What are alcohols in the context of Cambridge IGCSE Organic Chemistry?

In Cambridge IGCSE Organic Chemistry, alcohols are a group of organic compounds characterized by the presence of one or more hydroxyl (-OH) groups attached to a carbon atom. They are important in various chemical reactions and are used in numerous applications, including as solvents and fuels.

How are alcohols named according to IUPAC nomenclature?

Alcohols are named using IUPAC nomenclature by identifying the longest carbon chain containing the hydroxyl group and replacing the '-e' ending of the corresponding alkane with '-ol'. The position of the hydroxyl group is indicated by a number. For example, CH3CH2OH is named ethanol.

What are the physical properties of alcohols that are relevant to the IGCSE Chemistry syllabus?

Alcohols generally have higher boiling points than alkanes and alkenes of similar molecular weight due to hydrogen bonding. They are also polar, which makes lower alcohols like methanol and ethanol soluble in water. These properties are significant in understanding their behavior and applications in IGCSE Chemistry.

What are the common reactions involving alcohols studied in IGCSE Chemistry?

In IGCSE Chemistry, students learn about several reactions involving alcohols, including combustion, oxidation, and esterification. Alcohols can be oxidized to form aldehydes, ketones, or carboxylic acids, and they react with carboxylic acids to form esters in the presence of an acid catalyst.

Why are alcohols considered important in industrial applications?

Alcohols are crucial in industrial applications due to their versatility. Ethanol, for example, is used as a solvent, in alcoholic beverages, and as a biofuel. Methanol is used in the production of formaldehyde and as a fuel additive. Their ability to dissolve both polar and non-polar substances makes them valuable in various chemical processes.

Why is "Using too high a temperature for fermentation" a common mistake in Alcohols?

Why it happens: Wanting faster reaction. How to avoid it: Above 40C yeast enzymes denature → reaction stops. Optimum is 25-40C. Source: 0620/42 — recurring

Why is "Forgetting the phosphoric acid catalyst" a common mistake in Alcohols?

Why it happens: Skipping conditions. How to avoid it: Always mention H_3PO_4 catalyst, plus T and P.

Why is "Forgetting CO₂ in the fermentation equation" a common mistake in Alcohols?

Why it happens: Speed. How to avoid it: Two products: ethanol AND carbon dioxide. Glucose → 2C₂H₅OH + 2CO₂.

Organic ChemistryCambridge IGCSE Chemistry (0620)

Alcohols

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Alcohols — Cambridge IGCSE 0620 Chemistry Extended (2026)

Functional group -OH. Ethanol is the famous one. Two production methods (fermentation and addition of water to ethene). Combustion and oxidation reactions.

What you’ll learn

Mapped to the Cambridge IGCSE 0620 syllabus (2026-2028).

13.6 — Describe alcohols as containing the -OH functional group.
13.6 — Describe production of ethanol by fermentation and by hydration of ethene.
13.6 — Compare the two methods.
13.6 — Describe uses of ethanol and balance combustion equations.

Structure and the -OH functional group

Alcohol = OH group attached to a carbon. Confers polarity, water-solubility (for short chains), and reactivity.

Alcohol = a compound containing one (or more) -OH groups attached to a carbon.

General formula: $\text{C}_{n}\text{H}_{2n+1}\text{OH}$ .

First three.

Name	Formula	Structural
Methanol	CH₃OH	$\text{CH}_{3}\text{OH}$
Ethanol	C₂H₅OH	$\text{CH}_{3}\text{CH}_{2}\text{OH}$
Propanol (1-)	C₃H₇OH	$\text{CH}_{3}\text{CH}_{2}\text{CH}_{2}\text{OH}$

Note: propanol has TWO isomers — propan-1-ol and propan-2-ol — depending on where the OH is.

Properties.

The -OH group is polar; can hydrogen-bond with water.
Methanol, ethanol, propanol are MISCIBLE with water (any proportion).
Beyond ~ 4 carbons, alcohols become less water-soluble (long alkyl chain dominates).
All have b.p. higher than corresponding alkanes (hydrogen-bonding).

Worked qualitative. Ethanol b.p. $78\degree\text{C}$ ; ethane b.p. $-89\degree\text{C}$ . Why so different? Ethanol's -OH groups form hydrogen bonds between molecules → much stronger intermolecular forces → much higher b.p. Ethane is non-polar.

Cambridge tip. Always write the OH at the end of the structural formula: CH₃CH₂OH for ethanol, NOT C₂H₆O (ambiguous).

-OH functional group.
$\text{C}_{n}\text{H}_{2n+1}\text{OH}$ .
Methanol, ethanol, propanol.
Polar; short chains miscible with water.
Higher b.p. than corresponding alkanes.

Ethanol by fermentation

Yeast converts sugar to ethanol + CO₂. Slow, batch, sustainable.

Process. Yeast (a fungus) converts sugar (glucose) into ethanol and carbon dioxide: $\text{C}_{6}\text{H}_{12}\text{O}_{6} \xrightarrow{\text{yeast}} 2\text{C}_{2}\text{H}_{5}\text{OH} + 2\text{CO}_{2}.$

Conditions.

