Cyclic voltammetry (CV) is an electrochemical measuring technique used for the determination of the kinetics and mechanism of electrode reactions. The potential of the working electrode is controlled (typically with a potentiostat) and the current flowing through the electrode is measured. It is a linear-weep voltammetry with the scan continued in the reverse direction at the end of the first scan. This cycle can be repeated a number of times, and is used for corrosion studies.
Dielectric constant or permittivity (ε) is an index of the ability of a substance to attenuate the transmission of an electrostatic force from one charged body to another. The lower the value, the greater the attenuation. The standard measurement apparatus utilises a vacuum whose dielectric constant is 1. In reference to this, various materials interposed between the charged terminal have the following value at 20 °C:
vacuum | 1 |
air | 1.00058 |
glass | 3 |
benzene | 2.3 |
acetic acid | 6.2 |
ammonia | 15.5 |
ethanol | 25 |
glycerol | 56 |
water | 81 |
The exceptionally high value for water accounts for its unique behaviour as a solvent and in electrolytic solutions. Dielectric constant values decrease as the temperature rises.
Reaction layer (in electrochemistry) is that layer of solution adjacent to an electrode within which a stationary distribution of electroactive species is established as the result of homogeneous reaction.
In 1836 the British chemist John Frederic Daniell (1790-1845) proposed an improved electric cell that supplied an even current during continuous operation. Daniell cell consisted of a glass jar containing copper and zinc electrodes, each immersed in their respective acidic sulphate solutions. The two solutions were separated by a porous clay cylinder separator. It was a galvanic cell in which the spontaneous electrodissolution of zinc and electroplating of copper provided the electrical current.
Zn(s) |
→ | Zn2+ + 2e- |
+0.763 V |
Cu2+ + 2e- |
→ | Cu(s) |
+0.337 V |
Zn(s) + Cu2+ |
→← | Zn2+ + Cu(s) |
+1.100 V |
Titrant is the substance that quantitatively reacts with the analyte in a titration. The titrant is usually a standard solution added carefully to the analyte until the reaction is complete. The amount of analyte is calculated from the volume and concentration of titrant required for the complete reaction.
Universal gas constant R has the value of 8.314 472(15) J K-1 mol-1. It corresponds to the volume work performed by one mole of gas heated by 1 K at standard pressure.
Voltametry is a common name for a large group of instrumental techniques which are based on measuring the electric current formed by a continuous potential shifting on the electrodes.
Electrical double layer is the structure of charge accumulation and charge separation that always occurs at the interface when an electrode is immersed into an electrolyte solution. The excess charge on the electrode surface is compensated by an accumulation of excess ions of the opposite charge in the solution. The amount of charge is a function of the electrode potential. This structure behaves essentially as a capacitor. There are several theoretical models that describe the structure of the double layer. The three most commonly used ones are the Helmholtz model, the Gouy-Chapman model, and the Gouy-Chapman-Stern model.
Electrochemical cell is a device that converts chemical energy into electrical energy or vice versa when a chemical reaction is occurring in the cell. It consist of two electronically conducting phases (e.g., solid or liquid metals, semiconductors, etc) connected by an ionically conducting phase (e.g. aqueous or non-aqueous solution, molten salt, ionically conducting solid). As an electric current passes, it must change from electronic current to ionic current and back to electronic current. These changes of conduction mode are always accompanied by oxidation/reduction reactions.
An essential feature of the electrochemical cell is that the simultaneously occurring oxidation-reduction reactions are spatially separated. E.g., in a spontaneous chemical reaction during the oxidation of hydrogen by oxygen to water, electrons are passed directly from the hydrogen to the oxygen.
In contrast, in the spontaneous electrochemical reaction in a galvanic cell the hydrogen is oxidised at the anode by transferring electrons to the anode and the oxygen is reduced at the cathode by accepting electrons from the cathode. The ions produced in the electrode reactions, in this case positive hydrogen ions and the negative hydroxyl (OH-) ions, will recombine in the solution to form the final product of the reaction: water. During this process the electrons are conducted from the anode to the cathode through an outside electric circuit where the electric current can drive a motor, light a light bulb, etc. The reaction can also be reversed: water can be decomposed into hydrogen and oxygen by the application of electrical power in an electrolytic cell.
Generalic, Eni. "Standard hidrogen electrode." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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