Potassium nitrate

3658

June 23, 2025, 10:40 AM

Guide

Highlights at a glance

Potassium Nitrate (KNO₃), also known as saltpeter or nitre, is a white, odorless, crystalline solid with a molecular weight of 101.103 g/mol and CAS number 7757-79-1. It forms an ionic compound consisting of K⁺ and NO₃⁻ ions, crystallizing in the orthorhombic system at room temperature and transitioning to trigonal above 129°C. With a density of 2.109 g/cm³ and Mohs hardness of 2.0, it melts at 334°C and decomposes at around 400°C, releasing oxygen. Highly soluble in water—especially at elevated temperatures—it exhibits excellent solubility and remains stable under normal conditions, being non-hygroscopic. As a strong oxidizing agent, especially when molten, it reacts vigorously with reducing agents and organic materials, potentially forming explosive mixtures. In agriculture, it provides 13.8% nitrogen and 46.6% potassium (as K₂O), offering a chloride-free, fully water-soluble NPK ratio of 13.8-0-46.6, ensuring immediate nutrient availability for plants.

1.Chemical and Physical Properties

1.1 Chemical Identity

Chemical Name: Potassium Nitrate
Common Names: Saltpeter, Nitre, Chile Saltpeter (natural form), KNO₃
Molecular Formula: KNO₃
Molecular Weight: 101.103 g/mol
CAS Number: 7757-79-1
Chemical Structure: Ionic compound with K⁺ cation and NO₃⁻ anion
Crystal System: Orthorhombic (aragonite structure)

1.2 Physical Properties

Appearance: White, crystalline solid with no odor
Crystal Habit:
- Orthorhombic crystals at room temperature
- Trigonal above 129°C (phase transition)
- Needlelike or prismatic crystal formations
Density: 2.109 g/cm³ at 20°C
Hardness: 2.0 on the Mohs scale
Melting Point: 334°C (633°F)
Boiling Point: 400°C (752°F) - decomposes
Solubility in Water:
- 316 g/L at 20°C
- 383 g/L at 25°C
- 2580 g/L at 100°C
Bulk Density: 1.0-1.3 g/cm³ (depending on particle size and compaction)

1.3 Chemical Properties

Thermal Decomposition:
- 2KNO₃ → K₂O + N₂O₅ (at high temperatures)
- Further decomposition: 4KNO₃ → 2K₂O + 2N₂ + 5O₂
Oxidizing Properties: Strong oxidizing agent, especially when molten
pH: Nearly neutral in aqueous solution (pH 6.0-7.0)
Stability: Stable under normal conditions, non-hygroscopic
Reactivity:
- Reacts vigorously with reducing agents
- Forms explosive mixtures with organic materials
- Compatible with most inorganic compounds
Electrical Conductivity: Good ionic conductor in molten state

1.4 Nutrient Content(Agricultural Applications)

Nitrogen (N): 13.8%
Potassium (K₂O): 46.6%
NPK Rating: 13.8-0-46.6
Nutrient Availability:
- 100% water-soluble nitrogen and potassium
- Immediately available to plants
- No chloride content (chloride-free)