📚 Alcohols – IGCSE CIE Chemistry Revision Notes | 醇 – IGCSE CIE 化学考点精讲
Alcohols are an important homologous series in organic chemistry. They contain the hydroxyl (-OH) functional group and have the general formula CₙH₂ₙ₊₁OH (or CₙH₂ₙ₊₂O). This revision guide covers the key concepts required for the IGCSE CIE Chemistry syllabus, including naming, physical properties, chemical reactions, production of ethanol, and uses of alcohols.
醇类是有机化学中一个重要的同系物。它们含有羟基 (-OH) 官能团，通式为 CₙH₂ₙ₊₁OH（或 CₙH₂ₙ₊₂O）。本复习指南涵盖了 IGCSE CIE 化学教学大纲所要求的关键概念，包括醇的命名、物理性质、化学反应、乙醇的制备以及用途。
1. Introduction to Alcohols | 醇类简介
Alcohols are organic compounds that contain one or more hydroxyl (-OH) groups bonded to a saturated carbon atom. The simplest alcohol is methanol (CH₃OH), followed by ethanol (C₂H₅OH), propanol (C₃H₇OH), and butanol (C₄H₉OH). They form a homologous series with each member differing by a CH₂ unit.
醇类是含有与饱和碳原子相连的一个或多个羟基 (-OH) 的有机化合物。最简单的醇是甲醇 (CH₃OH)，其次是乙醇 (C₂H₅OH)、丙醇 (C₃H₇OH) 和丁醇 (C₄H₉OH)。它们构成一个同系物，各成员之间相差一个 CH₂ 单元。
2. Functional Group and General Formula | 官能团与通式
The functional group of alcohols is the hydroxyl group, -OH. The general formula for saturated monoalcohols is CₙH₂ₙ₊₁OH, which can also be written as CₙH₂ₙ₊₂O. For example, when n=2, we have C₂H₅OH (ethanol). This functional group is responsible for the characteristic chemical reactions of alcohols.
醇的官能团是羟基 (-OH)。饱和一元醇的通式为 CₙH₂ₙ₊₁OH，也可以写作 CₙH₂ₙ₊₂O。例如，当 n=2 时，得到 C₂H₅OH（乙醇）。该官能团决定了醇类特有的化学反应。
3. Naming Alcohols | 醇的命名
Alcohols are named using the IUPAC system. The suffix ‘-ol’ replaces the ‘-e’ ending of the parent alkane. A number is used to indicate the position of the -OH group if the molecule has three or more carbon atoms. For example, propan-1-ol (CH₃CH₂CH₂OH) and propan-2-ol (CH₃CH(OH)CH₃) are structural isomers. Methanol and ethanol do not require a number because the -OH can only be on the first carbon.
醇类按照 IUPAC 系统命名。将母体烷烃名称的词尾 ‘-e’ 替换为 ‘-ol’。如果分子含有三个或三个以上碳原子，则需要用数字标明羟基的位置。例如，丙-1-醇 (CH₃CH₂CH₂OH) 和丙-2-醇 (CH₃CH(OH)CH₃) 是结构异构体。甲醇和乙醇不需要编号，因为羟基只能位于第一个碳上。
4. Physical Properties | 物理性质
Short-chain alcohols (methanol, ethanol, propanol) are colourless liquids at room temperature, miscible with water, and have a characteristic smell. Their boiling points are higher than those of corresponding alkanes due to hydrogen bonding between alcohol molecules. As the carbon chain length increases, solubility in water decreases and boiling point increases due to stronger London dispersion forces.
短链醇（甲醇、乙醇、丙醇）在室温下为无色液体，可与水混溶，并具有特殊气味。其沸点高于相应的烷烃，这是因为醇分子间能形成氢键。随着碳链增长，在水中的溶解度下降，沸点则因伦敦色散力增强而升高。
- Hydrogen bonds → higher boiling points than alkanes.
- Small alcohols are soluble in water; solubility decreases with chain length.
- 氢键 → 比烷烃沸点更高。
- 小分子醇溶于水；随链长增加溶解度降低。
5. Combustion of Alcohols | 醇的燃烧
Alcohols burn readily in air with a clean, pale blue flame, producing carbon dioxide and water vapour. The combustion of ethanol is highly exothermic and can be represented by the equation:
醇在空气中容易燃烧，火焰洁净、淡蓝色，生成二氧化碳和水蒸气。乙醇的燃烧为高度放热反应，可用方程式表示：
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
Because they can be produced by fermentation, alcohols such as ethanol are considered renewable fuels and are used as biofuel additives in petrol (gasohol).
由于可通过发酵法制取，乙醇等醇类被视为可再生燃料，并用作汽油中的生物燃料添加剂（酒精汽油）。
6. Reaction with Sodium | 与金属钠的反应
Alcohols react with reactive metals such as sodium to form an alkoxide (e.g. sodium ethoxide) and hydrogen gas. The reaction is less vigorous than the reaction of sodium with water.
醇与钠等活泼金属反应，生成醇钠（如乙醇钠）和氢气。该反应不如钠与水的反应剧烈。
2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂
This reaction can be used to distinguish alcohols from alkanes, which do not react with sodium. However, the test is not specific because acids and water also react with sodium.
此反应可用于区分醇与烷烃（烷烃不与钠反应）。然而，该检验并非专属，因为酸和水也能与钠反应。
7. Oxidation of Ethanol | 乙醇的氧化
Ethanol can be oxidised to ethanoic acid (acetic acid) using an oxidising agent such as acidified potassium dichromate(VI) (K₂Cr₂O₇) or acidified potassium manganate(VII) (KMnO₄). The reaction requires heating.
乙醇可以被氧化成乙酸，使用的氧化剂如酸化重铬酸钾(VI) (K₂Cr₂O₇) 或酸化高锰酸钾 (KMnO₄)。该反应需要加热。
C₂H₅OH + 2[O] → CH₃COOH + H₂O
During the reaction, the orange dichromate(VI) ion (Cr₂O₇²⁻) is reduced to green chromium(III) ion (Cr³⁺), providing a clear colour change. If potassium manganate(VII) is used, its purple colour fades as Mn²⁺ ions form. Partial oxidation can produce ethanal (CH₃CHO), but under typical IGCSE conditions with excess oxidising agent and heating, the product is ethanoic acid. This reaction is used in breathalysers to detect alcohol.
在反应过程中，橙色的重铬酸根离子 (Cr₂O₇²⁻) 被还原为绿色的铬(III) 离子 (Cr³⁺)，产生明显的颜色变化。如果用高锰酸钾，其紫色会褪去，生成 Mn²⁺ 离子。部分氧化可生成乙醛 (CH₃CHO)，但是在标准的 IGCSE 条件下，使用过量氧化剂并加热，产物是乙酸。该反应可用于呼气测醉器检测酒精。
8. Production of Ethanol: Fermentation | 乙醇的制法：发酵法Published by TutorHao | IGCSE Chemistry Revision Series | aleveler.com
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