Potassium nitrate
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Chemical formula | {{#Chem:KNO3}} |
---|---|
OTP appearance | white crystal |
Molar Mass(g/mol) | 101.1032 |
Density(g/cc) | 2.109 |
Melting Point(°C) | 334 |
Solubility in water(g/L) | 316 |
Solubility in ethanol(g/L) | non |
NFPA 704 |
|
Thermal Decomposition | Potassium nitrate
400°C {{#Chem: KNO2, O2}} |
Uses
Primary
- Source of nitrate ions for nitric acid, paracetamol, etc.
- Oxidizer for blackpowder
- Fertilizer
Natural occurrence
- Chilean saltpeter is a mixture of potassium nitrate and sodium nitrate
- Baraud is another evaporite mineral which contains potassium nitrate
Hazards
- Oxidizer
Production
Synthesis
From nitric acid
- Combine nitric acid and aqueous potassium hydroxide. Keep cool in a water bath. Once reaction is complete, evaporate the water.
- {{#Chem: HNO3 + KOH = KNO3 + H2O}}
From calcium nitrate
Calcium nitrate is the most common nitrate from composting or ammonia biofiltration. Calcium easily forms insoluble salts, giving an easy metathesis reaction:
- Combine calcium nitrate and potassium carbonate
- {{#Chem: Ca(NO3)2(aq) + K2CO3(aq) = CaCO3(s) + 2KNO3}}
From sodium nitrate
This leverages the steep solubility curve of potassium nitrate.
- Prepare saturated solutions of sodium nitrate and potassium chloride at 99°C
- Combine the solutions such that they are in a 1:1 molar ratio
- Cool the mixture to near freezing
- The precipitate is potassium nitrate
- {{#Chem: NaNO3(aq) + KCl(aq) --> NaCl + KNO3|t=1|p=atm}}
Properties
- insoluble in 100% (dry) ethanol
- insoluble in diethyl ether