Post on 13-Dec-2015
Solutions• Homogeneous mixtures containing
two or more substances.–Solvent- The substance that
dissolves
–Solute- The substance being dissolved
Solutions• May exist as a solid, liquid, or a
gas
• Water is the most prevalent solvent for solutions
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
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
Solvation
Water Molecules
Na Cl
Na Hydration Sphere
Cl Hydration Sphere
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.
Ionic Solutions• The water surrounds the ions,
dissolving the compound.
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
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
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
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
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
Factors That Effect Solubility
• Temperature- As temperature increases –solubility increases for solid
substances
–Solubility decreases for gaseous substances
Factors the Effect Solubility
• Pressure- As pressure increases–Solubility for gases increases
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
Practice Problem On Board
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
Percent to Describe Concentration
• Percent by mass• Percent by mass= Mass of solute X 100
Mass of Solution
Percent by Volume• Percent by volume• Percent by volume = Volume of Solute x 100
Volume of Solution
Molarity• Molarity (M) = Moles of solute
Liters of Solution
Expressed in moles per liter
Assignment• P. 463 8-10
• P. 464 11-13
• P. 465 14-16
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
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
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
Molality• Molality= moles of solute
kg of solvent
Mole Fraction• XA = nA
nA + nB
What is the mole fraction of HCl in a solution that contains 21% HCl?
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
Mole Fraction• 21gHCl 1 mole = .583 moles
36g HCl
79gH2O 1 mole = 4.39 moles
18g H2O
Mole Fraction• XA = nA
nA + nB
XHCl = .583 = .117 HCl
.583 + 4.39
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
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
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
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
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
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
Assignment• P. 466 17-20
• P. 468 21-23
• P. 469 24-25
• P. 470 26-30
• P. 475 33-39