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Unformatted text preview: Chem 200 Dr. Saidane Lecture Notes Chapter 13 Properties of Solutions SOLUTIONS A solution is a homogeneous mixture of two or more substances in a single phase. In a solution, atoms, molecules, or ions are thoroughly mixed, resulting in a mixture that has the same composition and properties throughout. Components of Solutions The dissolving medium in a solution is called a solvent and the substance dissolved in a solution is called the solute. Types of Solutions Solutions can be solids, liquids, or gases. Examples of solid solutions are alloys. Any mixture of gas is a gaseous solution. Liquid solutions can be aqueous or organic. An example of aqueous solution is salt-water; an example of organic solution is gasoline, which is a mixture of hydrocarbons. In this chapter, we will focus largely on aqueous solutions, but must of this material apply to non-aqueous solutions. Molecular Nature of Dissolving Solids dissolve in water when individual molecules or ions are attracted to water molecules and break away from the solid. When dissolved, the molecules are surrounded by water and held in suspension by dipole-dipole interactions, whereas the ions are held by ion-dipole interactions. Solubility A given quantity of solvent can dissolve only so much solute. A solution is saturated when the solvent has dissolved all the solute it can and some undissolved solute remains. 1 The concentration of solid solute in a saturated solution has reached its greatest value and no more can dissolve. In other words, a saturated solution represents the limit of a solutes ability to dissolve in a given quantity of solvent. The molar solubility of a substance is its molar concentration in a saturated solution. A saturated solution is one in which the dissolved and undissolved solute are in dynamic equilibrium with one another. A solution that contains less solute than a saturated solution under the existing conditions is an unsaturated solution . A supersaturated solution is a solution that contains more dissolved solute than a saturated solution under the same conditions . A supersaturated solution may remain unchanged for a long time if it is not disturbed, but once it is disturbed, crystals start to form until the solution becomes saturated. WHY DOES ANYTHING DISSOLVE? Heats of Solutions The formation of a solution is accompanied by an energy change. Solvent and solute particles experience changes in their intermolecular interactions. The amount of heat energy change when a specific amount of solute dissolves in a solvent is the enthalpy of solution. Depending on the solute, the enthalpy of solution can be exothermic or endothermic....
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