Electrolysis
Electrolysis is a process of chemical decomposition of the electrolytes by the
passage of electric current . It is carried out in a
Electrolytic Cell.
Faraday's Law Of Electrolysis
1st Law : The
quantity of a substance produced by electrolysis
is proprotional to the
quantity of electricty used.
OR
The mass of a substance deposited or liberated at any electrode
is directly proportional to quantity of electric current passed.
If W grams of a substance is deposited or liberated on passing Q Coulomb of charge then :
W is proprtional to Q
and
W = Z x Q
where Z is the proportionality constant and is called the Electrochemical Equivalent
.
2nd Law : For a given quantity of electricity
the quantity of substance produced is proportional to its weight.
Chemical equivalent = atomic mass / valence
m
1 m
2 = E
1/E
2
where m
1 and m
2 are the respective masses liberated or deposited on the electrodes
and E
1 and E
2 are the chemical equivalents of the substances liberated or deposited.
Any change in the magnetic environment of a coil of wire will cause a
voltage (emf) to be
"induced" in the coil. No matter how the change is
produced,
the voltage will be generated. The change could be produced
by changing the magnetic field strength, moving a magnet toward or
away from the coil, moving the coil into or out of the magnetic field,
rotating the coil relative to the magnet, etc.
The
presence of a magnetic field is detected by the forces
of attraction or repulsion which these exert on similar objects
within the range of this field. This magnetic field is characterized
by the
presence of magnetic lines which seem to be non-intersecting
and oriented from one pole of the magnet to the other. A magnetic
field is a
vector quantity, one which is described by both magnitude
and direction. The magnetic field lines are not physical lines but
imaginary ones, which help in the understanding of the magnetic field.
In short, the orientation and the working range of the field is
represented and more easily understood by representing this field
in the form of magnetic lines.
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Oxidation-reduction or redox reactions take place in electrochemical cells.
There are two types of electrochemical cells.
Spontaneous reactions occur in
galvanic (voltaic) cells;
Nonspontaneous reactions occur in electrolytic cells.
Both types of cells contain electrodes where the oxidation and reduction
reactions occur. Oxidation occurs at the electrode termed the anode and
reduction occurs at the electrode called the cathode.
Galvanic Cells
The redox reaction in a galvanic cell is a
spontaneous reaction.
For this reason, galvanic cells are commonly used as batteries.
Galvanic cell reactions supply energy which is used to perform work.
The energy is harnessed by situating the oxidation and reduction reactions
in separate containers, joined by an apparatus that allows electrons to flow.
For Example :: >>
If we place a strip of zinc metal in a beaker containing a solution of CuSO4 Zn is oxidized to Zn2+ ions, while Cu2+ ions are reduced to metallic copper
Zn(s) + Cu
2+(aq)
→ Zn
2+(aq) + Cu(s)
The
electrons are transferred directly from the reducing agent, Zn,
to the oxidizing agent, Cu2+ in solution. We have already seen,
when we balanced redox equations, that we can separate a redox reaction
like the one above into two half- reactions. One of the half- reactions
being oxidation and the other being a reduction half- reaction.
Zn(s)
→ Zn
2+(aq) + 2 e
- oxidation half- reaction
Cu
2+(aq) + 2 e
- → Cu(s)
reduction half- reaction
Dry Cell
Dry cell batteries, regardless of their size, have the same components.
At the center of each dry cell battery is a rod called a
cathode, which
is
generally made of metal or graphite and is surrounded by an electrolyte
paste. The
cathode and electrolyte paste are wrapped in paper or cardboard.
One or more of these cells are sealed into a metal cylinder called an
anode,
which is
typically made of zinc or alkaline.
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