The phenomenon of electrolysis has been studied M. Faraday. Measuring leaking through the solution, the charge and mass of the cathode before and after electrolysis, Faraday found, the mass of the substance, released during the electrolysis, directly proportional to the amount of electricity, potekshego through the solution:

m= kq. (19.1)

Formula (19.1) is the mathematical expression of first law of Faraday.

The experiments of Faraday showed, the mass allocated in the electrolysis of a substance depends not only on the magnitude of the charge C, but from such substances. The coefficient of proportionality K, expressing the dependence of the mass selected in the electrolysis of the substance from his family, called electrochemical equivalent of the substance. Electrochemical equivalent is measured by the mass of the material, evolved at the electrode during the passage through the electrolyte of the unit of charge:

k= m/q. (19.1, α)

(Show, what is the SI unit of electrochemical equivalent k is 1 kg/KL.)

Since q =It, the first Faraday's law can be written as follows:

m = kIt. (19.2)

On experience it is possible to determine electrochemical equivalent with great accuracy. At the time it is allowed to use (19.1) to determine the Coulomb electrochemical equivalent of silver, which was carefully measured and was equal to 1,118*10^-6 kg/KL=1,118 mg/TC.

Find out, as the theory explains results of experiments of Faraday. Ion, discharge during electrolysis at the cathode, attaches to itself a certain number of electrons, for example, the silver ion — one electron, copper ion and two electron. Therefore, charge, are transferred through the electrolyte when current flows, must be directly proportional to the number of discharged ions. Because the masses of ions of a certain type is exactly the same, the total mass of all the ions is proportional to their number. This means, the mass allocated in the electrolysis of the substances must be directly proportional to the charge, passed through the solution, which corresponds to the Faraday's law.

Since ions of different species have different mass (for example, mass Nona silver 107,9 times, than the mass of hydrogen Nona), the mass allocated in the electrolysis of the substance should depend on its kind.