Molality determination

Because of solvent loss, which occurred even with covered crucibles and which was of the same order as the weighing errors ( 5 X 10 4 g), the correction of weighing for the vacuum was not considered. Then the mean error in the molality determination was 0.3%. In each desiccator, 2-3 standard solutions (KCl or CaCk) were present. Their osmotic coefficient was taken from the literature (11). In the system considered equilibrated, the molal concentrations of the standard solutions differed by no more than 0.5%. 

V for m - 0.02 molal. Determine 7 value calculated on the basis of the Debye-Huckel Theory. 

The freezing points of three glycerol solutions in water are — 1.918 C for 1.0 molal, — 3.932 C for 2.0 molal and — 10.68 for 5.0 molal. Determine the activities and activity coefficients of the water in these solutions on the basis of the usual standard state, and consider the departure from Raoult s law. The vapor pressure of pure (supercooled) water at — 1.92 C is 3.980 mm. what would be the aqueous vapor pressure of the 1.0 molal glycerol solution at this temperature ... 

Whenever the comparability between the two methods is impaired by the effects reported, the composition of whole blood is still relatively stable and predictable. The discussions of what should be measured and what should be reported are due to the extremely high quality requirements for most analytes. The evaluation of standard specimens for ion active molality determinations in a symmetric cell arrangement may be considered for future developments. 

Source Values taken from Bates, R. G. Determination of pH Theory and Practice, 2nd ed. Wiley New York, 1973. Concentrations are given in molality (moles solute per kilograms solvent). 

The direct-solution method of Akers and Wade [1] is among several which attempt to reduce the amount of trial-and-error solutions. This has been accomplished and has proven quite versatile in application. The adaptation outlined modifies the symbols and rearranges some terms for convenient use by the designer [3]. Dew point and bubble point compositions and the plate temperatures can be determined directly. Constant molal overflow is assumed, and relative volatility is held constant over sections of the column. 

A procedure like this has been adopted in the literature, except that it is the value for the hydrogen ion that has been set equal to zero. This involves a slightly more difficult concept for, when a proton is added to water, it converts an H20 molecule into an (HsO)+ ion. The entropy of the original water molecule is replaced by the entropy of the (HsO)+ ion and its co-sphere. When the partial molal entropy of HC1 in aqueous solution has been determined, the whole is assigned to the Cl- ion that is to say, the value for the hydrogen ion is set equal to zero, and the values for all other species of ions are expressed relative to this zero. 

To determine the number of moles of solute from the definition of molality, m = (moles solute)/(kg solvent), first find the mass of solvent using its density ... 

We now have the foundation for applying thermodynamics to chemical processes. We have defined the potential that moves mass in a chemical process and have developed the criteria for spontaneity and for equilibrium in terms of this chemical potential. We have defined fugacity and activity in terms of the chemical potential and have derived the equations for determining the effect of pressure and temperature on the fugacity and activity. Finally, we have introduced the concept of a standard state, have described the usual choices of standard states for pure substances (solids, liquids, or gases) and for components in solution, and have seen how these choices of standard states reduce the activity to pressure in gaseous systems in the limits of low pressure, to concentration (mole fraction or molality) in solutions in the limit of low concentration of solute, and to a value near unity for pure solids or pure liquids at pressures near ambient. 

The conductivity of sodium dodecyl sulfate in aqueous solution and in sodium chloride solutions was studied by Williams et al. [98] to determine the CMC. Goddard and Benson [146] studied the electrical conductivity of aqueous solutions of sodium octyl, decyl, and dodecyl sulfates over concentration ranges about the respective CMC and at temperatures from 10°C to 55°C. Figure 14 shows the results obtained by Goddard and Benson for the specific conductivity of sodium dodecyl sulfate and Table 25 shows the coefficients a and p of the linear equation of the specific conductivity, in mho/cm, vs. the molality of the solution at 25°C. Micellization parameters have been studied in detail from conductivity data in a recent work of Shanks and Franses [147]. 

A 1.00% by mass NaCI(aq) solution has a freezing point of —0.593°C. (a) Estimate the van t Hoff i factor from the data, (b) Determine the total molality of all solute species. 

C12-0001. Determine the molality of a sugar solution that contains 3.94 g of sucrose (C12 H22 On) dissolved in 285 g of water. 

Concentrated aqueous ammonia (also known as ammonium hydroxide) is 14.8 M and has a density of 0.898 g/mL. Determine the molality and mole fraction of ammonia in this solution. 

We have information about molarity (mol/L) and density (g/mL) and are asked to find molality (mol/kg) and mole fraction (mol/mol). A good way to approach conversions from molarity to another measure is to choose a convenient volume for the solution, determine its mass and the mass of solute, and find the mass of water by difference. Then convert mass of water to kilograms and to moles to complete the calculations. 

