好的样品在烧杯中溶解，转移至容量瓶，冲洗烧杯并转移洗液，然后定容至刻度线。倒置摇匀数次使其混合均匀。

• Weigh the solid accurately using a balance.
• 使用天平准确称量固体。
• Transfer all dissolved solid and washings into the flask.
• 将全部溶解后的固体及洗液转移至容量瓶。
• Add distilled water until the bottom of the meniscus touches the mark.
• 加入蒸馏水直到弯月面底部与刻度线相切。

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7. Titration Procedure and End Point | 滴定操作与终点判断

In acid-base titration, a pipette measures a fixed volume of one solution into a conical flask. A burette delivers the other solution until the indicator changes colour at the end point. Read the meniscus at eye level and record titre to 0.05 cm³.

在酸碱滴定中，移液管量取一定体积的一种溶液放入锥形瓶。滴定管滴加另一种溶液，直到指示剂在终点变色。读取弯月面时视线应与液面水平，滴定管读数记录至 0.05 cm³。

• Rinse the burette with the solution it will contain, not with water.
• 滴定管要用待装溶液润洗，不能只用水洗。
• Use a white tile under the flask to see the colour change clearly.
• 在锥形瓶下方放白色瓷砖，便于观察颜色变化。
• Swirl the flask continuously during titration.
• 滴定过程中不断摇动锥形瓶。

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8. Titration Calculations | 滴定计算

Use concordant titres within 0.10 cm³ to calculate an average titre. Then find n = cV for the known solution, use the balanced equation mole ratio, and convert to the unknown concentration.

使用相差不超过 0.10 cm³ 的连续滴定结果计算平均滴定体积。然后利用 n = cV 计算已知溶液的物质的量，根据配平方程式的摩尔比，换算为未知溶液的浓度。

nₐ = cₐVₐ

For the reaction NaOH + HCl → NaCl + H₂O, the mole ratio is 1:1. So n(NaOH) = n(HCl).

对于反应 NaOH + HCl → NaCl + H₂O，摩尔比为 1:1。因此 n(NaOH) = n(HCl)。

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9. Percentage Yield and Atom Economy | 产率与原子经济性

Percentage yield compares actual and theoretical product: (actual/theoretical) × 100%. Atom economy measures the efficiency of using starting materials: (molar mass of desired product / total molar mass of all products) × 100%.

产率比较实际产量与理论产量：(实际产量/理论产量) × 100%。原子经济性衡量原料利用率：(目标产物摩尔质量 / 所有产物摩尔质量总和) × 100%。

% yield = (actual yield / theoretical yield) × 100%

% atom economy = (molar mass of desired product / total molar mass of all products) × 100%

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10. Common Errors and Exam Tips | 常见错误与考试技巧

Common errors include not rinsing the burette with the solution, using the pipette filler incorrectly, and reading the meniscus from above. Always show units and convert cm³ to dm³ before using c = n / V.

常见错误包括：滴定管未用待装溶液润洗、移液管使用不当、从上方读取弯月面。计算时务必标明单位，并在使用 c = n / V 前将 cm³ 换算为 dm³。

Error | 错误	Correction | 纠正方法
Forgetting to convert cm³ to dm³ | 忘记将 cm³ 换算为 dm³	Divide by 1000 before calculation | 计算前除以 1000
Rinsing burette with water only | 只用水润洗滴定管	Rinse with the solution to be used | 用待装溶液润洗
Reading meniscus from above | 从上方读取弯月面	Read at eye level | 视线与液面水平

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