Key Terms Formation of Solution: • “Like dissolves like” rule-­‐ strongly polar and ionic solutes tend to dissolve in polar solvents, and nonpolar solutes tend to dissolve in nonpolar solvents • Hydration-­‐ the development in an aqueous solution of a cage of water molecules about ions or polar molecules of the solute • Solvation-­‐ the development of a cage-­‐like network of a solution’s solvent molecules around a molecule or ion of the solute Heats of Solution: • Heat of solution, ΔHsoln-­‐ the energy exchanged between the system and its surroundings when one mole of a solute dissolves in a solvent to make a dilute solution • Solvation energy-­‐ the enthalpy of the interaction of gaseous molecules or ions of solute with solvent molecules during the formation of a solution • Hydration energy-­‐ the enthalpy change associated with the hydration of gaseous ions or molecules as they dissolve in water • Ideal solution-­‐ a hypothetical solution that would obey the vapor pressure-­‐
concentration law (Raoult’s law) exactly Solubility: • Henry’s law-­‐ also known as Pressure-­‐solubility law, the concentration of a gas dissolved in a liquid at any given temperature is directly proportional to the partial pressure of this gas above the solution Colligative Properties: • colligative property-­‐ a property such as vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure whose physical value depends only on the ratio of the numbers of moles of solute and solvent particles and not on their chemical identities • Freezing point depression-­‐ a colligative property of a liquid solution by which the freezing point of the solution is lower than that of the pure solvent • Boiling point elevation-­‐ a colligative property of a solution by which the solution’s boiling point is higher than that of the pure solvent • Osmotic pressure-­‐ the back pressure that would have to be applied to prevent osmosis; one of the colligative properties •
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Raoult’s law-­‐ the vapor pressure of one component above a mixture of molecular compounds equals the product of its vapor pressure when pure and its mole fraction Molal freezing point depression constant, Kf-­‐ the number of degrees (°C) per unit of molal concentration that the freezing point of a solution is lower than that of the pure solvent Molal boiling point elevation constant, Kb-­‐ the number of degrees (°C) per unit of molal concentration that the boiling point of a solution is higher than that of the pure solvent Van’t Hoff factor-­‐ the ratio of the observed freezing point depression to the value calculated on the assumption that the solute dissolves as un-­‐ionized molecules Osmosis-­‐ the passage of solvent molecules, but not those of solutes, through a semipermeable membrane; the limiting case of dialysis Colloids: • Suspension-­‐ a homogeneous mixture in which the particles of at least one component are larger than colloidal particles (>1000 nm in at least one dimension) • Colloid-­‐ a homogeneous mixture in which the particles of one or more components have at least one dimension in the range of 1 to 1000 nm – larger than those in a solution but smaller than those in a suspension • Brownian movement-­‐ the random, erratic motions of colloidally dispersed particles in a fluid • Sol-­‐ the colloidal dispersion of a solid in a fluid • Emulsion-­‐ a colloidal dispersion of one liquid in another • Emulsifying agent-­‐ a substance that stabilizes an emulsion • Tyndall effect-­‐ the scattering of light by colloidally dispersed particles that gives a milky appearance to the mixture • Micelles-­‐ a colloidal-­‐sized group of ions, such as the anions of a detergent, that have clustered to maximize the contact between the ions’ hydrophilic heads and water and to minimize the contact between the ions’ hydrophobic parts and water • Hydrophobic group-­‐ a nonpolar molecular unit with no affinity for the molecules of a polar solvent, like water • Hydrophilic group-­‐ a polar molecular unit capable of having dipole-­‐dipole attractions or hydrogen bonds with water molecules