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TEACHERS EXPERIENCES FORM

Title of the Experience
The purple cloud
Name of the teacher
Josep Bernardo 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
Students have difficulty understanding how a chemical reaction takes place and how a change in the combination of atoms forms different molecules. This experiment shows a redox reaction that ends with a sublimation of the iodine, resulting in a purple cloud.

The practice is to grind separately the same amount of iodine (I2) and zinc (Zn) powder. The two reagents are mixed in a beaker and water are slowly added. Zinc iodide (ZnI2) is formed and the exothermic reaction releases purple vapours.
In this reaction, students can identify the physical state of the reactants and products formed, the valence with which the different elements are acting, the formation of mixtures or compounds, the type of reaction ...

A lot of students are surprised by this reaction when purple vapour is formed and are interested in finding out how it is formed.

Comments on this Teachers Experience

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Date: 2014.09.09

Posted by Laura capella (Italy)

I like this experience because it is easy to perform, and has a quick evolution. This is what the majority of students need, because their attention doesn't last very long. In addition it is colorful, that means extra attention and possibly more motivation for trying to understand why it happens. Some students are not very motivated because can't follow things that last too long.
I wonder if the reasction can take place also without water, because water doesn't enter in the reagent pool.
This remember to me another easy reaction that sometimes I had performed: NaI plus Pb(NO3)2, both solid: the product, a bright Yellow one, comes simply stiring the reagents in a mortar .

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