1. Properties of Solutions
Chapter 11

2. Composition of Solutions
Solutions = homogeneous mixtures, any state of matter
Solid
Gas
Liquid
Gas
Liquid
Solid

3. How to Calculate Concentration
Mole Fraction
Molarity
Molality
Mass Percent
Normality
Outdated

4. Energies of Solutions “Like Dissolves Like” WHY? ENTHALPY OF SOLUTION
Polar solvents dissolve polar solutes
Non-Polar solvents dissolve non-polar solutes
WHY?
ENTHALPY OF SOLUTION
3 part process
Solute components separate (endo)
Overcome IMF’s in solvent (endo)
Solvent and Solute interact (exo)

5. Enthalpy of Solution DHsoln = DH1 + DH2 + DH3
Heat of solution can either be + or –
DH is expected to be small for non-polar molecules except for when they are very large molecules.
DHsoln is large and +
This rarely occurs
DHsoln is large and -
This usually occurs
DHsoln is close to zero
Exceptions, because
Spontaneity does not
Depend solely on
enthalpy

6. Try Me!
Decide whether liquid hexane (C6H14) or liquid methanol (CH3OH) is more appropriate solvent for substances, grease (C20H42) and potassium iodide (KI).

7. Factors Affecting Solubility
Structure---Polarity
Non polar are hydrophobic
Polar are hydrophillic
Some are a combo with different ends.
Vitamin C and scurvy
Pressure---works only on gases
C = kP
[gas] a Pvapor
Temperature---not always a direct relationship
Gas in water; as T increases, solubility decreases
See solubility curves for individual compound reactions to temperature.

8. Colligative Properties
A property of a solution that depends only on the number, and not on the identity of the solute particles present.
Vapor Pressure
Boiling Point Elevation
Freezing Point Depression
Osmotic Pressure

9. Vapor Pressure Non-volatile Solute added to solvent
Reduces the tendency of the solvent molecules to escape (evaporate)
Equilibrium pressure of the solvent is higher than equilibrium pressure of solution. More of the solvent (pure) has to evaporate to be at equilibrium than is the case in a beaker full of solution.

10. François Raoult and his Law
Vapor pressure of a solution is directly proportional to the mole fraction of the solvent present.
Psoln = XsolventPosolvent
Just what I was thinking!! Me
Too!
I agree!

11. Try Me!
Calculate the expected vapor pressure at 25oC for a solution prepared by dissolving g of table sugar (sucrose molar mass = g/mol) in cm3 of water. The vapor pressure of water is torr at this temperature.

12. Answer
torr

13. More solute, lower vapor pressure
Predict the vapor pressure of a solution prepared by mixing 35.0 g solid Na2SO4 with 175 g water at 25oC. The vapor pressure of water is still torr.

14. Volatile solutes
Raoult’s Law is modified to account for the vapor pressure of both solute.
Ptotal = Pa + Pb = XaPao + XbPbo
Always some degree of deviation from ideal…more similar the solute is to the solvent the more ideal it behaves.

15. Boiling Point Elevation
When a solute is added, vapor pressure is lowered.
Must be heated to higher temperature to give reach normal boiling point.
Boiling point is higher than usual.
DT = Kbmsolute

16. Freezing Point Depression
When a solute is added, the vapor pressure is lowered.
Water in the solution has a lower vapor pressure than that of pure ice.
Ice will not form.
Freezing point has been lowered.
DT = Kfmsolute

17. Try Me!
A chemist is trying to identify a human hormone, which controls metabolism by determining its molar mass. A sample weighing g was dissolved in 15.0 g benzene, and the freezing point depression was determined was determined to be 0.240oC. Calculate the molar mass of the hormone.

18. Osmotic Pressure
Solvent, but not solute can pass through a semi-permeable membrane via osmosis.
When pure solvent and solution volumes are stabilized (the system is at equilibrium) there is a greater pressure on the solution side.
The difference in pressure is the Osmotic Pressure.

19. P = MRT Used to determine osmotic pressure. P is osmotic pressure
M is molarity of solution
R is the gas law constant ( Latm/Kmol)
T is the temperature in Kelvin

20. Colligative Properties of Electrolyte Solutions
The type of solute DOES matter sometimes
Only in ability to dissociate
Compare: 0.1 m glucose to 0.1m NaCl

21. Van’t Hoff Factor
Van’t Hoff Factor expresses the relationship between moles of solute and solution:
This is a multiplier number that describes the ratio of elevation or depression.
i = moles particles
moles solute
DT = iKbm
DT = iKfm
P = iMRT

22. Ion Pairing Van’t Hoff factor is fallible.
Ion Pairing: at a certain instant, some ions may not be dissociated, and thus count as a single particle.
Still use equations, but keep in mind that there can be some deviation.

23. Colloids
Suspension of tiny particles in a medium caused by electrostatic repulsion.
Tyndall Effect: Scattering of light effect by suspended particles.