Conductivity, electrical standard solutions

The conductance of a solution is the inverse of its resistance, and conductance has units of ohms 1 or mohs. The higher the conductance of a solution, the lower is its electrical resistance. A conductivity meter and conductivity cell are used to determine the effective resistance of a solution. The conductivity cell consists of a pair of platinized platinum electrodes with an area of approximately 1.0 cm2 with spacers designed to hold the electrodes rigidly parallel and at a fixed distance from each other. The cell can be standardized with solutions of known conductivity to obtain the cell constant, k so that the instrument response R... 

Electrical conductivity is a measure of a solution s ability to conduct electricity. The conductivity depends on the concentration of the ions present and the temperature of the solution. A standard conductivity flow cell is integrated into the instrument design. 

However, salinity values are easily obtained with a salinometer (which measures electrical conductivity and is appropriately calibrated with standard solutions and adjusted to account for T effects). The salinity of seawater increases if the loss of H2O (evaporation, formation of ice) exceeds the atmospheric input (rain plus rivers), and diminishes near deltas and lagoons. Salinity and temperature concur antithetically to define the density of seawater. The surface temperature of the sea reflects primarily the latitude and season of sampling. The vertical thermal profile defines three zones surface (10-100 m), where T is practically constant thermoclinal (100-1000 m), where T diminishes regularly with depth and abyssal... 

The conductance measured between the cell terminals is multiplied by (he cell constant given in reciprocal units of length to calculate the conductivity. To calculate the resistivity, the measured resistance between the cell terminals is divided by die cell constant. Althuugh the cell constant (in reciprocal units nf length) can he calculated from the dimensions of the conductivity cell by dividing the length of Ihe electrical path through the solution by the cross-sectional area of the path, in practice, these measurements are difficult to make and arc only used to approximate the cell constant, which is determined by use of standard solutions of known conductivity or by comparison with other conductivity cells which have been so standardized. 

Aluminium is a light metal with a density about one third of that of steel. It conducts electricity well and may be alloyed with other metals to improve its strength characteristics. The standard electrode potential of aluminium is -1.67 V and would be a highly reactive metal were it not for the protective oxide formed on its surface. If aluminium is immersed in a solution containing species which prevent the oxide film from reforming, then the metal corrodes rapidly with the evolution of hydrogen gas from the cathodic regions. 

The specific conductance (L or K) or conductivity of a solution is always obtained by measuring the resistance (R) of the solution taken in a suitable container of known dimensions called conductivity cell, the cell constant of which has been determined by calibration with a solution of accurately known conductivity e g. a standard KCl solution. The instrument used for electrical conductivity measurement is known as conductivity bridge. A typical system consists of an alternating current (A.C.) Wheatstone bridge, a primary element of conductivity cell and a null balance indicator (as in solubridge ) or an electronic eye as in the conductivity meter. 

Magnesium sulfate and calcium sulfate solutions of equal concentrations show approximately the same electrical conductivity [9]. If one compares electrical conductivity of the saturated calcium sulfate solution with the conductivity of various standard solutions of magnesium sulfate (see E6.5), one finds consistency in the concentration of the saturated solution ... 

Salinity (S) - A parameter used in oceanography to describe the concentration of dissolved salts in seawater. It is defined in terms of electrical conductivity relative to a standard solution of KCl. When expressed in units of parts per thousand, S may be roughly equated to the concentration of dissolved material in grams per kilogram of seawater. 

Salinity is a measure of the mass of dissolved salts in the solution. This quantity is commonly estimated using an empirical relation between some measured physical quantity, like conductivity, refractive index, sound speed, or density, and the dissolved salt content of a standard solution. The currently recommended methods to determine salinity use electrical conductivity or density. Details of the methods are given in Greenberg et al. (1992). Salinity is reported as a dimensionless number such as % or %o. 

J,m. The electric field applied is also simply calculated by dividing the applied voltage directly measured on the instrument by the distance between the electrodes. The effective inter-electrode distance is obtained by measuring the conductance of a standard electrolyte solution, say... 

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