📚 IGCSE Edexcel Chemistry: Alcohols – Key Points | IGCSE Edexcel 化学：醇 考点精讲
Alcohols are an important homologous series in organic chemistry, characterised by the –OH functional group. This revision guide covers the essential knowledge required for the IGCSE Edexcel Chemistry specification, including structure, naming, physical properties, chemical reactions, and industrial production of ethanol.
醇是一类重要的有机同系物，其官能团为羟基(–OH)。本复习指南涵盖IGCSE Edexcel化学大纲要求掌握的核心知识，包括醇的结构、命名、物理性质、化学反应以及乙醇的工业生产。
1. What are Alcohols? | 什么是醇？
Alcohols are organic compounds that contain one or more hydroxyl (–OH) groups attached to a carbon atom. In IGCSE, we focus on the simplest alcohols: methanol, ethanol, propan-1-ol and butan-1-ol. The –OH group is the functional group that determines the characteristic reactions of alcohols.
醇是含有一个或多个连接在碳原子上的羟基(–OH)的有机化合物。在IGCSE阶段，我们主要学习最简单的醇：甲醇、乙醇、丙-1-醇和丁-1-醇。–OH是醇的官能团，它决定了醇的特征反应。
2. Homologous Series and General Formula | 同系物与通式
Alcohols form a homologous series with the general formula CnH2n+1OH, where n is the number of carbon atoms. Each member differs from the next by a –CH2– unit. This gradual increase in chain length causes a trend in physical properties such as boiling point and viscosity. The general molecular formula can also be written as CnH2n+2O for saturated alcohols.
醇形成同系物，通式为CnH2n+1OH，其中n为碳原子数。相邻成员之间相差一个–CH2–单元。碳链长度的逐渐增加导致沸点和粘度等物理性质呈现规律性变化。对于饱和一元醇，分子通式也可写作CnH2n+2O。
3. Naming Alcohols | 醇的命名
For IGCSE, you must be able to name and draw the first four alcohols. The stem indicates the number of carbon atoms (meth-, eth-, prop-, but-) and the ending is ‘-anol’. The position of the –OH group is indicated by a number if there is more than one possibility. For example, propan-1-ol has the –OH on the first carbon, while propan-2-ol has it on the second carbon. Ethanol does not need a number because the –OH can only be on the end carbon in a two-carbon chain.
在IGCSE中，你需要能够命名并画出前四种醇。词干表示碳原子数（甲、乙、丙、丁），词尾为“醇”。如果–OH位置有不同可能，则用数字标明其位置。例如丙-1-醇的–OH在第一个碳上，而丙-2-醇的–OH在第二个碳上。乙醇不需要编号，因为在两个碳的链中–OH只能在末端碳上。
- Methanol: CH3OH | 甲醇：CH3OH
- Ethanol: C2H5OH | 乙醇：C2H5OH
- Propan-1-ol: C3H7OH | 丙-1-醇：C3H7OH
- Butan-1-ol: C4H9OH | 丁-1-醇：C4H9OH
4. Physical Properties of Alcohols | 醇的物理性质
Alcohols have relatively high boiling points compared to alkanes of similar molecular mass. This is because alcohol molecules can form hydrogen bonds between –OH groups, which are stronger than the van der Waals’ forces in alkanes. As the carbon chain length increases, the boiling point rises due to increased van der Waals’ forces. Short-chain alcohols like methanol and ethanol are completely miscible with water because they can form hydrogen bonds with water molecules. As the hydrocarbon chain becomes longer, solubility decreases because the non-polar part of the molecule dominates.
与相对分子质量相近的烷烃相比，醇的沸点较高。这是因为醇分子间能通过–OH形成氢键，氢键强于烷烃中的范德华力。随着碳链增长，范德华力增强，沸点升高。甲醇、乙醇等短链醇与水完全互溶，因为它们能与水分子形成氢键。随着烃链变长，非极性部分占据主导，溶解度下降。
| Alcohol | Formula | Boiling Point (°C) | Solubility in Water |
|---|---|---|---|
| Methanol | CH3OH | 65 | Miscible |
| Ethanol | C2H5OH | 78 | Miscible |
| Propan-1-ol | C3H7OH | 97 | Miscible |
| Butan-1-ol | C4H9OH | 118 | Slightly soluble |
5. Combustion of Alcohols | 醇的燃烧
Alcohols burn readily in a plentiful supply of oxygen to produce carbon dioxide and water, releasing a large amount of energy. This makes them useful as fuels. The complete combustion of ethanol, for example, is represented by the equation:
醇在充足的氧气中容易燃烧，生成二氧化碳和水，同时释放大量能量。这使得它们可用作燃料。例如乙醇的完全燃烧方程式为：
C2H5OH + 3 O2 → 2 CO2 + 3 H2O
In a limited supply of oxygen, incomplete combustion may occur, producing carbon monoxide (toxic) or carbon (soot) along with water.
