Properties of Solutions Chapter 13

What is a solution? Liquid? Solid? Gas? Defining characteristics of a solutions –Homogeneous mixture –Two or more components –Solvent: most abundant component –Solute(s): lesser abundant components List some examples of solutions

13.1 The Solution Process Intermolecular forces between solute and solvent –Dipole interactions Solvation: the surrounding of solute molecules by solvent molecules Hydration: solvation when water is the solvent

Interaction of Solute & Solvent During Solution Process

Hydration of Ions Solute ions & molecules are surrounded by solvent molecules Dipole-ionic interaction in this case

Energy Changes & Solution Formation The dissolving of NaCl: H 1 : Energy is involved in separating solute molecules (endothermic) H 2 : Energy is involved in separating solvent molecules (endothermic) H 3 : Energy is involved in hydration process (exothermic; formation of solute- solvent interactions) ΔH soln = H 1 + H 2 + H 3

Enthalpy changes during dissolution

13.2 Saturated Solutions & Solubility CrystallizationCrystallization: collision of dissolved solute molecules stick together and reform solid. Opposite of solution process SaturatedSaturated solution is in equilibrium with undissolved solute Carries maximum solute for a given temperature

Solubility SolubilitySolubility is the maximum amount of solute that can dissolve at a given temperature This forms a saturated solution UnsaturatedUnsaturated solution contains less solute than the maximum for a given temperature SupersaturatedSupersaturated solution contains more than the maximum for a given temperature

Effect of Temperature on Solubility

Viscosity Resistance to flow Variables: –temperature, ↑→↓ –intermolecular forces, ↑→↑ –molecular weight, ↑→↑

Viscosity of Motor Oils

Effect of Pressure on Gas Solubility

Supersaturated Solutions How would you make a solution that carries more than the maximum solute for a given temperature? Seems contradictory Inherently unstable

13.4 Ways of Expressing Concentration Concentration is a way of expressing the ratio of solute to solvent or volume of solution Mass % = mass of component/total mass of solution ppm = mass of component/total mass x 10 6 Mole Fraction X = moles of component / total moles Molarity M = moles solute / liter of solution Molality m = moles solute / kg of solvent

Converting Concentrations

13.5 Colligative Properties of Solutions quantitydissolved particlesColligative properties depend upon the quantity dissolved particles, but not the kind of solute They do not depend upon the kind of solute

Colligative Properties Lowering P vap P A = X A P A ˚ where X is mole fraction of solute A –Vapor pressure is? –What might explain this? –If vapor pressure is lowered, how would boiling point be affected?

Colligative Properties FP and BP FP depression ΔT f = K f m Due to solute interference w/ crystal formation BP elevation ΔT b = K b m molality where K is a constant, ( Table 13.4) m is molality Due to ↓P vap

Osmosis Net movement of water from lower solute to higher solute concentrations Diffusion of water BiologyRecall from Biology –Response of cell to hypertonic/hypotonic environments

Colligative Properties Osmotic Pressure Physical pressure required to prevent osmosis π = (n/V)RT π = MRT

13.6 Colloids Suspensionsparticles eventually separate Solutionsparticles do not separate Colloids“permanent suspension” “colloidal dispersion” Have large particles that would be expected to separate due to mass but do not Colloids show the Tyndall Effect

Hydrophobic Hydrophilic Colloids Larger molecules that have both hydrophobic and hydrophilic portions can form permanently suspended particles