Chapter Ten.doc

Chemistry II CHP10: Solutions Solution= homogeneous mixture of a solute (being dissolved) through a solvent (doing the dissolving) Physical states: gas, liquid, solid Concentration Units= Molarity (M): moles of solute / liters solution [1.0L] Concentrated solution = Dilute solution ; moles of solute always stay the same [McVc=MdVd] Mole fraction (X): moles / total moles [1mol] Mass percent: mass of solute or solvent / total mass solution x 100% [100g] Parts per million= 106 Parts per billion= 109 Molality (m): moles of solute / kilograms solvent [1000g] The extent to which a solute dissolves in solvent depend on: nature of solvent and solute particles and interactions between them temperature at which solution is formed pressure of gaseous solute Hydrogen bonds lead to low solubility Organic compounds that dissolve readily in water: methyl alcohol, ethyl alcohol, ethylene glycol; this is because of the ?OH group as molar mass increases, the polar ?OH group become increasingly smaller portion and nonpolar hydrocarbon portion becomes larger which makes solubility decrease (solubility also deals with vitamins because if it dissolves fast then you must consume everyday) Balance between two forces, both electrical in nature that deals with solubility: force of attraction between water molecules and ions which brings solid into solution force of attraction between oppositely charged ions which keeps them in solid state; low solubility *An increase in temperature always shifts the position of an equilibrium to favor an endothermic process Dissolving a solid or liquid is endothermic and heat must be absorbed [Cg=kPg] Henery?s law: concentration in the solution is equal to constant of gas-liquid system multiply by partial pressure of gas over solution (?bend? is when go from high pressure to low pressure really fast while SCUBA, cause bubbles) Colligative properties: properties of a solution that depend primarily on concentration of solute particles rather than their nature; vapor pressure lowering, osmotic pressure, boiling point elevation, freezing point depression Regarded as limiting laws when become more dilute; valid for nonelectrolytes to concentrations as high as 1 M; at higher concentrations, solute-solute interactions lead to larger deviations Vapor pressure lowering: true colligative property, independent of nature of solute but directly ] proportional to its concentration [P1=X1PO1] Raoult?s law: vapor pressure of solvent over solution is equal to vapor pressure of pure solvent at same temperature times the mole fraction of solvent or because X1=1-X2, [deltaP=X2PO1] Boiling point elevation or difference in temperature [deltaTb=Tb-TOb] Freezing point lowering [deltaTf=TOf-Tf]; direct result of solvent vapor pressure lowering Molal boiling and freezing point constant: kb=0.52oC/m ; kf=1.86oC/m Vapor pressure or mole fraction moves from high to low Osmosis: solvent moves from high pressure to low Reverse osmosis: when external pressure is larger than osmotic pressure Osmotic pressure: colligative property, nonelectrolyte is directly proportional to molarity [(=nRT/V = MRT] Colligative properties used to determine molar masses of nonelectrolytes and are directly proportional to concentration of solute particles; electrolyte have a greater effect than nonelectrolyte, this is because: electrostatic attraction, an ion in solution tends to surround itself with more ions of opposite charge oppositely charged ions may interact strongly enough to form a discrete specie called an ion pair