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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 LIKESubstances 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
Intermolecular Forces in Solution
Predicting Solubilities in Different Solvents
The Solution Process
Hsoln = Hlattice + Hhydration of ions
Hsoln = Hsolute + Hsolvent + Hmix
in ionic salt-aqueous solutions:
Hsoln < 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
Practice
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
Practice
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 SolventsTemperature 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!!!!
Concentration Term Ratio
Mass percent (m %) Mass of component in solnTotal mass of soln
Parts per millionMass of component in soln
Total mass of soln
Ways of Experessing Concentration
X 100
X 106
Parts per billionMass of component in soln
Total mass of solnX 109
Concentration Term Ratio
Molarity (M)amount (mol) of solutevolume (L) of solution
Molality (m) amount (mol) of solute
mass (kg) of solvent
Parts by massmass of solute
mass of solution
Parts by volumevolume of solute
volume of solution
Mole fraction amount (mol) of component
Total moles of all component
Ways of Experessing Concentration
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).
Practice
Practice 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 H2O2 is 30.0% by mass and has a density of 1.11 g/mL. Calculate its
(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, P, 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.
PROBLEM: 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: 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
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 MgCl2 in the above problem has a density of 1.006g/mL at 20.0°C. What is the osmotic pressure of the solution?
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