Explain why propanoic acid is less acidic than ethanoic acid ?

Propanoic acid is less acidic than ethanoic acid because the presence of the additional methyl group in propanoic acid makes it less stable compared to ethanoic acid. The methyl group in propanoic acid destabilizes the negative charge on the carboxylate ion formed when the acid dissociates in solution. This destabilization makes it harder for propanoic acid to donate a proton, resulting in it being less acidic than ethanoic acid. Additionally, the longer carbon chain in propanoic acid also contributes to its lower acidity as the electron-donating alkyl group further destabilizes the carboxylate ion.

Propanoic acid is less acidic than ethanoic acid due to inductive electron-withdrawing effect which stabilises the conjugate base of the acid.

- Inductive effect: Propanoic acid has a longer carbon chain than ethanoic acid, which results in a stronger inductive electron-withdrawing effect. The electron-withdrawing effect of the alkyl group decreases the electron density on the carboxyl group, making it less likely to donate a proton and thus less acidic.

- Conjugate base stability: The conjugate base of propanoic acid is more stable than the conjugate base of ethanoic acid. This is because the longer carbon chain in propanoic acid provides more electron delocalization in the conjugate base, which lowers its energy and makes it more stable. A more stable conjugate base means that the acid is less likely to ionize and donate a proton, resulting in lower acidity.