## Faraday’s Laws of Electrolysis – First and Second Law:

The laws governing the electrolytic processes were formulated by Michael Faraday, an English Scientist, and are known as Faraday’s Laws of Electrolysis. These may be stated as below:

According to this law the chemical deposition due to flow of current through an electrolyte is directly proportional to the quantity of electricity (coulombs) passed through it.

i.e., mass of chemical deposition,

where I is the steady current in amperes flowing through the electrolyte for t seconds and Z is a constant of proportionality and is known as the electrochemical equivalent of the substance.

If I = 1 A and t = 1 second, then Z = m

Thus electrochemical equivalent, Z, of a substance is defined as the amount of the substance deposited on passing a steady electric current of 1 A for one second through its solution. It is usually expressed in terms of milligrams per coulomb. The SI unit of electrochemical equivalent Z is the kilogram per coulomb (kg C-1).

This law states that when the same quantity of electricity is passed through several electrolytes, the mass of the substances deposited are proportional to their respective chemical equivalents or equivalent weights.

From this law it follows that the constant of proportionality Z in Eq, (8.1) is proportional to the chemical equivalent.

Table 8.1 gives the values of atomic weight, valency, chemical equivalent and electrochemical equivalent of various elements.

 Elements Symbol Atomic Weight Valency Chemical Equivalent Electrochemical Equivalent Kg/Coulomb Aluminium Al 27 3 9 9.5 x 10-8 Cadmium Cd 112.4 2 56.2 58.2 x 10-8 Calcium Ca 40.08 2 20.04 20.75 x 10-8 Chlorine Cl 35.45 1 35.37 36.74 x 10-8 Chromium Cr 52.01 3,6 17.3, 8.6 17.9 x 10-8, 9.1 x 10-8 Copper (Cupric) Cu 63.54 2 31.8 32.9 x 10-8 Gold Au 197 3 65.4 67.68 x 10-8 Hydrogen H 1.008 1 1 1.045 x 10-8 Ferrous Fe 55.9 2 27.95 29.02 x 10-8 Ferric Fe 55.5 3 18.63 19.35 x 10-8 Lead Pb 207.21 2 103.2 107.16 x 10-8 Magnesium Mg 24.32 2 11.97 12.43 x 10-8 Nickel Ni 58.7 2 29.3 30.43 x 10-8 Nitrogen Ni 14 3 4.67 4.85 x 10-8 Oxygen O 16 2 7.98 8.296 x 10-8 Potassium K 39.1 1 39.04 40.54 x 10-8 Silver Ag 107.88 1 107.67 111.81 x 10-8 Sodium Na 22.99 1 22.99 23.87 x 10-8 Tin Sn 118.7 2 59.3 61.4 x 10-8 inc Zn 65.38 2 32.45 33.88 x 10-8