Potassium chloride activity coefficient

The activity coefficient of the solvent remains close to unity up to quite high electrolyte concentrations e.g. the activity coefficient for water in an aqueous solution of 2 m KC1 at 25°C equals y0x = 1.004, while the value for potassium chloride in this solution is y tX = 0.614, indicating a quite large deviation from the ideal behaviour. Thus, the activity coefficient of the solvent is not a suitable characteristic of the real behaviour of solutions of electrolytes. If the deviation from ideal behaviour is to be expressed in terms of quantities connected with the solvent, then the osmotic coefficient is employed. The osmotic pressure of the system is denoted as jz and the hypothetical osmotic pressure of a solution with the same composition that would behave ideally as jt. The equations for the osmotic pressures jt and jt are obtained from the equilibrium condition of the pure solvent and of the solution. Under equilibrium conditions the chemical potential of the pure solvent, which is equal to the standard chemical potential at the pressure p, is equal to the chemical potential of the solvent in the solution under the osmotic pressure jt,... 

Table II. Calculated and Observed Values of the Activity Coefficients of Potassium, Sodium, Lithium, and Hydrogen Chlorides ...

With the use of thermodynamic relations and numerical procedure, the activity coefficients of the solutes in a ternary system are expressed as a function of binary data and the water activity of the ternary system. The isopiestic method was used to obtain water activity data. The systems KCl-H20-PEG-200 and KBr-H20-PEG-200 were measured. The activity coefficient of potassium chloride is higher in the mixed solvent than in pure water. The activity coefficient of potassium bromide is smaller and changes very little with the increasing nonelectrolyte concentration. PEG-200 is salted out from the system with KCl, but it is salted in in the system with KBr within a certain concentration range. 

The trend of activity coefficients of potassium chloride and potassium bromide is different in measured mixed solvent. The activity coefficient of potassium chloride is higher in the mixed solvent than in the pure water and rises smoothly with the nonelectrolyte content. The minimum value, about 2.0-3.0m in pure water, can be observed in the mixed solvent also. Because of the activity coefficient of the nonelectrolyte in the ternary system (also higher than that in pure water), both components are mutually salted out. 

ACTIVITY COEFFICIENT. A fractional number which when multiplied by the molar concentration of a substance in solution yields the chemical activity. This term provides an approximation of how much interaction exists between molecules at higher concentrations. Activity coefficients and activities are most commonly obtained from measurements of vapor-pressure lowering, freezing-point depression, boiling-point elevation, solubility, and electromotive force. In certain cases, activity coefficients can be estimated theoretically. As commonly used, activity is a relative quantity having unit value in some chosen standard state. Thus, the standard state of unit activity for water, dty, in aqueous solutions of potassium chloride is pure liquid water at one atmosphere pressure and the given temperature. The standard slate for the activity of a solute like potassium chloride is often so defined as to make the ratio of the activity to the concentration of solute approach unity as Ihe concentration decreases to zero. 

For the above reasons, the IFCC recommendations on activity coefficients [19] and the measurement of and conventions for reporting sodium and potassium [21] and chlorides [25] by ISEs were developed. At the core of these recommendations is the concept of the adjusted active substance concentration (mmol/L), as well as a traceable way to remove the discrepancy between direct and indirect determinations of these electrolytes in normal sera. Extensive studies of sodium and potassium binding to inorganic ligands and proteins, water binding to proteins, liquid-junction effects and the influence of ionic strength have demonstrated that the bias between sodium and potassium reports obtained from an average ISE-based commercial... 

Only mean activity coefficients can be experimentally determined for salts, not activity coefficients for single ions. The Maclnnes Convention is one method for obtaining single ion activity coefficients and states that because of the similar size and mobility of the potassium and chloride ions ... 

Calculate the mean activity coefficient of thallous chloride, the solubility of which has been measured in water and in the presence of various concentrations of potassium chloride soiutions at 25 °C, as given in Tabie P.l. The soiubiiity of this salt in pure water is 1.607 x 10 mol kg". (Constantinescu)... 

Some of the results are also depicted by the curves in Fig. 46 it will be observed that the activity coefficients may deviate appreciably from unity. The values always decrease at first as the concentration is increased, but they generally pass through a minimum and then increase again. At high concentrations the activity coefficients often exceed unity, so that the mean activity of the electrolyte is actually greater than the concentration the deviations from ideal behavior are now in the opposite direction to those which occur at low concentrations. An examination of Table XXXIV brings to light other important facts it is seen, in the first place, that electrolytes of the same valence type, e.g, sodium and potassium chlorides, etc., or calcium and zinc chlorides, etc.. 

The following values for the mean activity coefficients of potassium chloride were obtained by Macinnes and Shedlovsky [J. Am, Chem, Soc, 59, 503 (1937)] ... 

Other electrolytes in solution. For example, in a saturated solution of silver chloride in 0.01 M potassium chloride, the concentration of silver chloride is only about 10 M and so makes no appreciable contribution to the total ionic strength. Yet the activity coefficient of the silver ion is equal to that of potassium or chloride ions (0.89, from the DHLL). 

