Download The lead-acid cell

The lead-acid cell
Dilute (2.0 mol L–1) sulfuric acid is put in a
beaker.
Two clean lead plates are connected to
wires. The block of wood just keeps them
from touching each other.
Charging the cell
The lead plates are placed in the acid, with
the wires connected to a power supply with
a voltage of about 3 V.
We see small bubbles
of hydrogen (from the
acid) forming at the
negative electrode.
2H+ + 2e– → H2
If Pb2+ had been
present in the solution,
then Pb metal would
form at this electrode
instead.
When the plates are
withdrawn from the
beaker, we see that the
left-hand plate
(connected to the
positive terminal of the
power supply) is coated in
a very dark substance.
Compare the bottom of
this plate to the colour at
the very top.
It is PbO2(s).
Discharging the cell
The plates are put back in the acid and the
wires connected to a 2V light bulb. The bulb
glows brightly.
The charge-discharge cycle can occur many times: the
lead-acid cell is rechargable.
Each cell of a commercial
lead-acid battery
contains 2 lead plates
suspended in a sulfuric
acid solution. The cells
are connected in series,
and each delivers 2 V, so
a 12 V car battery
contains 6 cells.