Alcohols
Cambridge A-Level Chemistry (9701) · Unit 16: Hydroxy compounds · 7 flashcards
Alcohols is topic 16.1 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 16 — Hydroxy compounds . In one line: Tertiary alcohols cannot be oxidized because they lack a hydrogen atom bonded to the carbon atom that is also bonded to the -OH group, which is necessary for the oxidation reaction to occur. Oxidizing primary alcohols will yield aldehydes and carboxylic acids. Oxidizing secondary alcohols will yield ketones.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 7 flashcards — 1 definition, 5 key concepts and 1 calculation — covering the precise wording mark schemes reward. Use the definition card to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
What type of alcohol (primary, secondary, or tertiary) cannot be oxidized
Tertiary alcohols cannot be oxidized because they lack a hydrogen atom bonded to the carbon atom that is also bonded to the -OH group, which is necessary for the oxidation reaction to occur. Oxidizing primary alcohols will yield aldehydes and carboxylic acids. Oxidizing secondary alcohols will yield ketones.
What the Cambridge 9701 syllabus says
2025-2027 syllabus, in our words · A2 LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Recall how alcohols can be made, with reagents and conditions: adding steam, H₂O(g), to an alkene by electrophilic addition with an H₃PO₄ catalyst; reacting an alkene with potassium manganate(VII) that is cold, dilute and acidified, giving a diol; heating a halogenoalkane with NaOH(aq) (substitution); reducing an aldehyde or a ketone with NaBH₄ or LiAlH₄; reducing a carboxylic acid with LiAlH₄; heating an ester with dilute alkali or dilute acid to hydrolyse it.
- Describe these reactions of alcohols: (a) combustion in oxygen; (b) substitution to give halogenoalkanes, for example using HX(g), KCl with concentrated H₂SO₄ or concentrated H₃PO₄, PCl₃ with heat, PCl₅, or SOCl₂; (c) reaction with Na(s); (d) oxidation by acidified K₂Cr₂O₇ or acidified KMnO₄, giving (i) carbonyl compounds when distilled off or (ii) carboxylic acids when heated under reflux (primary alcohols form aldehydes, which can be oxidised further to carboxylic acids; secondary alcohols form ketones; tertiary alcohols are not oxidised); (e) dehydration to an alkene over a heated catalyst such as Al₂O₃, or with a concentrated acid; (f) forming esters by reacting with carboxylic acids, with concentrated H₂SO₄ as catalyst; ethanol is the example to know.
- (a) Classify an alcohol as primary, secondary or tertiary, including compounds with two or more alcohol groups. (b) State typical reactions that distinguish these classes, for example mild oxidation by acidified K₂Cr₂O₇, which changes colour from orange to green.
- Use the reaction with alkaline I₂(aq), which gives a yellow precipitate of tri-iodomethane and the ion RCO₂⁻, as evidence that an alcohol contains the CH₃CH(OH)- group, i.e. that it has the structure CH₃CH(OH)-R.
- Compare the acidity of alcohols with that of water and explain the difference.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Alcohols
- › Remember that alkyl groups are electron-donating; this concentrates negative charge on the oxygen, making the ethoxide ion a stronger base.
List the reagents and conditions required to produce an alcohol via electrophilic addition of steam to an alkene.
The reagents and conditions required are steam (H₂O(g)) and a phosphoric acid catalyst (H₃PO₄). This process converts alkenes to alcohols by adding water across the double bond.
What reagents and conditions are needed to reduce a carboxylic acid to a primary alcohol?
The reducing agent is Lithium Aluminium Hydride (LiAlH₄). This reaction typically requires an anhydrous solvent, such as ether, to prevent the LiAlH₄ from reacting violently with water.
What type of alcohol (primary, secondary, or tertiary) cannot be oxidized?
Tertiary alcohols cannot be oxidized because they lack a hydrogen atom bonded to the carbon atom that is also bonded to the -OH group, which is necessary for the oxidation reaction to occur. Oxidizing primary alcohols will yield aldehydes and carboxylic acids. Oxidizing secondary alcohols will yield ketones.
Outline the reaction, including reagents, conditions, and observations, used to test for the presence of a CH₃CH(OH)- group in an alcohol.
Iodoform test. Reagents: alkaline iodine (I₂(aq) in NaOH(aq)). Observation: A positive result is indicated by the formation of a yellow precipitate of tri-iodomethane (CHI₃).
Write a balanced chemical equation for the complete combustion of ethanol.
C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(g). Complete combustion requires sufficient oxygen to fully oxidize the alcohol to carbon dioxide and water.
Describe how an alcohol can be dehydrated to form an alkene.
Alcohols can be dehydrated using a heated catalyst, such as Al₂O₃ at high temperature, or by refluxing with a concentrated acid (
Explain why alcohols are less acidic than water.
The alkyl group in an alcohol is electron-donating (positive inductive effect). It increases the negative charge density on the oxygen of the alkoxide ion (RO⁻), making it less stable than the hydroxide ion (OH⁻) and more strongly attracted to H⁺. So an alcohol releases H⁺ less readily than water does.
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