📚 Alcohols in GCSE CCEA Chemistry | GCSE CCEA 化学：醇 考点精讲
Alcohols are an important homologous series in organic chemistry, characterised by the hydroxyl functional group. In the CCEA GCSE Chemistry specification, you need to understand their structure, naming, physical properties, and key chemical reactions, including combustion, oxidation, reaction with sodium, and the two industrial routes used to manufacture ethanol. This revision guide walks through every one of those points in turn, with the equations, definitions and exam wording you are expected to produce.
醇是有机化学中一类重要的同系物，其特征官能团是羟基。在 CCEA GCSE 化学考试大纲中，你需要理解醇的结构、命名、物理性质以及关键化学反应，包括燃烧、氧化、与钠的反应，以及乙醇的两种工业生产方法。本复习指南将逐条讲解上述每一个考点，并给出考试中要求你写出的方程式、定义与规范表述。
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 a hydrocarbon chain. They form a homologous series with the general formula CₙH₂ₙ₊₁OH, where n is the number of carbon atoms. Because they belong to a homologous series, each successive member differs from the previous one by a CH₂ unit, and all members show a gradual change in physical properties while sharing the same chemical behaviour.
醇是一类有机化合物，其分子中包含一个或多个连接在碳链碳原子上的羟基 (-OH)。它们组成通式为 CₙH₂ₙ₊₁OH 的同系物系列，其中 n 是碳原子数。由于属于同一同系物系列，相邻成员之间相差一个 CH₂ 单元，因此各成员的物理性质呈规律性递变，而化学性质基本相同。
The simplest alcohol is methanol (CH₃OH), followed by ethanol (C₂H₅OH), propanol (C₃H₇OH), butanol (C₄H₉OH) and so on. In ethanol, the -OH group replaces one hydrogen atom of ethane, so the skeleton of the molecule is still built from carbon and hydrogen, with oxygen appearing only inside the hydroxyl group.
最简单的醇是甲醇 (CH₃OH)，其次是乙醇 (C₂H₅OH)、丙醇 (C₃H₇OH)、丁醇 (C₄H₉OH) 等。在乙醇中，-OH 基团取代了乙烷的一个氢原子，因此分子的骨架仍由碳和氢构成，氧原子只出现在羟基内部。
It is worth remembering where you meet these compounds in everyday life, because CCEA questions often use real contexts. Methanol is an industrial feedstock and a solvent, ethanol is the alcohol in alcoholic drinks and in biofuel blends, and propan-1-ol and butan-1-ol are used as solvents in industry.
记住这些物质在生活中的出现场合很有价值，因为 CCEA 的题目常用真实情境。甲醇是工业原料和溶剂，乙醇是酒精饮料中的醇，也用于生物燃料调配，而丙-1-醇和丁-1-醇则用作工业溶剂。
2. Functional Group & General Formula | 官能团与通式
The functional group of alcohols is the hydroxyl group, -OH. This group is responsible for the characteristic chemical properties of alcohols. In the general formula CₙH₂ₙ₊₁OH, the 'OH' part is written separately to emphasise the functional group. Be careful: when counting carbon atoms, the carbon attached to -OH is included in n.
醇的官能团是羟基 -OH。该基团决定了醇的特征化学性质。在通式 CₙH₂ₙ₊₁OH 中，"OH" 部分单独写出以强调官能团。注意：计算碳原子数时，连接 -OH 的碳原子已计入 n 中。
e number of hydrogen atoms is always 2n + 1 in the alkyl part, plus the single hydrogen of the hydroxyl group.
例如，乙醇有 2 个碳原子：n = 2，因此化学式为 C₂H₅OH。甲醇 n = 1，为 CH₃OH。丙醇 n = 3，为 C₃H₇OH。注意烷基部分的氢原子数总是 2n + 1，再加上羟基上的那 1 个氢原子。
The three-way comparison below is a classic exam table. Learn it, because it also links alcohols to the alkanes you studied earlier.
