醇类

爱德思国际GCSE化学· 4.29C–4.33C· 12 分钟阅读

1. 醇类官能团与命名规则★★☆☆☆⏱ 2 min

✓ 计算器

📘 定义

醇

通式为 $C_{n} H_{2 n + 1} O H$ 的有机化合物同系物系列，特征是烷基链上连接有羟基（-OH）官能团。

根据本考纲要求，你仅需熟记直链1-醇异构体，即-OH基团连接在烷基链末端碳原子上的醇。答题时你可以使用未限定位置的名称“丙醇”和“丁醇”来代替丙-1-醇和丁-1-醇。

📐 例题

绘制丁-1-醇的展开结构式，写出它的分子式，并说明可使用的简写名称。

1
1. 画出由4个碳原子通过单共价键连接的直链，因为“丁烷（butan-）”代表4个碳原子。
2
1. 按照-1-醇后缀的要求，将-OH官能团连接在第一个（末端）碳原子上。
3
1. 用氢原子填充每个碳原子上剩余的所有成键空位，确保每个碳原子总共有4个共价键。
4
$C_4H_9OH$
5
1. 可接受的简写名称：丁醇。

✓ 快速检测

What is the defining functional group of alcohols?
- -COOH
- -OH
- -C=C-
- -COO-
显示答案
-OH —
The hydroxyl (-OH) group is the unique functional group for all alcohols.
What is the molecular formula of methanol?
- $C H_{3} O H$
- $C_{2} H_{5} O H$
- $C_{3} H_{7} O H$
- $C_{4} H_{9} O H$
显示答案
$CH_3OH$ —
Methanol has 1 carbon atom, following the $C_{n} H_{2 n + 1} O H$ general formula.

2. 乙醇的氧化反应★★★☆☆⏱ 3 min

乙醇有三种你必须为考试熟记的关键氧化反应。所有反应（除不完全燃烧外）的最终产物都是乙酸。

Complete combustion (burning) in air/oxygen to form carbon dioxide and water
Microbial oxidation by oxygen in air to form ethanoic acid (vinegar)
Heating with acidified potassium dichromate(VI) to form ethanoic acid

📐 例题

描述乙醇与稀硫酸、重铬酸钾(VI)共热时发生的可见变化与生成的产物。

1
1. 确定氧化剂：酸化重铬酸钾(VI)在反应过程中被还原。
2
1. 可见变化：橙色的重铬酸根离子（ $C r_{2} O_{7}^{2 -}$ ）转变为绿色的三价铬离子（ $C r^{3 +}$ ）。
3
1. 氧化产物：乙醇被完全氧化为乙酸，属于羧酸类。

Exam tip:

答题时务必指明重铬酸钾(VI)是用稀硫酸酸化的，才能拿到全部分数。

3. 乙醇制备：乙烯的水合反应★★★☆☆⏱ 2 min

📘 定义

乙烯水合反应

工业上的连续加成反应，乙烯与水蒸气在高温、高压和催化剂作用下反应生成纯乙醇。

你必须熟记该反应的精确条件：磷酸催化剂、约300°C的温度、60–70标准大气压。该工艺使用来源于原油裂解的不可再生乙烯作为原料。

📐 例题

写出乙烯水合生成乙醇的配平符号方程式，并说明该方法相比发酵法的一个优势。

1
1. 写出反应物分子式：乙烯 = $C_{2} H_{4}$ ，水蒸气 = $H_{2} O$
2
1. 写出产物分子式：乙醇 = $C_{2} H_{5} O H$
3
$C_2H_4 + H_2O \rightarrow C_2H_5OH$
4
1. 优势：该工艺是快速的连续生产过程，生成的乙醇纯度极高，且无废弃物产生。

4. 乙醇制备：葡萄糖的发酵★★★☆☆⏱ 2 min

📘 定义

发酵

植物来源的葡萄糖在酵母酶的作用下分解为乙醇和二氧化碳的厌氧分批反应。

发酵的所需条件：最适温度约为30 °C，隔绝空气（厌氧条件），酵母酶作为生物催化剂。该工艺使用甘蔗、玉米等农作物产出的可再生葡萄糖作为原料。

📐 例题

解释为什么发酵要在隔绝空气、约30 °C的条件下进行，而非100 °C。

1
1. 隔绝空气：空气中的氧气会使乙醇发生微生物氧化，生成不需要的乙酸（食醋），破坏产物。
2
1. 约30 °C是酵母酶的最适温度：温度过低会减慢反应速率，而温度高于约40 °C（例如100 °C）时酶会变性，无法再催化反应。

