Properties of Solutions SC 132 CHEM 2 Chemistry: The Central Science CM Lamberty
Homework • Chapter 13 • 14, 16, 18, 20 • 22a, 24, 28, 30, 32, 34 • 36, 38, 40, 42, 44, 46, 48, 50, 52, 54 • 60, 64, 66, 68, 70, 72, 74, 76, 78, 86, • 89, 91, 98, 112
The Solution Process • The Effect of Intermolecular Forces
The Solution Process LIKE DISSOLVES LIKE Substances with similar types of intermolecular forces dissolve in each other. When a solute dissolves in a solvent, solute-solute interactions and solvent-solvent interactions are being replaced with solute-solvent interactions. The forces must be comparable in strength in order to have a solution occur. Solvation: Interactions between solute and solvent molecules. Hydration: when solvent is water
The Solution Process DHsoln = DHsolute + DHsolvent + DHmix in ionic salt-aqueous solutions: DHsoln = DHlattice + DHhydration of ions DHsoln < 0 means that solution formation is favored!
Why Oil and Water do not mix • Give an explanation for this phenomena based on what we have just learned.
Sol’n Formation, Spontaneity & Entropy • CCl4 and C6H14 dissolve at all proportions • Similar bp, both nonpolar, similar forces • Spontaneity determined by • Energy • generally if E content decreases, or exothermic • Distribution of each component • generally greater entropy • Entropy: the randomness or dispersal in space of the system • System is no longer ordered substances
Saturated Solutions and Solubility • Crystallization • Solute particles reattaching to each other • Saturated • Solution in equilibrium w/ undissolved solute • Solubility • Max. amt of solute that will dissolve in given amt of solvent at specific temperature • Unsaturated • Less solute than needed for saturated solution • Supersaturated • More solute than needed for saturated solution
Factors Affecting Solubility • Solute-Solvent Interactions • The stronger the attractions between solute and solvent the greater the solubility • Like dissolves like • Miscible: mix in all proportions • Immiscible: do not dissolve in one another • Table 13.3 Sol of alcohols in water and hexane • solute-solute, solute-solvent and solvent-solvent
Factors Affecting Solubility • Pressure Effects • Solubilities of solids/liquids not affected • Great effect on gases • Solubility of gas increases in direct proportion to is partial pressure above the solution • Henry’s Law: Sg = kPg • Sg is solubility of gas • K is Henry’s constant (solvent-solute pair dependent) • Pg is partial pressure of gas over the solution • Carbonated Beverages
Factors Affecting Solubility in Liquid Solvents Pressure Only relevant to Sgas Sgas = kHPgas
Factors Affecting Solubility • Temperature Effects • Solubility of most solid solutes in water increases as the temperature of the solution increases • Solubility of gases in water decreases with increasing temperature • Decreased O2 solubility result of thermal pollution
Factors Affecting Solubility in Liquid Solvents Temperature • Ssolids increase w/temp increase • Sgases decrease w/temp increase
Solution Concentration • Measure of the proportion of a substance in a mixture • Units can always be expressed in fractions • Solute quantity is in numerator, solvent/solution quantity is in denominator • When solving problems involving solution concentration, use fraction representation of concentration unit • UNITS, UNITS, UNITS!!!!
Mass of component in soln Mass percent (m %) Total mass of soln Mass of component in soln Mass of component in soln Parts per million Parts per billion Total mass of soln Total mass of soln Ways of Experessing Concentration Concentration Term Ratio X 100 X 106 X 109
amount (mol) of solute Molarity (M) volume (L) of solution amount (mol) of solute Molality (m) mass (kg) of solvent mass of solute Parts by mass mass of solution volume of solute Parts by volume volume of solution amount (mol) of component Mole fraction Total moles of all component Ways of Experessing Concentration Concentration Term Ratio
Interconverting Concentration Terms • To convert a term based on amount (mol) to one based on mass, you need the molar mass. These conversions are similar to mass-mole conversions. • To convert a term based on mass to one based on volume, you need the solution density. • Molality involves quantity of solvent, whereas the other concentration terms involve quantity of solution (solvent + solute).
Hydrogen peroxide is a powerful oxidizing agent used in concentrated solution in rocket fuels and in dilute solution a a hair bleach. An aqueous solution H2O2 is 30.0% by mass and has a density of 1.11 g/mL. Calculate its PROBLEM: Practice (a) Molality (b) Mole fraction of H2O2 (c) Molarity PROBLEM: A sample of commercial concentrated hydrochloric acid is 11.8M and has a density of 1.190g/mL. Calculate its (a) Molality (b) Mole fraction of H2O2 (c) Mass %
Colligative Properties of Solutions • 4 properties for which only the amount of solute particles affect values, not chemical identity of solute • Vapor pressure lowering → P = XAP°A • Boiling point elevation → Tb = kbm • Freezing point depression → Tf = kfm • Osmotic pressure → = MRT • UNITS, UNITS, UNITS!!!!!
Colligative Properties of Electrolyte Solutions • P, Tf, Tb, and are always greater for an electrolyte solution with the same concentration as a nonelectrolyte one • This is because electrolyte solutions dissociate into separate pieces making the apparent solution concentration greater • Deviations from expected values can be quantified by the van’t Hoff factor, i
Practice PROBLEM: Calculate the vapor pressure lowering, DP, of a solution of 2.00g of aspirin (MM-180.15 g/mol) in 50g of methanol (CH3OH) at 21.2°C. Pure methanol has a vapor pressure of 101 torr at this temperature. You add 1.00 kg of ethylene glycol (C2H6O2) antifreeze to your car radiator which contains 4450g H2O. What are the boiling points and freezing points of the solution? (kf = 1.86°C/m and kb = 0.512°C/m for water) PROBLEM: PROBLEM: How many grams of NaCl must be added to a 5.00 gallon bucket filled with water (d = 1.00g/mL) to prevent the water from freezing at -10°C (kf = 1.86°C/m for water) PROBLEM: A physician studying a particular variant of hemoglobin associated with sickle cell anemia must first determine its molar mass, which she will do by measuring its osmotic pressure. She dissolves 21.5mg of hemoglobin in water at 5.0°C to make 1.50mL of solution and measures an osmotic pressure of 3.61 torr. What is the molar mass of this variety of hemoglobin
PROBLEM: PROBLEM: A 0.952-g sample of magnesium chloride is dissolved in 100. g of water in a flask. The MgCl2 in the above problem has a density of 1.006g/mL at 20.0°C. What is the osmotic pressure of the solution? (a) Which scene depicts the solution best? Practice (b) What is the amount (mol) represented by each green sphere? (c) Assuming the solution is ideal, what is its freezing point (at 1 atm)?
Colloids • Intermediate type of dispersion or suspension • Dividing line between solutions and heterogeneous solutions • Size of dispersed particle 5-1000nm • May be several atoms/ions or one large one • Scatter light • Homogenized milk
Colloids • Hydrophilic and Hydrophobic Colloids • Hydrophilic (water loving) • Hemoglobin, enzymes and antibodies • Molecules fold so that hydrophobic groups on inside away from water • Hydrophobic (water fearing) • Must be stabilized in water • Adsorption of ions on sfc • Oil slick on water • Bile from gallbladder helps digest fats (emulsify the fat)
Colloids • Removal • Filtration will not work • Coagulation: process by which the particles clump together • Semipermeable membranes • Dialysis