下面的三者对比是经典考点表格，务必掌握，因为它还把醇与你之前学过的烷烃联系起来。
| Homologous series | 同系物 | General formula | 通式 | Functional group | 官能团 |
| Alkanes 烷烃 | CₙH₂ₙ₊₂ | C-C single bonds 碳碳单键 |
| Alkenes 烯烃 | CₙH₂ₙ | C=C double bond 碳碳双键 |
| Alcohols 醇 | CₙH₂ₙ₊₁OH | -OH hydroxyl 羟基 |
3. Naming Alcohols | 醇的命名
Alcohol names are built in exactly the same way as alkane names, but the final '-e' of the alkane is replaced by '-ol'. So methane becomes methanol, ethane becomes ethanol, propane becomes propanol, and butane becomes butanol. The prefix tells you how many carbon atoms there are, and the suffix '-ol' tells you that an -OH group is present.
醇的命名方式与烷烃几乎相同，只需把烷烃词尾的 "-e" 换成 "-ol"。因此 methane 变为 methanol，ethane 变为 ethanol，propane 变为 propanol，butane 变为 butanol。前缀表示碳原子数，词尾 "-ol" 表示分子中存在 -OH 基团。
When the -OH group is not on the end carbon, you must add a number to show its position. The chain is numbered from the end that gives the -OH group the lowest possible number. So CH₃CH₂CH₂OH is propan-1-ol (the OH is on carbon 1), while CH₃CH(OH)CH₃ is propan-2-ol (the OH is on carbon 2). These two compounds have the same molecular formula, C₃H₈O, but different structures.
当 -OH 基团不在链端碳上时，必须加上数字标明其位置。编号应从使 -OH 获得最小可能编号的一端开始。因此 CH₃CH₂CH₂OH 是丙-1-醇（羟基在第 1 个碳上），而 CH₃CH(OH)CH₃ 是丙-2-醇（羟基在第 2 个碳上）。这两种化合物分子式相同，都是 C₃H₈O，但结构不同。
- Methanol, CH₃OH - one carbon, OH on the only carbon. | 甲醇 CH₃OH——只有 1 个碳，羟基连接在其上。
- Ethanol, C₂H₅OH - two carbons, OH on carbon 1. | 乙醇 C₂H₅OH——2 个碳，羟基在第 1 个碳上。
- Propan-1-ol, C₃H₇OH - three carbons, OH on carbon 1. | 丙-1-醇 C₃H₇OH——3 个碳，羟基在第 1 个碳上。
- Propan-2-ol, C₃H₇OH - three carbons, OH on carbon 2. | 丙-2-醇 C₃H₇OH——3 个碳，羟基在第 2 个碳上。
- Butan-1-ol, C₄H₉OH - four carbons, OH on carbon 1. | 丁-1-醇 C₄H₉OH——4 个碳，羟基在第 1 个碳上。
In CCEA examinations you will usually be asked either to name a given structure or to write the formula of a named alcohol. Practise both directions, and always check that your final formula satisfies CₙH₂ₙ₊₁OH.
在 CCEA 考试中，你通常会被要求给给定结构命名，或写出指定名称醇的化学式。两个方向都要练习，并且写完化学式后一定要检查它是否符合 CₙH₂ₙ₊₁OH。
4. Structure and Displayed Formulae | 结构与结构式的书写
A displayed formula shows every atom and every bond. For methanol you draw a carbon atom bonded to three hydrogen atoms and to one oxygen atom, and the oxygen atom bonded to one hydrogen atom. For ethanol you draw two carbon atoms joined together, with the -OH group on one of them and the remaining bonds filled by hydrogen atoms.
结构式（展开式）要画出每一个原子和每一根化学键。甲醇的画法是：一个碳原子分别与三个氢原子和一个氧原子成键，氧原子再与一个氢原子成键。乙醇的画法是：两个碳原子相连，其中一端连接 -OH 基团，其余价键由氢原子补齐。
You should be able to convert between three representations without hesitation, because examiners frequently move between them within a single question.
