1. Solutions
Chapter 11

2. Why do solutions form?
Energy lowering? Increase in disorder? (enthalpy) (entropy) ∆Hsln: separate solute ; ∆H1 endothermic separate solvent ; ∆H2 endothermic solute-solvent ; ∆H3 exothermic interactions

3. ∆Hsln= ∆H1 + ∆H2 + ∆H3 ∆Hhydration ∆H2 + ∆H3 No s`eparation of solute b/c H2O just surrounds molecule

4. Solution A mixture of two substances that has a uniform compostition
Can be
Solid – liquid (where solid dissolves)
Solid –Solid
Liquid – liquid
Gas –gas
Liquid - gas

5. 3 Factors Affecting Solubility
Structure
Polar Solvent (H2O)
Gaseous Solute
More LDF (more e-) = more soluble
More polar….more soluble
Liquid Solute:
More polar = more soluble
Solid Solute:
Ionic
Lower LE = more soluble
Covalent solids – polar= more soluble

6. Non-Polar solvents (CCl4, C6H6- benzene, C10H8-toluene)
Organic compounds – alcohols
C-H bond is non-polar
Not soluble (hydrophobic)
Alcohols C C-O-H
O-H is polar….soluble
More O-H bonds = more soluble
Non-Polar solvents (CCl4, C6H6- benzene, C10H8-toluene)
Non polar solutes

7. Pressure Gas-gas solution Gas – liquid No effect (Boyle’s Law)
Greater the pressure, the greater the solubility of a gas
Henry’s Law- the amount of gas dissolved is directly porportional to pressure
Has limitations: closely obeyed for dilute slns. Of gases that do not react or dissociate
O2 and H2O – obey
HCl and H2O –No
SO2 and H2O-

8. Temperature- Gas- Gas sln Gas-liquid sln Solid liquid solution
No affect
Gas-liquid sln
Increase temp = decrease solubility
Solid liquid solution
Depends on ∆Hsln
Hard to predict so must be tested in lab

9. Reminder of solution Concentrations
Molarity – 5M “five molar”
Moles solute/L solution
Mass Percent
Mass solute/mass solution
Mole fraction (usually used with gases)
Moles substance/total moles of mixture
Molality = 5m “five molal”
Moles solute/kg solvent

10. Colligative Properties
Colligative properties are properties of a solution that depend only on the number of solute particles not the identity of the solute.
Freezing Point Depression
Boiling point elevation
Vapor Pressure lowering
Osmotic pressure

11. Vapor Pressure Lowering
The addition of nonvolatile solute lowers the vapor pressure of the liquid solvent.
 PA = XAPA
Ex 1: The vapor pressure of water at 30C is 31.8 mm Hg. What is the vapor pressure of a solution prepared by dissolving 396 g of sucrose (C12H22O11) in 624 g of water?

12. PA = XAPA PB = XBPB PA + PB = Ptotal
Two or more volatile components:
PA = XAPA PB = XBPB PA + PB = Ptotal
  (Raoult’s Law)
Ex 2: The vapor pressures of ethanol (C2H5OH) and methanol (CH3OH) are 44 mm Hg and 94 mm Hg at 20C. A solution is prepared by mixing 30.0 g of methanol with 40.0 g of ethanol. What is the vapor pressure of the solution and what is the mole fraction of methanol in the vapor?

13. Ideal Solution
The vapor pressure of the mixture is = the sum of the vapor pressures of each substance Raoult’s Law
Positive deviation
adhesive forces b/t A and B weaker than cohesive forces between A-A and B-B
Solute-solvent – no attraction ….more evaporation….observed pressure > calculated
Negative deviation
adhesive forces between A and B are stronger than the cohesive forces of A-A to B-B solute-solvent attraction, less evaporation, lower V.P.
observed pressure < calculated

14. Boiling Point Elevation
The addition of a nonvolatile solute raises the boiling point of the solvent.
Tb = kb m
Freezing Point Depression
The addition of a nonvolatile solute lowers the freezing point of the solvent.
Tf = kf m

15. Ex 3: What are the freezing point and boiling point of a solution prepared by dissolving 651 g of ethylene glycol, CH2(OH)CH2(OH), in 2505 g of water?
Ex 4: A solution of 0.85 g of an organic compound in g of benzene has a freezing point of 5.16C. Determine the molar mass of the solute.

16. Osmotic Pressure  = MRT
Osmosis is the flow of solvent through a semi-permeable membrane. The osmotic pressure is the pressure required to just stop this osmosis.
 = MRT
Dilute solutions (small concentrations) can produce large, easily measured osmotic pressures 

17. Reverse Osmosis Semi –permeable membrane only allows water through.

18. Hypotonic with respect to urea--- flows with the concentration gradient
Remove water and urea