Electrolysis

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This article is about the chemical process. Electrolysis is also a method of depilation.

In chemistry and manufacturing, electrolysis is a method of separating bonded elements and compounds by passing an electric current through them.

Table of contents

1 Overview 2 Experimenters 3 First Law of Electrolysis 4 Second Law of Electrolysis 5 Industrial Uses 6 Domestic Uses

Overview

The source material is dissolved in an appropriate solvent, or melted, so that constituent ions are available in the solution. An electrical potential is applied across a pair of conductors immersed in the liquid. The negatively charged conductor is called the cathode, and the positively charged conductor is called the anode. Each conductor attracts the ions of the opposite charge. Therefore, positively charged ions (cations) move towards the cathode while negatively charged ions (anions) move to the anode. The energy required to separate the ions, and increase their concentration at the electrodes, is provided by an electrical power supply that maintains the potential difference across the electrodes. At the electrodes, electrons are absorbed or released by the ions, forming concentrations of the desired element or compound. For example, when water is electrolyzed, hydrogen will form at the cathode, and oxygen at the anode. This was first discovered by William Nicholson, an English chemist, in 1800.

Electrolysis does not depend on heat in any way. Although heat may be produced, electrolysis is not subject to thermodynamic limits on efficiency. Its efficiency can be quite close to 100%.

The following technologies are related to electrolysis:

• Electrochemical cells, including the hydrogen fuel cell, use the reverse of this process.
• Gel electrophoresis is an electrolysis where the solvent is a gel: it is used to separate substances, such as DNA strands, based on their electrical charge.

Experimenters

Scientific pioneers of electrolysis included:

• Humphry Davy
• Michael Faraday
• Paul Héroult
• Svante Arrhenius
• Adolph Wilhelm Hermann Kolbe

More recently, electrolysis of heavy water was performed by Fleischmann and Pons in their famous experiment, resulting in anomalous heat generation and the controversial claim of cold fusion.

First Law of Electrolysis

In 1832, Michael Faraday reported that the quantity of elements separated by passing an electrical current through a molten or dissolved salt was proportional to the quantity of current passed through the circuit. This became the basis of the first law of electrolysis.

Second Law of Electrolysis

Faraday also discovered that the weight of the resulting separated elements was directly proportional to the atomic weights of the elements when an appropriate integral divisor was applied. This provided strong evidence that discrete particles of electricity existed as parts of the atoms of elements.

Industrial Uses

• Manufacture of aluminium, lithium, aspirin.
• Manufacture of hydrogen for hydrogen cars and fuel cells.

Domestic Uses

Chlorine is extracted from sodium chloride brine by electrolysis and one use of the chlorine is as a swimming pool disinfectant.

de:Elektrolyse es:Electrólisis fr:Électrolyse gl:Electrólise ja:電気分解 nl:Elektrolyse nds:Elektrolyse

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