Electrolysis

Electrolysis is a non-spontaneous chemical reaction involving a redox reaction, which is triggered by an electric current.

For electrolysis to take place, the electrical current involved must be continuous and have sufficient voltage.

So that the ions involved have freedom in the movement they perform, these can occur by melting (igneous electrolysis) or by dissolution (solution electrolysis).

Applications of Electrolysis

Many materials and chemical compounds are produced from the electrolysis process, for example:

• aluminum and copper
• hydrogen and chlorine in cylinder
• costume jewelry (galvanization process)
• pressure cooker
• magnesium wheel (car hubcaps).

Laws of Electrolysis

The Laws of Electrolysis were developed by the English physicist and chemist Michael de Faraday (1791-1867). Both laws govern the quantitative aspects of these.

The first law reads as follows:

“ The mass of an element, deposited during the electrolysis process, is directly proportional to the amount of electricity passing through the electrolytic cell ”.

Q = i . t

Where,

Q : electric charge (C)
i : intensity of electric current (A)
t : time interval for the passage of electric current (s)

The second law reads as follows:

“ The masses of various elements, when deposited during electrolysis by the same amount of electricity, are directly proportional to their chemical equivalents ”.

M = K . AND

Where,

M : mass of the substance
K : constant of proportionality
E : gram-equivalent of the substance

Learn more in the article: Faraday constant .

Classification

The electrolysis process can occur through melting or dissolution:

Igneous Electrolysis

It is the one that is processed from a molten electrolyte, that is, by the melting process .

As an example, let’s use NaCl (Sodium Chloride). When we heat the substance to 808 °C, it melts and the ions present (Na ⁺ and Cl ^– ) start to have greater freedom of movement, in the liquid state.

When electric current passes through the electrolytic cell, the Na ⁺ cations are attracted to the negative pole, called the cathode. The Cl ^– anions, on the other hand , are attracted to the positive pole, or the anode.

In the case of Na ⁺ a reduction reaction takes place, while in the case of Cl ^{– an} oxidation reaction takes place .

Aqueous Electrolysis

The ionizing solvent used is water. In aqueous solution, electrolysis can be performed with inverted electrodes or active (or reactive) electrodes.

Inert Electrodes : the water in the solution ionizes according to the equation:

H ₂ O ↔ H ⁺ + OH ^–

With the dissociation of NaCl we have:

NaCl → Na ⁺ + Cl ^–

^{Thus, H +} and Na ⁺ cations can be discharged in the negative pole, while OH ^– and Cl ^– anions can be discharged in the positive pole.

In cations, a reduction reaction occurs (cathodic reduction), while in anions, an oxidation reaction (anodic oxidation).

So we have the electrolysis reaction:

2 NaCl + 2 H ₂ O → 2 Na ⁺ + 2 OH ^– + H ₂ + Cl ₂

From this, we can conclude that NaOH molecules remain in solution, while H ₂ is released in the negative pole and Cl ₂ in the positive pole.

This process will result in the equivalent equation:

2 NaCl + 2 H ₂ O → 2 NaOH + H ₂ + Cl ₂

Active Electrodes : in this case, the active electrodes participate in the electrolysis, however, they suffer corrosion.

As an example, we have the electrolysis of copper sulfate (CuSO ₄ ) in aqueous solution:

CuSO ₄ → Cu ₂ + SO ^2- ₄
H ₂ O → H ⁺ + OH ^–

In this case, the copper anode will corrode:

Cu ⁰ → Cu ²⁺ + 2e ^–

This occurs because, according to the standard potentials of the electrodes, the electric current is more likely to remove electrons from Cu ⁰ than from SO ^2- ₄ or OH ^– .

Thus, at the negative pole, the following electrolysis reaction takes place:

2e ^– + Cu ²⁺ → Cu

At the positive pole, we have the electrolysis reaction:

Cu → Cu ²⁺ +2e ^–

Finally, when we add the two electrolysis equations we get zero as a result.

Battery and Electrolysis

Electrolysis is based on an inverse phenomenon to that of the battery . In electrolysis, the process is not spontaneous, as it happens in batteries. That is, electrolysis converts electrical energy into chemical energy, whereas the battery generates electrical energy from chemical energy.