What happens inside a battery
The essential elements in a battery are:
• Two electrodes, often but not always made of different
metals. One of them is more electronegative than the other one,
that means it has a stronger tendency to attract electrons. This
tendency is called electrical potential.
• A substance, called electrolyte (an acid, a salt or a base) which has
the property to dissolve spontaneously into ions (i.e. particles carrying a positive
or e negative charge).
In the fruit battery the electrolyte is the lemon juice, in the hand battery
it consists of charged particles that circulate inside our body and of the
sweat on the hands, in the can battery the electrolyte is the common salt.
If the two electrodes were in direct contact, an immediate,
random transfer of electrons between them would take place and
the result would be heat production.
Instead, in a battery the electrodes are connected by a copper wire and the
electrons flow along it in the same direction, i.e. electrical current is produced.
The flow of charges continues inside the solution, thanks to the presence of
the electrolyte; in this way the equilibrium of charges between the two electrodes
is guaranteed and the current keeps circulating.
![]() The
home-made elecrolitic cells
| ELECTROLYSIS
OF WATER. The glass is half full of water,
where some drops of acid (or a tablespoon of washing
soda – not baking soda!) have been added. Two copper
wires are connected to a battery and their two free ends
are inserted inside the glass. Bubbles of gas form into
the water, near the immersed wires. These gas can be
collected inside two small test tubes. |
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| ELECTRIC
DEPOSITION OF COPPER. The becker is half
full of a copper sulphate solution, where two steel screws
have been immersed. The screws don’t touch each
other After few seconds a thin layer of copper deposits
on a screw, while other chemical phenomena (blackening,
production of gas) happen to the other electrode. |
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What happens in an electrolytic cell
In the electrolytic cells the process is the direct opposite
than in the batteries In the electrolysis of water, the
electric current separates the water into two particles,
one of them carrying a positive charge, which migrates
to the negative electrode, the other carrying a negative
charge, which migrates to the positive electrode. Two positive
charged particles join together to form hydrogen gas at
one electrode, two negative charged particles form oxygen
gas on the surface of the other electrode. If the hydrogen
gas is collected in a test tube and then lit with a match,
it makes a little explosion. If a match is held close to
the end of the tube test where the oxygen has been collected,
the flame brightens.
Also in the copper electric deposition chemical effects of the electric current
can be observed. In this case the copper is deposited on the surface of one
electrode and at the same time the other electrode becomes black. The copper
comes from the copper sulphate dissolved in water. The chemical transformation
is evident, because the copper sulphate is a blue salt, while the copper
metal on the electrode surface is lucid and red.
![]() During
the national scientific week (in March 2005) our students
met primary school children and taught them.
In their comments about the experience, students say
they enjoyed it and think they have improved some attitudes
and skills. They highlight these aspects:fun,
playing, direct involvement, hands-on activities, challenge,
pleasure of discoveries, reward, cooperation, relationship
with peers…
We think that motivation can be improved by increasing
students’ responsibility for their own learning and
engaging them on a physical, mental and emotional level.
This kind of activities give an intrinsic reward.
What the pupils say...
:: At the
beginning I was a little afraid and anxious for the task,
but later all things became easy…It was nice for
me to see that the children had fun and at the same time
they were able to understand what we were explaining
them …. The children said that we were nice and
good teachers … it was rewarding. This experience
must certainly be proposed again. (Chiara)
:: We
had a lot of fun having the role of teacher, but we also
understood the difficulties of this job. We experienced
what means looking after pupils who sometimes are paying
attention but sometimes are talking or laughing… we
had to find the way to capture their attention… we
reached the best results involving them in hands-on activities
(Cesare)
:: There
was a climate that made all comfortable … even
when I didn’t remember something I wasn’t
embarrassed! (Viola)
:: The
open laboratory gave me the opportunity to deepen the
subject and to considerate and memorize some aspects
that would have been neglected if I had studied as usual
(Lisa)
:: It was
useful for me to listen to my classmates’ explanations
and I was also able to tell the children the few things
I had learnt! It was great to work with my classmates and
to communicate with the children, though some of them were
more clever than me… (Rahamatou)
With this experience I overtook the difficulties I had had before in making
a public speech… and the children, in my opinion, better understood
the subject because the lesson was like a play (Giacomo)
:: Thanks
to this activity I improved my self control and I enriched
my communication skills… (Tommaso)
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