Hydrogen bromide

Hydrogen bromide is the diatomic molecular compound with the formula HBr, a hydrogen halide consisting of hydrogen and bromine. In pure form it is a colorless gas.

Hydrogen bromide is very soluble in water, forming hydrobromic acid, which is saturated at 68.85% HBr by weight at room temperature. Aqueous solutions that are 47.6% HBr by mass form a constant-boiling azeotrope mixture that boils at 124.3 °C. Boiling less concentrated solutions releases H₂O until the constant-boiling mixture composition is reached.

Both the anhydrous and aqueous solutions of HBr are common reagents in the preparation of bromide compounds.