Nernst factor

Definitive measurements by fundamental quantities complemented by an empirical factor, e.g. titre (titrimetry), as well as by well-known empirical (transferable) constants like molar absorption coefficient (spectrophotometry), Nernst factor (potentiometry, ISE), and conductivity at definite dilution (conductometry)... 

Depending on the type of relationships between the measured quantity and the measurand (analytical quantity) it can be distinguished (Danzer and Currie [1998]) between calibrations based on absolute measurements (one calibration is valid for all1 on the basis of the simple proportion y = b x, where the sensitivity factor b is a fundamental quantity see Sect. 2.4 Hula-nicki [1995] IUPAC Orange Book [1997, 2000]), definitive measurements (b is given either by a fundamental quantity complemented by an empirical factor or a well-known empirical (transferable) constant like molar absorption coefficient and Nernst factor), and experimental calibration. 

E = electrode potential of the half-ceU E° - standard electrode potential when aRed/ ox = 1 n = number of electrons involved in the reduction reaction N= RxTxhi 10) fF (the Nernst factor if n = 1)... 

Expression (5.7) is, in fact, built into the routine measurement of pH with a commercial pH meter. Such meters have a scale graduated in pH units, obviating the need to convert volts to pH units. Prior to pH measurement, the buffer solution and unknown solution are brought to the same temperature. The temperature compensation dial on the meter is then turned to that temperature. This sets the meter with the appropriate Nernst-factor value for pH respon.se at the temperature of measurement. The pH and reference electrode pair (preferably available in a single, combination pH electrode) are then immersed in a buffer solution of known pH, and the meter is set to that pH. Immersion of the electrodes in the unknown solution then yields that solution s pH. 

The hydrogen electrode is the standard method of measuring pH. How is the voltage measured by the electrode related to the pH What is the Nernst factor ... 

Define the Nernst factor, E° and pE. For a given redox reaction how are they related to each other and to AG and Eh ... 

Usually, the most accurate determinations are made when Ac is such that the total concentration is approximately doubled. The only requirement is that the electrode be in a linear portion of its calibration curve over the concentration range of interest. The slope of the calibration need not be precisely equal to the Nernst factor, RTjnF if it is not, the empirically determined slope S of the calibration curve can be substituted. 

This expression can in principle be used to define a composition/potential relationship. The first term on the rhs is the standard electrode potential the second quantifies occupied site interactive effects. The last logarithmic terms describe the usual Nernst factor and also take into account that counterion activity may vary with the extent of redox conversion. 

The Nernst factor, 0.059 V for room temperature, does not always reach its theoretical value. In experimental work, it is better to use the expression Nernstian slope S of the function E = f(a). The slope must be determined empirically. The constant const in Eq. (7.8) is a combination of all terms not dependent on concentration. In practical work, the name asymmetry potential ( as) is preferred. This expression is derived from the expectation that the constant should be zero for a completely symmetric cell, i.e. if inner and outer solutions are of equal pH and if inner and outer reference electrodes are of identical types. In practice, Eas is not always zero but must be calibrated empirically by means of buffer solutions with known pH. By setting - log alHsO" ) = pH, the common form of the Nernst equation for the glass electrode results ... 

E is the total potential, in millivolts, developed between the sensing and reference electrodes varies with the choice of electrodes, temperature, and pressure 2.3RTInF is the Nernst factor (R and F are constants, n is the charge on the ion, including sign, T is the temperature in degrees Kelvin), and Oi is the activity of the ion to which the electrode is responding. 

Nernst factor (5, slope) The term 23RTInF is the Nernst equation, which is equal (at T = 25°C) to 59.16 mV when n = 1 and 29.58 mV when n = 2, and which includes the sign of the charge on the ion in the term n. The Nernst factor varies with temperature. (See Table A.l.)... 

Slope (electrode sensitivity, span) See Nernst factor. 

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