ELECTROLYTIC CELL: PARTS, HOW IT WORKS AND APPLICATIONS - CHEMISTRY - 2025

The electrolytic cell is a medium where energy or an electric current is used to carry out a non-spontaneous oxide-reduction reaction. It consists of two electrodes: the anode and the cathode.

At the anode (+) oxidation occurs, since at this site some elements or compounds lose electrons; while in the cathode (-), the reduction, since in it some elements or compounds gain electrons.

Source: By RodEz2, from Wikimedia Commons

In the electrolytic cell, the decomposition of some substances, previously ionized, occurs through a process known as electrolysis.

The application of the electric current produces an orientation in the movement of the ions in the electrolytic cell. Positively charged ions (cations) migrate towards the charging cathode (-).

Meanwhile, the negatively charged ions (anions) migrate towards the charged anode (+). This charge transfer constitutes an electrical current (top image). In this case, the electric current is conducted by solutions of electrolytes, present in the container of the electrolytic cell.

Faraday's Law of electrolysis states that the amount of substance that undergoes oxidation or reduction at each electrode is directly proportional to the amount of electricity that passes through the cell or cell.

Parts

An electrolytic cell is made up of a container where the material that will undergo the reactions induced by the electric charge is deposited.

The container has a pair of electrodes that are connected to a direct current battery. The electrodes that are usually used are made of an inert material, that is, they do not take part in the reactions.

An ammeter can be connected in series with the battery to measure the intensity of the current flowing through the electrolyte solution. Also, a voltmeter is placed in parallel to measure the voltage difference between the pair of electrodes.

How does an electrolytic cell work?

Electrolysis of molten sodium chloride

Molten sodium chloride is preferred to solid sodium chloride, since the latter does not conduct electricity. The ions vibrate within your crystals, but they are not free to move.

Cathode reaction

Electrodes made of graphite, an inert material, are connected to the battery terminals. An electrode is connected to the positive terminal of the battery, constituting the anode (+).

Meanwhile, the other electrode is connected to the negative terminal of the battery, constituting the cathode (-). When the current flows from the battery, the following is observed:

In the cathode (-) there is a reduction of the Na ⁺ ion, which when gaining an electron is transformed into metallic Na:

Na ⁺ + e ^- => Na (l)

The silvery-white metallic sodium floats on top of the molten sodium chloride.

Anode reaction

On the contrary, in the anode (+) the oxidation of the Cl ^- ion occurs, since it loses electrons and is transformed into chlorine gas (Cl ₂), a process that is manifested by the appearance in the anode of a gas of pale green color. The reaction that occurs at the anode can be outlined as follows:

2Cl ^- => Cl ₂ (g) + 2 e ^-

The formation of metallic Na and Cl ₂ gas from NaCl is not a spontaneous process, requiring temperatures higher than 800º C for it to occur. The electric current supplies the energy for the indicated transformation to take place at the electrodes of the electrolytic cell.

Electrons are consumed at the cathode (-) in the reduction process and are produced at the anode (+) during oxidation. Therefore, electrons flow through the external circuit of the electrolytic cell from the anode to the cathode.

The direct current battery supplies the energy for electrons to flow non-spontaneously from the anode (+) to the cathode (-).

Down Cell

The Down cell is an adaptation of the electrolytic cell described and used for the industrial production of metallic Na and chlorine gas.

Down's electrolytic cell has devices that allow the collection, separately, of metallic sodium and chlorine gas. This method of producing metallic sodium is still very practical.

Once released by electrolysis, the liquid metallic sodium is drained, cooled, and cut into blocks. Later, it is stored in an inert medium, since sodium can react explosively by contact with water or atmospheric oxygen.

Chlorine gas is produced in industry mainly by electrolysis of sodium chloride in a less expensive process than the production of metallic sodium.

Applications

Industrial syntheses

-In industry, electrolytic cells are used in the electrorefining and electroplating of various non-ferrous metals. Almost all high-purity aluminum, copper, zinc, and lead are produced industrially in electrolytic cells.

-Hydrogen is produced by electrolysis of water. This chemical procedure is also used in obtaining heavy water (D ₂ O).

-Metals such as Na, K and Mg are obtained by the electrolysis of molten electrolytes. Also, non-metals like fluorides and chlorides are obtained by electrolysis. Furthermore, compounds such as NaOH, KOH, Na ₂ CO ₃ and KMnO ₄ are synthesized by the same procedure.

Coating and refining of metals

-The process of coating an inferior metal with a higher quality metal is known as electroplating. The purpose of this is to prevent corrosion of the lower metal and make it more attractive. Electrolytic cells are used in electroplating for this purpose.

-Impure metals can be refined by electrolysis. In the case of copper, very thin sheets of metal are placed on the cathode and large rods of the impure copper to be refined on the anode.

-The use of veneered items is common in society. Jewelry and tableware are usually silver; gold is electrodeposited on jewelry and electrical contacts. Many objects are covered with copper for decorative purposes.

-The cars have chrome steel fenders and other parts. The chrome plating of a car bumper takes just 3 seconds of chrome electrodeposition to produce a 0.0002mm thick shiny surface.

-Rapid electrodeposition of metal produces black and rough surfaces. Slow electrodeposition produces smooth surfaces. The "tin cans" are made of steel coated with tin by electrolysis. Sometimes these cans are chrome plated in a fraction of a second with the thickness of the chrome layer extremely thin.

References

1. Whitten, Davis, Peck & Stanley. Chemistry. (8th ed.). CENGAGE Learning.
2. eMedical Prep. (2018). Applications of Electrolysis. Recovered from: emedicalprep.com
3. Wikipedia. (2018). Electrolytic cell. Recovered from: en.wikipedia.org
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5. Bodner Research Web. (sf). Electrolytic Cells. Recovered from: chemed.chem.purdue.edu