Hydrobromic Acid

Cas Number


Other Names

Hydronium bromide

The formula



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.

Physical and Chemical Properties
Physical state and Appearance : Colorless or faintly yellow liquid (fuming liquid)
Odor : Sharp, irritating odor, Acrid odor
Molecular Weight: 80.91194 [g/mol]
Color: a clear or faintly yellow
Boiling Point(˚C): -66.8 deg C at 760 mm Hg
Melting Point: -86.9 deg C
Critical Temperature: 89.8 deg C; critical pressure: 84.5 atm
Specific Gravity: 3.307 g/L
Heat of Vaporization: 51.3 cal/g at boiling point
Solubility: Freely soluble in water; 1 volume of water dissolves 600 volumes of HBr at 0 deg C; soluble in alcohol; soluble in organic solvents 221 g/100 cc water at 0 deg C; 130 g/100 cc water at 100 deg C 204.0 g/ 100 g water at 15 deg C
Henry's Law constant : 1.32X10+9 mol/L atm (7.58X10-13 cu m atm/mol) /Hydrobromic acid/
pH: Aqueous solutions are strongly acidic
Vapor Density: 2.71 (Air = 1)
Vapor Pressure: 18,410 mm Hg at 25 deg C

Hydrobromic acid is used as an important agent in the industrial processes of isomerization, polymerization, hydration, and dehydration, as well as in the classical esterification reactions.