Calcium nitrate
Calcium nitrate is an inorganic compound with the chemical formula Ca(NO₃)₂, typically encountered as the tetrahydrate Ca(NO₃)₂·4H₂O, appearing as a white to light gray granular solid that readily absorbs moisture from the air.[1] It is highly soluble in water (121.2 g/100 mL at 20°C for the anhydrous form) and serves as a key source of both calcium and nitrate ions, making it essential in agriculture for plant nutrition and in construction as a concrete accelerator.[1] The anhydrous form has a molecular weight of 164.09 g/mol and an ionic crystal structure consisting of calcium cations and nitrate anions in a cubic lattice; it decomposes upon heating above 560°C, releasing nitrogen dioxide and oxygen.[1] Produced industrially by reacting nitric acid with calcium carbonate (limestone) or calcium hydroxide, the process generates calcium nitrate along with carbon dioxide and water, enabling large-scale manufacturing for commercial applications.[2] In agriculture, it functions as a fertilizer supplying readily available nitrogen (about 15.5% total, including 14.5% nitrate and 1% ammoniacal) and calcium (about 19%), providing calcium to help prevent disorders like blossom-end rot in tomatoes and peppers, promoting root development, and enhancing overall plant structure when applied via soil, foliar sprays, or drip irrigation.[3][1] In the construction industry, calcium nitrate acts as a set accelerator in concrete and mortars, reducing curing time, improving early strength, and serving as a plasticizer and long-term strength enhancer without significantly affecting carbonation resistance. Beyond these primary uses, calcium nitrate finds applications in wastewater treatment to control odors by preventing sulfide formation, in pyrotechnics and explosives as an oxidizer, and in regenerable cold packs due to its endothermic dissolution in water.[1] As a strong oxidizer, it poses safety risks including skin and eye irritation, potential toxicity if ingested (LD50 oral rat: 302 mg/kg), and the ability to intensify fires or release toxic fumes when heated, necessitating careful handling and storage away from combustibles.[1] The tetrahydrate form has a monoclinic crystal structure, contributing to its hygroscopic nature and solubility profile.[1]Properties
Physical properties
Calcium nitrate is commonly found as the tetrahydrate, Ca(NO₃)₂·4H₂O, which consists of colorless to white, hygroscopic crystals or granules that readily absorb atmospheric moisture. The anhydrous form appears as a white to light gray granular solid. Both forms are deliquescent, meaning they can form aqueous solutions upon exposure to humid air.[1][4] Key physical properties of calcium nitrate are summarized in the following table, distinguishing between the anhydrous and tetrahydrate forms where applicable:| Property | Anhydrous Ca(NO₃)₂ | Tetrahydrate Ca(NO₃)₂·4H₂O |
|---|---|---|
| Molecular weight (g/mol) | 164.09 | 236.15 |
| Density (g/cm³) | 2.5 | 1.82 |
| Melting point (°C) | 561 | 42 |
| Boiling point | Decomposes before boiling | Decomposes at 132 °C |
| Crystal structure | Cubic | Monoclinic (space group P2₁/c) |