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Me10 What happens with aluminium and iron while electricity is flowing?
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In the previous
experiment the multimeter connected with two different metals of a
Cola can red a voltage and a current was flowing. By the following experiment
you will learn what happens in a Galvanic Cell
while current is flowing
What
you need: Cola
can (recycling icon FE), scissors, sand paper, 2
insulated copper wires with 4 crocodile clips, digital multimeter,
2 vials, wick from tissue paper, salt water.
Experiment:
The
preparations are the same like in the previous
experiment.
* Left: Dip the free ends
of the metals into two different vials full of water.
Observation:
No voltage at the digital multimeter.
Dip the wick wetted with
salt water into the two vials.
Observation:
middle: The multimeter reads a voltage of 0.21 V and a current few
mA.
Explanation
right:
The model visualises what happens in the metals, in the vials and in the
wire.
1. Al atoms of the negative
electrode
push electrons into the wire: 2Al ----oxidation-->Al3++
6e-.
2. Spontaneous electron
flow to the positive iron electrode (Fe) through the wire.
3. Water molecules pull
electrons from the positive electrode. 6 H2O
+ 6e-----reduction--> 3 H2
+ 6 OH-.
Observation:
Universal indicator turns violet by hydroxide ions (OH-) in
the right vial.
4. Ion flow (OH-)
to the vial with the negative electrode through the wick.