📚 GCSE AQA Chemistry: Alcohols Revision | GCSE AQA 化学：醇 考点精讲
Alcohols are a vital homologous series in organic chemistry, recognised by the hydroxyl functional group. In AQA GCSE Chemistry, you must understand their structure, naming, key reactions, and the two ways to produce ethanol, plus the trends in their physical properties and their everyday uses. This comprehensive revision guide breaks down every exam-relevant point with paired English and Chinese explanations to boost your confidence.
醇是有机化学中一个重要的同系物，特征官能团为羟基。在AQA GCSE化学中，你需要掌握醇的结构、命名、重要反应、两种制取乙醇的方法，还要理解其物理性质的变化规律和日常用途。这份详细的复习指南用中英双语解释每一个考点，帮助你在考试中自信作答。
1. What are Alcohols? | 什么是醇？
Alcohols are organic compounds containing one or more hydroxyl (-OH) groups attached to a saturated carbon atom. They form a homologous series, sharing a common general formula and displaying a gradual trend in physical properties. The first four members are methanol, ethanol, propanol and butanol.
醇是含有一个或多个羟基（-OH）连接在饱和碳原子上的有机化合物。它们组成同系物，具有相同的通式，且物理性质呈现规律性变化。前四个成员依次是甲醇、乙醇、丙醇和丁醇。
At room temperature the first four alcohols are colourless liquids, and they all dissolve completely in water to give neutral solutions. This last point is examinable: alcohols are not alkalis, even though they contain an -OH group.
室温下前四个醇都是无色液体，且都能完全溶于水，形成中性溶液。这一点是考点：虽然醇含有 -OH 基团，但它们并不是碱。
| Name 名称 | Molecular formula 分子式 | Displayed structure 结构简式 |
| Methanol 甲醇 | CH₃OH | CH₃-OH |
| Ethanol 乙醇 | C₂H₅OH | CH₃-CH₂-OH |
| Propanol 丙醇 | C₃H₇OH | CH₃-CH₂-CH₂-OH |
| Butanol 丁醇 | C₄H₉OH | CH₃-CH₂-CH₂-CH₂-OH |
2. Functional Group & General Formula | 官能团与通式
The functional group of an alcohol is the hydroxyl group, -OH. For saturated straight-chain alcohols with just one -OH group, the general formula is CₙH₂ₙ₊₁OH, where n ≥ 1. This can also be expressed as CₙH₂ₙ₊₁O, but the -OH form directly shows the functional group.
醇的官能团是 -OH。对于饱和直链一元醇，通式为 CₙH₂ₙ₊₁OH（n ≥ 1）。也可写作 CₙH₂ₙ₊₁O，但带 -OH 的形式能直接展示官能团。
C₈H₁₇OH. Note that the -OH group is always written separately at the end of the formula, not simply folded into the H count.
利用通式可以推出同系物中任一成员的化学式。例如 n = 4 时为 C₄H₉OH（丁醇），n = 8 时为 C₈H₁₇OH。注意 -OH 基团通常单独写在化学式末尾，而不是简单并入氢原子计数中。
CₙH₂ₙ₊₁OH ⇌ CₙH₂ₙ₊₁O
Because the carbon that carries the -OH group has four single bonds to other atoms, alcohols are described as saturated. This is why alcohols will not decolourise bromine water - a useful way to tell them apart from alkenes in a test question.
由于带 -OH 的碳原子与其他原子之间都是单键，醇属于饱和化合物。因此醇不能使溴水褪色——这就是考试中区分醇与烯烃的一个实用方法。
3. Naming Alcohols | 醇的命名
Select the longest carbon chain that includes the carbon bonded to the -OH group. The suffix is "-ol", is '-ol', and a number indicates the position of the -OH group along the chain. The number should be as low as possible.
命名时先找出包含与 -OH 相连碳原子的最长碳链，词尾用 "-ol"，并加数字标明 -OH 在碳链上的位置，该数字应尽可能小。
- CH₃OH -> methanol (甲醇)
- CH₃CH₂OH -> ethanol (乙醇)
- CH₃CH₂CH₂OH -> propan-1-ol (丙-1-醇)
- CH₃CH(OH)CH₃ -> propan-2-ol (丙-2-醇)
- CH₃CH₂CH₂CH₂OH -> butan-1-ol (丁-1-醇)
The position number matters whenever there is more than one possible place for the -OH group, because propan-1-ol and propan-2-ol are different compounds with different properties. You must be able to name an alcohol from its displayed formula and also draw the structure from a name.
