Potassium Nitrate
Properties
| State | Solid at room temperature |
| Color | White crystalline powder |
| Solubility | Soluble in water (31.6 g/100 mL at 20°C, 247 g/100 mL at 100°C) |
| Melting Point | 334°C |
| Boiling Point | 400°C (decomposes) |
About Potassium Nitrate
Potassium nitrate, KNO3 at 101.103 g/mol, is the chemical that ran the world's wars from the Tang dynasty until smokeless powder displaced it in the 1880s. Black powder is roughly 75% KNO3, 15% charcoal, 10% sulfur — the nitrate is the oxygen carrier that lets the carbon and sulfur burn fast enough to deflagrate inside a confined chamber. KNO3 is also why pre-industrial empires built saltpeter plantations: piles of dung, straw, and lime turned by laborers for years to grow nitrifying bacteria, then leached with water and crystallized. Today the largest single use is fertilizer, especially for chloride-sensitive crops like tobacco, citrus, grapes, and potatoes that suffer leaf burn from KCl-based potash. KNO3 supplies both K and NO3-N in one shot, all of which are immediately plant-available. In food preservation, sodium and potassium nitrate (E251 and E252) have cured hams, salami, and bacon for centuries — the bacteria reduce nitrate to nitrite, the nitrite reacts with myoglobin to give cured meat its pink color, and it suppresses Clostridium botulinum spore germination. Toothpaste for sensitive teeth uses KNO3 (typically 5%) because the K+ ions desensitize tubule nerve endings within a few weeks of use. The temperature-dependent solubility — 32 g/100 mL at 20°C jumping to 247 g/100 mL at 100°C — makes KNO3 the textbook recrystallization demo in undergraduate labs.
Where you'll encounter it
If you've ever lit a sparkler on the Fourth of July, brushed with Sensodyne, eaten a salami slice, or fertilized a tomato plant with bloom-booster, KNO3 has been in your hand. In a Sensodyne formulation, the 5% KNO3 is what does the desensitizing — the silica abrasive and fluoride do the cleaning and remineralizing, but the K+ ions diffusing into open dentin tubules are what numb the sharp cold-air response over 2-4 weeks of twice-daily brushing. In a pyrotechnics lab or a high school chemistry demo, the classic recrystallization experiment dissolves 50 g of KNO3 in 50 mL of boiling water, cools the saturated solution slowly in an ice bath, and yields long needle crystals that show up the dramatic temperature dependence in a single classroom session.
Common Uses
- Premium fertilizer for tobacco, citrus, grapes, and potatoes sensitive to chloride
- Oxidizer in black powder for fireworks, model rocket motors, and hobby pyrotechnics
- Curing salt E252 in dry-cured ham, salami, and pepperoni production
- 5% active ingredient in Sensodyne and other dentinal hypersensitivity toothpastes
- Molten salt heat transfer fluid in concentrated solar power thermal storage
- Stump remover for accelerating decay of cut tree stumps in landscaping
- Recrystallization teaching demonstration in undergraduate general chemistry
Safety Information
GHS: H272 oxidizer Cat 3, H319 eye irritation Cat 2A. Oral LD50 in rats is around 3750 mg/kg — low acute toxicity, but contact with combustibles like sawdust, paper, or organic solvents can ignite a fire that's hard to extinguish because the salt provides its own oxygen. Never grind KNO3 with sulfur or charcoal outside a controlled pyrotechnics setup. Excessive ingestion converts to nitrite in the gut, oxidizes hemoglobin to methemoglobin, and causes cyanosis — infants and people with G6PD deficiency are most vulnerable. Store dry away from organics and reducing agents. Decomposes above 400°C to KNO2 and O2; at higher temperatures evolves NOx fumes. Compatible with glass and most plastics.
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.