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