The chemical compound represented by the formula HBr is known as hydrogen bromide. It is a diatomic molecule consisting of one hydrogen atom and one bromine atom.
This compound plays a significant role in both inorganic and organic chemistry, frequently used in various industrial and laboratory processes.
Understanding the naming, properties, and applications of HBr can provide insightful knowledge about its importance in chemistry. This article explores the name, structure, properties, and uses of hydrogen bromide in detail.
Basic Information About HBr
Hydrogen bromide is classified as a binary hydrogen halide, which means it is composed of hydrogen and a halogen element. In this case, the halogen is bromine (Br), a member of Group 17 in the periodic table.
| Property | Details |
|---|---|
| Chemical Formula | HBr |
| Common Name | Hydrogen bromide |
| Molecular Weight | 80.91 g/mol |
| Physical State | Colorless gas at room temperature |
| Boiling Point | -66.8 °C |
| Density (gas) | 3.12 g/L at 0 °C and 1 atm |
Naming Conventions of HBr
The name hydrogen bromide follows the standard IUPAC nomenclature for binary hydrogen halides. The naming rule involves:
- Indicating the hydrogen atom first.
- Naming the halogen with the suffix -ide, which in this case is bromide.
Thus, the combination results in the name hydrogen bromide.
“In chemical nomenclature, the suffix -ide is used to denote a negatively charged ion or an anion derived from a halogen.” – IUPAC Guidelines
Alternative Names
In addition to hydrogen bromide, when dissolved in water, HBr forms hydrobromic acid. This is an aqueous solution of hydrogen bromide and is a strong acid used extensively in chemical synthesis and industry.
Summary of Names:
| Compound Form | Name |
|---|---|
| Pure gas/liquid | Hydrogen bromide |
| In aqueous solution | Hydrobromic acid |
Chemical Structure and Bonding of HBr
The molecule consists of a single covalent bond between the hydrogen and bromine atoms. The electronegativity difference between hydrogen (2.20) and bromine (2.96) creates a polar bond, with bromine bearing a partial negative charge and hydrogen a partial positive charge.
This polarity is crucial because it determines many chemical properties such as acidity, reactivity, and solubility.
| Aspect | Description |
|---|---|
| Bond Type | Polar covalent bond |
| Electronegativity Difference | 0.76 (between H and Br) |
| Dipole Moment | Approximately 0.73 D (Debye) |
| Molecular Geometry | Linear (diatomic molecule) |
Physical Properties of Hydrogen Bromide
Hydrogen bromide is a colorless gas under standard conditions. It has a pungent, irritating odor and is heavier than air.
The boiling point of -66.8 °C indicates that it can be liquefied under moderate pressure or low temperature.
When cooled below its boiling point, it condenses into a colorless liquid, which is highly soluble in water. The solubility in water leads to the formation of hydrobromic acid as mentioned earlier.
Key Physical Characteristics
| Property | Value |
|---|---|
| State at Room Temperature | Gas |
| Odor | Pungent and irritating |
| Density (gas) | 3.12 g/L (at 0 °C, 1 atm) |
| Melting Point | -87.7 °C |
| Boiling Point | -66.8 °C |
| Solubility in Water | Highly soluble |
Chemical Properties and Reactions
Hydrogen bromide exhibits typical behavior of hydrogen halides. It is a strong acid when dissolved in water and participates in various chemical reactions such as addition to alkenes, substitution, and reduction.
Its acidic nature comes from its ability to dissociate completely in aqueous solution:
HBr (aq) → H+ (aq) + Br– (aq)
This complete ionization is what makes hydrobromic acid a strong acid.
Common Reactions Involving HBr
| Reaction Type | Description | Example |
|---|---|---|
| Addition to Alkenes | Electrophilic addition across the double bond | CH2=CH2 + HBr → CH3-CH2Br |
| Substitution Reaction | Replacement of hydroxyl groups with bromine | R-OH + HBr → R-Br + H2O |
| Reduction Reaction | Reduction of certain functional groups | R-COOH + HBr → R-CH2Br + … |
Preparation of Hydrogen Bromide
Hydrogen bromide can be prepared through several methods, both in the laboratory and on an industrial scale. The primary methods include the direct combination of hydrogen and bromine gases, and the reaction of bromides with strong acids.
Direct Combination
When hydrogen gas reacts with bromine vapor, hydrogen bromide gas is formed:
H2 (g) + Br2 (g) → 2 HBr (g)
This reaction is highly exothermic and typically requires a catalyst or initiation by light (UV radiation) because of its activation energy.
Reaction of Bromide Salts with Sulfuric Acid
Metal bromides like sodium bromide react with concentrated sulfuric acid to produce hydrogen bromide gas:
NaBr + H2SO4 → NaHSO4 + HBr (gas)
This method is commonly used in laboratories for generating HBr on demand.
Applications of Hydrogen Bromide
Hydrogen bromide has a wide range of applications across various fields including organic synthesis, pharmaceuticals, and materials science.
Organic Synthesis
In organic chemistry, HBr is used to add bromine atoms to organic molecules. The addition of HBr to alkenes results in alkyl bromides, which are valuable intermediates for further chemical transformations.
This reaction is often regioselective, favoring Markovnikov addition where the bromine attaches to the more substituted carbon.
Pharmaceutical Industry
Hydrogen bromide derivatives are used to synthesize several pharmaceuticals. Alkyl bromides produced from HBr are essential in creating compounds with biological activity.
Material Science
HBr is employed in the preparation of brominated polymers and as a reagent in the modification of materials requiring bromine incorporation.
Summary of Uses
| Field | Application |
|---|---|
| Organic Chemistry | Alkylation and bromination of organic compounds |
| Pharmaceuticals | Synthesis of active pharmaceutical ingredients |
| Materials Science | Production of brominated polymers and materials |
| Laboratory | Reagent for generating hydrobromic acid |
Safety and Handling
Hydrogen bromide is a hazardous substance and must be handled with proper safety measures. It is corrosive, irritating to the respiratory system, eyes, and skin.
Exposure to HBr gas or hydrobromic acid can cause severe burns and respiratory distress.
Proper ventilation, use of protective gloves, goggles, and respiratory protection are essential when working with this compound.
Warning: Avoid inhalation and skin contact with hydrogen bromide. In case of exposure, seek immediate medical attention.
Storage
HBr gas is typically stored in corrosion-resistant containers under pressure. Hydrobromic acid solutions should be kept in tightly sealed containers away from incompatible materials like oxidizers and strong bases.
Summary
The compound HBr is named hydrogen bromide when in its pure gaseous or liquid form. When dissolved in water, it forms hydrobromic acid, a strong acid widely used in chemical synthesis.
Hydrogen bromide consists of a polar covalent bond between hydrogen and bromine, and its physical properties include being a colorless, pungent gas with high solubility in water. It participates in important chemical reactions such as electrophilic addition and substitution, making it valuable in organic chemistry and industry.
Despite its utility, HBr requires careful handling due to its corrosive and toxic nature.