在氧气供应不足时会发生不完全燃烧，生成一氧化碳（有毒）或碳（黑烟）以及水。
6. Reaction with Sodium | 与钠的反应
Alcohols react with elemental sodium to form a salt called an alkoxide and hydrogen gas. The reaction is less vigorous than the reaction of sodium with water, but it still produces effervescence. Using ethanol as an example:
醇与金属钠反应生成醇钠盐和氢气。该反应不如钠与水反应剧烈，但仍会产生气泡。以乙醇为例：
2 C2H5OH + 2 Na → 2 C2H5ONa + H2
The product, sodium ethoxide, is an ionic compound containing the ethoxide ion C2H5O−. This reaction is a useful test for the –OH group in an organic compound, but it is not exclusive to alcohols (water and carboxylic acids also react).
产物乙醇钠是一种含有乙醇根离子C2H5O−的离子化合物。该反应可用于检验有机物中的–OH基团，但并非醇所独有（水和羧酸也能反应）。
7. Oxidation of Ethanol | 乙醇的氧化
Ethanol can be oxidised by warming with acidified potassium dichromate(VI) solution. During the reaction, the orange dichromate(VI) ions (Cr2O72−) are reduced to green chromium(III) ions (Cr3+). This colour change from orange to green is the key observation. The initial oxidation product is ethanal (an aldehyde).
乙醇与酸化的重铬酸钾(VI)溶液共热可被氧化。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+)。这种由橙变绿的颜色变化是关键观察现象。最初的氧化产物是乙醛。
C2H5OH + [O] → CH3CHO + H2O
The symbol [O] represents an oxygen atom supplied by the oxidising agent.
符号[O]代表由氧化剂提供的氧原子。
8. Oxidation to Carboxylic Acids | 氧化生成羧酸
If the oxidising agent is in excess and the mixture is heated under reflux, the aldehyde is further oxidised to a carboxylic acid. In the case of ethanol, the final product is ethanoic acid. The overall transformation is:
如果氧化剂过量并采用回流加热，醛会进一步氧化成羧酸。对乙醇而言，最终产物是乙酸。整个过程可表示为：
C2H5OH + 2[O] → CH3COOH + H2O
Ethanoic acid is the main acid in vinegar. This oxidation sequence (alcohol → aldehyde → carboxylic acid) is a common pathway for primary alcohols. You should be able to describe the conditions and recognise the colour change from orange to green.
乙酸是食醋中的主要酸性成分。这种氧化顺序（醇→醛→羧酸）是伯醇的常见转化路径。你需要能描述反应条件，并识别橙色变为绿色的现象。
9. Esterification | 酯化反应
Alcohols react with carboxylic acids in the presence of a concentrated sulfuric acid catalyst to form esters and water. This reversible reaction is called esterification. The concentrated sulfuric acid acts as a dehydrating agent and a catalyst. Using ethanol and ethanoic acid as an example:
醇与羧酸在浓硫酸催化下反应生成酯和水。这个可逆反应称为酯化反应。浓硫酸既作为脱水剂又作为催化剂。以乙醇和乙酸为例：
C2H5OH + CH3COOH ⇌ CH3COOC2H5 + H2O
The ester produced, ethyl ethanoate, has a pleasant, fruity smell and is used in flavourings and solvents. Esters are named with the alcohol part first (ethyl) and the acid part second (ethanoate).
