Golden Rain

Golden Rain

"I want to hide sunlight in a bottle, and let pieces of golden light fall like rain."

In one of the first club experiments of the semester, we recreated the classic "golden rain" demonstration. The "gold" is lead iodide, a bright yellow precipitate formed when iodide ions react with lead ions. When the crystals form and slowly sink through solution, they look like shimmering raindrops.

Reaction

In this activity, the club used lead nitrate solution and potassium iodide solution:

Pb(NO3)2 + 2KI -> PbI2 v + 2KNO3

Reagents and Equipment

• 0.6 g potassium iodide
• 0.6 g lead nitrate
• one 50 mL beaker
• one 100 mL beaker
• Erlenmeyer flask
• iron stand
• alcohol lamp
• matches
• filter paper
• funnel

Procedure

1. Prepare the KI solution: dissolve 0.6 g potassium iodide in 50 mL distilled water.
2. Prepare the lead nitrate solution: dissolve 0.6 g lead nitrate in 50 mL distilled water.
3. Mix the two solutions and heat them on an iron stand until the upper layer becomes clear.
4. Let the mixture cool to room temperature, then filter it into an Erlenmeyer flask.
5. Leave the filtered solution undisturbed. As the solution stands, golden lead iodide crystals appear and fall like rain.

Notes

1. Do not use too much KI. If KI is excessive, lead iodide can dissolve again:

Pb(NO3)2 + 4KI -> K2PbI4 + 2KNO3

2. Try to perform the hot filtration while the mixture is still above room temperature. Otherwise, too much PbI2 may precipitate before filtration and the final flask may no longer show the falling crystals clearly.

Final Result