1. Define solution (two parts) and give example
Solutions have variable composition, measured with concentration (define them)
Molarity, M
mass % you know these already
mole fraction

2. What is the mass percent of solute in a solution made by dissolving 13
What is the mass percent of solute in a solution made by dissolving 13.5 g glucose in kg of water?
What is the mole fraction of HCl in a solution that is 36% HCl by mass?
What is the M of a solution with a density of g/mL that contains 5.0 g toluene (C7H8) in 225 g benzene (C6H6)?

3. To prepare a solution must consider
Solubility: what factors affect solubility?
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this is the first factor that affects solubility and is based on molecular structure and IM forces
2. Thermodynamics; enthalpy and entropy
3. Does concentration (amount solute per solvent)
change properties of solution? (colligative properties)

4. Thermodynamics: ∆Hsoln
Three steps to dissolving
Solute must expand/separate
Solvent must expand to “mingle” with solute
Solute and solvent interact (form solution)
First two steps are endo/exo?
Third step is endo/exo?
Overall ∆Hsoln = ∆H1 + ∆H2 + ∆H3
∆Hhyd

5. Dissolve NaCl (s) in water
NaCl (s) → Na+ (g) + Cl- (g)
∆H1 = 786 kJ
Na+ (g) + Cl- (g) + H2O (l) → Na+ (aq) + Cl- (aq)
∆Hhyd = -783 kJ
∆Hsoln = 3 kJ (endothermic)
Why does NaCl dissolve in water if unfavorable reaction in terms of enthalpy?

6. Factors Affecting Solubility
Structure
Polar vs. nonpolar
IM forces
Pressure
Henry’s Law
Temperature
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7. Structure
Which solvent water or carbon tetrachloride to dissolve? What IM interactions in each solution?
Carbon dioxide
Ammonium nitrate
Pentane
Acetone

8. Arrange the following in order of increasing solubility in water
Arrange the following in order of increasing solubility in water. Pentane 1-pentanol 1,5-dipentanol 1-chloropentane

9. Pressure Generally, ↑P, ↑solubility Shown with Henry’s Law
Little effect on solids and liquds, larger effect for gases
Shown with Henry’s Law
C = kP or Sg = kPg
Can you explain this?

10. Temperature
↑T, ↑rate at which things dissolve, not necessarily the amount
Most solids and gases in non-aq solvent show that an ↑T, ↑solubility (next slide)
In water, gases ↓solubility with ↑T (thermal pollution)
Why these trends? Think about thermodynamics and KMT.

12. Physical Properties of Solutions
Presence of a solute affects properties of the solvent
Pvap lowering
Add solute to solvent, Pvap of solvent decreases
bp elevation
Add solute to solvent, bp solution > bp solvent
This why people put salt in water and why people in mtns have different cooking times
fp depression
Add solute to solvent, fp solution < fp solvent

13. Calculate the Pvap of the solution when 50
Calculate the Pvap of the solution when 50.0 g NaCl are added to 500 mL H2O. Pvap H2O = Torr