Lead Iodide Precipitation
Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★★☆ Some safety precautions required to perform safely
Categories: Chemical Reactions, Colour Changes, Water and Solubility
Alternative titles: Golden Rain
Summary
When aqueous lead(II) nitrate reacts with aqueous potassium iodide, a double displacement reaction occurs. Potassium nitrate remains dissolved, while lead(II) iodide precipitates as a bright yellow solid.
Procedure
- Dissolve lead(II) nitrate in water to form a clear solution.
- Dissolve potassium iodide in a separate container of water.
- Mix the two solutions together.
- Observe the immediate formation of a bright yellow precipitate of lead(II) iodide.
Links
Lead Nitrate and Potassium Iodide - Chemistry and Biochemistry Demo lab at OSU:
📄 What happens when lead nitrate reacts with potassium iodide - Unacademy: https://unacademy.com/content/question-answer/chemistry/what-happens-when-lead-nitrate-reacts-with-potassium-iodide/
Variations
- Compare the reaction at room temperature with the heated and cooled version (Golden Rain).
- Vary concentrations to see how the intensity of the precipitate changes.
- Demonstrate other double displacement reactions (e.g., silver nitrate with sodium chloride) for comparison.
Safety Precautions
- Lead salts are highly toxic — avoid ingestion, inhalation, or skin contact.
- Always wear safety glasses, gloves, and a lab coat.
- Do not dispose of lead-containing waste down the drain; collect and store as hazardous waste.
Questions to Consider
- What type of reaction occurs between lead nitrate and potassium iodide? (Double displacement, also called metathesis.)
- Why does a precipitate form immediately? (PbI₂ is insoluble in cold water, unlike KNO₃ which remains dissolved.)
- What color is the precipitate and why? (Yellow, due to the properties of lead(II) iodide crystals.)
- How does heating the solution change the result? (PbI₂ dissolves in hot water and recrystallizes as golden flakes upon cooling.)
- What real-world hazards are associated with lead compounds? (They are toxic and environmentally harmful.)