Molal concentration

Molal concentration of ammonia in the solutions in percentages (Weight concentration of ammonia in die solution in percentages)... 

Gangue minerals and salinity give constraints on the pH range. The thermochemical stability field of adularia, sericite and kaolinite depends on temperature, ionic strength, pH and potassium ion concentration of the aqueous phase. The potassium ion concentration is estimated from the empirical relation of Na+/K+ obtained from analyses of geothermal waters (White, 1965 Ellis, 1969 Fournier and Truesdell, 1973), experimental data on rock-water interactions (e.g., Mottl and Holland, 1978) and assuming that salinity of inclusion fluids is equal to ffZNa+ -h m + in which m is molal concentration. From these data potassium ion concentration was assumed to be 0.1 and 0.2 mol/kg H2O for 200°C and 250°C. 

The resulting species distribution (Table 6.7), as would be expected, differs sharply from that in seawater (Table 6.4). Species approach millimolal instead of molal concentrations and activity coefficients differ less from unity. In the Amazon River water, the most abundant cation and anion are Ca++ and HCOJ in seawater, in contrast, Na+ and Cl- predominate. Seawater, clearly, is not simply concentrated river water. 

Fig. 8.7. Molal concentrations m, and activities a, of calcium and sulfate species in equilibrium with gypsum at 25 °C as functions of NaCl concentration, calculated using the B-dot equation (left) and the hmw activity model (right).

Here m>u and m>UCd++ are molal concentrations of the unoccupied and occupied sites, respectively, and aCd++ is the activity of the free ion. Activity coefficients for the surface sites are not carried in the equation they are assumed to cancel. Equilibrium constants reported in the literature are in many cases tabulated in terms of the concentrations of free species, rather than their activities, as assumed here, and hence may require adjustment. 

To allow for its numerical solution, we formalize our discussion of the ion exchange model by including in the basis a species Ap (e.g., >X Na+) representing the exchanging site (Eqn. 9.21). This species has a molal concentration mp, and the... 

As before, mq are the molal concentrations of the sorbing species Aq, and vwq, etc., are the coefficients of the reaction forming Aq from the basis. In these equations, we have taken minerals and sorbed species as being immobile, although this assumption might be relaxed to account, for example, for the migration of colloids or suspended sediment. 

Do not forget that nearly all the concentration units use the total for the solution in the denominator. For these units it is important to remember to combine the quantities for the solvent and all solutes present. Molal concentrations are exceptions. Molality uses only the kilograms of solvent in the denominator. Do not make the mistake of using the entire solution in the denominator for molal concentrations. 

At 25°C the partial molar volume of urea [CO(NH2)2] solution in water is found by a nonlinear least-squares fitting procedure to be the following function of m2 up to 17-molal concentration (with V in cm mol ), with experimental data from Gucker et al. [10] and the form of the equation from Stokes ... 

Electrostatic and statistical mechanics theories were used by Debye and Hiickel to deduce an expression for the mean ionic activity (and osmotic) coefficient of a dilute electrolyte solution. Empirical extensions have subsequently been applied to the Debye-Huckel approximation so that the expression remains approximately valid up to molal concentrations of 0.5 m (actually, to ionic strengths of about 0.5 mol L ). The expression that is often used for a solution of a single aqueous 1 1, 2 1, or 1 2 electrolyte is... 

In the molality concentration scale, the molality m. of solute i is the amount of solnte i per kg of solvent. If the solvent is water (subscript w), the following relation between mole fraction and molahty of solute i can be derived ... 

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