Physical and Chemical Properties of Carboxylic Acids

Introduction to Carboxylic Acids

• Carboxylic acids contain the carboxyl group: a carbonyl with oxygen attached to the carbon that’s attached to a hydrogen

• Some common carboxylic acids are shown below:

  

Physical Properties of Carboxylic Acids

• They are the most polar functional group due to the carboxyl group
• They have the highest melting and boiling points of all the functional groups
• They tend to form dimers in the solid, liquid, and gaseous phases
  • this makes their apparent molar mass higher than their actual molar mass
• carboxylic acids up to 6 carbons long tend to be water soluble
  • benzoic acid (benzene ring attached to carboxyl group) is soluble in hot water

Chemical Properties of Carboxylic Acids

• Carboxylic acids are weak acids

• Most carboxylic acids have a pKa of approximately 5

• The dissociation reaction of acetic acid is shown below

  • it will be similar for all carboxylic acids
  • Acetic acid has a pKa of 4.74

  

• carboxylic acids are more acidic than alcohols because of

  • the resonance effect of the anion
  • inductive effect of the carbonyl group

• They can react with sodium hydroxide and sodium bicarbonate to form carboxylates (salts of carboxylic acids)

• The reaction of benzoic acid with sodium hydroxide is shown below