The electrolyte always has a certain number of ions with plus and minus signs resulting from the interaction of the molecules of the dissolved substance with the solvent. When an electric field appears in it, the ions begin to move toward the electrodes, the positive ones rush toward the cathode, the negative ones toward the anode. When they reach the electrodes, the ions give them their charges, turn into neutral atoms and are deposited on the electrodes. The more ions approach the electrodes, the more matter will be deposited on them.
We can come to this conclusion experimentally. Let the current pass through an aqueous solution of copper sulfate and we will observe the release of copper at the carbon cathode. We will find that at first it is covered with a barely noticeable layer of copper, then with the passage of current it will increase, and with long-term transmission of current it is possible to obtain a layer of copper on a carbon electrode of considerable thickness, to which it is easy to solder, for example, a copper wire.
The phenomenon of substance release on the electrodes during the passage of current through the electrolyte is called electrolysis.
Passing different currents through different electrolysis and carefully measuring the mass of the substance released on the electrodes from each electrolyte, the English physicist Faraday in 1833 - 1834. discovered two laws for electrolysis.
The first Faraday law establishes the relationship between the mass of the released substance during electrolysis and the amount of charge that passed through the electrolyte.
This law is formulated as follows: the mass of the substance that was released during electrolysis at each electrode is directly proportional to the amount of charge that passed through the electrolyte:
m = kq,
where m is the mass of the substance that is released, q is the charge.
The value of k is the electrochemical equivalent of a substance. It is characteristic of every substance released during electrolyte.
If q = 1 pendant is taken in the formula, then k = m, i.e. the electrochemical equivalent of a substance will be numerically equal to the mass of the substance isolated from the electrolyte during the passage of a charge into one pendant.
Expressing the charge in the formula through the current I and time t, we obtain:
m = kIt.
The first law of Faraday is tested experimentally as follows. Let the current pass through electrolytes A, B and C. If they are all the same, then the masses of the selected substance in A, B and C will be referred to as currents I, I1, I2. In this case, the amount of substance released in A will be equal to the sum of the volumes allocated in B and C, since the current I = I1 + I2.
The second Faraday law establishes the dependence of the electrochemical equivalent on the atomic weight of a substance and its valency and is formulated as follows: the electrochemical equivalent of a substance will be proportional to their atomic weight, and also inversely proportional to its valency.
The ratio of the atomic weight of a substance to its valency is called the chemical equivalent of a substance. Introducing this quantity, the second Faraday law can be formulated differently: the electrochemical equivalents of a substance are proportional to their own chemical equivalents.
Let the electrochemical equivalents of different substances are respectively equal to k1 and k2, k3, ..., kn, the chemical equivalents of the same substances x1 and x2, x23, ..., xn, then k1 / k2 = x1 / x2, or k1 / x1 = k2 / x2 = k3 / x3 = ... = kn / xn.
In other words, the ratio of the value of the electrochemical equivalent of a substance to the value of the same substance is a constant value, which has the same value for all substances:
k / x = c.
It follows that the ratio k / x is constant for all substances:
k / x = c = 0,01036 (mEq) / k.
The value of c shows how many milligram equivalents of the substance are released on the electrodes during the passage of an electric charge through the electrolyte , equal to 1 coulomb. The second law of Faraday is represented by the formula:
k = cx.
Substituting the obtained expression for k into the first Faraday law, both can be combined in one expression:
m = kq = cxq = cxIt,
where c is the universal constant equal to 0, 00001036 (g-eq) / k.
This formula shows that by passing the same currents over the same period of time through two different electrolytes, we will isolate from both electrolytes the quantities of substances related as chemical equivalents thereof.
Since x = A / n, we can write:
m = cA / nIt,
i.e., the mass of the substance released on the electrodes during electrolysis will be directly proportional to its atomic weight, current, time and inversely proportional to valency.
The second Faraday law for electrolysis, just like the first, directly follows from the ionic nature of the current in the solution.
The law of Faraday, Lenz, as well as many other prominent physicists played a huge role in the history of the formation and development of physics.