Hydrobromic acid (HBr) is a strong acid. 1 It completely dissociates in water, releasing all of its hydrogen ions (H+) to form hydronium ions (H3O+) and bromide ions (Br-). This results in a high concentration of H+ ions in the solution, making it a strong acidic solution.
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Key Takeaways: Is HBr a Strong or Weak Acid?
- HBr is a strong acid because it completely dissociates in water, releasing all of its hydrogen ions (H+).
- The strength of HBr is due to the weak H-Br bond, which makes it easy for the hydrogen atom to be released as a proton.
- HBr finds various applications in chemical synthesis, hydrobromination, bromination reactions, pH control in industrial processes, semiconductor manufacturing, laboratory use, pharmaceutical and chemical intermediates, cleaning and surface treatment, and petroleum refining.
Why is HBr a strong acid?
Hydrobromic acid (HBr) is considered a strong acid due to its ability to fully dissociate into ions when it is dissolved in water. A strong acid is one that readily donates a proton (H+) to water molecules, resulting in the formation of positively charged hydrogen ions (H+) and negatively charged bromide ions (Br-) in solution.
The strength of an acid is determined by its tendency to dissociate into ions. In the case of HBr, it dissociates completely, meaning that nearly all the HBr molecules present in the solution break apart into ions. This full dissociation is represented by the following equation:
HBr (aq) → H+ (aq) + Br- (aq)
The reason HBr is a strong acid lies in the nature of the H-Br bond. The hydrogen-halogen (H-X) bond strength decreases as we move down the halogen group in the periodic table (from fluorine to iodine).
As we go down the group, the atomic size of the halogen increases, and the bonding electrons become further away from the nucleus. This leads to a weaker bond between hydrogen and the halogen, making it easier for the hydrogen atom to be released as a proton.
Since bromine (Br) is a halogen that is larger and less electronegative than fluorine and chlorine, 2 the H-Br bond is relatively weak. Consequently, HBr can easily lose a proton when it comes into contact with water, resulting in the formation of H+ and Br- ions.
It’s important to note that the strength of an acid depends on the solvent as well. HBr is a strong acid in water because of its complete dissociation, but its acidity might differ in other solvents.
In non-aqueous solvents, HBr might not dissociate to the same extent, and its acidity might be different.
How does the dissociation of HBr differ from that of a weak acid?
Below is a comparison of the dissociation of hydrobromic acid (HBr), a strong acid, with that of a typical weak acid, acetic acid (CH3COOH):
| Aspect of Dissociation | HBr (Strong Acid) | CH3COOH (Weak Acid) |
| Dissociation Equation | HBr (aq) → H+ (aq) + Br- (aq) | CH3COOH (aq) ⇌ H+ (aq) + CH3COO- (aq) |
| Degree of Dissociation | Complete dissociation 3 | Partial dissociation 4 5 |
| Ionization State in Solution | Fully ionized 6 | Partially ionized |
| Reaction with Water | Easily donates H+ ions | Reluctantly donates H+ ions |
| Equilibrium Position | Far to the right (products) | Far to the left (reactants) |
This table highlights the key differences in the dissociation behavior of strong acid (HBr) and weak acid (acetic acid) in an aqueous solution.
Applications of HBr based on its strong acidic nature
Hydrobromic acid (HBr) finds various applications primarily due to its strong acidic nature. Here are some of the key applications:
- Chemical Synthesis: HBr is commonly used as a reagent in organic synthesis. Its strong acidic properties allow it to act as a proton donor, enabling it to catalyze numerous reactions. For example, it can be used to promote electrophilic additions and substitutions in organic compounds. 7
- Hydrobromination: HBr is often utilized for the hydrobromination of alkenes (olefins). 8 9 It adds a bromine atom across the double bond of an alkene, leading to the formation of alkyl bromides. This reaction is valuable for creating various brominated organic compounds.
- Bromination Reactions: HBr serves as a source of bromine in different bromination reactions. It can introduce bromine into various organic compounds, leading to the synthesis of a wide range of brominated products.
- Semiconductor Manufacturing: HBr is employed in the semiconductor industry for cleaning and etching processes. 10 It is used to remove oxide layers and contaminants from semiconductor surfaces during chip manufacturing.
- Laboratory Use: In chemical laboratories, HBr is commonly utilized as a strong acid for various purposes, such as titrations, pH adjustments, and organic synthesis.
- Pharmaceutical and Chemical Intermediates: HBr is used in the production of various pharmaceuticals and chemical intermediates, contributing to the synthesis of diverse compounds.
- Cleaning and Surface Treatment: HBr can be used for cleaning metal surfaces, especially in situations where hydrobromic acid is preferred over hydrochloric acid due to specific chemical properties. 11
- Petroleum Refining: In the petroleum industry, HBr is employed for various refining processes, including alkylation and cracking reactions, where it plays a crucial role as a catalyst or reactant.
Further reading
Is HI (Hydroiodic Acid) a Strong or Weak Acid?
Is HF (Hydrofluoric Acid) a Strong or Weak Acid?
Is H2SO4 (Sulfuric Acid) a Strong or Weak Acid?
Is H2S a Strong or Weak Acid?
Is HClO a Strong or Weak Acid?
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References
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- P. (n.d.). Electronegativity | Periodic Table of Elements. Electronegativity | Periodic Table of Elements – PubChem. https://pubchem.ncbi.nlm.nih.gov/periodic-table/electronegativity
- Ufl.edu https://christou.chem.ufl.edu/wp-content/uploads/sites/62/2017/01/Chapter-18-Acids-and-Bases-Week-1.pdf
- Weak acid-base equilibria (article) | Khan Academy. (n.d.). Khan Academy. https://www.khanacademy.org/science/chemistry/acids-and-bases-topic/copy-of-acid-base-equilibria/a/weak-acid-base-equilibria
- Utexas.edu https://ch302.cm.utexas.edu/chemEQ/ab-theory/selector.php?name=weak-acid-base
- Foundation, C. (n.d.). CK12-Foundation. CK12-Foundation. https://flexbooks.ck12.org/cbook/ck-12-chemistry-flexbook-2.0/section/21.12/primary/lesson/strong-and-weak-acids-and-acid-ionization-constant-ka-chem/
- 6.5: An Example of a Polar Reaction – Addition of HBr to Ethylene. (2015, May 3). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(Morsch_et_al.)/06%3A_An_Overview_of_Organic_Reactions/6.05%3A_An_Example_of_a_Polar_Reaction_-_Addition_of_HBr_to_Ethylene
- Karki, M., & Magolan, J. (2015, March 12). Bromination of Olefins with HBr and DMSO. The Journal of Organic Chemistry, 80(7), 3701–3707. https://doi.org/10.1021/acs.joc.5b00211
- 10.8: Anti-Markovnikov additions to alkenes and alkynes. (2020, July 2). Chemistry LibreTexts. https://chem.libretexts.org/Courses/SUNY_Potsdam/Book%3A_Organic_Chemistry_I_(Walker)/10%3A_Electrophilic_Addition/10.08%3A_Anti-Markovnikov_additions_to_alkenes_and_alkynes
- Haass, M., Darnon, M., Cunge, G., Joubert, O., & Gahan, D. (2015, April 9). Silicon etching in a pulsed HBr/O2 plasma. I. Ion flux and energy analysis. Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 33(3). https://doi.org/10.1116/1.4917230
- Nasa.gov https://ntrs.nasa.gov/api/citations/19700032723/downloads/19700032723.pdf