只要 -OH 有多个可能的位置，就必须标出位置编号，因为丙-1-醇和丙-2-醇是性质不同的两种化合物。你需要既能根据结构式写出名称，也能根据名称画出结构式。
When you write the name in an answer, remember the hyphens: "propan-1-ol" is correct, while "propan1ol" or "1-propanol" may lose you the mark in a strict AQA mark scheme.
书写名称时注意连字符：正确写法是 "propan-1-ol"，而 "propan1ol" 或 "1-propanol" 在严格的 AQA 评分标准中可能拿不到分。
4. Physical Properties & Trends | 物理性质与变化规律
As the length of the carbon chain increases, the boiling point of the alcohol rises, its volatility decreases and its viscosity increases. The -OH group allows hydrogen bonding between molecules, so alcohols have much higher boiling points than the alkanes of similar relative molecular mass.
随着碳链变长，醇的沸点升高、挥发性降低、黏度增大。-OH 基团使分子间可以形成氢键，因此醇的沸点远高于相对分子质量相近的烷烃。
Methanol, ethanol, propanol and butanol are all soluble in water because the -OH group forms hydrogen bonds with water molecules. Longer-chain alcohols become less soluble as the hydrocarbon part of the molecule grows.
甲醇、乙醇、丙醇和丁醇都能溶于水，因为 -OH 基团可与水分子形成氢键。碳链更长时，分子中烃基部分增大，溶解度会下降。
| Property 性质 | Trend down the series 同系物变化趋势 | Reason 原因 |
| Boiling point 沸点 | Increases 升高 | Stronger intermolecular forces 分子间作用力增强 |
| Volatility 挥发性 | Decreases 降低 | More energy needed to escape 需要更多能量才可汽化 |
| Viscosity 黏度 | Increases 增大 | Longer molecules tangle 分子链更长更易缠结 |
| Solubility in water 水溶性 | Decreases 降低 | Hydrocarbon part dominates 烃基部分占主导 |
5. Combustion of Alcohols | 醇的燃烧
Alcohols burn in oxygen to release energy, which is why ethanol is used as a fuel. In a good supply of air, complete combustion produces carbon dioxide and water only, giving a clean blue flame.
醇在氧气中燃烧会释放能量，这正是乙醇可作燃料的原因。空气充足时完全燃烧只生成二氧化碳和水，火焰呈干净的蓝色。
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
rect state symbols is a very common exam question: C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l).
燃烧是放热反应，因此环境温度升高。配平并写对状态符号的方程式是常见考题：C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)。
If the oxygen supply is limited, incomplete combustion occurs and carbon monoxide or soot (carbon) is produced instead. Carbon monoxide is toxic and odourless, so alcohols are described as burning more cleanly than petrol or diesel.
若氧气不足则发生不完全燃烧，会生成一氧化碳或炭黑（碳）。一氧化碳无色无味且有毒，因此人们认为醇比汽油、柴油燃烧得更清洁。
6. Reaction with Sodium | 醇的 Reaction with Sodium | 醇与钠的反应
Ethanol reacts with sodium metal to produce sodium ethoxide and hydrogen gas. The reaction is similar to the reaction of sodium with water, but noticeably less vigorous.
乙醇与金属钠反应生成乙醇钠和氢气。该反应与钠和水的反应相似，但明显更平缓。
2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂
Observations you should be able to describe: the sodium sinks and fizzes, bubbles of gas are given off, the sodium gradually dissolves, and no flame is usually seen. The gas produced gives a squeaky pop with a lit splint, confirming it is hydrogen.
需要能描述的实验现象：钠沉在液体中并不断冒气泡，有气体放出，钠逐渐溶解，通常看不到火焰。放出的气体遇到点燃的木条会发出爆鸣声，证明是氢气。
This reaction is a useful way to show that the -OH hydrogen in an alcohol is slightly reactive, and it also explains why alcohols must be kept away from reactive metals in storage.
