.
.
.
salt14 Coloured
copper salts from a wire or from a Pfennig
Nitric
acid is corrosive! Goggles, tray. Experiment only outdoor and in presence
of an adult.
* Left: In a previous
experiment you have made a blue copper salt solution from copper and
a drop of conc. nitric acid. This solution can be used again:
* Photo 2: Dilute
with 3 ml of distilled water and transfer the solution to three small bottles.
* Photo 3: Add table
salt (NaCl) to the bottle in the middle and drops of ammonia solution (NH3)
to the right one.
Observation:
NaCl
causes a colour change from light blue to green, ammonia produces a dark
blue colour.
Explanation
Right:
Copper
salts contain crystal water like cobalt
chloride does. In this sketch of a model the copper ion (small grey
ball) is in the center of an octahedron (double pyramid with 8 planes).
The Cu ion is surrounded
by water molecules on four sides and by 2 sulfate (SO4) ions
on the top and below.
In aqueous solution these
sulfate ions are replaced by two more water molecules. These 6 water molecules
bonded to the Cu2+ ion in the center are called Ligands,
the coloured ions are complex ions.
The colour changes to green
and to blue can be explaned by exchange of ligands:
Water molecules are replaced
by chloride ions and by ammonia molecules: Visualize
by models.
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modification: 25.10.2001