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SolutionsReview Voc. and the following concepts for quiz.
crystall lattice energyenthalpy of solutionsolvationhydrationhydration energymiscibilityimmisciblesaturatedunsaturated supersaturated
Dissolution depends on 2 factors. Name them.
Ionic solids dissolve by endo or exo process?
Which way does equilibrium shift when you raise the temperature of an endothermic reaction?
What is thermal pollution? What effect does it have on the environment?
The magnitude of the crystal lattice energy increases, with an increase or decrease charge and increase or decrease size of atoms.
Describe how you dilute an acid? Why do you do it this way?
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The colligative properties of a solution depend on the relative numbers (concentration) of solute and solvent particles, they do not depend on the nature of the particles. Colligative properties change in proportion to the concentration of the solute particles. We distinguish between four colligative properties: • vapor pressure lowering • freezing point depression • boiling point elevation • osmotic pressure.
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Enthalpy of Solution ΔHsoln = ΔH1 + ΔH2 + ΔH3
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Factors Affecting SolubilityStructure EffectsHydrophobic (waterfearing) nonpolar molecules are not likely to be watersolubleHydrophilic (waterloving) – molecules with many Hbonding sites
Pressure EffectsHenry’s Law gas solubility is directly proportional to the pressure of the gasover the solution.C = kPIf the gas reacts with the solution (i.e., NH3, CO2, O2 in blood) c will be muchhigher
Temperature EffectsSaturated Solution maximum amount of substance is dissolved at a given TUnsaturated Solution
Supersaturated solution unstablesolubility vs T solubility doesn’t change as ΔHsoln
Fractional Crystallization separation o f a mixture into pure components onbasis of varying solubility. Works best if substance has steep sol vs. T curve or ifamt of impurity is small
Gas solubility and T solubility always decreases with increasing TThermal pollution causes deoxygenization of water
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Hydrophobic (waterfearing) nonpolar molecules are not likely to be watersolubleHydrophilic (waterloving) – molecules with many Hbonding sites
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Compounds With Solubilities That Decrease with Increasing Temperature
CaSO4 Ca(OH)2 Na2SO4∙10H2O Ca(C2H3O2)2 Ce2(SO4)3 Li2SO4
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***Watch the units some chemist use the equation S=KP (solubility= Henrys constant x pressure)Henrys constant will have the units of M/atm for this equation
http://www.youtube.com/watch?v=8yU5ycFXoo
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P=KC
P=pressure of the gas (atm) K=Henry's Law Constant (atm/M)
C=Concentration of the Gas (M)
ExamplesThe Henry's law constant for He gas in water at 30°C is 2.70 x 103 atm/M.
The constant for N2 at the same temperature is 1.67 x 103 atm/M.
If the two gases are each present at 1.43 atm pressure, calculate the solubility, in M, of each gas.
C=P/K
He
1.43 atm / 2.70x103 atm/M = 5.30 x104 Molar
N2
1.43 atm/ 1.67 x 103 atm/M = 8.56 x104 Molar
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Vaporpressure lowering The equilibrium vapor pressure of a liquid is achievedwhen the rates of evaporation and condensation are equal. When particles ofsolute are added, the rate of evaporation of solvent is diminished, simply becausethe number of molecules close to the surface is reduced.
EXAMPLE: Determine the vapor pressure of a solution of 25.00 g sugar(C12H22O11) dissolved in 100.00 g water. The vapor pressure of pure water atroom temperature is 23.76 mm Hg.
SOLUTION: Sugar is a nonvolatile nonelectrolyte, so the vapor pressure of thesolution is the partial pressure of water by Raoult's Law. Determine the molefraction of water:
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Negative deviation occurs when unlike molecules are more strongly attracted to each other than are like molecules, thus, it is harder for molecules to escape the liquid phase. ΔHsoln < 0 Example, nitric acid and water.
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Positive deviation occurs when unlike molecules are less strongly attracted to each other than are like molecules, thus, it is easier for molecules to escape the liquid phase. ΔHsoln > 0 Example, ethanol and water.
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Freezingpoint depression is more sensitive to the number of moles of solute than the boilingpoint elevation because for the same solvent Kf is larger then Kb. The most sensitive method for the determination of the molar mass of a solute is to measure the osmotic pressure. The equation for osmotic pressure then becomes useful in the following form:
These methods are particularly useful for determining the molar masses of large molecules such as proteins and polymers.
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