Electrolysis: Process, Applications, and Cells

Study Notes

Electrolysis

Electrolysis is a chemical process where electricity breaks down a compound, typically through ionization. It occurs when a direct electric current (DC) passes from one electrode to another through an electrolyte solution, causing mineral compounds to dissolve in water. This process can result in several outcomes depending on the specific application of electrolysis.

Electrolysis of Water

Water is an excellent example of an electrolyte and can conduct electricity under certain conditions. When subjected to electrolysis, water molecules break apart into hydrogen and oxygen gases, forming water clusters with varying degrees of molecular separation called hydrated electrons. These hydrated electrons are thermally unstable and can recombine to form neutral water molecules. This reaction is described by the equation:

2H2O + 2e- = H2(g) + O2(g).

The efficiency of this process depends on factors like electrode materials, applied voltage, temperature, pressure, and concentration of impurities in the water. An electrolytic cell used for water splitting requires an external power source applied across the two electrodes.

Electroplating

Electroplating is a common industrial application of electrolysis. In this process, metal ions (cations) present in the electrolyte solution get reduced and deposited onto the cathode (a negatively charged electrode), creating a new layer of the desired metal. The most common metals plated through electrolysis are copper, nickel, gold, silver, tin, zinc, chromium, cadmium, cobalt, mercury, lead, platinum, rhodium, osmium, and palladium.

However, some elements known as noble metals do not readily oxidize; they don't lose electrons easily. Platinum, gold, and silver will never be found as ions in nature, so electrolytic methods cannot plate these metals directly in their pure state. Instead, other more active metals like nickel or copper must be plated first, followed by a series of additional treatments called cyanide washes to create a low vacuum porous surface suitable for plating on noble metals.

Electrolyte Solutions

An electrolyte solution is a liquid, solid, or gas mixture containing free ions in an electrostatic field. Commonly, it consists of soluble salts, acids, bases, and electrolytes derived from complex organic compounds. Examples of such electrolytes include sodium chloride, potassium nitrate, ammonium sulfate, and sugar.

In an electrolytic cell, the electrolyte acts as a bridge between the electrodes and allows the flow of ions to occur. For instance, in the case of water electrolysis, the electrolyte may be an acid, base, salt, or even pure water itself. If the water contains contaminants or foreign substances, impure water is usually filtered before being introduced into the electrolytic cell for electrolysis.

Electrolytic Cells

An electrolytic cell is a device that employs electrochemical reactions to convert electrical energy from a DC power supply into chemical energy stored as a product inside the cell. As mentioned earlier, the primary purpose of electrolysis is the process of passing an electric current through an electrolyte solution to induce a redox reaction.

There are various types of electrolytic cells designed for different applications. Some common ones include the Daniell cell, Bunsen cell, Leclanche cell, Kipp cell, and Volta pile. These cells differ in their construction material, electrolyte composition, voltage range, and usage. Each type has unique properties and characteristics that make them suitable for specific purposes.

Description

Explore the chemical process of electrolysis, its various applications like water electrolysis and electroplating, and the different types of electrolytic cells used. Learn about the breakdown of compounds through ionization by passing an electric current through electrolyte solutions.