9701 · 32.1
Alcohols flashcards
Revision flashcards for Cambridge 9701 Alcohols (syllabus 32.1). Flip, recall, then mark a real past-paper question.
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What is a primary (1°) alcohol?
An alcohol where the carbon atom bonded to the -OH group is attached to only one other alkyl group (or none, for methanol). General structure: RCH₂OH.
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What is a secondary (2°) alcohol?
An alcohol where the carbon atom bonded to the -OH group is attached to two other alkyl groups. General structure: R₂CHOH.
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What is a tertiary (3°) alcohol?
An alcohol where the carbon atom bonded to the -OH group is attached to three other alkyl groups. General structure: R₃COH.
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Reagents and conditions for oxidation of a primary alcohol to an aldehyde?
Reagent: Acidified potassium dichromate(VI) ($K_2Cr_2O_7 / H_2SO_4$). Conditions: Gentle heating and immediate distillation of the product to prevent further oxidation.
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Reagents and conditions for oxidation of a primary alcohol to a carboxylic acid?
Reagent: Acidified potassium dichromate(VI) ($K_2Cr_2O_7 / H_2SO_4$). Conditions: Strong heating under reflux to ensure the reaction goes to completion.
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What is the product of oxidizing a secondary alcohol?
A ketone. The reaction requires heating under reflux with an oxidising agent like acidified potassium dichromate(VI).
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What happens when you try to oxidise a tertiary alcohol with acidified $K_2Cr_2O_7$?
Tertiary alcohols are resistant to oxidation under these conditions because the carbon atom attached to the -OH group has no hydrogen atoms to be removed. The orange solution remains orange.
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What is the colour change observed when a primary or secondary alcohol is oxidised with acidified potassium dichromate(VI)?
The orange solution, due to the dichromate(VI) ion ($Cr_2O_7^{2-}$), turns green as the chromium is reduced to the chromium(III) ion ($Cr^{3+}$).
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What are the reagents and conditions for the dehydration of an alcohol to an alkene?
Either heat with a concentrated acid catalyst (e.g., conc. $H_2SO_4$ at 170°C or conc. $H_3PO_4$), or pass the alcohol vapour over a heated solid catalyst like aluminium oxide ($Al_2O_3$) at ~300°C.
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What is esterification?
The reversible reaction between an alcohol and a carboxylic acid to form an ester and water. It is an example of a condensation reaction and is catalysed by a strong acid (e.g., concentrated $H_2SO_4$).
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Why is reflux used to produce a carboxylic acid from a primary alcohol?
Reflux involves continuous boiling, vaporisation, and condensation, returning reactants to the flask. This allows for prolonged heating at the boiling point without losing volatile substances, ensuring the intermediate aldehyde is fully oxidised to the carboxylic acid.
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What is the Lucas test?
A test to distinguish between primary, secondary, and tertiary alcohols using a reagent of anhydrous zinc chloride in concentrated HCl. Tertiary alcohols react fastest (cloudy immediately), secondary react slower (cloudy in minutes), and primary react very slowly or not at all at room temperature.