Hydrobromic acid

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Hydrobromic acid
Hydrobromic acid
Identifiers
CAS number 10035-10-6 YesY
PubChem 260
ChemSpider 255 YesY
EC number 233-113-0
ChEBI CHEBI:47266 YesY
RTECS number MW3850000
Jmol-3D images Image 1
Properties
Molecular formula HBr
Molar mass 80.91
Appearance colorless/faint yellow liquid
Odor acrid
Density 1.49 g/cm3 (48% w/w aq.)
Melting point −11 °C (12 °F; 262 K) (47–49% w/w aq.)
Boiling point 122 °C (252 °F; 395 K) at 700 mmHg (47–49% w/w aq.)
Solubility in water 221 g/100 mL (0 °C)
204 g/100 mL (15 °C)
130 g/100 mL (100 °C)
Acidity (pKa) −9[1]
Viscosity 0.84 cP (-75 °C)
Thermochemistry
Specific
heat capacity
C
29.1 J/K mol
Std molar
entropy
So298
198.7 J/K mol
Std enthalpy of
formation
ΔfHo298
-36.3 kJ/mol
Hazards
MSDS ICSC 0282
EU Index 035-002-01-8
EU classification Corrosive (C)
R-phrases R34, R37
S-phrases (S1/2), S7/9, S26, S45
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Related compounds
Other anions Hydrofluoric acid
Hydrochloric acid
Hydroiodic acid
Related compounds Hydrogen bromide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

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.

Uses[edit]

Hydrobromic acid is mainly used for the production of inorganic bromides, especially the bromides of zinc, calcium, and sodium. It is a useful reagent for generating organobromine compounds. Certain ethers are cleaved with HBr. It also catalyzes alkylation reactions and the extraction of certain ores. Industrially significant organic compounds prepared from hydrobromic acid include allyl bromide, tetrabromobis(phenol), and bromoacetic acid.[2]

Syntheses[edit]

Hydrobromic acid can be prepared in the laboratory via the reaction of Br2, SO2, and water.[3]

Br2 + SO2 + 2 H2O → H2SO4 + 2 HBr

More typically laboratory preparations involve the production of anhydrous HBr, which is then dissolved in water.

Hydrobromic acid has commonly been prepared industrially by reacting bromine with either sulfur or phosphorus and water. However, it can also be produced electrolytically.[3] It can also be prepared by treating bromides with non-oxidising acids like phosphoric or acetic acids.

Alternatively the acid can be prepared with dilute (5.8M) sulfuric acid and potassium bromide:[4]

H2SO4 + KBr → KHSO4 + HBr

Using more concentrated sulfuric acid or allowing the reaction solution to exceed 75 °C further oxidizes HBr to bromine gas. The acid is further purified by filtering out the KHSO4 and by distilling off the water until the solution reaches an azeotrope (≈ 126 °C at 760 torr). The yield is approximately 85%.[4]

Hydrobromic acid is available commercially in various concentrations and purities.

References[edit]

  1. ^ Bell, R.P. The Proton in Chemistry, 2nd ed., Cornell University Press, Ithaca, NY, 1973.
  2. ^ Dagani, M. J.; Barda, H. J.; Benya, T. J.; Sanders, D. C. (2005), "Bromine Compounds", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a04_405 
  3. ^ a b Scott, A. (1900). "Preparation of Pure Hydrobromic Acid". Journal of the Chemical Society, Transactions 77: 648–651. doi:10.1039/ct9007700648. 
  4. ^ a b Brauer, Georg (1963). Handbook of Preparative Inorganic Chemistry Vol. 1, 2nd Ed.. Newyork: Academic Press. p. 285. ISBN 978-0121266011. 

External links[edit]

Media related to Hydrogen bromide at Wikimedia Commons