Presentation on theme: "Chapter 13- Unit 2 Colligative Properties - are properties of solutions that depend on the number of molecules in a given volume of solvent and not on."— Presentation transcript:
1 Chapter 13- Unit 2Colligative Properties - are properties of solutions that depend on the number of molecules in a given volume of solvent and not on the properties/identity (e.g. size or mass) of the molecules
2 Vapor-Pressure Lowering Nonvolatile Substance- A substance that has little tendency to become a gas under existing conditions.Adding a nonvolatile solute to a solvent always lowers the vapor pressure.
3 Freezing-Point Depression Freezing-Point Depression(Δtf)- the difference between the freezing points of the pure solvent and a solution of a non- electrolyte in that solvent, and it is directly proportional to the molal concentration of the solutionΔtf = KfmMolal freezing point constant (Kf)- the freezing point depression of the solvent in a 1-molal solution of a nonvolatile, nonelectrolyte solute.Molality (m) – mol solute/kg of solvent
5 Practice ProblemA water solution containing an unknown quantity of a nonelectrolyte solute is found to have a freezing point of -0.23°C. What is the molal concentration of the solution?m= / KfΔtf = f.p of solution – f.p of pure solvent = -0.23°C – 0.00°C = -0.23°Cm= 0.12mΔtf
6 Boiling-Point Elevation Boiling-Point Elevation- the difference between the boiling points of the pure solvent and a solution of a non-electrolyte in that solvent, and it is directly proportional to the molal concentration of the solutionΔtb= Kbm*Molal freezing point constant (Kb)Example - antifreeze
7 Osmotic PressureOsmosis- The movement of solvent through a semipermeable membrane from the side of lower solute concentration to the side of higher solute concentrationSemipermeable membrane- allows the passage of some particles while blocking the passage of othersOsmotic Pressure- the external pressure that must be applied to stop osmosisBecause osmotic pressure is dependent on the concentration of solute particles and not on the type of solute particles, it is a colligative propertyThe greater the concentration of a solution, the greater the osmotic pressure