C12-0005. Determine the molarity and molality of quinine in the tonic water described in Section Exercise, assuming that the density of tonic water is 1.00 g/mL. 

The freezing point depression constant for water is known from experiments and can be found in tables Tf = 1.858 ° C kg/mol. To calculate the freezing point, we must first determine the molality of the... 

The activities have by now been determined for binary solutions of most electrolytes. As a rule, the values determined by different methods are in good mutual agreement (the scatter is not over 0.5%). These data are reported in special tables listing coefficients/+ as functions of concentrations [in the tables the concentrations are usually quoted in molalities (m), i.e., the number of moles of the given substance in 1 kg of the solvent]. 

Interesting is a comparison of the volumes occupied by individual complexes in solution and in the solid state. The partial molal volumes can be obtained from precise measurements of the solution densities of the complexes as a function of concentration [177]. These values may be subsequently compared with the unit cell volumes per complex molecule derived from the crystal structure. For Fe[HB(pz)3]2, the apparent molal volume in tetrahydrofuran solution was determined as 340.9 em mol Taking into account that the complex in solution forms an equilibrium between 86% LS and 14% HS isomers and employing the volume difference between the two spin states AF° = 23.6 cm mol S the volume of the LS isomer was calculated as 337.6 cm mol This value agrees closely with the volume of 337.3 cm mol for the completely LS complex in solid Fe[HB(pz)3]2 [105]. 

Major determinants of membrane fluidity may be grouped within two categories [53] (1) intrinsic determinants, i.e., those quantifying the membrane composition and phase behavior, and (2) extrinsic determinants, i.e., environmental factors (Table 1). In general, any manipulation that induces an increase in the molal volume of the lipids, e.g., increase in temperature or increase in the fraction of unsaturated acyl chains, will lead to an increase in membrane fluidity. In addition, several intrinsic and extrinsic factors presented in Table 1 determine the temperature at which the lipid molecules undergo a transition from the gel state to liquid crystalline state, a transition associated with a large increase in bilayer fluidity. 

In the example just studied, the electrolysis of HC1 solution, the ions that transport the current (H+ and Cl-) are also the ones that are discharged at the electrodes. In other cases, however, the main ionic transporters of current may not be of the same species as the ions that are discharged. An excellent example is the electrolysis of CuS04 solution between platinum electrodes. A one molal CuS04 solution is quite acid so that the positive current transporters are both Cu2+ and H+ ions. The main negative transporter is the S04 ions. The solution contains, however, a small concentration of OH- ions. In order to determine which ions will be discharged at the electrodes, it is necessary to consider standard electrode potentials of the concerned species ... 

By plotting the left-hand side of eqn. 2.65 against to and extrapolating back to to = 0 the intercept at to = 0 gave the value of J lgci/Ag = 0.2225 V at 25° C20 (cf., 0.2223 V21). Once E° is known, the measurement of E as a function of to provides an important method for determining molal ionic activity coefficients and a paH scale with the above type of cell, which permits a comparison with the Sorensen psH scale (cf., p. 33). 

Calcium-sodium-chloride-type brines (which typically occur in deep-well-injection zones) require sophisticated electrolyte models to calculate their thermodynamic properties. Many parameters for characterizing the partial molal properties of the dissolved constituents in such brines have not been determined. (Molality is a measure of the relative number of solute and solvent particles in a solution and is expressed as the number of gram-molecular weights of solute in 1000 g of solvent.) Precise modeling is limited to relatively low salinities (where many parameters are unnecessary) or to chemically simple systems operating near 25°C. 

If Type I adsorption behavior is obeyed, a plot of PA/v versus PA should be linear with slope l/vm. Once the volume corresponding to a mono-layer has been determined, it can be converted to the number of molecules adsorbed by dividing by the molal volume at the reference conditions and multiplying by Avogadro s number (N0). When this number of molecules is multiplied in turn by the area covered per adsorbed molecule (a), the total surface area of the catalyst (S) is obtained. Thus,... 

The summation involves the effluent molal flow rates. This equation and equation 10.4.2 must be solved simultaneously in order to determine the tubular reactor size and to determine the manner in which the heat transfer requirements are to be met. For either isothermal or adiabatic operation one of the three terms in equation 10.4.7 will drop out, and the analysis will be much simpler than in the general case. In the illustrations which follow two examples are treated in detail to indicate the types of situations that one may encounter in practice and to indicate in more detail the nature of the design calculations. 

We now wish to examine the heat capacity per unit mass to determine if it varies significantly with conversion. At the inlet conditions, the molal heat capacity of the gaseous feed will be equal to X(y CPi). Hence at / = 0, with Cp in units of calories per gram degree Kelvin and T in degrees Kelvin. 

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