Equilibrium in saturated solutions

Until now, we have looked primarily at equilibrinm systems that involve gases. However, there are also eqnilibrium systems that involve aqneous saturated solutions between solid solutes of slightly soluble salts and their ions. Everyday examples of solubility equilibrium in solution are found in the slightly soluble salts that are found in bone and kidney stones. Bone is composed of calcium phosphate, Ca3(P04)2, which produces ions during bone loss. Kidney stones are composed of calcium salts such as calcium oxalate, CaC204. 

In a saturated solution, a solid slightly soluble salt is in equilibrium with its ions. As long as the temperature remains constant, the concentration of the ions in the saturated solution is constant. Let us look at the solubility equilibrium equation for CaC204, which is written with the solid solute on the left and the ions in solution on the right 

The solubility of a substance is the quantity that dissolves to form a saturated solution. We represent the solubility in a saturated aqueous solution of solid CaC204 by the solubility product expression, K p, which is the product of the ion concentrations. As in other heterogeneous equilibria, the concentration of the solid CaC204 is constant and is not included in the solubihty product expression. 

In another example, we look at the equilibrium of solid calcium phosphate and its 

Write the solubility product expression for a slightly soluble salt and calculate the K p use K p to determine the solubility. 

---

Equilibrium in Saturated Solutions LEARNING GOAL Write the solubility product expression... 

CI2O is very soluble in water, a saturated solution at —9.4°C containing 143.6 g CI2O per 100 g H2O in fact the gas is the anhydride of hypochlorous acid, with which it is in equilibrium in aqueous solutions ... 

Fluorides of the lantlmnides, yttrium, and scsmdium normally precipitate from aqueous media as the hemihydrates, LnF3-MsH20. It is these hemihydrates which are in equilibrium with saturated solution, and the solubility-product measurements refer to these hemihydrates. 

The enneahydrate is the solid phase in equilibrium with saturated solution in all cases. 

In what manner is the junction of the two branches of the solubility curve made One might be tempted, in replying to this question, to apply again to each of these two branches the law of the displacement of equilibrium with change of temperature this would be an unwarranted application of this principle in fact, the equilibrium state of the saturated solution at the temperature 6 is no longer a state of stable equilibrium the saturated solution having, at this temperature, the same composition as the precipitate, one may, without varying the composition of the two phases... 

This equilibrium is stable in general, 214.—X84. Solutions. Saturation. Solubility curve, 216.—X85. For a hydrated salt two saturated solutions correspond to each temperature. The solubility curve has two branches, 216.—x86. Non-saturated and supersaturated solutions, 217.—X87. Heat of solutions in saturated solutions, 219.— x88. Displacement of equilibrium by variation of temperature, 219. 

The solvent activity coefficient of a polar transition state can be measmred in the following way (Evans and Parker, 1966). Because in all saturated solutions of the salt AB, which would be in equilibrium with the same crystalline solid, AB has the same chemical potential, then the reactants in saturated solutions start at the same free energy level for reaction (10) in all solvents. 

Such a solution is said to be saturated. Saturation occurs at very low concentrations of dissolved species for slightly soluble substances and at high concentrations for very soluble substances. When imperfect crystals are placed in saturated solutions of their ions, surface defects on the crystals are slowly patched with no net increase in mass of the solid. Often, after some time has passed, we see fewer but larger crystals. These observations provide evidence of the dynamic nature of the solubility equilibrium. After equilibrium is established, no more solid dissolves without the simultaneous crystallization of an equal mass of dissolved ions. 

In saturated solutions, equilibrium exists between soUd and dissolved solute. The equation for the dissolution of barium sulfate in water and its solubility product expression are... 

From what we have said above, it follows that the acid-base equilibrium in the solutions containing metal cations and oxide ions in different sections of the titration curve is described either by the dissociation constant (in unsaturated solutions) or by the values of solubility product (in saturated solutions). In Refs. [175, 330] we proposed a method based on the analysis of the scatter in the calculated equilibrium parameters corresponding to the titration process. Indeed, in the unsaturated solution section there is no oxide precipitation and the calculated value of the solubility product increases monotonously (the directed shift) whereas the calculated value of the dissociation constant fluctuates about a certain value, which is the concentration-based dissociation constant of the studied oxide. 

The solubility method of determining medium effects is more generally applicable. The chemical potentials of a solute MX in saturated solution in solvent S and in water are equal since each is in equilibrium with the same solid phase, provided no crystal solvates are formed (sect. 2.3.1), thus... 

Many solid phases have been reported or suggested as being in equilibrium with saturated solutions in the Na20-P20 -H20 system. These are ... 

Soluble salt flotation occurs in saturated solution in which the salt crystal surface is in dynamic balance between crystallization and dissolution, making it difficult to examine the interfacial properties using traditional experimental measures. In this regard, the water structure at selected alkali halide salt surfaces has been studied using MD simulation. Equilibrium surface charge signs for these salt minerals in saturated solution have been calculated by considering the ion hydration and water dipole distribution at salt-saturated brine interfaces, and the results are compared with... 

Solution Equilibrium A saturated solution in a closed system is at equilibrium.The solute is recrystallizing at the same rate that it is dissolving, even though it appears that there is no activity in the system. 

Important examples of chemical equilibrium systems include (1) the Haber process for the manufacture of ammonia from hydrogen gas and nitrogen gas, (2) the ionization of weak electrolytes in water, and (3) the ionization and dissolution of ionic solids in saturated solutions. 

---