CH 11: Properties of Solutions Describing Solutions – concentration units Energetics of solution formation Factors impacting solubility – P and T Colligative Properties of solutions BP elevation FP depression Osmotic pressure Vapor Pressure

Terms Solution – homogeneous mixture Solvent – generally the larger component of the solution Determines the physical state of the solution Solute – generally the smaller component of the solution Solute is dispersed in the solvent

Solution Composition Concentrated solution – relatively large amount of solute Dilute solution – relatively small amount of solute

Solution Composition Unsaturated solution –solution with less than the maximum amount of solute that will normally dissolve at a given temperature Saturated solution - solution with maximum amount of solute that will normally dissolve at a given temperature

Solution Composition Super-saturated solution - solution with more than the maximum amount of solute that will normally dissolve at a given temperature

Concentration Units Molarity (M) = moles solute/Liters solution Molality (m) = moles solute/kg solvent Mass % = Mass solute/mass solution x100% Mole fraction (cA) = moles A/total moles

Normality Normality (N) = # gram equivalent wt./L solution Gew = mass of an acid or base that produces 1 mole of H+ or OH -1 Normality = Molarity x (# H+ or OH -1 /mol) 1 M HCl = 1 N HCl 1 M H2SO4 = 2 N H2SO4 For acid base titrations: (NAcid) (VAcid) = (NBase) (VBase)

Practice! Start by writing definitions for the concentration units M = Mass % = Mole fraction =

Starting with Molarity Solution: 3.75 M H2SO4 solution with a density of 1.23 g/mL Calculate: Mass % Molality mole fraction of H2SO4

Starting with Masses Solution: Calculate: A solution is made by combining 66.0 grams of acetone (C3H6 O) with 146.0 grams of water. Solution has a density of 0.926 g/mL Calculate: Molarity – need volume of solution Mass % Molality Mole fraction of acetone

Starting with Mass % Solution: Calculate: 35.4 % H3PO4 Density of 1.20 g/mL Calculate: Molarity Molality Mole fraction of H3PO4

Starting with Molality Solution: 2.50 m HCl solution Density of 1.15 g/mL Calculate: Molarity – need _______ Mass % Mole fraction of HCl

Solution Formation Formation of a solution involves 3 steps Separate the solute particles expand the solute Separate the solvent particles Expand the solvent Form the solution Solute and solvent interact

Solution Formation Each step of solution formation involves energy and has a DH. DH1 = energy needed to separate the solute DH2 = energy needed to separate the solvent DH3 = energy released when solution forms

Solution Formation DHsolution = DH1 + DH2 + DH3 Solutions form when the DHsolution is a small value – see page 504

Factors Impacting Solubility Structure – like dissolves like #44 on page 533

Factors Impacting Solubility Pressure Pressure has little impact on the solubility of liquids and solids Pressure has a significant impact on the solubility of gases in a liquid The higher the pressure of gaseous solute above a liquid the higher the concentration of the gas in the solution

Henry’s Law Henry’s Law: C = kP C = Concentration of dissolved gas k = solution specific constant P = partial P of the solute gas above the solution What does Henry’s Law mean? No calculations required. Page 506

Temperature and Solubility Temperature has variable effects on the amount of solid that will dissolve in an aqueous solution! See figure 11.6 page 508 Solutes will dissolve more rapidly at higher temperatures

Temperature and Solubility The solubility of a gas in water decreases as temperature increases. See figure 11.7 on page 508 Thermal pollution – read the story on page 510 when you get a chance

Vapor Pressure of Solutions See Raoult’s Law on page 510 Psolution = csolvent P0 solvent

Colligative Properties properties of a solution that depend upon the amount of dissolved solute, not the identity of the solute. Freezing point depression Boiling point elevation Osmotic Pressure Note: I will be weaving section 11.7 and the van’t Hoff factor (i) into my consideration of these properties and not consider it separately.

Colligative Properties FP = Kf m i BP = Kb m i See page 517 for needed constants

Calculating the bp or fp of a solution Calculating the molar mass of a solute from fp or bp data

Osmotic Pressure Osmotic Pressure (P) is often used to determine the molar mass of large biological molecules P = MRTi