Potassium Sulfate

Potassium sulfate K₂SO₄ is a salt of potassium and sulfuric acid. It is colorless, water-soluble crystalline solid, mainly used as fertilizer.

Properties

• Crystal system: Orthorhombic

• Mineral name: Arcanite

• Crystal shape: apparently, hexagonal bipyramid. I don't know how it is compatible with orthorhombic crystal system. Probably, twinning?

• Stability on air: very stable. Also, it is one of the hardest soluble materials.

Growing notes

Solubility in water: 12g/100ml at room temperature.

Grows slowly because of low solubility. Solution is prone to bacterial infestation and mold growth. To get rid of it, filtering and boiling solution (without crystal, of course) sometimes helps. Also, adding few drops of iodine tincture also prevents infestation for some time.

Safety

Potassium sulfate is not toxic. Fertilizer-grade compound may contain significant amounts of potassium carbonate (K2CO3) which can irritate skin because if its alcaline pH.

Obtaining

• Fertilizer stores (usually requires filtering and recrystallization)
• Chemicals shops
• Synthesis is not practical since source reagents are more expensive than the product, but possible:
  • 2KOH + H₂SO₄ → K₂SO₄ + H₂O
    Reaction is highly exotermic, solution starts boiling!
  • K₂CO₃ + H₂SO₄ → K₂SO₄ + H₂O + CO₂
    Produces lots of gas, beware acidic foam.

More pictures