你应当能够毫不犹豫地在三种表示方式之间转换，因为出题人经常在同一道题中来回切换。
- Molecular formula: C₂H₆O for ethanol - shows only the numbers of atoms. | 分子式：乙醇为 C₂H₆O——只表示各原子的数目。
- Structural formula: CH₃CH₂OH - shows the order in which atoms are joined. | 结构简式：CH₃CH₂OH——表示原子的连接顺序。
- Displayed formula: every bond drawn out in full. | 结构式：把所有化学键完整画出。
The O-H bond is strongly polar because oxygen is much more electronegative than hydrogen. This single fact explains most of the physical behaviour of alcohols, from their high boiling points to their ability to dissolve in water.
O-H 键具有强极性，因为氧的电负性远大于氢。正是这一事实解释了醇的大部分物理行为，从高沸点到能溶于水。
5. Physical Properties | 物理性质
Alcohols have much higher boiling points than the alkanes of similar molecular mass. The reason is hydrogen bonding: the partially positive hydrogen of one -OH group is attracted to the lone pair on the oxygen atom of a neighbouring molecule. These intermolecular hydrogen bonds must be broken before the molecules can escape as a gas, so extra energy is needed.
与分子质量相近的烷烃相比，醇的沸点要高得多。原因是氢键：一个 -OH 上带部分正电的氢原子，会被相邻分子氧原子上的孤对电子吸引。分子要汽化逸出，必须先破坏这些分子间氢键，因此需要额外能量。
The smallest alcohols are completely miscible with water. Methanol, ethanol and propanol dissolve in water in all proportions because their -OH groups form hydrogen bonds with water molecules. As the hydrocarbon chain gets longer, the non-polar part of the molecule dominates and solubility falls sharply; butanol is only partly soluble, and longer alcohols are effectively insoluble.
最小的几种醇可与水完全互溶。甲醇、乙醇和丙醇能与水以任意比例混合，因为它们的 -OH 基团能与水分子形成氢键。随着碳链变长，分子中非极性部分占主导，溶解度急剧下降；丁醇只能部分溶解，更长的醇实际上不溶于水。
- Boiling point increases as chain length increases, because the molecules have more electrons and stronger van der Waals forces in addition to hydrogen bonding. | 沸点随碳链增长而升高，因为分子电子数增加，除氢键外范德华力也增强。
- Volatility decreases down the series, so methanol is the most volatile and evaporates fastest. | 挥发性随系列依次下降，因此甲醇最易挥发。
- Viscosity increases down the series, so longer alcohols pour more slowly. | 黏度随系列依次增大，因此较长的醇流动更慢。
- All alcohols burn with a clean flame in plenty of air, releasing carbon dioxide and water. | 在充足空气中，所有醇都能完全燃烧，生成二氧化碳和水。
6. Combustion of Alcohols | 醇的燃烧
Like other organic compounds, alcohols burn in oxygen. Complete combustion produces carbon dioxide and water and releases a large amount of energy, which is why ethanol and methanol are both used as fuels. The general equation for the complete combustion of an alcohol is shown below.
与其他有机物一样，醇能在氧气中燃烧。完全燃烧生成二氧化碳和水，并释放大量能量，这正是乙醇和甲醇都被用作燃料的原因。醇完全燃烧的通式如下。
CₙH₂ₙ₊₁OH + 3n/2 O₂ → n CO₂ + (n + 1) H₂O
For ethanol specifically, the equation is easier to remember in its whole-number form, and you should be able to balance it yourself rather than recite it.
对乙醇而言，写成整数系数的形式更容易记忆，而且你应当能够自己配平，而不是死记硬背。
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
For methanol, the balanced equation is written with two molecules of alcohol so that the oxygen count works out in whole numbers.
对甲醇而言，为了使氧原子数配成整数，方程式中要写两个醇分子。
2CH₃OH + 3O₂ → 2CO₂ + 4H₂O
Combustion is an exothermic reaction, so the energy change is negative if you are asked for the sign of ΔH. If the oxygen supply is limited, incomplete combustion occurs instead, producing carbon monoxide (a toxic, odourless gas) and carbon (soot). This is the same behaviour you met with hydrocarbons, and it is the reason a badly adjusted alcohol burner produces a yellow, smoky flame.
