Golden rain

Beautiful crystals of bright yellow colour are formed under cooling.

Scientific name: Golden rain - formation of small lead II iodide crystals from oversaturated solution when it is colded down

YouTube

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Safety

Wear goggles and disposable gloves. The lead nitrate solution is very toxic, be extremely careful in handling it.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

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

Step-by-step instruction

  1. Prepare 5 ml Pb(NO3)2 solution and 5 ml KI solution.
  2. Add a few drops of Pb(NO3)2 solution to the test-tube with KI solution. Gradually add all available solution.
  3. Observe the formation of the yellow precipitate. At room temperature it looks silky.
  4. Heat the test-tube carefully. Avoid boiling. The precipitate will dissolve.
  5. Cool the solution down in cold water. Do not let water into the test-tube.
  6. In a few minutes small yellow crystals will appear.

Scientific background

Golden rain is one of the most beautiful chemical demonstrations. When Pb(NO3)2 is added to KI solution the reaction between the components takes place:

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

The formation of a yellow silky precipitate is observed. The solubility of PbI2 depends on temperature. At room temperature it is slightly soluble. Its solubility is ten times higher in hot water. When the test tube with the precipitate is heated it dissolves and the solution becomes clear again. By cooling the solution down we promote the formation of tiny very beautiful shiny crystals of PbI2 since the temperature decrease lowers the PbI2 solubility.

Danger:
Coolness:
Difficulty:

Published on 10 January 2016

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst