Chemistry 1 Chapter 15 Part 2

Definitions Colligative properties: physical properties of solutions that are affected by the number of particles but not the identity of dissolved solute particles, means “depending on the collection” Vapor pressure lowering Boiling point elevation Freezing point depression Osmotic pressure

Definitions Electrolytes  ionic compounds that ionize to form ions in solution and may conduct electricity Non-electrolytes  molecular compounds (covalently bonded) may dissolve but do not ionize and are non conductive. Vapor Pressure Lowering occurs when solute particles (Non-volatile) in solution cause the vapor pressure to be lowered and is a colligative property.

Definitions Boiling Point Elevation: the temperature difference between a solution’s boiling point and a pure solvent’s boiling point Freezing Point Depression: the difference in temperature between a solution’s freezing point and the freezing point of its pure solvent

Solution Composition Reminder 1. Molarity (M) = 2. Mass or Volume percent = 3. Mole fraction (A) = 4. Molality (m) =

Colligative Properties of Electrolyte Solutions van’t Hoff factor, “i”, relates to the number of ions per formula unit. NaCl = 2, K2SO4 = 3

Freezing-Point Depression A solution always has a lower freezing point than the corresponding pure solvent. If you are interested only in aqueous solutions, this means that any aqueous solution will have a freezing point lower than 0°C. The amount that the freezing point is depressed relative to 0°C depends only upon the concentration of the solute.

Freezing Point Depression A nonvolatile solute depresses the freezing point of the solvent. T = iKfmsolute Kf = molal freezing point depression constant m = molality of the solute

Boiling-Point Elevation You have just learned that the freezing point of a solution is lower than the freezing point of the pure solvent. It turns out that the boiling point of a solution is higher than the boiling point of the pure solvent.

Boiling Point Elevation A nonvolatile solute elevates the boiling point of the solvent. T = iKbmsolute Kb = molal boiling point elevation constant m = molality of the solute Kb units oC*kg/mol

Boiling-Point Elevation For aqueous solutions this means that the solution boiling point will be greater than 100°C, assuming standard atmospheric pressure. The solute must also be nonvolatile; that is not able to evaporate readily.

Osmosis The flow of solvent molecules through a selectively permeable membrane, driven by concentration difference, is called osmosis.

Colloids Sometimes, mixtures are partway between true solutions and heterogeneous mixtures. Such mixtures, called colloids, contain particles that are evenly distributed through a dispersing medium, and remain distributed over time rather than settling out. The major difference between a colloid and a solution is the size of the solute particles.

Colloids Colloid particles are generally clumps that are ten to 100 times larger than typical ions or molecules dissolved in solutions. Because of their relatively large particle size, colloids play important roles in a variety of processes. Some biological molecules, such as proteins, are large enough that their behavior is often best understood using a colloid model.

Definitions Brownian Motion Erratic movement (vibrations) of colloid particles (As seen if viewed in a microscope) Brownian_motion_large.gif

Definitions Tyndall Effect  scattering of light by colloid particles

Suspension A mixture containing particles that settle out of solution if left undisturbed.