Quantity of electricity

Quantity of electricity, electric charge Q Retarded van der Waals constant B,P... 

Faraday s Law of electrolysis states that the amount of chemical change, ie, amount dissolved or deposited, produced by an electric current is proportional to the quantity of electricity passed, as measured in coulombs and that the amounts of different materials deposited or dissolved by the same quantity of electricity are proportional to their gram-equivalent weights (GEW) defined as the atomic weight divided by the valence. The weight in grams of material deposited, IF, is given by... 

The quantity of electric charge is measured m coulombs, and the unit of electric current—the number of coulombs per second that go past any point— is the ampere (A), named after French physicist Andre Marie Ampere ... 

Two inventions in the 1740s changed the electrical scene dramatically. One was the frictional machine, which made it possible to generate continuous streams of electricity relatively easily the other was the condenser, or Leyden jar, which made possible the storage and sudden discharge of substantial quantities of electric charge. 

The major facility for generating electricity from geothermal sources is at The Geysers iu Northern California. Generation at The Geysers is declining both for economic reasons and because of reduced steam pressure. However, other facilities continue to produce steady quantities of electricity. 

Capacitance (C) is the property that describes the quantity of electricity that can be stored when two conductors are separated by a dielectric material. The unit of capacitance is the farad. The capacitance of two equal-area, conducting parallel plates (see Figure 2-64) separated by a dielectric is given by... 

Faraday Constant (F) the quantity of electric charge involved in the passage of one Avagadro number (or one mole) of electrons. The value of F (universal) is 96 485 C mol . ... 

On the other hand, this same amount of electricity will deposit exactly twice as much mercury, 2 x (6.03) = 12.1 grams, from a solution of mercurous perchlorate, Hg2(ClCh)2. If we restate Faraday s experimental finding in terms of the atomic theory, we see that the number of atoms of mercury deposited by a certain quantity of electricity is a constant or a simple multiple of this constant. Apparently this certain quantity of electricity can count atoms. A simple interpretation is that there are packages of electricity. During electrolysis, these packages are parcelled out, one to an atom, or two to an atom, or three. 

The amounts of substances liberated (or dissolved) at the electrodes of a cell are directly proportional to the quantity of electricity which passes through the solution. 

The amounts of different substances liberated or dissolved by the same quantity of electricity are proportional to their relative atomic (or molar) masses divided by the number of electrons involved in the respective electrode... 

The unit quantity of electricity is the coulomb (C), and is defined as the quantity of electricity passing when a current of one ampere flows for one second. 

Coulometric analysis is an application of Faraday s First Law of Electrolysis which may be expressed in the form that the extent of chemical reaction at an electrode is directly proportional to the quantity of electricity passing through the electrode. For each mole of chemical change at an electrode (96487 x n) coulombs are required i.e. the Faraday constant multiplied by the number of electrons involved in the electrode reaction. The weight of substance produced or consumed in an electrolysis involving Q coulombs is therefore given by the expression... 

The fundamental requirement of a coulometric analysis is that the electrode reaction used for the determination proceeds with 100 per cent efficiency so that the quantity of substance reacted can be expressed by means of Faraday s Law from the measured quantity of electricity (coulombs) passed. The substance being determined may directly undergo reaction at one of the electrodes (primary coulometric analysis), or it may react in solution with another substance generated by an electrode reaction (secondary coulometric analysis). 

Two distinctly different coulometric techniques are available (1) coulometric analysis with controlled potential of the working electrode, and (2) coulometric analysis with constant current. In the former method the substance being determined reacts with 100 per cent current efficiency at a working electrode, the potential of which is controlled. The completion of the reaction is indicated by the current decreasing to practically zero, and the quantity of the substance reacted is obtained from the reading of a coulometer in series with the cell or by means of a current-time integrating device. In method (2) a solution of the substance to be determined is electrolysed with constant current until the reaction is completed (as detected by a visual indicator in the solution or by amperometric, potentiometric, or spectrophotometric methods) and the circuit is then opened. The total quantity of electricity passed is derived from the product current (amperes) x time (seconds) the present practice is to include an electronic integrator in the circuit. 

In electrolysis at controlled potential, the quantity of electricity Q (coulombs) passed from the beginning of the determination to time t is given by... 

Originally, the number of coulombs passed was determined by including a coulometer in the circuit, e.g. a silver, an iodine or a hydrogen-oxygen coulometer. The amount of chemical change taking place in the coulometer can be ascertained, and from this result the number of coulombs passed can be calculated, but with modern equipment an electronic integrator is used to measure the quantity of electricity passed. 

Since a small quantity of electricity can be readily measured with a high degree of accuracy, the method has high sensitivity. Coulometric titrimetry has several important advantages. 

Stoichiometrically, the total quantity of electricity passed is exactly the same as it would have been if the Fe(II) ions had been directly oxidised at the anode and the oxidation of Fe(II) proceeds with 100 percent efficiency. The equivalence point is marked by the first persistence of excess Ce(IV) in the solution, and may be detected by any of the methods described above. The Ce3+ ions added to the Fe(II) solution undergo no net change and are said to act as a mediator. 

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