Mercury (II) Iodide CAS#7774-29-0
Appearance: Exists in two crystalline forms
α-HgI₂ (stable): Bright red, tetragonal crystals or powder
β-HgI₂ (metastable): Yellow, orthorhombic crystals
Odor: Odorless
Key Characteristic: Thermochromic. Red form turns yellow at 127°C, reverts to red upon cooling.
Sensitivity: Light-sensitive, decomposes and darkens under prolonged exposure.
Density: Very high (6.36 g/cm³ for red form).
Physical & Chemical Properties
| Property | Value |
|---|---|
| Melting Point | 259 °C |
| Boiling Point | 354 °C (sublimes) |
| Solubility in Water | Practically insoluble: 0.006 g/100 mL (25°C) |
| Solubility | Soluble in: ethanol, ether, acetone, chloroform, CS₂, KI solution |
| Stability | Stable under normal conditions; decomposes on heating/light |
| pH (slurry) | 6–7 (neutral) |
Hazard Information (VERY TOXIC)
| Hazard Category | Details |
|---|---|
| Acute Toxicity | Fatal if swallowed, inhaled, or absorbed through skin. |
| Target Organs | Nervous system, kidneys, respiratory system. |
| Chronic Hazard | Cumulative poison. Can accumulate in the body. |
| Environmental Hazard | Very toxic to aquatic life, long-term adverse effects. |
| Safety Codes (S) | S13: Keep away from food.S28: After skin contact, wash immediately.S45: Seek medical help immediately.S60/S61: Dispose as hazardous waste; avoid release. |
| Risk Codes (R) | R26/27/28: Extremely toxic by inhalation, skin, ingestion.R33: Cumulative effects.R50/53: Toxic to aquatic life. |
| UN Number | UN 1645 (Poison) |
Primary Applications
Analytical Chemistry: Key component of Nessler's Reagent for detecting ammonia/ammonium ions.
Materials Science: Used as a semiconductor in room-temperature X-ray and gamma-ray detectors.
Pharmaceutical: Historically used in topical antiseptic/medicinal ointments.
Chemical Synthesis: Precursor for other mercury compounds and complexes.
Storage & Handling
Store sealed, dark, cool, dry place.
Strictly separate from food, feed, and household chemicals.
Personnel must wear protective clothing, gloves, and masks.
Not permitted for use in food, cosmetics, or household products.
