Learning objectives Know the factors that affect solubility Know the different ways to measure concentration and how to convert between them Understand the effect of solutes on solution properties Solubility = like dissolves like interactions broken are of similar strength hexanol in water hexanol Effect of Temperature Solids: Gases: solids gases similar for all gasses more heat energy ? more E to overcome forces depends on the solid Effect of Pressure: Gases gas + solvent saturated solution Henry?s Law Sgas = kH ? pgas How do we describe solutions? Solubility (S) Maximum amount of solute in a solvent at some temp S(NaCl) = 39.12 g NaCl / 100. mL water at 100 °C Molarity (M) Moles solute / volume (L) solution Molality (m) Moles solute / kg solvent Parts by mass (% mass) or volume Mass solute/(mass solute + mass solvent) × 100% Volume solute/(volume solute + volume solvent) × 100% Mole fraction (C) Moles solute / (moles solute + moles solvent) Colligative Properties properties that depend on the number of particles, not their type Vapor pressure lowering Boiling point elevation Freezing point depression Osmotic pressure Strong electrolytes Strong electrolyte: NaCl(s) ? FeCl3(s) ? Nonelectrolyte: CH3CH2OH(l) ? Vapor pressure lowering Vapor pressure: the pressure of gas X above X in the liquid- (or solid-) phase when # molecules condensing = # molecules vaporizing Raoult?s Law DP= i ? Csolute ? P?solvent ConcepTest A solution is made from two liquids. To make the solution, the liquids are mixed in equal proportions. The vapor pressure of pure A is 25 mm Hg. The vapor pressure of pure B is 75 mm Hg. A. There is more A than B in the vapor phase . B. The amounts of A and B in the vapor phase are equal. C. There is less A than B in the vapor phase . Boiling point elevation & Freezing point depression Condition for boiling: Condition for freezing: DTb= iKbm DTf= iKfm ConcepTest Under identical experimental circumstances, if NaCl is replaced an equal number of moles of CaCl2 as a solute in water, how will the freezing point compare? A. Higher temperature with CaCl2 B. Same temperature with CaCl2 C. Lower temperature with CaCl2 Osmotic Pressure (?) ??? nsolute Vsolution ??= nRT V ??= MRT
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