Chapter 14 - Alcohols Flashcards
What is the functional group of an alcohol?
OH
What does the OH group in an alcohol determine?
The physical and chemical properties of it
Why is methanol used as a fuel?
It combusts efficiently
What is methanol used for? (2)
Fuel
Chemical feedstock - it can be made into polymers, solvents and adhesives
What is ethanol used for? (3)
Fuel
Drinks
Solvent
How are alcohols named?
-ol is added to the prefix and the position of the OH group is indicated using a number
Physical properties of alcohols compared to alkanes
Less volatile
Higher melting points
Greater water solubility
Why are the physical properties of alcohols and alkanes very different?
Whilst alkanes are on-polar, alcohols are polar. This means that whilst there are still weak London forces present in alcohols, there are also strong hydrogen bonds
Why are alkanes non-polar?
Hydrogen and carbon have very similar electronegativities
What forces are present in alkanes?
Weak London forces
Why are alcohols polar?
The O-H bond - oxygen and hydrogen have very different electronegativities
Why are alcohols less volatile than alkanes?
The strong hydrogen bonds in alcohol molecules require much more energy to overcome in order to turn the alcohol into a gas than the weak London forces in alkanes
Why are alcohols soluble in water but alkanes aren’t?
Hydrogen bonds form between the OH group of an alcohol and the water molecule. This can’t occur in alkanes because they are non-polar
Why does solubility decrease as the hydrocarbon chain increases?
The influence of the OH group decreases
What are the three types of alcohols?
Primary, secondary, tertiary
What is the general formula for an alcohol?
Cn H2n+1 OH
What are primary alcohols?
The OH group is attached to a carbon that is attached to two hydrogens and one alkyl group
What is a secondary alcohol?
The OH group is attached to a carbon that is attached to one hydrogen atom and two alkyl groups
What is a tertiary alcohol?
The OH group is attached to a carbon atom that is attached to no hydrogen atoms and three alkyl groups
What is produced when alcohols completely combust?
CO2 and H2O
What type of reaction is combustion?
Exothermic
What happens to the amount of energy released when an alcohol combusts as chain length increases?
It increases
How do you oxidise a primary or secondary alcohol?
Add an oxidising agent
What oxidising agent do we use?
Potassium dichromate (K2Cr2O7) and dilute sulfuric acid (H2SO4)
What colour change occurs when an alcohol is oxidised?
Orange to green
Why does the solution go green when an alcohol is oxidised?
The dichromate (VI) ions are reduced to chromium (III) ions
What are the two products that can form when a primary alcohol is oxidised?
Carboxylic acids and aldehydes
What is produced when a primary alcohol is heated and the product distilled immediately?
An aldehyde and water
What is the general formula for both ketones and carboxylic acids?
CnH2nO
What is produced when a primary alcohol is heated under reflux?
A carboxylic acid and water
How to prepare an aldehyde?
Use distillation to remove the aldehyde from the reaction mixture
How to prepare a carboxylic acid?
Heat a primary alcohol under reflux
What is produced when secondary alcohols are oxidised?
Ketones and water
How to prepare a ketone?
Heat a secondary alcohol under reflux
Suffix for a ketone
-one
Suffix for an aldehyde
-al
What will happen when a tertiary alcohol is oxidised?
They can’t be oxidised so the solution stays orange
What is dehydration of an alcohol?
When a molecule of water is removed
What type of reaction is dehydration?
Elimination
How do you dehydrate an alcohol?
Heat it under reflux in the presence of an acid catalyst - either sulfuric or phosphoric acid
What is produced when an alcohol is dehydrated?
An alkene and water
What is produced when an alcohol reacts with hydrogen halide?
A haloalkane and water
How to prepare a haloalkane?
Heat the alcohol under reflux with sulfuric acid and a sodium halide and a hydrogen halide is produced