Gutbezahl and Grunwald considered liquid-junction potentials between a solution of aqueous potassium chloride and solutions of acids in ethanol-water mixtures both theoretically and experimentally. They concluded that for mixtures containing up to 33% ethanol the liquid-junction potential should be 6 mV or less. For solvents containing higher percentages of alcohol, the liquid-junction potential increases rapidly—25 mV for 50%, 44 mV for 65%, and 75 mV for 80% ethanol. These numerical values should not be interpreted too literally, particularly as the composition approaches 100% ethanol. Calculated liquid-junction potentials contain an indeterminate term that involves all quantities other than those arising from unequal transfer activity coefficients (such as dipole orientation effects). 

From the values of the osmotic coefficient for potassium chloride solutions at 25 C given below, determine the activity coefficients at the various molalities by means of equation (39.54). 

Rov, R. N. et ul. 1983. The first ionization of carbonic acid in aqueous solutions ol potassium chloride including the activity coefficients of potassium bicarbonate. J. Cheni. Thermo. 15 37-47. 

The activity coefficient of hydrogen and hydroicyl ions in hydrochloric acid, sodium chloride, and potassium chloride solutions. 

Values of/x = Ac/A may be calculated from Kohlrausch s measurements of electrical conductivity of hydrochloric acid solutions. /h and fci can be evaluated from the potentiometric measurements on hydrochloric acid solutions performed by Scatchaed. These data are very reliable since the concentration chain was so arranged as to eliminate diffusion potentials. In this way, ScATCHARD determined the mean activity coefficient V/h/ci instead of the individual ion activities. If we assume that in a potassium chloride solution/ = /ci— which is plausible when we recall that both ions have the same structure—and that fci is the same in hydrochloric acid solutions and potassium chloride solutions of the same concentration, then we can calculate/h and fci in hydrochloric acid solutions. Naturally these values are not strictly correct since the effect of the potassium ions on the activity of the chloride ions probably is different from that of the hydrogen ions at the same ionic strength. In the succeeding table are given values of /x, /h, and fci calculated by the above method. 

It is distinctive of both of these examples and of this type of cell in general that two types of electrodes are involved, each of which must be reversible to an ion constituent in the solutions contained in the cells. Since the mechanism of operation of such cells is relatively simple they should be used whenever possible. However, experimental difficulties which may make the construction of such cells impossible or limit their range of usefulness frequently arise when measurements on such cells are attempted. For instance a cell which may be used to obtain data on the activity coefficients of the ions of potassium chloride is as follows ... 

In addition to hydrochloric acid, the results for which have just been described in detail, the method utilizing concentration cells with transference has been used in obtaining the activity coefficients of potassium chloride,17 sodium chloride,18 silver nitrate,10 and calcium chloride.17 The resulting activity coefficients, /, and comparisons with equation (45), Chapter 7, of the Debye-Hiickel theory,... 

Precise values of the activity coefficients of aqueous ammonium chloride solutions at 25 °C, determined from e.m.f. measurements of cells with transference, have been reported for the concentration range 0—0.2moll. The results show no anomalous behaviour with respect to the Debye-Hiickel limiting law. An interpretation of excess thermodynamic functions of potassium and ammonium chloride solutions has been made in terms of ionic influences on solvent structure. ... 

Figure 3. The mean molal activity coefficient of sodium perchlorate (left) and potassium chloride (right). The curves show the predictions of our model, fit to data for the osmotic coefficient. The squares represent the data tabulated by Robinson and Stokes (11).

In their study Dwyer, Gyarfas and O Dwyer (1951, 1956) measured the solubilities of the perchlorates of optically active m-o-phenanthroline ruthenium(II) in solutions of optically active substances finding, for example, that in aqueous 1% (+)bromocamphorsulphonate the solubilities of the (-f-) and (—complexes are 0.232 and 0.235 grams per 100 ml solution. In 2% potassium equally soluble in water. It follows that the activity products are equal and hence aa+=ai+. Addition of sodium chloride affects the solubility of the enantiomers to the same extent. This is not so in the presence of a second chiral anionic species. From the existence of solubility differences Dwyer and collaborators concluded that, for activity a and activity coefficient (y). 

The activity coefficient of sodium ion in normal human serum has been estimated, using ion-selective electrodes, to be 0.780 0.001, and in serum water to be 0.747 (serum contains about 96% water by volume). Standard solutions of sodium chloride and potassium chloride are usually used to calibrate electrodes for the determination of sodium and potassium in serum. Concentrations of 1.0, 10.0, and 100.0 mmol/L can be prepared with respective activities of 0.965, 9.03, and... 

The potential of a glass cation-sensitive electrode is measured against an SCE. In a sodium chloride solution of activity 0.100 M, this potential is 113.0 mV, and in a potassium chloride solution of the same activity, it is 67.0 mV. (a) Calculate the selectivity coefficient of this electrode for potassium over sodium, using the relationship derived in Problem 21. (b) What would be the expected potential in a mixture of sodium (a = 1.00 X 10 M) and potassium (a = 1.00 X 10 - M) chlorides Assume Nemstian response, 59.2 mV/decade. 

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