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

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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
Already a member?
Go to Top