Lead Nitrate + Potassium Iodide

Lead nitrate reacts with potassium iodide to produce a beautiful precipitate. The reaction, known as the “Golden Rain” experiment, produces beautiful hexagonal crystals of lead iodide that resemble plates of gold.

The golden rain reaction takes advantage of the increased solubility of lead iodide in hot water. Stoichiometric amounts of lead nitrate and potassium iodide are combined, with enough water to dissolve all of the lead iodide precipitates at 80 degrees Celsius. When the solution cools, beautiful lead iodide crystals will fall out of solution.

Materials needed:

Lead (II) nitrate 1.65 grams (.005 moles)

Potassium iodide 1.66 grams (.01 moles)

Erlenmeyer flask 1000ml

Hotplate-stirrer

Procedure:

Dissolve each salt in 400ml of distilled water in separate beakers.

Combine the liquids in the Erlenmeyer flask so you have 800ml in total. You will see a yellow precipitate of lead iodide fall out of solution.

PbI2 will immediately precipitate out, as it is insoluble in cold water.

Heat the solution until all of the lead iodide dissolves, you may need to heat it above 80 degrees Celsius. Heating the solution causes the solubility to increase just enough to dissolve all of the lead iodide.

Here is the equation for this double-replacement reaction. Lead ii nitrate reacts with potassium iodide forming lead (II) iodide and potassium nitrate.

Pb(NO₃)₂ + 2KI -> PbI₂ + 2KNO₃

Net ionic equation: Pb⁺² + 2I– -> PbI₂(s)

Don’t use too much iodide, or the following reaction will occur, forming the soluble colorless tetraiodoplumbate(II) complex ion:

PbI₂ + 2I– -> PbI₄^-2

Safety & Disposal

Lead nitrate is toxic, the lethal oral dose is approximately 8 grams for an 80kg human. Do not ingest any and avoid skin contact or breathing the dust.

The lead iodide should be filtered and stored in your compound collection. Lead salts should not be washed down the drain. The remaining lead in the solution can be precipitated out with sodium sulfide, as lead sulfide is extremely insoluble. PbS should be stored in a hazardous waste drawer until it can be disposed of properly. Sodium carbonate can be used if a sulfide compound is not available.

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