📖 Theory & Concepts

What are Double Salts?

Compounds containing two different cations or anions that exist only in crystalline form. In solution, they dissociate into constituent ions.

Mohr's Salt

FeSO₄·(NH₄)₂SO₄·6H₂O

Light green crystals, stable to air oxidation

Potash Alum

K₂SO₄·Al₂(SO₄)₃·24H₂O

White octahedral crystals, used in purification

Double Salt vs Complex

  • Double Salt: Loses identity in solution (gives all ions)
  • Complex: Retains identity (complex ion stays intact)
Preparation Method:

Mix equimolar solutions of component salts, concentrate, and crystallize. Cool slowly for good crystal formation.

Predict Before You Crystallize

Select a salt above, then predict what its crystals will look like and why. The procedure stays locked until you commit a prediction.

Select a salt to enable prediction.

Select a Salt to Begin

1️⃣
Dissolve
Dissolve salts in water
2️⃣
Mix
Combine solutions
3️⃣
Concentrate
Heat to reduce volume
4️⃣
Crystallize
Cool for crystal formation
Reaction Vessel
Waiting...

Lab Journal — Observation vs Interpretation

Select Mohr's salt or Potash alum...

⚠️ Safety — Double Salt Preparation