Alcohols (OCR A Level Chemistry A): Flashcards
Exam code: H432
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Define alcohol
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Cards in this collection (15)
Define alcohol
An alcohol is an organic compound containing at least one hydroxy (-OH) group bonded to a carbon chain.
Why do alcohols have higher boiling points than alkanes of similar molecular mass?
Alcohols form hydrogen bonds between molecules, which are stronger than the temporary induced dipole-dipole forces present in alkanes and require more energy to overcome.
True or False?
Solubility in water increases as the length of the hydrocarbon chain in an alcohol increases.
False.
Solubility decreases as chain length increases because the larger hydrocarbon chain disrupts hydrogen bonds between water molecules without forming new ones, so the energy balance becomes unfavourable.
A primary alcohol has the carbon bearing the -OH group attached to .......... other carbon atom(s).
A secondary alcohol has that carbon attached to .......... other carbon atoms.
A tertiary alcohol has that carbon attached to .......... other carbon atoms.
A primary alcohol has the carbon bearing the -OH group attached to one other carbon atom.
A secondary alcohol has that carbon attached to two other carbon atoms.
A tertiary alcohol has that carbon attached to three other carbon atoms.
What type of intermolecular force is responsible for the increasing boiling points of alcohols as chain length increases?
Temporary induced dipole-dipole forces increase as chain length increases because more electrons create larger temporary dipoles, requiring more energy to overcome.
Define primary alcohol (1°)
A primary alcohol is one in which the carbon atom bonded to the -OH group is attached to only one other carbon atom (or alkyl group).
True or False?
The general formula for alcohols is CnH2n+1OH.
True.
This formula applies to monohydric alcohols — those containing exactly one -OH group in an unbranched chain.
Define complete combustion (of an alcohol)
A complete combustion is the reaction of an alcohol with excess oxygen to produce only carbon dioxide and water.
What are the two oxidation products that can be formed from a primary alcohol?
A primary alcohol is first oxidised to an aldehyde, then further oxidised (by reflux with excess oxidising agent) to a carboxylic acid.
True or False?
Tertiary alcohols can be oxidised by acidified potassium dichromate(VI).
False.
Tertiary alcohols cannot be oxidised because the carbon bearing the -OH group has no hydrogen atom attached to it, so no oxidation can occur.
Acidified potassium dichromate(VI) solution starts .......... in colour.
When a primary or secondary alcohol is oxidised, the solution turns .......... .
Acidified potassium dichromate(VI) solution starts orange in colour.
When a primary or secondary alcohol is oxidised, the solution turns green (as Cr2O72- ions are reduced to Cr3+ ions).
How is an aldehyde prevented from being further oxidised to a carboxylic acid during the oxidation of a primary alcohol?
The aldehyde is distilled off as it forms because it has a lower boiling point than the alcohol, removing it from contact with the oxidising agent.
What conditions are used to dehydrate an alcohol to form an alkene?
The alcohol is heated with a hot concentrated acid catalyst (such as H2SO4) or passed over hot aluminium oxide (Al2O3) as a catalyst.
True or False?
The dehydration of an alcohol is an example of an elimination reaction.
True.
Water is eliminated from the alcohol (the -OH group and a hydrogen from an adjacent carbon are removed) to produce an alkene.
What product is formed when an alcohol undergoes a substitution reaction with HBr?
A bromoalkane (haloalkane) is formed as the -OH group is replaced by a bromine atom.
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