生成的酯——乙酸乙酯，具有宜人的水果香味，用于香精和溶剂。酯的命名以醇的部分开头（乙基），酸的部分结尾（乙酸酯）。
| Alcohol used | Carboxylic acid used | Ester formed | Smell |
|---|---|---|---|
| Ethanol | Ethanoic acid | Ethyl ethanoate | Pear drops / nail varnish |
| Methanol | Ethanoic acid | Methyl ethanoate | Glue / fruity |
| Ethanol | Methanoic acid | Ethyl methanoate | Rum / raspberry |
10. Production of Ethanol: Fermentation | 乙醇的生产：发酵
Ethanol for alcoholic drinks and biofuels is produced by the fermentation of sugars (such as glucose) using yeast. Yeast provides the enzyme zymase that catalyses the anaerobic respiration of glucose. The conditions include: a warm temperature (30–40 °C), absence of oxygen, and an aqueous solution of the sugar. The overall equation is:
饮料酒精和生物燃料中的乙醇是通过酵母发酵糖类（如葡萄糖）生产的。酵母提供酶——酒化酶，催化葡萄糖的无氧呼吸。反应条件包括：温暖的环境（30–40°C）、缺氧以及糖的水溶液。总方程式为：
C6H12O6 → 2 C2H5OH + 2 CO2
If the temperature is too high, the enzymes in yeast denature and fermentation stops. Once the ethanol concentration reaches about 15%, the yeast is killed and fermentation ceases. The ethanol is then separated by fractional distillation to obtain a higher concentration.
如果温度过高，酵母中的酶会变性，发酵停止。一旦乙醇浓度达到约15%，酵母死亡，发酵即终止。然后通过分馏分离乙醇以获得更高浓度的产品。
11. Production of Ethanol: Hydration of Ethene | 乙醇的生产：乙烯水合
Ethanol can also be manufactured by the direct hydration of ethene, an alkene. Ethene is obtained from crude oil by cracking. The reaction uses steam, a phosphoric acid catalyst, a temperature of about 300 °C and a pressure of 60 atmospheres:
乙醇也可以通过乙烯（一种烯烃）的直接水合制备。乙烯来自石油的裂解。该反应使用水蒸气、磷酸催化剂，温度约300 °C，压强60个大气压：
C2H4 + H2O → C2H5OH
This is an addition reaction and produces ethanol in a continuous process with a high yield and fast rate. Unlike fermentation, it uses a non-renewable resource (crude oil) and requires high energy input. The ethanol produced is exactly the same chemical, but the method is more suitable for industrial solvent and fuel production.
这是一个加成反应，可以在连续流程中以高产率和高速度生产乙醇。与发酵不同，该方法使用不可再生资源（石油），且需要高能量投入。制得的乙醇在化学上完全相同，但该方法更适合于工业溶剂和燃料生产。
| Factor | Fermentation | Hydration of Ethene |
|---|---|---|
| Raw material | Sugar (renewable) | Ethene from petroleum (non-renewable) |
| Type of process | Batch | Continuous |
| Temperature | 30–40 °C | 300 °C |
| Rate of production | Slow | Fast |
| Product purity | Low (ethanol in water, requires distillation) | High (pure ethanol made directly) |
12. Uses of Alcohols | 醇的用途
Alcohols have a wide range of uses that you should recall for the exam:
- Ethanol: main solvent in perfumes, medicines, and varnishes; used as a biofuel (often blended with petrol); in alcoholic beverages; as a disinfectant and antiseptic.
- Methanol: important feedstock for making other chemicals such as methanal (a disinfectant) and plastics; used as a racing fuel; as a laboratory solvent.
- Propan-1-ol and butan-1-ol: used as solvents and in the manufacture of other organic compounds, including esters for flavourings.
醇有着广泛的用途，你应在考试中牢记：
- 乙醇：香水、药品和清漆的主要溶剂；用作生物燃料（常与汽油混合）；用于酒精饮料；作为消毒剂和防腐剂。
- 甲醇：制造其他化学品（如消毒剂甲醛）和塑料的重要原料；用作赛车燃料；实验室溶剂。
- 丙-1-醇和丁-1-醇：用作溶剂，用于制造其他有机化合物，包括食用香精酯。
Ethanol’s ability to burn cleanly and mix with petrol makes it particularly important in the context of renewable energy, as it can be produced by fermenting plant materials.
乙醇能够清洁燃烧并与汽油混合，使其在可再生能源领域尤为重要，因为它可以通过发酵植物材料来生产。
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