CIE AS Chemistry (9701) exams from 2022

Revision Notes

3.6.1 Carboxylic Acids

Production of Carboxylic Acids

  • Carboxylic acids are compounds with a -COOH functional group
  • They can be prepared by a series of different reactions

Oxidation of primary alcohols & aldehydes

  • Carboxylic acids can be formed from the oxidation of primary alcohols and aldehydes by either acidified K2Cr2O7 or acidified KMnO4 and reflux
  • The oxidising agents themselves get reduced causing the solutions to change colour
    • In K2Cr2O7 the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions
    • In KMnO4  the purple manganate ions (MnO4) are reduced to colourless Mn2+ ions

 

Carboxylic Acids & Derivatives Oxidation of Primary Alcohols and Aldehydes, downloadable AS & A Level Chemistry revision notes

Oxidation of primary alcohols (1) and aldehydes (2) gives carboxylic acids

Hydrolysis of nitriles

  • Carboxylic acids can also be prepared from the hydrolysis of nitriles using either dilute acid or dilute alkali followed by acidification
    • Hydrolysis by dilute acid results in the formation of a carboxylic acid and ammonium salt
    • Hydrolysis by dilute alkali results in the formation of a sodium carboxylate salt and ammonia; Acidification is required to change the carboxylate ion into a carboxylic acid
  • The -CN group at the end of the hydrocarbon chain is converted to a -COOH group

Hydrolysis of nitriles by either dilute acid (1) or dilute alkali and acidification (2) will form a carboxylic acid

Hydrolysis of esters

  • Esters are formed from the condensation reaction between an alcohol and carboxylic acid
  • Hydrolysis of esters by dilute acid or dilute alkali and heat followed by acidification will reform the alcohol and carboxylic acid
    • Hydrolysis by dilute acid, is a reversible reaction and an equilibrium is established
    • Hydrolysis by dilute alkali is an irreversible reaction as all the ester is broken down to form a sodium carboxylate salt and an alcohol; acidification is required to change the carboxylate ion into a carboxylic acid

Carboxylic Acids & Derivatives Hydrolysis of Esters, downloadable AS & A Level Chemistry revision notes

Hydrolysis of esters by either dilute acid (1) or dilute alkali and heat followed acidification (2) will form a carboxylic acid

Reactions of Carboxylic Acids

  • Carboxylic acids are weak acids as they do not completely dissociate in water
  • This means that the position of the equilibrium lies to the left and that the concentration of H+ is much smaller than the concentration of the carboxylic acid
  • The solution has a pH value of less than 7

 

Carboxylic Acids & Derivatives Dissociation Carboxylic Acids, downloadable AS & A Level Chemistry revision notes

Carboxylic acids are weak acids that do not fully dissociate in water, the position of the equilibrium lies to the left

  • Carboxylic acids are reactive compounds which can undergo many types of reactions including:
    • Redox reactions with reactive metals
    • Neutralisation reactions with alkali
    • Acid-base reactions with carbonates
    • Esterification with alcohols
    • Reduction by LiAlH4

 

Carboxylic Acids & Derivatives Reactions of Carboxylic Acids_1, downloadable AS & A Level Chemistry revision notes

Carboxylic acids undergo a wide variety of reactions

Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Go to Top