该反应可用来说明醇中 -OH 上的氢具有一定活性，也解释了为什么储存醇时要远离活泼金属。
7. Oxidation of Alcohols | 醇的氧化
Alcohols can be oxidised in two ways that AQA expects you to know. The first is microbial oxidation: bacteria in warm, air-rich conditions convert ethanol into ethanoic acid, which is the acid in vinegar. The second uses an oxidising agent such as acidified potassium dichromate(VI).
AQA 要求掌握两种氧化方式。第一是微生物氧化：在有空气的温暖环境中，细菌把乙醇转化为乙酸，也就是醋中的酸。第二是使用氧化剂，例如酸化的重铬酸钾(VI)溶液。
C₂H₅OH + 2[O] → CH₃COOH + H₂O
With acidified potassium dichromate(VI), the solution changes from orange to green as the alcohol is oxidised. In AQA GCSE you are expected to know that the product of oxidising ethanol is ethanoic acid, and that this is the reaction used when wine or beer goes sour in the air.
使用酸化的重铬酸钾(VI)溶液时，随着醇被氧化，溶液颜色由橙色变为绿色。AQA GCSE 要求知道乙醇被氧化的产物是乙酸，这也是葡萄酒或啤酒接触空气后变酸的原因。
Do not confuse this with combustion: oxidation by chemical agents or bacteria happens at much lower temperatures and does not produce carbon dioxide and water as the only products.
不要把它与燃烧混淆：化学氧化剂或细菌氧化在低得多的温度下进行，产物也不是仅有二氧化碳和水。
8. Producing Ethanol by Fermentation | 用发酵法制取乙醇
Fermentation uses sugar from plants such as sugar cane or sugar beet. Yeast is added and the mixture is kept warm at about 25 to 35 °C with no oxygen present, so the yeast respires anaerobically and produces ethanol and carbon dioxide.
发酵法使用甘蔗或甜菜等植物中的糖。加入酵母后，在约 25 至 35 °C 的温暖条件下隔绝氧气，酵母进行无氧呼吸，生成乙醇和二氧化碳。
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
If the temperature is too low the yeast is inactive and the reaction is very slow; if it is too high the enzymes in the yeast are denatured and fermentation stops. The dilute ethanol produced is then concentrated by fractional distillation.
温度过低酵母不活跃，反应非常缓慢；温度过高酵母中的酶会变性，发酵停止。得到的稀乙醇再通过分馏浓缩。
Advantages of fermentation: the raw material is a renewable resource, the process uses gentle conditions and cheap apparatus. Disadvantages: it is slow, it takes place in batches, and the ethanol concentration is limited because the yeast is eventually killed by the alcohol it makes.
发酵法的优点：原料是可再生资源，条件温和、设备便宜。缺点：速度慢、属于间歇（分批）生产，而且乙醇浓度有限，因为酵母最终会被自身产生的酒精杀死。
9. Producing Ethanol from Ethene | 用乙烯制取乙醇
The second industrial route starts with ethene obtained from the cracking of crude oil fractions. Ethene is reacted with steam in the presence of a phosphoric acid catalyst at about 300 °C and 60 to 70 atmospheres of pressure.
第二种工业路线以裂解石油馏分得到的乙烯为原料。乙烯在磷酸催化下与水蒸气反应，温度约 300 °C，压强约 60 至 70 个大气压。
C₂H₄ + H₂O → C₂H₅OH
This is an addition reaction: the double bond in ethene opens up and the -OH group and a hydrogen atom add across it. No other product is formed, so the ethanol obtained is very pure.
这是加成反应：乙烯中的双键打开，-OH 基团和氢原子分别加到两个碳原子上。反应没有其他产物，因此得到的乙醇纯度很高。
Advantages of this route: it is fast, continuous and gives a very pure product. Disadvantages: ethene comes from crude oil, which is a finite, non-renewable resource, and the high temperature and pressure make the process energy-intensive and expensive to run.
该路线的优点：速度快、可连续生产、产品纯度很高。缺点：乙烯来自原油，属于有限且不可再生的资源，而且高温高压使工艺能耗高、成本大。
10. Comparing the Two Methods | 两种方法的比较
Exam questions often ask you to compare fermentation and hydration of ethene and to decide which is better, so you must be able to give advantages and disadvantages of each and justify a conclusion with a reason.
