Module 4.2.1: Alcohols

Comprehensive practice flashcards covering the classification, physical properties, and chemical reactions of alcohols based on the OCR Chemistry curriculum.

What is the definition of a functional group?

An atom or group of atoms that give molecules their characteristic reactions.

What is the general formula for an aliphatic alcohol with a single hydroxyl group?

    $C_nH_{2n+2}O$

What is the bond angle around the oxygen atom in the hydroxyl group of an alcohol?

    $104.5^\circ$

How does the volatility of alcohols compare to alkanes of similar size?

Alcohols have lower volatility because they can form hydrogen bonds with each other, which are stronger than induced dipole-dipole interactions and require more energy to overcome.

Why does the water solubility of alcohols decrease as the hydrocarbon chain length increases?

The hydrophobic hydrocarbon chain increases in size and its lack of solubility becomes more dominant, while the $-OH$ group has less influence.

How is a secondary alcohol classified?

The $-OH$ group is attached to a carbon atom with only one hydrogen atom and two alkyl groups.

What are the common acid catalysts and conditions used for the dehydration of an alcohol?

Concentrated $H_3PO_4$ or concentrated $H_2SO_4$ and heat under reflux.

What organic product is formed when an alcohol undergoes an elimination reaction via dehydration?

An alkene.

In the context of alcohol reactions, what does the term 'in situ' mean?

It means the reagent (such as a hydrogen halide) is generated 'in place' within the reaction mixture.

What reagents are used to perform the substitution of an $-OH$ group with a halide ion?

Sodium halide (e.g., $NaBr$) and sulfuric acid ($H_2SO_4$).

What is the standard oxidising agent mixture used for the oxidation of alcohols?

Acidified potassium dichromate ($K_2Cr_2O_7 / H_2SO_4$).

What is the observed colour change when dichromate (VI) ions are reduced to chromium (III) ions?

Orange to green.

How can the oxidation product of a primary alcohol be controlled to form an aldehyde rather than a carboxylic acid?

By using distillation to remove the aldehyde from the reaction mixture as it forms, preventing further oxidation.

What conditions are required to ensure a primary alcohol is fully oxidised to a carboxylic acid?

Excess acidified potassium dichromate and heating under reflux.

What organic product is formed from the oxidation of a secondary alcohol?

A ketone.

Why are tertiary alcohols resistant to oxidation by acidified potassium dichromate?

Because there are no hydrogen atoms attached to the carbon atom that is bonded to the hydroxyl ($-OH$) group.

What is the primary difference in apparatus setup between reflux and distillation?

In reflux, the condenser is in an upright position; in distillation, the condenser is attached diagonally and a thermometer is used to collect the liquid at its boiling point.

What happens during the complete combustion of ethanol?

Ethanol burns in excess oxygen to produce carbon dioxide and water: $C_2H_6O + 3O_2 \rightarrow 2CO_2 + 3H_2O$.

In the dehydration of butan-2-ol, why can three isomeric alkenes be produced?

Hydrogen can be removed from carbon-1 or carbon-3; removal from carbon-3 creates but-2-ene, which exists as both $E$ and $Z$ stereoisomers.