Calcium Nitrate
Properties
| State | Solid at room temperature (hygroscopic/deliquescent) |
| Color | White crystalline solid |
| Solubility | Very soluble in water (121.2 g/100 mL at 20°C) |
| Melting Point | 561°C |
| Boiling Point | Decomposes above 500°C |
About Calcium Nitrate
Calcium nitrate is the rare calcium salt that is genuinely freely soluble in water — 121 g per 100 mL at 20 °C — and is deliquescent enough to liquefy itself in humid air. That solubility is what makes it useful agriculturally: most calcium-bearing fertilizers (CaCO3, CaSO4, gypsum) are slow-release at best, while Ca(NO3)2 puts both Ca²⁺ and NO3⁻ into the root zone immediately. In a hydroponic recirculating system, where every nutrient must be in solution to be plant-available, calcium nitrate is essentially the only cost-effective calcium source that doesn't precipitate against phosphate or sulfate from a competing fertilizer salt. Historically, the 'Norwegian saltpeter' name comes from the 1903 Birkeland–Eyde process, in which Norwegian engineers ran air through an electric arc to oxidize N2 to NO and then to NO2, dissolved the resulting nitric acid in water, and neutralized it with limestone to give Ca(NO3)2 — the first industrial atmospheric-nitrogen fixation, briefly viable until the Haber–Bosch process undercut it on energy cost. In concrete chemistry, calcium nitrate is added at 1–2% of cement weight as a set accelerator and corrosion inhibitor; the nitrate ion passivates rebar by maintaining the protective Fe2O3 film against chloride attack, which is why bridge decks in marine environments often spec it. The compound is also a strong oxidizer (UN 1454, Class 5.1) and decomposes above 500 °C to give CaO, NO2, and O2.
Where you'll encounter it
Greenhouse tomato growers know calcium nitrate as the bag of soluble white crystals that goes into Tank A of a typical two-tank fertigation setup, kept separate from the phosphate-sulfate Tank B because mixing the concentrates would precipitate gypsum and tricalcium phosphate within minutes. Lettuce growers use it to head off tip burn; tomato and pepper growers use it to prevent blossom end rot, which is purely a calcium translocation problem rather than a soil deficiency. In civil engineering, calcium nitrate liquid concentrate is metered into ready-mix trucks below 5 °C ambient to keep cement hydration moving. Around a chemistry stockroom it appears as the tetrahydrate Ca(NO3)2·4H2O, an oxidizer to keep separated from organic solvents and reducers — the same compound that gives an orange-red flame test for calcium and a pleasing reddish color in pyrotechnic compositions.
Common Uses
- Calcium-plus-nitrogen feed in hydroponic and fertigation systems for tomatoes, peppers, lettuce
- Foliar spray to prevent blossom end rot and tip burn in calcium-deficient crops
- Set accelerator and rebar corrosion inhibitor in cold-weather concrete pours at 1–2% of cement
- Wastewater odor control by nitrate dosing to suppress sulfide-producing bacteria in sewers
- Reusable cold pack contents based on endothermic dissolution
- Oxidizer in pyrotechnic compositions for orange-red calcium flame color
- Latex coagulant in glove-dipping plants to set the rubber film on the former
- Component in some explosive ANFO-replacement formulations as the calcium counterpart to ammonium nitrate
Safety Information
UN 1454, Class 5.1 oxidizer. Will intensify a fire involving combustible material; do not store with organics, fuels, or reducers. Decomposition above 500 °C releases NO2 (toxic, IDLH 13 ppm). Acute toxicity is low — oral LD50 (rat) about 3.9 g/kg for the tetrahydrate — but ingestion can cause methemoglobinemia in infants. GHS H272/H319/H335. Concentrated solutions are mildly corrosive to galvanized steel and aluminum.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.