On November 24th, 2008 we have explained and shown Chemical Reactions to a group of visiting young students from middle school, in our lab.
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Sulphuric acid plus Sodium Bichromate (sorry for tilted video)
Sulphuric acid added to a sodium carbonate solution (sorry for rotated image)
A student form middle school try the same carbonate - acid reaction.
Soxhlet Liquid - solid extraction of lemmon flavours to make "Limoncello".
The yellow lemmon skin is extracted in fresh ethanol continuously distilled.
Part one: fist cycle begins, the ethanol is yet colorless.
Sorry for having to rotate your head.
Second cycle: ethanol in the boiling balloon is now yellow,
because it has extracted for the first time the lemmon skin.
Fresh ethanol is continuously regenerated by distillation.
Please rotate your head.
At the end of our class we have experimented new forms of CHEMICAL ART.
This is our best composition: a multicolor World map
Roberto the Author, would thank for anybody who wants to award it.
The following picture was taken by Tommaso, on 24th May 2008, the last lab class of the year.
In this demonstraton we dissolved first cobalt dichloride in concentrated chloridric acid, obtaining a deep blue coloured solution (left).
The blue color is due to [CoCl4(H2O)2]= octahedral complex ion, stable in an excess of chlodide ions.
By slow addition of water to this solution we can substitute two or more chlorine atoms with water molecules in the complex, obtaining pink ions as CoCl2(H2O)4] (right becher). If we add again concentrated chloridric acid and water we can go back and forth through various different equilibrium states.
An intermediate violet solution has been divided among the three test tubes in the back of the photo. The central test tube has remained at room temperature, while the left one has been heated in hot water (some condensed vapour can be seen from that becher) and the right test tube was cooled by means of an instant ice pocket (back right becher).
The colour changed to the blue (equilibrium shifted on the left) by raising temperature, demonstrating a decreasing equilibrium constant. Analogously reducing the temperature provoked an increasing equilibrium constant. These observations are consistent with an exothermic reaction, i.e. Cobalt(II) - water bond being stronger than Cobalt(II) - chlorine bond.
In fact the Le Chatelier principle affirms that "adding heath" to an equilibrium system, it will drive the system towards the endothermic side.