Double Displacement Reactions

📚 Key Concepts

🔹 Real-Life Example

When you mix solutions of barium chloride and sodium sulphate, a white precipitate (solid) of barium sulphate forms instantly, like snowflakes appearing in the liquid. This happens because the ions “swap partners” – barium pairs with sulphate, and sodium pairs with chloride. It’s like two couples switching dance partners!

Double Displacement Reaction: Reactions in which ions are exchanged between two reactants forming new compounds are called double displacement reactions.

🧪 Important Formulas

🔸 General Formula

AB + CD → AD + CB

Where A and C swap places, and B and D swap places.

🔸 Examples

  1. BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl (Precipitation reaction – white precipitate forms)
  2. NaOH + HCl → NaCl + H₂O (Neutralization reaction – acid + base → salt + water)

🔹 Special Types

1. Precipitation Reactions

  • Form an insoluble solid (precipitate)
  • Example: Silver chloride precipitation

2. Neutralization Reactions

  • Acid + Base → Salt + Water
  • Example: Antacid neutralizing stomach acid

🔍 Advanced: Precipitation Test

Double displacement reactions that form precipitates are used in analytical chemistry to test for specific ions. For example, adding silver nitrate to a solution will form a white precipitate if chloride ions are present.