Golden rain

 

Lead nitrate reacts with potassium iodide to form a nice precipitate. This reaction is called the "Golden Rain" experiment. It produces beautiful hexagonal lead iodide crystals, similar to a gold plate, which is a good proof of chemistry. 

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

Requirements:

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

2.Potassium iodide 1.66 grams (.01 moles)

3.Erlenmeyer flask 1000ml

4.Hotplate-stirrer

Experiment:

1) Dissolve each salt in 400 ml of distilled water in a separate beaker. 

2) Mix the liquid in the Erlenmeyer flask so that the total volume is 800 ml. If you want to switch to a 500-ml flask, just halve the amount of compound and water. You will see yellow lead iodide precipitate in the solution. PbI2 precipitates immediately because it is insoluble in cold water. 

3) Heat the solution until all the lead iodide is dissolved. You may need to heat them above 80 degrees Celsius. Heating the solution will increase the solubility enough to dissolve all lead iodide. 

4) Let cool. PbI2 is much better this time. It is best to watch in the dark, when bright sunlight is shining on the bottle, such as through a garage window in the late afternoon. If lead iodide settles too quickly, stir with a long stir bar or start magnetic stirring to keep the particles in suspension-this will produce a "golden rain" effect.

Explanations:

The honeysuckle experiment involves two soluble ionic compounds, potassium iodide (KI) and lead nitrate (II) (Pb (NO3) 2). They are first dissolved in a separate colorless aqueous solution. 

Mix two solutions of potassium iodide (KI) and lead nitrate (Pb (NO3) 2) to produce soluble potassium nitrate (KNO3) and insoluble lead iodide (PbI2). This can be seen as a yellow precipitate in the solution. The resulting lead iodide dissolves in the solution when heated so that the yellow precipitate disappears and leaves a colorless solution. If the solution is allowed to cool down slowly, 

Lead iodide crystals begin to form, creating a sparkling "golden rain" effect. Although this is only a reaction of dissociating ions in solution, it is sometimes called a double displacement reaction: 

        Pb (NO3) 2 + 2KI → 2KNO3 + PbI2 

At higher temperatures, this substance can easily dissolve back to itself By dissociating colorless ions. So the actual change (net ionic equation) is:

Lead Iodide Solubility at 100˚C Increases to about 0.41 g per milliliter. 

Solubility of salts in 100ml water (at 20˚C) 

 a) KI              -  140g 

 b) Pb(NO3)2 -  66g 

 c) KNO3        -  31.6g 

 d) PbI2          -  0.0756g

Caution:

Lead nitrate is toxic, and the oral lethal dose for a person weighing 80 kg is about 8 grams. Do not swallow anything and avoid skin contact or inhalation of dust. 

Lead iodide should be filtered and stored in your active ingredient collection. Lead salt should not be washed into the sewer. The remaining lead in the solution can be precipitated with sodium sulfide because lead sulfide is extremely difficult to dissolve. PbS should be kept in a hazardous waste drawer until it can be disposed of properly.

References:

1) https://chemistrytalk.org/lead-iodide-reaction/

2) https://edu.rsc.org/exhibition-chemistry/golden-rain/2000048.article

3) https://www.compoundchem.com/2015/04/23/golden-rain/

4) https://en.wikipedia.org/wiki/Golden_rain_demonstration

5) https://www.youtube.com/watch?v=4xSUvSGywXo