Electrochemical cell without liquid junction

The essential feature of a primary method is that it must operate according to a well-defined measurement equation in which aU of the variables can be determined experimentaUy in terms of SI units. Any limitation in the determination of the experimental variables, or in the theory, must be included within the estimated uncertainty of the method if traceabUity to the SI is to be established. If a convention were used without an estimate of its uncertainty, true traceability to SI would not be established. The electrochemical cell without liquid junction, known as the Harned cell (5), fulfils the definition of a primary method for the measurement of the acidity function, p( h7ci)> subsequently of the pH of buffer solutions. 

NB Very careful work performed using an electrochemical cell without liquid junction potentials. 

NB Very careful work using an electrochemical cell without liquid junction potentials. Activity coefficients were calculated for measurements made on carbonate-free solutions at the following temperatures ... 

In electrochemical cells without liquid junctions, the two electrodes are in contact with the same electrolyte of uniform concentration. For example, the cell shown in Figure 2.23 is made of a lead electrode and a lead amalgam electrode (lead dissolved in mercury), in contact with an aqueous solution of PbCl2. This cell corresponds to the schematic representation (2.123), where M and M" refer to the metal of the two conductors attached to the voltmeter. 

The hydrogen electrode is still the basis for all pH measurements to date. The pH of the standard buffers used to calibrate pH electrodes is traced back to primary buffer solutions [11]. The primary method for pH is based on the measurement of the potential of an electrochemical cell without liquid junction, involving a selected buffer solution, a platinum hydrogen electrode, and a silver/silver chloride reference electrode. The standard potential of the silver/silver chloride electrode in hydrochloric acid at a molality of 0.01 mol kg is determined simultaneously. 

The primary procedure for pH is based on the measurement of the potential difference of a electrochemical cell without liquid junction, involving a selected buffer solution, a platinum hydrogen electrode, and a silver/silver chloride reference electrode, in cell I [15] ... 

It has been stated [42] that the spectrophotometric method (or other spectroscopic methods) can be as precise as the EMF method based on electrochemical cells without liquid jimction potentials. However, for this to be true, the pH term in Eq. (5) must not be measured with a pH meter, but replaced by a similar term based on the hydronium ion activities, aHjO )/ from cells without liquid junction potential. This approach was used in earlier years, for example, the work of Robinson [70] (see Vanillin, no. 1492 in the database) and of Bates and Schwarzenbach [71] on phenols. For the usual spectrophotometric method based on conventional pH measurements, additional factors which control overall accuracy include ... 

Manov GG, Schuette KE and Kirk FS, Ionization constant of 5,5-diethylbarbituric acid, /. Res. NtU. Bur. Stand, 48,84r-91 (1952). NB Exceedingly careful work performed using an electrochemical (hydrogat) cell without liquid junction potentials. 

Figure 8.2 schematically depicts a particular electrochemical cell. A figure such as this is called a cell diagram. This cell belongs to a class called cells without liquid junction, which means that both electrodes are in contact with the same solution. If a cell contains two different solutions in contact with each other the interface between the solutions is called a liquid Junction. The electrode at the left in Figure 8.2 is a hydrogen electrode. It has a platinum surface that has been platinized (plated with... 

Most of the electrochemical cells have liquid junction (diffusion) potential. The electrochemical cells without transfer are free of it. The example of the electrochemical cell without transfer is the famous Harned cell. 

When an electrochemical cell is set up without liquid junctions it can be used to study the thermodynamic properties of the electrolyte involved. This requires that one electrode be reversible to the cation of the electrolyte and the other to the anion. A simple example is the cell... 

The imprecision of 0.02 in the definition of pH is made up of approximately equal contributions from two quite different sources. One source of imcertainty is the variability in the liquid jimction potential [45, 59, 61] under different conditions of solution composition and dynamics. This is an intrinsic feature of the glass electrode-reference electrode combination used for pH measurements. This uncertainty does not arise in conductance measurements, and can be neglected in measurements of hydronium ion activity only by the use of reversible electrochemical (electrometric) cells that are constructed without liquid junction potentials. These approaches require considerable technical expertise and attention to detail in order to obtain results with maximal accuracy and precision. 

Figure 2.6 Levels of electric potential in an electrochemical cell without a liquid junction. Standard hydrogen electrode...

Jordan, D. O., Kurucsev, T., Martin, M. L, Comparative physical chemical Study of isotactic and atactic poly (styrene sulphonic acid) solutions. Part 1. Electrochemical measurements using cells with and without liquid junction. Trans. Faraday Soc. 65, 598 (1969). 

Oxygen electrode. In principle, a classical oxygen electrode in a liquid electrolyte would be possible if an electrode material were known on the surface of which the redox system 02/0H is electrochemically reversible however, Luther26 measured its standard potential from the following cell without a liquid junction ... 

The cell in this problem would not give an accurate result, because of the junction potential at each liquid junction (Section 15-3). A cell without a liquid junction is described by P. A. Rock, Electrochemical Double Cells, J. Chem. Ed. 1975,52, 787. 

In the second approach to the electrochemical determination of the ion solvation energy, a cell without a liquid junction is used. Such a cell consists of an electrode formed by the ions to be studied, and as a reference a solvent-independent reference electrode (SIRE) ... 

An electrode in contact with an electrolyte is called a half-cell, often also written half cell. Thus, a simple two-electrode electrochemical cell is composed of two half-cells that contain either the same electrolyte but different electrodes or different electrodes and electrolytes. The first type of chemical cell, where there is no phase boundary between different electrolytes, is a cell without transference. The other type, in which a liquid-liquid junction potential or diffusion potential is developed across the boundary between the two solutions, is a cell with transference. Commercially available reference electrodes can be considered half-cells. ... 

When there is an external flow of current, there must be a compensating current within the cell. This can be accomplished in many ways, hence there are electrochemical cells of many types. The choice of electrodes is also decided by the experimental conditions and the need to use the electrode without undesirable side reactions. Electrochemical cells often incorporate salt bridges and liquid junctions. 

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