Golden Rain

Lead nitrate reacts with potassium iodide to form a bright yellow precipitate of lead iodide. When heated, the precipitate dissolves in hot water, but as the solution cools, thin hexagonal crystals fall out of solution like golden flakes, creating the “golden rain” effect.

1. Dissolve 1.65 g of lead(II) nitrate in 400 mL of distilled water in one beaker.
2. Dissolve 1.66 g of potassium iodide in 400 mL of distilled water in another beaker.
3. Combine the two solutions in a flask (about 800 mL total). A yellow precipitate of lead iodide forms immediately.
4. Heat the mixture to about 80 °C, stirring until all the lead iodide dissolves.
5. Allow the flask to cool slowly. As it cools, brilliant golden-yellow crystals of lead iodide form and fall, creating the golden rain effect.
6. For best viewing, place the flask where bright sunlight can shine through it against a dark background.

Golden Rain - mrhomescientist:

📄 Golden Rain Experiment - Chem Talk: https://chemistrytalk.org/lead-iodide-reaction/

• Repeat the experiment with smaller volumes for a quicker classroom demo.
• Place the flask on a magnetic stirrer during cooling to keep crystals suspended longer.
• Compare the rapid precipitation of PbI₂ at room temperature with the slower, more ordered crystallization upon cooling.

• Lead nitrate and lead iodide are toxic — avoid ingestion, inhalation, and skin contact.
• Always wear safety glasses, gloves, and a lab coat.
• Perform the experiment in a well-ventilated lab or fume hood.
• Do not dispose of lead salts down the drain. Collect precipitates for proper hazardous waste disposal.
• Keep all lead compounds away from food and student handling.

• Why does lead iodide precipitate immediately when the two salts are first mixed? (PbI₂ is insoluble in cold water.)
• Why does heating dissolve the precipitate? (The solubility of PbI₂ increases with temperature.)
• Why does crystallization produce hexagonal plate-like crystals? (PbI₂ has a hexagonal crystal lattice structure.)
• What would happen if excess iodide ions were added? (A soluble plumbate complex, [PbI₄]²⁻, could form instead of PbI₂ precipitating.)
• Why must lead salts be disposed of carefully? (They are toxic and harmful to the environment.)