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Coulometry
In analytical electrochemistry, coulometry is the measure of charge (coulombs) transfer during an electrochemical redox reaction. It can be used for precision measurements of charge, but coulometry is mainly used for analytical applications to determine the amount of matter transformed.
There are two main categories of coulometric techniques. Amperostatic coulometry, or coulometric titration keeps the current constant using an amperostat. Potentiostatic coulometry holds the electric potential constant during the reaction using a potentiostat.
The term coulometry was introduced in 1938 by Hungarian chemist László Szebellédy and Zoltan Somogyi. Coulometry is the measure of charge, thus named after its unit the coulomb.
Michael Faraday, known for his work in electricity and magnetism, made critical contributions to the field of electrochemistry. He discovered the laws of electrolysis, and in his recognition is the eponym of the Faraday constant. In the earliest developments of coulometry, Faraday proposed the first instrument to measure charge by utilizing the electrolysis of water.
Surface coulometry, the method of determining metallic layers or oxide films on metals, was first applied by American Chemist G. G. Grower in 1917 by checking the quality of tinned copper wire.
Coulometric methods were used widely in the middle of the twentieth century but voltammetric methods and non-electrochemical analytical methods took over decreasing the use for coulometry, but one method widely used today is the Karl Fischer method.
Potentiostatic coulometry utilizes a constant electric potential and is a technique most commonly referred to as "bulk electrolysis". Also called direct coulometry, the analyte is oxidized or reduced at the working electrode without intermediate reactions. The working electrode is kept at a constant potential and the current that flows through the circuit is measured. This constant potential is applied long enough to fully reduce or oxidize all of the electroactive species in a given solution. As the electroactive molecules are consumed, the current also decreases, approaching zero when the conversion is complete. The sample mass, molecular mass, number of electrons in the electrode reaction, and number of electrons passed during the experiment are all related by Faraday's laws. It follows that, if three of the values are known, then the fourth can be calculated.
Bulk electrolysis is often used to unambiguously assign the number of electrons consumed in a reaction observed through voltammetry. It also has the added benefit of producing a solution of a species (oxidation state) which may not be accessible through chemical routes. This species can then be isolated or further characterized while in solution.
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Coulometry
In analytical electrochemistry, coulometry is the measure of charge (coulombs) transfer during an electrochemical redox reaction. It can be used for precision measurements of charge, but coulometry is mainly used for analytical applications to determine the amount of matter transformed.
There are two main categories of coulometric techniques. Amperostatic coulometry, or coulometric titration keeps the current constant using an amperostat. Potentiostatic coulometry holds the electric potential constant during the reaction using a potentiostat.
The term coulometry was introduced in 1938 by Hungarian chemist László Szebellédy and Zoltan Somogyi. Coulometry is the measure of charge, thus named after its unit the coulomb.
Michael Faraday, known for his work in electricity and magnetism, made critical contributions to the field of electrochemistry. He discovered the laws of electrolysis, and in his recognition is the eponym of the Faraday constant. In the earliest developments of coulometry, Faraday proposed the first instrument to measure charge by utilizing the electrolysis of water.
Surface coulometry, the method of determining metallic layers or oxide films on metals, was first applied by American Chemist G. G. Grower in 1917 by checking the quality of tinned copper wire.
Coulometric methods were used widely in the middle of the twentieth century but voltammetric methods and non-electrochemical analytical methods took over decreasing the use for coulometry, but one method widely used today is the Karl Fischer method.
Potentiostatic coulometry utilizes a constant electric potential and is a technique most commonly referred to as "bulk electrolysis". Also called direct coulometry, the analyte is oxidized or reduced at the working electrode without intermediate reactions. The working electrode is kept at a constant potential and the current that flows through the circuit is measured. This constant potential is applied long enough to fully reduce or oxidize all of the electroactive species in a given solution. As the electroactive molecules are consumed, the current also decreases, approaching zero when the conversion is complete. The sample mass, molecular mass, number of electrons in the electrode reaction, and number of electrons passed during the experiment are all related by Faraday's laws. It follows that, if three of the values are known, then the fourth can be calculated.
Bulk electrolysis is often used to unambiguously assign the number of electrons consumed in a reaction observed through voltammetry. It also has the added benefit of producing a solution of a species (oxidation state) which may not be accessible through chemical routes. This species can then be isolated or further characterized while in solution.