Temperature: $25-35\degree\text{C}$ (yeast enzymes work best in this range).
Anaerobic (no air) — otherwise yeast respires, giving CO₂ and water instead.
Sugar feedstock from grapes (wine), barley (beer), sugar cane, corn, etc.

Limitations.

Yeast cells DIE at $\sim 14\%$ alcohol — fermentation can't go above that concentration.
For higher concentrations, need to distil after fermentation.
Slow (hours to days).
Batch process (one fermenter, stop, restart).

Use. Drinks (wine, beer, spirits), bioethanol fuel.

Sustainability. Sugar crops are renewable — fermentation is considered carbon-neutral (the CO₂ released equals what was absorbed by the crop). Often used for biofuel.

Worked. Calculate maximum mass of ethanol from $90\,\text{g}$ glucose.

$M_r$ glucose: $180$ . Moles glucose: $90/180 = 0.5\,\text{mol}$ .
Ethanol moles: $2 \times 0.5 = 1.0\,\text{mol}$ .
$M_r$ ethanol: $46$ . Mass: $1.0 \times 46 = 46\,\text{g}$ .

Yeast + sugar → ethanol + CO₂.
$25-35\degree\text{C}$ , anaerobic.
Stops at $\sim 14\%$ — yeast dies.
Slow, batch, sustainable.

Ethanol by addition of water to ethene

Catalytic hydration of ethene. Continuous, fast, but uses fossil-fuel ethene.

Process. $\text{CH}_{2}=\text{CH}_{2} + \text{H}_{2}\text{O} \xrightarrow{\text{H}_{3}\text{PO}_{4}, 300\degree\text{C}, 60\,\text{atm}} \text{CH}_{3}\text{CH}_{2}\text{OH}.$

Conditions.

Temperature: $\sim 300\degree\text{C}$ .
Pressure: $\sim 60\,\text{atm}$ .
Catalyst: phosphoric acid ( $\text{H}_{3}\text{PO}_{4}$ ).

Source of ethene. Cracking of long-chain alkanes (from petroleum). So this process depends on a non-renewable resource.

Compare with fermentation.

Aspect	Fermentation	Hydration
Speed	Slow (days)	Fast (continuous)
Mode	Batch	Continuous
Source	Renewable (sugar crop)	Non-renewable (petroleum)
Conditions	Mild ( $30\degree\text{C}$ , atm pressure)	Harsh ( $300\degree\text{C}$ , $60\,\text{atm}$ )
Energy cost	Low	High (high T and P)
Purity of product	Needs distillation (yeast at $\sim 14\%$ )	High purity directly
Yield	$\sim 50\%$ ethanol from glucose mass	Near $100\%$ (no by-products)

Cambridge tip. Cambridge often asks: "compare fermentation and hydration of ethene as methods of producing ethanol". Mention all SIX axes above for full marks.

Hydration: ethene + water → ethanol.
Conditions: $300\degree\text{C}$ , $60\,\text{atm}$ , H₃PO₄ catalyst.
Continuous, fast, high yield.
Non-renewable source.
Cambridge wants to compare fermentation AND hydration.

Reactions and uses of alcohols

Combustion (clean burning), oxidation to carboxylic acid. Uses: fuel, solvent, drinks.

Combustion. Ethanol burns cleanly with a pale blue flame: $\text{C}_{2}\text{H}_{5}\text{OH} + 3\text{O}_{2} \to 2\text{CO}_{2} + 3\text{H}_{2}\text{O}.$

Used as a FUEL — bioethanol added to petrol (E10, E85), or used neat in some Brazilian cars.

Oxidation to carboxylic acid. Ethanol left in air slowly oxidises to ethanoic acid (vinegar): $\text{C}_{2}\text{H}_{5}\text{OH} + 2[\text{O}] \to \text{CH}_{3}\text{COOH} + \text{H}_{2}\text{O}.$

(Also done in the lab with an oxidising agent like acidified KMnO₄.)

That's why old wine becomes vinegar — bacteria in the wine oxidise ethanol to ethanoic acid.

Reaction with carboxylic acid: esterification. See carboxylic acids note.

Uses of ethanol.

Fuel (alone or blended with petrol — bioethanol).
Solvent in perfumes, cosmetics, paints, printing inks.
Drinks (beer, wine, spirits).
Antiseptic (kills bacteria; hand sanitisers are typically $\sim 70\%$ ethanol).

Methanol. Highly TOXIC — can cause blindness or death even in small doses. Used industrially as solvent and as antifreeze. NOT for drinks.

Cambridge tip. When asked "give two uses of ethanol", pick from: fuel, solvent, antiseptic, drinks. Avoid using "fuel" twice with different examples.

Combustion: clean burning, used as fuel.
Oxidation: ethanol → ethanoic acid (vinegar).
Uses: fuel, solvent, drinks, antiseptic.
Methanol: TOXIC; not for drinks.

How it’s examined

Alcohols appear every Paper 4 (6-8 marks): write fermentation equation, compare production methods, balance combustion. Examiner reports flag missing the conditions (temperature, catalyst) for hydration of ethene.

