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.
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.
Zimmermann-Reinhardt’s reagent is a mixture of manganese(II) sulphate, sulphuric acid and phosphorus acid. It is used for preventing oxidation of chloride ion while titrating iron(II) ion with permanganate solution.
Electrochemical series is a series of chemical elements arranged in order of their standard electrode potentials. The hydrogen electrode
is taken as having zero electrode potential. An electrode potential is, by definition, a reduction potential.
Elements that have a greater tendency than hydrogen to lose electrons to their solution are taken as electropositive; those that gain electrons from their solution are below hydrogen in the series and are called electronegative.
The series shows the order in which metals replace one another from their salts; electropositive metals will replace hydrogen from acids.
Electrogravimetry is an electroanalytical technique in which the substance to be determined (usually a metal) is deposited out on an electrode which is weighed before and after the experiment. The potential of the electrode must be carefully chosen to ensure that only the metal do be determined will deposit.
Electrolysis is the decomposition of a substance as a result of passing an electric current between two electrodes immersed in the sample.
Electrophoresis is a technique for the analysis and separation of colloids, based on the movement of charged colloidal particles in an electric field. The migration is toward electrodes of charge opposite to that of the particles. The rate of migration of the particles depends on the field, the charge on the particles, and on other factors, such as the size and shape of the particles.
Electrophoresis is important in the study of proteins. The acidity of the solution can be used to control the direction in which a protein moves upon electrophoresis.
Faraday’s laws of electrolysis are two laws found by British chemist and physicist Michael Faraday (1791-1867) in his experiments on electrolysis:
1. The quantity of matter extracted on the electrode is proportional to the quantity of charge (Q = I·t) which has flown in electrolysis time.
where z = number of electrons changed in reaction and F = Faraday’s constant which equals 96 487 C mol-1.
2. The masses of the elements liberated by the same quantity of electricity are directly proportional to their chemical equivalents.
96 487 C will discharge 1 mol Ag and 1/2 mol Cu. The relevant half reactions are:
Filter paper is a quantitative paper used for filtering and made of pure cellulose treated with hydrochloric and hydrofluoric acid. This kind of paper burns out practically without any remains (less than 0.0001 g ashes). Different types of paper are marked with numbers; qualitative bears marking 595 or 597 and quantitative 589 or 590. Dependable upon precipitate character, different types of filter paper are used:
Generalic, Eni. "Srebro%2Fsrebrov klorid elektroda." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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