Solution and volume

After the usual corrections for analyte impurity, potential drop in the solution and volume increase during titration, the experimental results were in perfect agreement with the theoretical hyperbolic curve. 

Here we will use a simplified example to illustrate some basic aspects of the mass transport process for carbonates that avoids most of the more complex relationships. In this example, the calcium and carbonate ion concentrations are set equal, and values of the activity coefficients, temperature, and pressure are held constant. The carbonate ion concentration is considered to be independent of the carbonic acid system. The resulting simple (and approximate) relation between the change in saturation state of a solution and volume of calcite that can be dissolved or precipitated (Vc) is given by equation 7.4, where v is the molar volume of calcite. 

The concept of solutions was introduced in Chapter 1, and molarity was considered in Chapter 11. Molarity is defined in terms of volume of solution, and volume can change with temperature, even if the masses of solvent and solute do not change. When dealing with solution concentrations in systems at varying temperatures, we need concentration units that do not vary with temperature. Three such units are introduced here. 

An important practical generalisation from Thomsen s results is that the heat capacity of an aqueous solution is approximately equal to that of the water it contains this is used in calorimetry. Thomsen pointed out that the difference between the volume of solution and volume of water also decreases with dilution, so that dilution causes a contraction. This effect is called electrostriction ( 4. VIIIB). 

The z-dependent potential F(z), in zero current conditions, is related to streaming potential Vp. In the case of ceramic membranes (])d and Vp are the two quantities which influence both retention of charged solutes and volume flux. 

Use molarity to convert between moles of solute and volume of solution. 

Between this chapter and Chapter 10, we have now seen three different ways to convert between a measurable property and moles in equation stoichiometry problems. The different paths are summarized in Figure 13.10 in the sample study sheet on the next two pages. For pure liquids and solids, we can convert between mass and moles, using the molar mass as a conversion factor. For gases, we can convert between volume of gas and moles using the methods described above. For solutions, molarity provides a conversion factor that enables us to convert between moles of solute and volume of solution. Equation stoichiometry problems can contain any combination of two of these conversions, such as we see in Example 13.8. 

Stoichiometry concerns calculations based on balanced chemical equations, a topic that was presented in Chapter 8. Remember that the coefficients in the balanced equations indicate the number of moles of each reactant and product. Because many reactions take place in solution, and because the molarity of solutions relates to moles of solute and volumes, it is possible to extend stoichiometric calculations to reactions involving solutions of reactants and products. The calculations involving balanced equations are the same as those done in Chapter 8, but with the additional need to do some molarity calculations. Let s get our feet wet by working a couple of problems involving solutions in chemical reactions. 

The volume changes which occur during dissolution can be directly obtained, by subtraction, from measurements of the volumes of the constituents before mixing and after mixing. However, these changes of volume can be observed in a more indirect manner, which turns out to be more precise. This method consists in measuring the mass per volume of solution as a function of composition. We shall describe this measurement method in the following sections, but first we must establish the relations which exist between masses per volume, partial volumes per mass for the solvent and the solute, and volume of solution. 

Products. The experiments were carried out at room temperature by adding a solution of the nitronium salt in the organic solvent to a solution of the amine in the same solvent, the weight of the solutes and volumes of solvent in both solutions being known. The concentration of the amine was more than two-fold that of the nitronium salt so that after complete reaction (shown for N-nitration in equation (1)) an excess of the free amine should still be present. This should reduce the acidity of the solution to the point where rearrangement of the nitramine can be ignored. 

We next consider the heat of solution and volume increment of solution for the case of ideal solutions. The partial molal enthalpy of component i is given by Eq. (7-142) in the form... 

The intuitive appeal of this scheme was strengthened by the actual construction of such a composite system and the observation of its functioning as predicted [31-32], The analysis of the model behavior in terms of the component membrane properties was undertaken by Patlak et al. [33], These workers derived expressions for the net solute and volume flows in terms of the rate of solute transport into the middle compartment and the solute concentrations in the outer solutions. The essential message of this mathematical effort was that the middle compartment model would be compatible, at least qualitatively, with the observed physiology of epithelial transport. 

Be able to calculate molarity and use it to convert between moles of a substance in solution and volume of the solution. (Section 4.5)... 

S. Degrange, V. Hynek, and V. Majer, Heats of solutions and volumes of aqueous hydrocarbons in the critical region of water... 

Just as molarity provides a way to convert in either direction between moles of solute and volume of solution, normality offers a unit path between equivalents of solute and volume of solution. 

Liquid solute and volume percent Solid solute and weight to volume percent Solid solute and molarity... 

The energy of the bottom of the conduction band is one factor influencing electron kinetics. Anions formed by attachment are stabilized in solution, and volume changes are manifestations of the free energy... 

Another possibility is to express the mass of solute and volume of solution. An aqueous solution with 0.9 g NaCl in 100.0 mL of solution is said to be 0.9% NaCl (mass/volume). Mass/volume percent is extensively used in the medical and pharmaceutical fields. 

---