考试常要求比较发酵法和乙烯水化法，并判断哪种更好，因此你必须能说出各自的优缺点，并给出理由支持你的结论。
| Feature 对比项 | Fermentation 发酵法 | Ethene + steam 乙烯水化法 |
| Raw material 原料 | Sugar from plants 植物中的糖 | Ethene from crude oil 原油中的乙烯 |
| Renewable? 可再生？ | Yes 是 | No 否 |
| Conditions 条件 | 25-35 °C, no oxygen 无氧 | 300 °C, 60-70 atm, catalyst 催化剂 |
| Speed 速度 | Slow, batch 慢，分批 | Fast, continuous 快，连续 |
| Purity 纯度 | Low, needs distillation 低，需分馏 | High 高 |
A strong answer links the choice to the context. For a country with plenty of farmland and a need for a sustainable fuel, fermentation may be preferred; for a factory that needs large volumes of pure ethanol quickly, hydration of ethene is more suitable.
高分答案会把选择与情境结合。若有大量农田且需要可持续燃料，发酵法可能更合适；若工厂需要快速获得大量高纯度乙醇，乙烯水化法更合适。
11. Uses of Alcohols | 醇的用途
Ethanol is used as a fuel, either on its own or blended with petrol as a biofuel. It burns cleanly and is made from plants, so it is considered a greener alternative to fossil fuels.
乙醇可用作燃料，既可单独使用，也可与汽油混合作为生物燃料。它燃烧较清洁且由植物制得，因此被视为比化石燃料更环保的选择。
Alcohols are also excellent solvents because they dissolve both water-soluble and many oil-soluble substances. Ethanol is the solvent in perfumes, aftershaves, inks and some medicines, and it is used in hand sanitisers and antiseptics because it kills microorganisms.
醇还是优良的溶剂，既能溶解水溶性物质，也能溶解许多油溶性物质。乙醇是香水、须后水、油墨和部分药物的溶剂，也因能杀灭微生物而用于免洗洗手液和消毒剂。
- Fuel and biofuel 燃料与生物燃料
- Solvent in perfumes, inks and medicines 香水、油墨和药物中的溶剂
- Alcoholic drinks 酒精饮料
- Antiseptic and disinfectant 消毒杀菌
- Feedstock for making other chemicals 制造其他化学品的原料
Methanol is used as an industrial solvent and feedstock, but it is highly toxic, so it must never be confused with ethanol in a question about drinks.
甲醇用作工业溶剂和化工原料，但毒性很强，因此在涉及饮料的题目中绝不能与乙醇混淆。
12. Exam Technique & Common Mistakes | 考试技巧与常见错误
Read the command word carefully. "Name" requires only the word, "describe" requires the observations or the method, and "explain" requires a reason linked to particles, bonding or energy.
注意题目中的指令词。"Name" 只需写出名称，"describe" 需要描述现象或步骤，而 "explain" 则要给出与粒子、化学键或能量相关的原因。
- Always balance equations and include state symbols when asked 方程式必须配平，要求时写出状态符号
- Write -OH, not OH⁻, because alcohols are neutral 写作 -OH 而非 OH⁻，因为醇是中性的
- Use the lowest possible position number in naming 命名时位置编号取最小
- Do not say alcohols turn bromine water colourless 不要说醇能使溴水褪色
- Give a temperature range for fermentation, not just "warm" 发酵要给出温度范围，而不只是"温暖"
- Link each advantage or disadvantage to a reason 每个优缺点都要给出理由
A very common error is to describe the reaction of ethanol with sodium as being "the same as water". It is similar but slower, and the salt formed is sodium ethoxide, not sodium hydroxide. Another frequent mistake is to forget that the oxidation of ethanol by bacteria produces ethanoic acid, not carbon dioxide.
最常见的错误之一是把乙醇与钠的反应说成"和水一样"。二者相似但更缓慢，生成的盐是乙醇钠，而不是氢氧化钠。另一个常见错误是忘记乙醇被细菌氧化生成的是乙酸，而不是二氧化碳。
Finally, practise writing full structural formulae from names and naming structures from formulae. These short questions appear in almost every paper and are the easiest marks to secure if you are careful with numbers and hyphens.
最后，要练习根据名称写完整结构式、根据结构式写名称。这类小题几乎每份试卷都会出现，只要数字和连字符写得准确，就是最容易拿到手的分数。
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