solutions homogeneous mixtures containing two or more substances. –solvent- the substance that...
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Solutions• Homogeneous mixtures containing
two or more substances.–Solvent- The substance that
dissolves
–Solute- The substance being dissolved
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Solutions• May exist as a solid, liquid, or a
gas
• Water is the most prevalent solvent for solutions
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Solubility• Soluble- Can be dissolved• Insoluble- Cannot be dissolved• Immiscible- When one liquid will
not dissolve in another• Miscible- When one liquid will
dissolve in another liquid
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Solvation• The act of dissolving a solute• A solute will dissolve when the
attractive forces between the solute and the solvent are greater than the attractive forces holding the molecule together
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Solvation
Water Molecules
Na Cl
Na Hydration Sphere
Cl Hydration Sphere
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Ionic Solutions• As you recall H2O is a polar molecule
(charged on each end)• An ionic compound is composed of a
+ and – Ion. These ions are attracted to the oppositely charged end of the water molecule, pulling the ionic compound apart.
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Ionic Solutions• The water surrounds the ions,
dissolving the compound.
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Covalent Molecules• Water is also a good solvent for some
molecular compounds. • Sucrose is a polar molecular compound.
Water is also a polar molecule attracts the oppositely charged end of the sugar molecule.
• This pulls them apart causing solvation by water
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Factors that Affect the Rate of Solvation
• Increasing the collisions of solvent and solute increases the solvation rate–Ways to increase collisions
• Increase the surface area of the solute
• Increase the temperature of the solution
• Agitate the mixture
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Heat of Solution• The amount of energy required to
form a solution–It takes energy to overcome the
attractive forces that hold solute molecules together
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Solubility• The maximum amount of solute
that can be dissolved at a given temperature and pressure
• Expressed in grams of solute per 100g of solvent
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Types of Solutions• Saturated Solution- A solution that
contains the maximum amount of solute that it can hold.
• Unsaturated Solution- A solution that can dissolve more solute
• Supersaturated Solution- A solution that contains more solute than can normally be held in solution
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Factors That Effect Solubility
• Temperature- As temperature increases –solubility increases for solid
substances
–Solubility decreases for gaseous substances
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Factors the Effect Solubility
• Pressure- As pressure increases–Solubility for gases increases
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Henry’s LawS1 = S2P1 P2At a given temperature the solubility
of a gas in a liquid is directly proportional to the pressure of a gas above the liquid
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Practice Problem On Board
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Concentration• A measure of how much solute is
dissolved in a specific amount of solvent–Concentrated- Lots of solute per
volume
–Dilute- Little solute per volume
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Percent to Describe Concentration
• Percent by mass• Percent by mass= Mass of solute X 100
Mass of Solution
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Percent by Volume• Percent by volume• Percent by volume = Volume of Solute x 100
Volume of Solution
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Molarity• Molarity (M) = Moles of solute
Liters of Solution
Expressed in moles per liter
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Assignment• P. 463 8-10
• P. 464 11-13
• P. 465 14-16
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Preparing Molar Solutions
• How would you make a 1.5 molar solution of sucrose?
• 1.5 mol X 342g = 513g
• 1 L 1 mol 1 L
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Preparing Molar Solutions
• How would you prepare 100ml of a 1.5 molar solution?
• 100ml X 1L X 513g = 51.3g
1000 ml 1 L
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Diluting Solutions• M1V1=M2V2
• What volume (in ml) of a 12 M stock solution would be needed to make 50ml of a 2.5 M solution?
• (12M)(V1) = (2.5M)(.050L)
• 12V1= .125 V1= .0104L= 10.4ml
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Molality• Molality= moles of solute
kg of solvent
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Mole Fraction• XA = nA
nA + nB
What is the mole fraction of HCl in a solution that contains 21% HCl?
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Mole Fraction• Assume there is 100g of solution
• This means that 21g of the solution is HCl and that 79g of the solution is water
• Convert both to moles
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Mole Fraction• 21gHCl 1 mole = .583 moles
36g HCl
79gH2O 1 mole = 4.39 moles
18g H2O
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Mole Fraction• XA = nA
nA + nB
XHCl = .583 = .117 HCl
.583 + 4.39
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Colligative Properties• Properties that depend on the number
of particles in the solution but not the identity of the particles–Freezing point depression–Vapor pressure lowering–Boiling point elevation–Osmotic pressure
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Electrolytes and Nonelectrolytes
• Electrolytes- Compounds that completely ionize in solution causing it to conduct electricity–Usually ionic compounds
• Nonelectrolytes- Compounds that do not ionize in solution and do not conduct electricity–Usually molecular compounds
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Vapor Pressure Lowering• When a solute is dissolved in a liquid
the vapor pressure is lower above the solution than the vapor pressure of the pure solvent
• This is due to fewer solvent particles at the interface between the air and the surface of the solvent
• See diagram on p. 472
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Boiling Point Elevation• The boiling point of a solvent increases
as solute is added to the solventTb = Kbm• Kb= molal boiling point constant• m = molality of the solutionTb =Value of boiling point elevation
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Freezing Point Depression• As solute is added to a solvent the
freezing point is loweredTf = Kfm• Kf= molal freezing point constant• m = molality of the solutionTf =Value of freezing point depression
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Osmosis and Osmotic Pressure
• Osmotic pressure increases with increase in amount of solvent
• Solute increases the number of solvent molecules that move across a membrane increasing the pressure
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Assignment• P. 466 17-20
• P. 468 21-23
• P. 469 24-25
• P. 470 26-30
• P. 475 33-39