Saturated-salt half cell

It s called a bridge because it connects the two half-cells, and salt because we saturate it with a strong ionic electrolyte. 

The outer tube has a porous fiber tip, which acts as the salt bridge to the analyte solution and the other half-cell. A saturated solution of potassium chloride is in the outer tube. The saturation is evidenced by the fact that there is some undissolved KC1 present. Within the inner tube is mercury metal and a paste-like material known as calomel. Calomel is made by thoroughly mixing mercury metal (Hg) with mercurous chloride (Hg2Cl2), a white solid. When in use, the following half-cell reaction occurs ... 

A counter electrode of constant potential is obtained making use of a half-cell system in which the components are present in concentrations so high as to be appreciably unaffected by a flow of current through it. The saturated calomel electrode (SCE) is the most common example of such an electrode. As shown in Figure 7, it is comprised of a mercury pool in contact with solid mercury(I) chloride and potassium chloride that lie at the bottom of the KC1 saturated solution. The aqueous solution is thus saturated with Hgl+, K+ and Cl- ions, the concentrations of which are governed by the solubility of the respective salts. 

Salt Bridge concentrated solution of electrolyte used to complete the circuit in an electrochemical cell that helps to equalize charge distribution in each half cell Saltpeter potassium nitrate, KNO3 Saponification conversion of a fat to soap by reacting with an alkali Saturated solution that contains the maximum amount of solute under a given set of conditions... 

Until recently, the most popular reference half-cell for potentiometric titrations, polarography, and even kinetic studies has been the saturated aqueous calomel electrode (SCE), connected by means of a nonaqueous salt bridge (e.g., Et4NC104) to the electrolyte under study. The choice of this particular bridge electrolyte in conjunction with the SCE is not a good one because potassium perchlorate and potassium chloride have a limited solubility in many aprotic solvents. The junction is readily clogged, which leads to erratic junction potentials. For these practical reasons, a calomel or silver-silver chloride reference electrode with an aqueous lithium chloride or quaternary ammonium chloride fill solution is preferable if an aqueous electrode is used. 

Figure 2.4.4 (A) Time-dependent electric current generated from the oxidation of HTC coal in an indirect carbon fuel cell. Solutions of Fe 111 and Vv were prepared in 0.5 mol L 1 H2SO4. (B) Development of open-circuit potential Eoc (up) and current I (down) due to Fe2+ formation in the anodic half-cell via oxidation of HTC coal, indicating the reducing potential of bare hydrothermal carbon (HC) dispersions. Charge equalization between the two half-cells was assured by a salt bridge containing a saturated KC1 solution. Carbon felt was used as electrodes. (C) Comparison of hydrothermal and fossil carbon sources in the same setup.

Salt Bridge Saturated An apparatus that allows ions to migrate from one half cell to another. Describing a solution in which a dissolved solute and an undissolved solute are in equilibrium. 

Calomel Electrode. In addition to pH measnrements, there are many other emf cell measurements for which it is convenient to nse the calomel electrode as a reference electrode against which a measuring electrode is compared. Actnally this electrode is really a half-cell that is connected via a KCl salt bridge to another half-cell containing the solution of interest. The saturated calomel electrode can be written as... 

Another way of determining the solvent transport by emf measurements has been proposed by C. Wagner The two half cells contain two solvent mixtures of similar composition which are both saturated with a sparingly soluble salt, e.g. a silver salt AgX. Though the chemical potential of is the same throughout the galvanic cell with transport, the emf is different from zero since the chemical potential of the solvent is different in the two half cells and A moles of the non-aqueous solvent component are transported into the cathode compartment per Faraday. 

RNA (ribonucleic acid) Long chainlike molecules that occur throughout cells and take part in the construction of proteins, salt An ionic compoimd that usually remains dissolved in a solution after an acid-base reaction has occurred, salt bridge An inverted, U-shaped tube containing a strong electrolyte completes the circuit in an electrochemical cell by allowing the flow of ions between the two half-cells, saturated fat A triglyceride composed of saturated fatty acids. Saturated fat tends to be solid at room temperature, saturated hydrocarbon A hydrocarbon that contains no double or triple bonds between the carbon atoms, saturated solution A solution that holds the maximum amoimt of solute imder the solution conditions. If additional solute is added to a saturated solution, it wiU not dissolve, scientific law A statement that summarizes past observations and predicts future ones. Scientific laws are usually formulated from a series of related observations. 

Other types of salt bridges consist of electrolyte-saturated linen wicks or bundles of camel s hair. These are useful when one wishes to minimize the trauma to delicate tissues which occurs with electrode contact. Occasionally linen membranes are used in half-cells to maintain the physical position of the reactants, especially in standard emf cell construction. 

Reference electrodes are commonly used with a saturated solution and an excess of salt crystals. The extra salt dissolves into the half-cell solution as some of the ions diffuse out of the reference cell body through the liquid junction during normal use. This extra buffer of salt extends the time before the reference cell starts to drift due to the depletion of ions as predicted by Nernst equation [Eq. (4.12)]. 

FIG. 11. Em values obtained for membranes prepared for the indicated plating times. The solution on the I side of the membrane was 0.1 mM KCl. The solution on the h side of the membrane was varied from 0.1 mM KCl to 1 M KCl. The values were measured by using two Ag/AgCl (KCl saturated) electrodes placed in each half-cell through agar salt-bridges. The dashed line is for ideal cation-permselective behavior. 

Figure 4.3 shows the half cells for the Cu/Cu and the Zn/Zn " xmples separated by a salt bridge containing saturated (approx-mately 5 m) aqueous potassium chloride solution. If the couples were not... 

At the anode, a silver electrode is placed in a saturated aqueous solution of silver iodide. At the cathode, a second silver electrode is placed in a solution with [Ag" "] = 0.100 M. The two half-cells are connected by a salt bridge, and the measured cell voltage is 0.417 V (Fig. 19-12). The cell reaction occurring in this concentration cell is... 

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