.
.
Me4 Reduction
of copper by electrolysis
In a previous
experiment copper was corroded by nitric acid: Cu
(s) --ox--> Cu2+ + 2 e-
Now you will take the
electricity of a battery for reduction of copper ions..
What
you need: 9-Volt battery, 2 insulated
copper wires with 4 crocodile clops, 2 pieces of pencil lead, blister,
1 ml copper salt solution from experiment Su13,
grains of salt.
Experiment
left:
Transfer the copper salt solution into the blister, add salt, stirr for
dissolving.
* Connect
the two pencil leads to the battery by the wires, dip the electrodes into
the solution.
Observations
middle:
Gas
bubles at both electrodes. Smell of chlorine at the right electrode (+).
Cathode (-) covered by a copper brown substance.
Explanation
by bead modelsright:
* Negative chloride ions (Cl-, green big beads with one white
micro bead) are attracted by the right (positive) electrode and deprived
from one electron (white micro bead). The resulting chlorine atom (Cl,
small green bead) and a second one form a chlorine molecule (Cl-Cl = Cl2).
2
Cl-(aq) - 2e- ----(ox)--> 2 Cl ---> Cl2(g)
* Electrons
(white micro beads) are pushed from the positive to the negative electrode
by the battery ("electron pump")
* Positive
copper ions (Cu2+) are attracted by the negative electrode
and supplied with 2 electrons each:
Cu2+(aq)
+ 2e- --(red)--> Cu(s)
back.......
go
on.................................................................................................last
modification: 25.10.2001