Step 10: Obtainin a "Gold Rain"
Procedure: In a beaker mix 25 ml 0.2 M solution of Pb(NO3)2 and 0.25 ml of KI with 0.4M concentration. Observe the formation of an abundant amorphous precipitate of lead iodide. Then let it decant and add hot distilled water in a ratio of 1:4 to the yellow suspension initially obtained, then heat to dissolve the precipitate. If it doesn't completely dissolve, distilled water is added and continue heating. By slow cooling, we observe the formation of small "flaps" of gold that are actually lead iodide. By rapid cooling, is observed a large number of crystallization centers that give the appearance of yellow-pearl.
The reaction is:
Pb(NO3) 2 +2KI → PbI2 + 2KNO3.