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Properties of Solutions SC 132 CHEM 2 Chemistry: The Central Science CM Lamberty
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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
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The Solution Process The Effect of Intermolecular Forces
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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
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Intermolecular Forces in Solution
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Predicting Solubilities in Different Solvents
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The Solution Process H soln = H lattice + H hydration of ions H soln = H solute + H solvent + H mix in ionic salt-aqueous solutions: H soln < 0 means that solution formation is favored!
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Why Oil and Water do not mix Give an explanation for this phenomena based on what we have just learned.
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Sol’n Formation, Spontaneity & Entropy CCl 4 and C 6 H 14 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
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Practice
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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
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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
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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: S g = kP g S g is solubility of gas K is Henry’s constant (solvent-solute pair dependent) P g is partial pressure of gas over the solution Carbonated Beverages
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Factors Affecting Solubility in Liquid Solvents Pressure Only relevant to S gas S gas = k H P gas
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Practice
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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
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Factors Affecting Solubility in Liquid Solvents Temperature S solids increase w/temp increase S gases decrease w/temp increase
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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!!!!
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Concentration TermRatio Mass percent (m %) Mass of component in soln Total mass of soln Parts per million Mass of component in soln Total mass of soln Ways of Experessing Concentration X 100 X 10 6 Parts per billion Mass of component in soln Total mass of soln X 10 9
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Concentration Term Ratio Molarity (M) amount (mol) of solute volume (L) of solution Molality ( m ) amount (mol) of solute mass (kg) of solvent Parts by mass mass of solute mass of solution Parts by volume volume of solute volume of solution Mole fraction amount (mol) of component Total moles of all component Ways of Experessing Concentration
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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).
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Practice
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PROBLEM: 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 H 2 O 2 is 30.0% by mass and has a density of 1.11 g/mL. Calculate its (a) Molality(b) Mole fraction of H 2 O 2 (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 H 2 O 2 (c) Mass %
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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 = X A P° A Boiling point elevation → T b = k b m Freezing point depression → T f = k f m Osmotic pressure → = MRT UNITS, UNITS, UNITS!!!!!
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Colligative Properties of Electrolyte Solutions P, T f, T b, 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
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Practice PROBLEM: Calculate the vapor pressure lowering, P, of a solution of 2.00g of aspirin (MM-180.15 g/mol) in 50g of methanol (CH 3 OH) at 21.2°C. Pure methanol has a vapor pressure of 101 torr at this temperature. PROBLEM: You add 1.00 kg of ethylene glycol (C 2 H 6 O 2 ) antifreeze to your car radiator which contains 4450g H 2 O. What are the boiling points and freezing points of the solution? (k f = 1.86°C/m and k b = 0.512°C/m for water) 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 (k f = 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
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Practice PROBLEM:A 0.952-g sample of magnesium chloride is dissolved in 100. g of water in a flask. (a) Which scene depicts the solution best? (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)? PROBLEM:The MgCl 2 in the above problem has a density of 1.006g/mL at 20.0°C. What is the osmotic pressure of the solution?
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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
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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)
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Colloids Removal Filtration will not work Coagulation: process by which the particles clump together Semipermeable membranes Dialysis
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