Silver chloride conductivity

There are two procedures for doing this. The first makes use of a metal probe coated with an emitter such as polonium or Am (around 1 mCi) and placed above the surface. The resulting air ionization makes the gap between the probe and the liquid sufficiently conducting that the potential difference can be measured by means of a high-impedance dc voltmeter that serves as a null indicator in a standard potentiometer circuit. A submerged reference electrode may be a silver-silver chloride electrode. One generally compares the potential of the film-covered surface with that of the film-free one [83, 84]. 

Silver chloride is a solid that shows this effect. This solid does not dissolve readily in water. When solid silver chloride is placed in water, very little solid enters the solution and there is only a very slight increase in the conductivity of the solution. Yet there is a real and measurable increase—ions are formed. Careful measurements show that even though silver chloride is much less soluble in water than sodium chloride, it is like sodium chloride in that all the solid that does dissolve forms aqueous ions. The reaction is... 

When we study a solid that does not have the characteristic lustrous appearance of a metal, we find that the conductivity is extremely low. This includes the solids we have called ionic solids sodium chloride, sodium nitrate, silver nitrate, and silver chloride. It includes, as well, the molecular crystals, such as ice. This solid, shown in Figure 5-3, is made up of molecules (such as exist in the gas phase) regularly packed in an orderly array. These poor conductors differ widely from the metals in almost every property. Thus electrical conductivity furnishes the key to one of the most fundamental classification schemes for substances. 

Reference electrodes are usually a calomel or a silver-silver chloride electrode. It is advisable that these be of the double-junction pattern so that potassium chloride solution from the electrode does not contaminate the test solution. Thus, for example, in titrations involving glacial acetic acid as solvent, the outer vessel of the double junction calomel electrode may be filled with glacial acetic acid containing a little lithium perchlorate to improve the conductance. 

A second method which is now probably the most widely used method in the Pediatric Laboratory is to use amperometric titration. In this connection, a constant current flows through the solution. The silver dissolves and reacts stolchlometrlcally with chloride, precipitating silver chloride. When all of the chloride has reacted, there is a sharp increase in conductivity which is read as an end point. This instrument, therefore, measures the amount of time a current flows. Instruments are now available for which 5 microliters can be used routinely, rapidly, titration being of the order of about 20 seconds. 

Salts such as silver chloride or lead sulfate which are ordinarily called insoluble do have a definite value of solubility in water. This value can be determined from conductance measurements of their saturated solutions. Since a very small amount of solute is present it must be completely dissociated into ions even in a saturated solution so that the equivalent conductivity, KV, is equal to the equivalent conductivity at infinite dilution which according to Kohlrausch s law is the sum of ionic conductances or ionic mobilities (ionic conductances are often referred to as ionic mobilities on account of the dependence of ionic conductances on the velocities at which ions migrate under the influence of an applied emf) ... 

Silver(I) halide complexes of oA could not be prepared. The phosphine ap, however, reacts with silver iodide to give a colourless, unstable, non-conducting compound of empirical formula Agl(ap). This compound reacts with excess ap to give the stable 2 1 adduct Agl(ap)2- Silver bromide and silver chloride react directly with the ligand to give similar 2 1 adducts. These complexes are essentially monomeric, contain three-coordinate silver (I) and uncoordinated olefinic groups. The structure of the 1 1 adduct is unknown. 

The ligand properties of the related phosphonites P(OR)2R and phosphinites P(OR)R2 have attracted little attention.199,200 Reaction with silver chloride generally produced 1 1 complexes of the type AgCIL, whilst with silver nitrate, complex cations of the type AgL4 were generated. The products were characterized by elemental analysis, 7H and 31P NMR spectroscopy and conductivity measurements. 

The key common property of such membranes is their ionic conductivity. An example is the Ag/AgCl electrode discussed previously. Although the primary charge-transfer reaction at this interface is that of the silver ion (6.27), the electrode will respond also to chloride ion (6.33), because of the low solubility product of AgCl. Let us now consider what happens if other ions that also form an insoluble silver salt are present in the solution. If the solubility product of the other salt (AgX) is lower than that of silver chloride and/or the activity ax is sufficiently high... 

Figure 8. Experimental conductivity data for nominally pure and doped AgCl as a function of 1/T. Here Ig (

The properties of ionic compounds in solution are actually the properties of the individual ions themselves (Figure 9.1). These compounds are called strong electrolytes because their solutions conduct electricity well. For example, an aqueous solution of sodium chloride consists essentially of sodium ions and chloride ions in water. A similar solution of calcium chloride consists of calcium ions and chloride ions in water. If either solution is treated with a solution containing silver ions, the chloride ions will form silver chloride, which is insoluble. The chloride ions act independently of the cation that is also present, regardless of whether it is sodium ion, calcium ion, or any other ion. Because the properties of the compound are the properties of the component ions, we need to learn to write equations for only the ions that react, omitting the ions that remain unchanged throughout the reaction (Section 9.2). 

A saturated solution of silver chloride, when placed in a conductance cell with aconstant/c = 0.180cm , has a resistance of67.953kf2 at 25 °C. The resistance of the water used as solvent was found to be 212.180 ki2 in the same ceU. Calculate the solubility S of the salt at 25 °C assuming it to be completely dissociated in its saturated solution in water. (Constantinescu)... 

In order to determine the equivalent conductance of a sparingly soluble salt it is the practice to add the conductances of the constituent ions thus for silver chloride and barium sulfate the results are as follows ... 

From Kohlrausch s measurements on the conductance of saturated solutions of pure silver chloride the specific conductance at 25 may be estimated as 3.41 X lO" ohm cm. the specific conductance of the water used was 1.60 X 10 ohm cm. , and so that due to the salt may be obtained by subtraction as 1.81 X 10 ohm cm. This is the value of K to be employed in equation (26). From Table XIII the equivalent conductance of silver chloride at infinite dilution is 138.3 ohms cm.2 at 25 , and so if this is assumed to be the equivalent conductance in the saturated solution of the salt, it follows from equation (26) that... 

By means of this first approximation for the concentration of the saturated solution of silver chloride, it is poasible to make a more exact estimate of the actual equivalent conductance by means of the Onsager equation (p. 89) a more precise value of the solubility may then be determined. In the particular case of silver chloride, however, the difference is probably within the limits of the experimental error. 

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