Quantitative Aspects of Electrolysis

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chemistry 12th class cbse notes

Michael Faraday was the first scientist who described the quantitative aspects of electrolysis. Faraday published his results during 1833-34 in the form of the following well known Faraday’s two laws of electrolysis.

Laws Of Electrolysis

  1. First Law: The amount of chemical reaction which occurs at any electrode during electrolysis by a current is proportional to the quantity of electricity passed through the electrolyte (solution or melt).
  2. Second Law: The amounts of different substances liberated by the same quantity of electricity passing through the electrolytic solution are proportional to their chemical equivalent weights (Atomic Mass of Metal ÷ Number of electrons required to reduce the cation).
  • There were no constant current sources available during Faraday’s times.
  • The general practice was to put a coulometer (a standard electrolytic cell) for determining the quantity of electricity passed from the amount of metal (generally silver or copper) deposited or consumed.
  • Coulometers are now obsolete and we now have constant current (I) sources available and the quantity of electricity Q, passed is given by

Q = It

Q is in coulombs when I is in ampere and t is in second

  • The amount of electricity (or charge) required for oxidation or reduction depends on the stoichiometry of the electrode reaction.
  • We know that charge on one electron is equal to 1.6021 x 10-19 C.
  • Therefore, the charge on one mole of electrons is equal to NA x 1.6021 x 10-19

C = 6.02 x 1023 mol-1 x 1.6021 x 10-19 = 96487 C mol-1

  • This quantity of electricity is called Faraday and is represented by the symbol F.

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