1. Physical Characteristics
Sodium bromate is an inorganic compound with distinct physical properties that influence its handling and industrial use:
- Appearance: White crystalline powder or granules.
- Solubility: Highly soluble in water (~27 g/100 mL at 0°C; ~90 g/100 mL at 100°C), but insoluble in organic solvents like ethanol.
- Melting Point: Decomposes at ~381°C (718°F) rather than melting, releasing oxygen.
- Density: ~3.34 g/cm³ (denser than water).
- Stability: Stable under dry conditions but decomposes upon heating or exposure to reducing agents.
2. Chemical Properties
Sodium bromate exhibits strong oxidative properties, which define its reactivity and applications:
- Oxidizing Agent:
- Powerful oxidizer in acidic or neutral media (BrO₃⁻ + 6H⁺ + 6e⁻ → Br⁻ + 3H₂O).
- Reacts violently with combustible materials (e.g., sulfur, metals, organic compounds).
- Decomposition:
- Thermal decomposition releases oxygen (2NaBrO₃ → 2NaBr + 3O₂↑).
- Light or catalysts (e.g., MnO₂) accelerate decomposition.
- Redox Reactions:
- Reduces to bromide (Br⁻) in the presence of reducing agents (e.g., sulfites, iodide ions).
- pH Dependency:
- More reactive in acidic conditions (e.g., used with H₂SO₄ in gold extraction).
3. Industrial Applications Linked to Its Properties
The unique combination of physical and chemical traits determines sodium bromate’s industrial roles:
(1) Hair Dye and Cosmetics
- Property Utilized: Oxidative bleaching capability.
- Application: Permanent hair dyes use NaBrO₃ to oxidize dye precursors (e.g., coupling with persulfates for lightening).
- Safety Note: Regulated due to carcinogenicity concerns (banned in the EU).
(2) Gold Mining and Metallurgy
- Property Utilized: Strong oxidation under acidic conditions.
- Application: Extracts gold from ores by oxidizing sulfide minerals (alternative to cyanide in some processes).
(3) Food Additive (Discontinued)
- Property Utilized: Dough strengthening via oxidation.
- Historical Use: Improved bread texture by cross-linking gluten (banned in many countries due to toxicity risks).
(4) Laboratory and Chemical Synthesis
- Property Utilized: Controlled oxidation.
- Application: Synthesizes brominated compounds or serves as a bromine source in organic reactions.
(5) Water Treatment
- Property Utilized: Disinfection byproduct formation.
- Caution: Not directly used, but bromate (BrO₃⁻) can form during ozonation of bromide-containing water, requiring monitoring.
4. Safety and Handling Considerations
- Toxicity: Classified as a Group 2B carcinogen (IARC); ingestion causes kidney damage.
- Storage: Kept dry, away from combustibles, and separated from reducing agents.
- Regulations: Restricted in food and cosmetics (e.g., FDA, EU REACH).
Conclusion
Sodium bromate’s high solubility, oxidative strength, and thermal instability make it valuable in niche industries like hair dyes and metallurgy, but its toxicity limits broader use. Alternatives (e.g., sodium persulfate) are increasingly adopted where safety is prioritized.
