Potassium chloride osmotic coefficients

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,... 

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). 

Figures 1 and 2 show the results of fitting the osmotic coefficient of the aqueous electrolytes sodium perchlorate and potassium chloride, respectively. Analysis of the variance in fitting the osmotic coefficient indicates that the fits are about as good as those obtained using Pitzer s equations, despite the fact that our equations have one less fitting parameter. For sodium perchlorate, the standi d deviation in our fit is 0.0011, whereas Pitzer ( ) reports 0.001 using his equation. For potassium chloride, the standard deviation in our fit is 0.00036, that in Pitzer s,...

Figure 2. The fit of our hydration theory model to osmotic coefficient data for potassium chloride tabulated by Robinson and Stokes (11).

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).

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