Presentation on theme: "Solutions of Nonelectrolytes"— Presentation transcript:
1Solutions of Nonelectrolytes When several nonreacting substances are mixed, three possible types of mixtures may be obtained:a coarse mixture, such as that of salt and sugar;a colloidal dispersion, such as results when fine clay is shaken with watera true solution, obtained when a substance like sugar dissolves in water
2a coarse mixturethe individual particles are readily discernible and may be separated from each other by mechanical means.a colloidal dispersionin a colloidal dispersion the particles are much finer and the heterogeneity is not so readily apparent, the dispersion is, nevertheless, not homogeneous.a true solutionin the true solution the constituents cannot be separated from each other by mechanical means, and every part of the solution is found to be like every other part; i.e., a true solution constitutes a homogeneous phase.
3Unsaturated solutionAny solution which contains less than the amount of solute in saturated solutionSaturated solutionA solution which contains at a given temperature as much solute as it can hold in presence of the dissolving substance is said to be saturated.Supersaturated solutionA supersaturated solution can exist only in the absence of dissolving substance and is at best very unstable. Jarring and stirring may, and introduction of solute will, cause the precipitation of excess solute in solution, leading to the formation of a saturated solution.
4On theoretical grounds it is convenient to subdivide solutions into: (a) solutions of non-electrolytesthe solute dissolved in the solvent persists in molecular, uncharged form and exhibits no tendency to dissociate into electrically charged ions.(b) solutions of electrolytes.the solute dissociates to a greater or lesser degree into ions, increasing thereby the total number of particles in solution.
5Factors Affecting Solubility The extent to which a substance will dissolve in another varies greatly with different substances and depends onthe nature of the solute and solvent,In general, compounds of similar chemical character are more readily soluble in each other than are those whose chemical character is entirely different.completely miscible.completely immiscible.partially miscible.
6the temperatureThe direction in which the solubility of a substance in a solvent changes with temperature depends on the heat of solution. If a substance dissolves at saturation with evolution of heat, the solubility decreases with rising temperature. On the other hand, if a substance dissolves with absorption of heat, the solubility increases as the temperature is raised.the pressureIn general the effect of pressure on solubility is small unless gases are involved.
7Methods of Expressing Solution Concentration Weight basis (a weight basis are temperature- independent):Per cent or fraction of dissolved substance by weight.Weight of dissolved substance per definite weight of one of the constituents.Weight of dissolved substance per definite total weight of solution.Molality-number of moles of dissolved substance per 1 grams of solvent.Mol fraction.
8Volume basis (vary with temperature in a manner dependent upon the thermal expansion of the solution):Per cent or fraction of dissolved substance by volume.Weight of dissolved substance per given volume of solution.Molarity-number of moles of dissolved substance per liter of solution.Normality-number of equivalents of dissolved substance per liter of solution.
9Types of SolutionsAlthough solutions with many components can be prepared, attention will be confined to binary solutions, i.e., solutions containing two components only. Since the solvent and solute may be either gaseous, liquid, or solid, the number of possible types namely:Solution of a gas in a gasAll gases are miscible in all proportions, yielding solutions whose physical properties are very nearly additive provided the total pressure is not too high. Under the latter conditions the partial and total pressures are governed by Dalton’s law, the partial and total volumes by Amagat’s law.
10Solution of a liquid in a gas Solution of a solid in a gasThe vaporization of a liquid and the sublimation of a solid into a gas phase may be considered as solution of these substances in a gas.These processes involve first the conversion of the liquid or solid to vapor, and the subsequent solution of the vapor in the gas.Because the vaporization and sublimation pressures of a substance are fixed at any given temperature, the amounts of liquid and solid that can vaporize into a given volume of gas are limited to the amount necessary to establish the equilibrium pressures.
11Solution of a gas in a solid Solution of a liquid in a solidSolution of a solid in a solidSolution of a gas in a liquidSolution of a solid in a liquidSolution of a liquid in a liquid
12The Thermodynamic Properties of a Solution The Gibbs free energy, originally called available energy of a body as such:The greatest amount of work which can be obtained from a given quantity of a certain substance in a given initial state, without increasing its total volume or allowing heat to pass to or from external bodies, except such as at the close of the processes are left in their initial condition.
13Condition for Equilibrium Between Phases The Solution ProcessCondition for Equilibrium Between Phasesthe condition for equilibrium between phases of a pure substance at constant temperature and pressure is that the molar free energy of the substance be the same in all phases.for equilibrium at constant temperature and pressure in a multicomponent system composed of a number of phases, the partial molal free energy of each of constituent must be the same in all the phases.