Potassium nitrate

 

Potassium nitrate

Chemical formula	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	0 1 0 OX
Thermal Decomposition	Potassium nitrate 400°C 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.

  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

  Ca(NO₃)₂(aq) + K₂CO₃(aq) → CaCO₃(s) + 2 KNO₃

From sodium nitrate

This leverages the steep solubility curve of potassium nitrate.

1. Prepare saturated solutions of sodium nitrate and potassium chloride at 99°C
2. Combine the solutions such that they are in a 1:1 molar ratio
3. Cool the mixture to near freezing
4. The precipitate is potassium nitrate

   NaNO₃(aq) + KCl(aq) → NaCl + KNO₃

Properties

• insoluble in 100% (dry) ethanol
• insoluble in diethyl ether

See Also

• compost
• saltpeter