Sources: Cambridge IGCSE Chemistry 0620 syllabus 2026-2028 (13.6); 0620/42 Oct/Nov 2024 — Q25 (ethanol production); 0620 Examiner Reports 2022-2024. Last reviewed 2026-05-07.

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Step-by-step worked examples — Alcohols

Step-by-step solutions to past-paper-style questions on alcohols, written exactly the way a tutor would explain them at the board.

1Fermentation of glucose
Core• Adapted from 0620/22 May/Jun 2024 Q14• fermentation
Question
Write the equation and conditions for the fermentation of glucose.
Step-by-step solution
1. Step 1
  Yeast (enzymes) at $25\text{-}40\degree\text{C}$ , anaerobic.
  $\text{C}_{6}\text{H}_{12}\text{O}_{6} \xrightarrow{\text{yeast}} 2\text{C}_{2}\text{H}_{5}\text{OH} + 2\text{CO}_{2}$
Answer
Glucose → ethanol + CO₂ (yeast, 25-40°C, no oxygen).
2Hydration of ethene
Extended• hydration
Question
Write the equation and conditions for making ethanol from ethene.
Step-by-step solution
1. Step 1
  Ethene + steam, $\text{H}_{3}\text{PO}_{4}$ catalyst, 300°C, 60 atm.
  $\text{C}_{2}\text{H}_{4} + \text{H}_{2}\text{O} \xrightarrow{\text{H}_{3}\text{PO}_{4}} \text{C}_{2}\text{H}_{5}\text{OH}$
Answer
$\text{C}_{2}\text{H}_{4} + \text{H}_{2}\text{O} \to \text{C}_{2}\text{H}_{5}\text{OH}$ (steam, H₃PO₄, 300°C, 60 atm).
3Compare fermentation and hydration
Extended• compare
Question
Compare fermentation and hydration as methods of making ethanol.
Step-by-step solution
1. Step 1
  Fermentation: BATCH; cheap renewable feedstock (sugar/grain); slow; gives dilute, impure ethanol.
2. Step 2
  Hydration: CONTINUOUS; non-renewable feedstock (ethene from oil); fast; gives pure ethanol.
Answer
Fermentation: renewable but slow & impure. Hydration: fast & pure but uses fossil-fuel feedstock.
4Combustion of ethanol
Extended• combustion
Question
Write the equation for the complete combustion of ethanol.
Step-by-step solution
1. Step 1
  $\text{C}_{2}\text{H}_{5}\text{OH}$ + O₂ → CO₂ + H₂O.
  $\text{C}_{2}\text{H}_{5}\text{OH} + 3\text{O}_{2} \to 2\text{CO}_{2} + 3\text{H}_{2}\text{O}$
Answer
$\text{C}_{2}\text{H}_{5}\text{OH} + 3\text{O}_{2} \to 2\text{CO}_{2} + 3\text{H}_{2}\text{O}$

Key Formulae — Alcohols

The formulae you need to memorise for alcohols on the Cambridge IGCSE 0620 paper, with every variable defined in plain English and a note on when to use it.

Alcohol general formula
$\text{C}_{n}\text{H}_{2n+1}\text{OH}$
When to use
Any straight-chain alcohol.

Key Definitions and Keywords — Alcohols

Definitions to memorise and the exact keywords mark schemes credit for alcohols answers — sharpened from recent examiner reports for the 2026 0620 sitting.

Alcohol
Examiner keyword
Organic compound containing the $-\text{OH}$ functional group.
Fermentation
Examiner keyword
Anaerobic conversion of sugar to ethanol and carbon dioxide, catalysed by yeast enzymes at 25-40°C.
Biofuel
Examiner keyword
Fuel made from biological material — bioethanol from fermentation can be added to petrol.

Common Mistakes and Misconceptions — Alcohols

The traps other students keep falling into on alcohols questions — taken from recent Cambridge IGCSE 0620 examiner reports and mark schemes — and how to avoid them.

✕Using too high a temperature for fermentation
0620/42 — recurring
Why it happens
Wanting faster reaction.
How to avoid it
Above $\sim 40\degree\text{C}$ yeast enzymes denature → reaction stops. Optimum is $25\text{-}40\degree\text{C}$ .
✕Forgetting the phosphoric acid catalyst
Why it happens
Skipping conditions.
How to avoid it
Always mention $\text{H}_{3}\text{PO}_{4}$ catalyst, plus T and P.
✕Forgetting CO₂ in the fermentation equation
Why it happens
Speed.
How to avoid it
Two products: ethanol AND carbon dioxide. Glucose → 2C₂H₅OH + 2CO₂.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

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Video lesson

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Alcohols — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Alcohols

Short Study Notes in the form of Slides

Detailed Study Notes

What you’ll learn

How it’s examined

1Fermentation of glucose

2Hydration of ethene

3Compare fermentation and hydration

4Combustion of ethanol

Alcohol general formula

Alcohol

Fermentation

Biofuel

✕Using too high a temperature for fermentation

✕Forgetting the phosphoric acid catalyst

✕Forgetting CO₂ in the fermentation equation

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Alcohols — frequently asked questions