Electrochemistry

Faraday's Law Of Electrolysis
Kohlrausch's Law Electrolytic Cells & Batteries

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

m1 m2 = E1/E2

where m1 and m2 are the respective masses liberated or deposited on the electrodes and E1 and E2 are the chemical equivalents of the substances liberated or deposited.

Kohlrauch Law

   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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Electrochemical Cells

   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) + Cu2+(aq) Zn2+(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) Zn2+(aq) + 2 e -         oxidation half- reaction

Cu2+(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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