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TEACHERS EXPERIENCES FORM

Title of the Experience
The golden raining
Name of the teacher
Josep Bernado i Vera
Country where it took place
Spain
School typology
High Secondary School
Thematic Area
Chemistry
Experience typology
Laboratory
Type of contact
Direct
Description of the Experience
The aim of this experiment is to observe a precipitation reaction and check that the solubility of the substance varies with temperature.

In this experiment two soluble substances are mixed to form an insoluble compound. We have two aqueous solutions, one of lead II nitrate and other of potassium iodide. In a test tube, 2 mL of the two solutions are mixed and an amorphous yellow precipitate of lead II iodide appears, this precipitate is very insoluble. The test tube is heated until the precipitate is redissolved. The test tube is cooled and lead II iodide reprecipitated in small crystals resembling a shower of gold.

Students are surprised to discover that lead II iodide has two allotropic forms, one that is formed by the chemical reaction and the other is obtained by cooling. Students also test that the solubility of lead iodide increases with temperature.

Comments on this Teachers Experience

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Date: 2014.10.16

Posted by Nevenka Kostova (Bulgaria)

In the minds of my students chemistry is the science of violent reactions. They always ask me first if it will rumble and rattle and they become very disappointed if I just tell them a precipitate is what we expect as result. Some students could not imagine the beauty of different colored crystals or power of water (solvent) or diversity of clusters in the formation of hydrogen bonds and whatnot. This practice for me is an incredible example that clarifies the relationship solubility - temperature and at the same time is presented as a point in a story. Golden memories of rain will remain in my 10 grade students and it even will be told to their children and grandchildren. Memorable experiences are much easier and lasting than very well explained concept, phenomenon or process.

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