5. 乙醇制备方法的对比★★★★☆⏱ 3 min

Feature	Hydration of Ethene	Fermentation of Glucose
Raw material	Ethene (crude oil, non-renewable)	Glucose (crops, renewable)
Process type	Continuous 24/7 operation	Batch (stopped when product forms)
Conditions	~300 °C, 60-70 atm, $H_{3} P O_{4}$ catalyst	~30 °C, 1 atm, no air, yeast
Product purity	Very pure ethanol	Dilute ethanol (requires distillation)
Reaction rate	Fast	Slow (takes days)

✓ 快速检测

Which method produces a renewable ethanol product?
- Hydration of ethene
- Fermentation
- Both
- Neither
显示答案
Fermentation —
Fermentation uses glucose from regrowable crops, making it a renewable process.
What catalyst is used for ethene hydration?
- Yeast
- Iron
- Phosphoric acid
- Nickel
显示答案
Phosphoric acid —
Phosphoric acid is the required catalyst for the industrial hydration reaction.

6. 常见陷阱

错误做法:

Drawing the -OH group bonded to hydrogen instead of a carbon atom in the alkyl chain

原因:

The hydroxyl group is covalently attached to the carbon chain, not a free ion, so this structure is chemically incorrect.

正确做法:

Always attach the oxygen atom of the -OH group directly to a carbon atom in the alkyl chain.

错误做法:

Stating potassium dichromate(VI) oxidises ethanol without mentioning it is acidified with dilute sulfuric acid

原因:

Potassium dichromate only acts as an oxidising agent in acidic conditions, so this missing detail costs you marks.

正确做法:

Always refer to 'acidified potassium dichromate(VI)' or explicitly mention the dilute sulfuric acid.

错误做法:

Stating fermentation is done at 100 °C to speed up the reaction

原因:

Temperatures above ~40 °C denature yeast enzymes, stopping the reaction entirely.

正确做法:

Recall fermentation uses an optimum temperature of ~30 °C to maximise enzyme activity without denaturing.

错误做法:

Forgetting to specify that fermentation must be carried out in the absence of air

原因:

Oxygen in air oxidises ethanol to unwanted ethanoic acid, ruining the desired product.

正确做法:

Always state fermentation uses anaerobic (no air) conditions.

错误做法:

Drawing the -OH group on the second carbon for propanol or butanol

原因:

Only propan-1-ol and butan-1-ol are required for this specification; 2-ol isomers are out of scope.

正确做法:

Attach the -OH group to the first (end) carbon in the chain for propanol and butanol.

7. 速查表

Concept	Key Recall Point
Functional group	-OH (hydroxyl)
Methanol formula	$C H_{3} O H$
Ethanol formula	$C_{2} H_{5} O H$
Propanol formula	$C_{3} H_{7} O H$
Butanol formula	$C_{4} H_{9} O H$
Ethanol combustion products	$C O_{2} + H_{2} O$
Ethanol oxidation product	Ethanoic acid
Dichromate colour change	Orange → Green
Hydration conditions	~300°C, 60-70 atm, $H_{3} P O_{4}$ catalyst
Fermentation conditions	~30°C, no air, yeast catalyst
Fermentation no air reason	Prevents ethanol → ethanoic acid
Fermentation temp reason	Max enzyme activity, no denaturing

8. 常见问题

本次考试我需要掌握丙-2-醇或丁-2-醇的相关内容吗？

不需要，仅要求掌握丙-1-醇和丁-1-醇。使用未限定位置的名称“丙醇”和“丁醇”指代这两种1-醇异构体也是可接受的答案。

乙醇被酸化重铬酸钾(VI)氧化时会出现什么颜色变化？

在乙醇被氧化为乙酸的过程中，橙色的重铬酸根离子溶液会变为绿色，因为重铬酸根被还原为三价铬离子。

深入阅读

sub_topic烯烃
sub_topic羧酸
sub_topic酯类

下一步

Now you have mastered alcohol content for Edexcel IGCSE Chemistry, move on to related organic chemistry topics that build directly on this knowledge. First, study carboxylic acids, the product of ethanol oxidation, including their functional group, structure and reactions. Next, learn about esters, which form when alcohols react with carboxylic acids, another high-frequency Paper 2C topic. You can also revisit alkenes to reinforce your understanding of the hydration reaction raw material, or practice organic synthesis questions that combine multiple functional group reactions to prepare for longer 4-6 mark exam questions.

→Alkenes