Precipitation Reaction

Purpose

Show the nature of a precipitation reaction and explain the name.

Procedure

1. Solution Preparation:
   • Prepare roughly 1 M solutions of lead nitrate (Pb(NO₃)₂) and potassium iodide (KI).
2. Reaction Setup:
   • Place some potassium iodide solution in a large (100 mL) graduated cylinder.
   • Add a few drops of lead nitrate to the potassium iodide solution.
   • Observe the formation of a yellow precipitate (lead iodide, PbI₂) that sinks to the bottom of the cylinder.
3. Demonstration:
   • Repeat the experiment using a petri dish on a document projector.
   • Show that the yellow precipitate is a solid by scraping it with a spatula.

Reactions Overview

1. Single Displacement/Oxidation-Reduction

Zn₀​(s) + Pb(NO_3​)₂​ (aq) → Zn(NO₃​)₂​ (aq) + Pb₀​ (s)

2. Double Replacement/Precipitation

2 NaI (aq) + Pb(NO₃​)₂​ (aq) → 2 NaNO₃​ (aq) + PbI₂​ (s)

3. Gas Evolution

Na_2​CO₃​ (aq) + 2 H₃​CCOOH (aq) →H₂​O (l) + CO_2​ (g) + 2 CH₃​COO−Na+ (aq)

4. Decomposition

MnO₂​ (s) + 2 H₂​O₂​ (aq) → 2 H₂​O (aq) + O₂​(g) + MnO₂​(s)

5. Organic Decomposition

C_6​H₁₂​O₆​ + H₂​SO₄​ → 6 H₂​O + 6 C (s)