燃烧是放热反应，因此若题目问 ΔH 的符号，答案应为负。若氧气供应不足，则发生不完全燃烧，生成一氧化碳（有毒、无味的气体）和碳（炭黑）。这与你在烃类中学过的行为一致，也是酒精灯调节不良时产生黄色冒烟火焰的原因。
7. Oxidation of Alcohols | 醇的氧化
Alcohols can be oxidised by heating with an acidified solution of potassium dichromate(VI), K₂Cr₂O₇, acidified with dilute sulfuric acid. When ethanol is oxidised in this way, ethanoic acid is formed. This is one of the reactions specifically required by the CCEA specification, and you must be able to describe what you see as well as what is made.
醇可以在酸性重铬酸钾 (VI) 溶液 (K₂Cr₂O₇，用稀硫酸酸化) 中加热被氧化。乙醇经此氧化生成乙酸（醋酸）。这是 CCEA 大纲明确要求的反应之一，你不仅要写出产物，还要能描述观察到的现象。
CH₃CH₂OH + 2[O] → CH₃COOH + H₂O
The observation is a colour change: the orange dichromate(VI) ions are reduced to green chromium(III) ions. If you are asked to state the change for two marks, write 'orange to green' - examiners look for both colours.
观察到的现象是颜色变化：橙色的重铬酸根 (VI) 离子被还原为绿色的铬 (III) 离子。如果题目要求用两分写出该变化，就写"橙色变为绿色"——评分时需要两个颜色都出现。
- Oxidising agent: acidified potassium dichromate(VI). | 氧化剂：酸性重铬酸钾 (VI) 溶液。
- Starting colour: orange. | 起始颜色：橙色。
- Final colour: green. | 最终颜色：绿色。
- Product from ethanol: ethanoic acid, CH₃COOH. | 乙醇的产物：乙酸 CH₃COOH。
This same chemistry happens slowly in everyday life. Wine left open to the air turns sour because bacteria oxidise the ethanol to ethanoic acid, which is exactly what vinegar is. In the human body, ethanol is also oxidised in the liver, which is why alcohol acts as a depressant and why excessive drinking damages the liver.
同样的化学变化在日常生活中缓慢发生：敞口放置的葡萄酒会变酸，因为细菌把乙醇氧化成了乙酸，而醋的主要成分正是乙酸。在人体内，乙醇也在肝脏中被氧化，这既是酒精具有抑制作用的原因，也是过量饮酒损伤肝脏的原因。
8. Reaction with Sodium | 醇与钠的反应
Alcohols react with sodium metal to give a sodium alkoxide and hydrogen gas. For ethanol the equation is shown below. Fizzing is observed as hydrogen is released, and if the alcohol is warm the reaction can be vigorous enough to ignite the gas.
醇能与金属钠反应，生成醇钠和氢气。乙醇的反应方程式如下。反应中可观察到气泡（氢气）放出，若醇温度较高，反应可能剧烈到足以点燃氢气。
2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂
This reaction is much less vigorous than the reaction of sodium with water, because the alcohol molecule releases its -OH hydrogen less readily than water does. Even so, the reaction is a useful test: only compounds containing an -OH group will fizz with sodium in this way, and the same test works for carboxylic acids, although those react faster and more vigorously.
该反应比钠与水的反应缓和得多，因为醇分子释放 -OH 上氢原子的能力不如水。即便如此，它仍是一个有用的检验方法：只有含 -OH 基团的化合物才会与钠反应放出气泡；同样的检验也适用于羧酸，不过羧酸反应更快、更剧烈。
The product, sodium ethoxide (CH₃CH₂ONa), is an ionic solid once the alcohol solvent is removed. You are not required to know its detailed chemistry at GCSE, but you should be able to write and balance the equation.
产物乙醇钠 (CH₃CH₂ONa) 在除去醇溶剂后是一种离子型固体。GCSE 阶段不要求掌握它的详细化学性质，但你必须能写出并配平该方程式。
9. Uses of Alcohols | 醇的用途
Ethanol is by far the most important alcohol in everyday and industrial contexts, and the CCEA specification expects you to link its uses to its properties. Because it dissolves both polar and non-polar substances, it is an excellent solvent; because it burns readily, it is a fuel; and because it is produced naturally by fermentation, it is also the alcohol in drinks.
