1. Mole fraction, Molarity
Moles of solute
Molarity =
Liters of solution
What is the molarity of an ascorbic acid solution (C6H8O6) prepared by dissolving
1.80 grams in enough water to make 125 mL of solution. How many milliliters of this
solution contain mol ascorbic acid.
1 mol C6H8O6
= mol C6H8O6
1.80 g C6H8O6
176 g C6H8O6
mol C6H8O6
Molarity =
= M
.125 L soln

2. Solvation or hydration
Properties of Solutions: The Solution Process
Solvation or hydration
Cl-
Na+
Na+ -
Na+ +
Cl- -
Cl- -
Na+ +
Na+ +
Cl- -
Na+ +
Cl-
Cl-
Cl-

3. Properties of Solutions: The Solution Process
Energy Changes and Solution Formation
Solute-solute interactions
Solvent-solvent interactions
Solute-solvent interactions
 Hsoln =  H1 +  H2 +  H3

4. Properties of Solutions: The Solution Process
Energy Changes and Solution Formation
NaOH:  Hsoln =
NH4OH:  Hsoln = 26.4
The overall change in enthalpy can be exo- or endothermic
This explains why “like dissolves like”

5. Properties of Solutions: Solution Formation, Spontaneity
and Disorder…WHY DOES THIS STUFF DISSOLVE?
London dispersion forces
bp = 77
bp = 69
Little energy is exchanged

6. Properties of Solutions: Solution Formation, Spontaneity
and Disorder…WHY DOES THIS STUFF DISSOLVE?
Processes in which the energy content of the system decreases tend to occur
spontaneously.
Processes in which the disorder of the system increases tend to occur spontaneously
When molecules of different types are brought together, an increase in disorder occurs
spontaneously unless the molecules are restrained sufficiently by strong intermolecular
forces. Salt does not dissolve in gasoline because strong forces are holding the Na+ and
Cl- ions together and the intermolecular forces associated with nonpolar substances is
not sufficient to dislodge them.

7. Properties of Solutions: Saturated Solutions and Solubilityc
As solid solute begins to dissolve in a solvent, the concentrations of solute particles
in solution increases, so the chances of their colliding with the surface of the solid
increases. This may lead to crystallization.
Saturated: a solution with undissolved
solute
dissolve
Solute + Solvent  Solution
crystallize
Supersaturated: a solution which contains
a greater amount of solute than needed to
form a saturated solution

8. Properties of Solutions: Factors Affecting Solubility
As a rule, solubility increases with increasing molecular mass
Polar liquids tend to dissolve in polar solvents. If the dissolve they are miscible.
If they do not dissolve they are immiscible

9. Properties of Solutions: Factors Affecting Solubility
Hydrogen-boning interactions between solute and solvent may lead to high solubility
Because of H-bonding, solute-solute, solvent-solvent, and solute-solvent
interactions are not appreciably different.
Ethanol and ethanol
Ethanol and water
There is no significant change in the environment

10. Properties of Solutions: Factors Affecting Solubility
However, the numbers carbon atoms in an alcohol does effect it solubility in water.
As the length of the chain increases, the OH groups decrease leading to a decrease in
solubility

11. Properties of Solutions: Factors Affecting Solubility
Substances with similar intermolecular attractive forces tend to be soluble
in one another….LIKE DISSOLVES LIKE
Glucose has 5-OH groups on a six carbon framework which makes the
molecule fairly soluble in water

12. Properties of Solutions: Factors Affecting Solubility
Substances with similar intermolecular attractive forces tend to be soluble
in one another….LIKE DISSOLVES LIKE
Predict whether each of the following substances is more likely to dissolve in carbon
tetrachloride or water: C7H16. NaHCO3, HCl

13. Pressure Effects
The solubility of a gas in any solvent is increased as the pressure of the gas over the solvent increases
By contrast the solubility of solids and liquids are not appreciable affected by pressure.

14. The relationship between pressure and solubility is expressed by Henry’s Law:
Cg = kPg where Cg is the solubility of the gas in the solution phase, Pg is the partial pressure of the gas over the solution, and k is a Henry’s law constant which differs from one solute-solvent pair to another.
For example the solubility of N2 gas in water at 25 ° C and 0.78 atm. is 5.3 x 10-4 M
k = 5.3 x 10-4 M/0.78 = 6.8 x 10-4 mol/l-atm. Assume that the partial pressure of the N2 is doubled, Henry’s law, Cg = kPg predicts that the solubility will also double.
Cg = kPg
Cg = (6.8 x 10-4 mol/l-atm)(1.56 atm)
Cg =

15. In general, the solubility of gases decreases as temperature increases
Temperature Effects
In general, the solubility of gases decreases as temperature increases

16. Temperature Effects
In general, the solubility of of ionic compounds, solids, normally increases as the temperature increases.

17. Lowering the Vapor Pressure: Explaining How it is Done!!
A non-volatile solute added to a solvent reduces the capacity of the
solvent molecules in the liquid phase to move into the gas phase
The extent to which a nonvolatile solute lowers the vapor pressure
is proportional to the concentration

18. Colligative Properties are the first evidence that salts break up into ions.
Xa = Mole of solvent
Moles of solvent + moles of solute x i
If 10g of MgCl2 is added to 100ml of H2O at 23ºC, what would be the vapor pressure. The vapor pressure for water at this temperature is torr.

19. Properties of Solutions:Colloids
Suspensions that are the dividing Line Between Solutions and Heterogeneous Mixtures
Tyndell effect: a scattering of light by colloidal particles

20. Properties of Solutions:Colloids
The most important colloids are those in which the dispersing medium is water
Hydrophilic and Hydrophobic Colloids
Hydrophilic colloids are kept in
suspension by interaction
with surrounding water
molecules

21. Properties of Solutions:Colloids
The most important colloids are those in which the dispersing medium is water
Hydrophilic and Hydrophobic Colloids
Hydrophobic colloids can be stabilized in water by the adsorption of ions onto
their surface

22. Properties of Solutions:Colloids
The most important colloids are those in which the dispersing medium is water
Hydrophilic and Hydrophobic Colloids