Classification of Matter Solutions are homogeneous mixtures
Solute A solute is the dissolved substance in a solution. A solvent is the dissolving medium in a solution. Solvent Salt in salt water Sugar in soda drinks Carbon dioxide in soda drinks Water in salt waterWater in soda
Calculations of Solution Concentration Mass percent - the ratio of mass units of solute to mass units of solution, expressed as a percent
Calculations of Solution Concentration Mole fraction – the ratio of moles of solute to total moles of solution
Calculations of Solution Concentration Molality – moles of solute per kilogram of solvent
Calculations of Solution Concentration Molarity - the ratio of moles of solute to liters of solution
Heat of Solution The Heat of Solution is the amount of heat energy absorbed (endothermic) or released (exothermic) when a specific amount of solute dissolves in a solvent. Substance Heat of Solution (kJ/mol) NaOH-44.51 NH 4 NO 3 +25.69 KNO 3 +34.89 HCl-74.84
Steps in Solution Formation H 1 Expanding the solute H 2 Expanding the solvent H 3 Interaction of solute and solvent to form the solution Separating the solute into individual components Overcoming intermolecular forces of the solvent molecules
“Like Dissolves Like” Fats Benzene Benzene Steroids Steroids Hexane Hexane Waxes Waxes Toluene Toluene Polar and ionic solutes dissolve best in polar solvents Nonpolar solutes dissolve best in nonpolar solvents Inorganic Salts Water Water Sugars Sugars Small alcohols Small alcohols Acetic acid Acetic acid
Predicting Solution Formation Solvent/Solute H1H1H1H1 H2H2H2H2 H3H3H3H3 H sol’n Outcome Polar/Polar + large - large +/- small Solutionforms Polar/Nonpolar + small + large +/- small + large No solution forms Nonpolar/Nonpolar + small +/- small +/-smallSolutionforms Nonpolar/polar + large + small +/- small + large No solution forms
Solubility Trends The solubility of MOST solids increases with temperature. The rate at which solids dissolve increases with increasing surface area of the solid. The solubility of gases decreases with increases in temperature. The solubility of gases increases with the pressure above the solution.
Therefore… Solids tend to dissolve best when: o Heated o Stirred o Ground into small particles Liquids tend to dissolve best when: o The solution is cold o Pressure is high
Saturation of Solutions A solution that contains the maximum amount of solute that may be dissolved under existing conditions is saturated. A solution that contains less solute than a saturated solution under existing conditions is unsaturated. A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.
Henry’s Law The concentration of a dissolved gas in a solution is directly proportional to the pressure of the gas above the solution Applies most accurately for dilute solutions of gases that do not dissociate or react with the solvent Yes CO 2, N 2, O 2 No HCl, HI
Raoult’s Law The presence of a nonvolatile solute lowers the vapor pressure of the solvent. P solution = Observed Vapor pressure of the solution P 0 solvent = Vapor pressure of the pure solvent solvent = Mole fraction of the solvent
Liquid-liquid solutions in which both components are volatile Modified Raoult's Law: P 0 is the vapor pressure of the pure solvent P A and P B are the partial pressures
Raoult’s Law – Ideal Solution A solution that obeys Raoult’s Law is called an ideal solution
Negative Deviations from Raoult’s Law Strong solute-solvent interaction results in a vapor pressure lower than predicted Exothermic mixing = Negative deviation
Positive Deviations from Raoult’s Law Weak solute-solvent interaction results in a vapor pressure higher than predicted Endothermic mixing = Positive deviation
An electrolyte is: A substance whose aqueous solution conducts an electric current. A nonelectrolyte is: A substance whose aqueous solution does not conduct an electric current. Try to classify the following substances as electrolytes or nonelectrolytes… Definition of Electrolytes and Nonelectrolytes
The ammeter measures the flow of electrons (current) through the circuit. If the ammeter measures a current, and the bulb glows, then the solution conducts. If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting. Electrolytes vs. Nonelectrolytes
ELECTROLYTES: NONELECTROLYTES: Tap water (weak) NaCl solution HCl solution Lactate solution (weak) Pure water Sugar solution Ethanol solution Pure NaCl Answers to Electrolytes
Colligative Properties Colligative properties are those that depend on the concentration of particles in a solution, not upon the identity of those properties. Boiling Point Elevation Freezing Point Depression Osmotic Pressure
Freezing Point Depression Each mole of solute particles lowers the freezing point of 1 kilogram of water by 1.86 degrees Celsius. K f = 1.86 C kilogram/mol m = molality of the solution van’t Hoff i = van’t Hoff factor
Boiling Point Elevation Each mole of solute particles raises the boiling point of 1 kilogram of water by 0.51 degrees Celsius. K b = 0.51 C kilogram/mol m = molality of the solution van’t Hoff i = van’t Hoff factor
Freezing Point Depression and Boiling Point Elevation Constants, C/ m SolventKfKf KbKb Acetic acid3.903.07 Benzene5.122.53 Nitrobenzene8.15.24 Phenol7.273.56 Water1.860.512
The van’t Hoff Factor, i Electrolytes may have two, three or more times the effect on boiling point, freezing point, and osmotic pressure, depending on its dissociation.
Dissociation Equations and the Determination of i NaCl(s) AgNO 3 (s) MgCl 2 (s) Na 2 SO 4 (s) AlCl 3 (s) Na + (aq) + Cl - (aq) Ag + (aq) + NO 3 - (aq) Mg 2+ (aq) + 2 Cl - (aq) 2 Na + (aq) + SO 4 2- (aq) Al 3+ (aq) + 3 Cl - (aq) i = 2 i = 3 i = 4
Ideal vs. Real van’t Hoff Factor The ideal van’t Hoff Factor is only achieved in VERY DILUTE solution.
Osmotic Pressure The minimum pressure that stops the osmosis is equal to the osmotic pressure of the solution
Osmotic Pressure Calculations = Osmotic pressure M = Molarity of the solution R = Gas Constant = 0.08206 L atm/mol K = Osmotic pressure
Suspensions and Colloids Suspensions and colloids are NOT solutions. Suspensions: The particles are so large that they settle out of the solvent if not constantly stirred. Colloids: The particles intermediate in size between those of a suspension and those of a solution.