Hydrobromic acid is a
strong acid formed by dissolving the diatomic molecule
hydrogen bromide (HBr) in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at 124.3 °C and contains 47.6% HBr by weight, which is 8.89 mol/L. Hydrobromic acid has a
pKa of -9, making it a stronger acid than
hydrochloric acid, but not as strong as
hydroiodic acid. Hydrobromic acid is one of the strongest
mineral acids known.