C3: Alcohols, Carboxylic Acids and Esters

Alcohols are carbon-based molecules that contain the functional group -OH. Methanol, ethanol and propanol are the first three members of the homologus series of alcohols.

Alcohols...

• dissolve in water to form neutral solutions
• react with sodium to produce hydrogen
• burn in air
• are used as fuels and solvents.

Alcoholic drinks contain ethanol. Ethanol can be oxidised to ethanoic acid either by chemical oxidising agents or by microbial action.

Ethanoic acid is the main acid in vinegar.

Methanol  =  CH3OH

Ethanol  =  CH3CH2OH

Propanol  =  CH3CH2CH2OH

Carboxylic acids are carbon-based molecules that contain the functional group -COOH.

Carboxylic acids...

• dissolve in water to form acidic solutions
• react with carbonates (e.g. sodium carbonate) to produce carbon dioxide
• react with alcohols (in the prescence of an acid catalyst) to form esters.

Carboxylic acids don't ionise (dissociate) fully in water, so they are called weak acids.

Aqueous solutions of weak acids have a higher pH than aqueous solutions of strong acids with the same concentration.

Methanoic acid  =  COOH

Ethanoic acid  =  CH3COOH

Propanoic acid  =  CH3CH2COOH

Alcohols and carboxylic acids react together to form esters. When ethanol and ethanoic acid react together the ester formed is ethyl ethanoate.

Esters contain the functional group -COO.

Esters are volatile compounds (meaning they have a low boiling point).

They have distinctive smells, so are used in perfummes and as flavourings in food.