S135 Prep Notes

Introduction

A 100mm petri dish containing water is placed on an overhead projector.  When solid Pb(NO3)2 is place on one side and solid KI on the other, PbI2 precipitates in the center.

Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)

Supplies

Short List

  •   100mm petri dish or larger
  •   Distilled water in wash bottle
  •   Paper towels
  •   Bottle for disposal
  •   Goggles and gloves

Chemicals

  •   Lead Nitrate   Pb(NO3)2
  •   Potassium Iodide   KI

Prior to Lecture  (prep time ~ ? min.)

Assemble the following:

  • 100mm petri dish or larger
  • A few grams of Pb(NO3)2
  • A few grams of KI

To Conduct Demonstration

  1. Place petri dish on stage of overhead projector.
  2. Pour water into dish to a depth of ¼” to 3/8”
  3. Scoop a small amount of Pb(NO3)2 into the water at one side of the dish.
  4. Scoop a small amount of KI into the water directly opposite the Pb(NO3)2
  5. A precipitate of PbI2 will form near the center of the dish.

Demo Time: ~1 minute

Safety and Disposal

Pb(NO3)2 is toxic.  Care should be taken to avoid breathing KI dust.  Dispose waste in Qual drum in room M124.