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When two chemicals are combined, the atoms may rearrange to form new substances. Mixing solid lead nitrate (Pb(NO3)2) with solid potassium iodide (KI) initiates a double‑replacement reaction that produces a distinct yellow precipitate of lead iodide (PbI2) and a clear, white solution of potassium nitrate (KNO3).
Adding lead nitrate to potassium iodide creates a bright yellow lead‑iodide cloud and a white potassium‑nitrate solution—proof of a successful double‑displacement reaction.
The lead nitrate solution contains lead ions (Pb2+), while the potassium iodide solution carries iodide ions (I–). When the two solutions mix, the cations and anions exchange partners: Pb2+ pairs with I– to form insoluble PbI2, and K+ pairs with NO3– to form soluble KNO3.
With Solutions
1. Measure equal volumes of 0.1 M lead nitrate and 0.1 M potassium iodide into separate beakers.
2. Transfer the lead nitrate solution to a clean test tube and slowly add the potassium iodide solution while stirring.
3. Observe the sudden appearance of a yellow, milky cloud—lead iodide precipitate. The remaining clear liquid contains potassium nitrate.
With Dry Powders
1. Place equal masses of lead nitrate and potassium iodide into a test tube.
2. Seal the tube briefly and shake vigorously. The friction initiates a limited reaction, producing a fine yellow powder that is a mixture of PbI2 and KNO3. The reaction is less efficient than with liquids because solid ions have limited mobility.
Lead compounds are toxic. Conduct the experiment in a well‑ventilated area, wear gloves and safety goggles, and avoid inhalation or ingestion of powders. Dispose of waste according to local hazardous‑waste regulations.