乙醇是日常生活和工业中最重要的一种醇，CCEA 大纲要求你把它的用途与其性质联系起来。由于它既能溶解极性物质又能溶解非极性物质，是优良的溶剂；由于容易燃烧，它是燃料；由于可由发酵天然产生，它也是饮品中的酒精。
- Solvent in perfumes, cosmetics, tinctures and cleaning products. | 用作香水、化妆品、酊剂和清洁用品的溶剂。
- Fuel, either alone or blended with petrol as E10 or E85 bioethanol. | 用作燃料，可单独使用，也可与汽油混合成 E10 或 E85 生物乙醇。
- Alcoholic drinks - ethanol produced by fermentation of sugars. | 酒精饮料——由糖类发酵产生的乙醇。
- Feedstock for making other chemicals, including ethanoic acid and esters. | 作为原料制造其他化学品，包括乙酸和酯类。
- Methanol is used as an industrial solvent and as a feedstock for producing other chemicals, and is extremely toxic if swallowed. | 甲醇用作工业溶剂和生产其他化学品的原料，若误食则剧毒。
You should also be aware of the wider social and environmental context: ethanol is a renewable fuel when produced by fermentation, but burning it still releases carbon dioxide, and growing sugar crops uses land and water.
你还需要了解更广泛的社会与环境背景：由发酵产生的乙醇是可再生燃料，但燃烧它仍然释放二氧化碳，而且种植糖料作物需要占用土地和水资源。
10. Manufacture of Ethanol by Fermentation | 乙醇的制备：发酵法
Fermentation uses yeast to convert sugars into ethanol and carbon dioxide. The sugar source is usually glucose obtained from sugar cane, sugar beet or other plant material. Yeast contains enzymes that catalyse the reaction, and the process is carried out in the absence of oxygen, that is, anaerobically, in a warm environment.
发酵法利用酵母把糖转化为乙醇和二氧化碳。糖源通常是来自甘蔗、甜菜或其他植物的葡萄糖。酵母含有能催化该反应的酶，整个过程在无氧条件下（厌氧）于温暖环境中进行。
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
The optimum temperature is about 25 °C to 35 °C. If the mixture is too cold the enzymes work too slowly; if it is above about 40 °C the enzymes are denatured and fermentation stops. The reaction is carried out in a closed container so that air is excluded, because in the presence of oxygen the yeast respires aerobically and produces carbon dioxide and water instead of ethanol.
最适温度约为 25 °C 至 35 °C。温度过低，酶促反应太慢；温度高于约 40 °C，酶变性失活，发酵停止。反应在密闭容器中进行以隔绝空气，因为有氧时酵母进行有氧呼吸，产物是二氧化碳和水而不是乙醇。
- Raw material: glucose from sugar cane, sugar beet or maize. | 原料：来自甘蔗、甜菜或玉米的葡萄糖。
- Catalyst: enzymes in yeast (a biological catalyst). | 催化剂：酵母中的酶（生物催化剂）。
- Conditions: about 25-35 °C, anaerobic, closed vessel. | 条件：约 25-35 °C，无氧，密闭容器。
- Product strength: about 10-15% ethanol; yeast is killed at higher concentrations. | 产物浓度：约 10-15% 的乙醇；浓度再高酵母会死亡。
- Purification: fractional distillation to obtain concentrated ethanol. | 提纯：通过分馏得到较浓的乙醇。
- Type of process: batch, slow, and using a renewable raw material. | 工艺类型：批量（间歇）式，速度慢，使用可再生原料。
11. Manufacture of Ethanol by Hydration of Ethene | 乙醇的制备：乙烯水化法
The second industrial route is the catalytic addition of steam to ethene. Ethene is obtained by the cracking of crude oil fractions, so this route depends on a non-renewable fossil fuel feedstock. The reaction is reversible, so the ethene and steam are passed over a phosphoric acid catalyst at high temperature and pressure, and unreacted gases are recycled.
第二条工业路线是乙烯与蒸汽的催化加成反应。乙烯来自石油馏分的裂解，因此该路线依赖不可再生的化石燃料原料
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