Experiments

Golden Rain Experiment

golden rain experiment - lead iodide synthesis

Lead Nitrate + Potassium Iodide

Lead nitrate reacts with potassium iodide to produce a beautiful precipitate, as we will show you. The reaction, known as the “Golden Rain” experiment, produces beautiful hexagonal crystals of lead iodide that resemble plates of gold, and makes a great chemistry demonstration.

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 precipitate at 80 degrees Celsius. When the solution cools, beautiful lead iodide crystals will fall out of solution.

Lead iodide golden rain experiment requirements

Lead (II) nitrate 1.65 grams (.005 moles)
Potassium iodide 1.66 grams (.01 moles)
Erlenmeyer flask 1000ml
Hotplate-stirrer

Golden Rain Procedure – Tips & Tricks

Lead nitrate and potassium iodide are both solid, soluble ionic compounds. We will combine them for some amazing results.

  1. Dissolve each salt in 400ml of distilled water in separate beakers.
  2. Combine the liquids in the Erlenmeyer flask so you have 800ml in total. If you wish to use a 500 ml flask instead, simply cut the amounts of compounds and water in half. You will see a yellow precipitate of lead iodide fall out of solution.

Mastering chemistry challenge: How would you calculate the amounts needed yourself? Leave your answer in the comments.

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

3. 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.

Lead iodide precipitate – how to best view it

4. Let it cool. This time, the PbI2 precipitates out in a much more beautiful fashion. This is best viewed in a dark with bright sunlight shining onto the flask, for example through a garage window in the late afternoon. If the lead iodide settles too quickly, stir it with a long stirring rod or start magnetic stirring to keep the particles suspended – giving the “golden rain” effect.

The Golden Rain reaction

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)

Interesting fact: Lead is in the +2 oxidation state in this reaction. Lead (IV) iodide does not exist, because lead (IV) can oxidize iodide to iodine.

Lead / iodine complexes

Don’t use too much iodide, or this 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.

If you are doing a lab report, here is an example.

Lead Iodide / Golden Rain experiment video

We filmed this short clip on the golden rain reaction to show how beautiful the flakes of lead iodide look in the sun, when they precipitate in the cooled down solution. The video was taken in a dark garage, with sunlight coming through a window.

About Lead Iodide

Lead (II) iodide is a bright yellow solid, that is slightly soluble in hot water. It is stable in air. The formula for lead iodide is PbI2, and its molar mass is 461.01 grams/mole. The symbol for lead is Pb because its latin name is plumbum.

Lead iodide is quite a heavy molecule from a molar mass perspective, because both lead and iodine are heavier atoms. It has a hexagonal close-packed crystal structure, which is why it crystallizes in thin hexagonal-shaped plates. If you love math and crystals, read this.

Lead iodide is used in the manufacturing of solar cells, and also as a photon-detector for x-rays and gamma rays.

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If you enjoyed this article about lead iodide and the golden rain experiment, check out making tin crystals, and read about standard reduction potentials and how to name ionic compounds

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