Which is More Acidic: Ethanol or Acetic Acid?

Q: Which is more acidic, Ethanol or Acetic Acid?

Acetic Acid (pKa 4.8) is more acidic than Ethanol (pKa 16). A lower pKa indicates a stronger acid.

Which is more acidic, Ethanol or Acetic Acid?

Acetic acid (pKa 4.8) is about 11 orders of magnitude more acidic than ethanol (pKa 16). The difference is resonance stabilization: acetate ion delocalizes its negative charge equally over two oxygen atoms. Acetic Acid has a pKa of 4.8, while Ethanol has a pKa of 16.

Molecule A	Ethanol (C₂H₅OH), pKa 16
Molecule B	Acetic Acid (CH₃COOH), pKa 4.8
More Acidic	Acetic Acid
Governing Factor	Resonance
Difficulty	Intermediate

Introduction

Both molecules have an O-H bond that can lose a proton. But one is a much stronger acid than the other. Can you predict which?

Acidic Protons

The acidic proton in each molecule is the hydrogen on the oxygen (the O-H). Ethanol has a simple alcohol O-H, while acetic acid has a carboxylic acid O-H next to a C=O.

Governing Factor: Resonance

The key factor is resonance. In the acetate ion (conjugate base of acetic acid), the negative charge is delocalized equally over two oxygen atoms through resonance. The ethoxide ion has its charge localized on a single oxygen.

Conjugate Base Stability

Ethoxide (CH3CH2O-) has its negative charge stuck on one oxygen. Acetate (CH3COO-) spreads the charge over two equivalent oxygens, each bearing only half a negative charge. This delocalization makes acetate far more stable.

pKa Comparison

Acetic acid has a pKa of 4.8 (moderately weak acid), while ethanol has a pKa of 16 (very weak acid). The ~11 pKa units difference shows how powerful resonance stabilization is.

Interactive side-by-side 3D viewer with acidic proton highlights, conjugate base overlays, and pKa labels.

Compare Ethanol and Acetic Acid in 3D