1. Chapter 12: Solutions
Solutions are homogeneous mixtures consisting of a solute and solvent.
Not all solutions are liquids!
A solution can be a solid, liquid, or a gas.

2. Types of Solutions

3. Solution Process
The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles.

4. Solution Process
As an ionic compound dissolves in water, the ions are surrounded by six water molecules.

5. Solution Process

6. Solution Process
Energy of solution formation for ionic compounds has two factors.
Factor One: Lattice energy of ionic compound.
Factor Two: Ion-dipole force formed between water and ions.
Which one requires energy?
Which one produces energy?
NH4NO3(s) and MgSO4(s)

7. Ion-Dipole Force
Intermolecular force between water and ion is called the Ion-Dipole force.
Hydration energy = combined interactions of all six waters with the ion.

8. Energy of Ionic Solutes
DHsolution = DHhydration – DHlattice energy

9. Insoluble Ionic Compounds
Compounds with very LARGE lattice energies are insoluble.
Compounds with smaller lattice energies are highly soluble.
Ex) KBr(s) vs. PbS(s)
Ex) Al2O3(s) vs. KNO3(s)

10. Energy of Solution
Energy to overcome solute-solute interaction (requires energy = endothermic)
Energy to overcome solvent-solvent interaction (requires energy = endothermic)
Energy of solute-solvent interaction (produces energy = exothermic)

11. Energy of Solution
If – 3 > 0, then net process is endothermic.
If – 3 < 0, then net process is exothermic.
If – 3 >> 0, then the two substances will NOT mix.

12. Spontaneity Enthalpy is not the sole factor in why things dissolve.
Natural tendency of the universe is to go from order to disorder.
A solution is going from order to disorder when mixing occurs.
The amount of disorder is called the entropy of the system.

13. Spontaneity
Both CCl4 and C6H14 are non-polar molecules with similar boiling points.
Adding the two together will produce a solution increasing the entropy of the system.

14. Non-polar and Polar “Like dissolves like”
Polar substances dissolve in polar solvents.
Non-polar substances dissolve in non-polar solvents.
Non-polar substances do NOT dissolve in polar solvents!

15. Intermolecular Forces

16. Types of Solvents

17. Molecular Compounds
Molecular compounds will dissolve in water IF they are polar or have hydrogen bonding.
CH3CH2OH, CH3CHO
Size, though matters!
CH3CH2CH2CH2CH2CH2OH
W14, #1
Vitamins

18. Solubility of Alcohols

19. Saturated Solutions
When more solid solute is added to a liquid and the solid does NOT dissolve, the solution is said to be saturated.
Solubility limit = maximum amount solute that can be dissolved in a given quantity of solvent.
KNO3 = 36g / 100mL.
Super-saturated solution.

20. Sodium Acetate Solution

21. Temperature Effects
The solubility limits of most solid solutes INCREASES with increasing temperature.

22. Temperature Effects
The solubility of ALL gases decreases with an increase in temperature.
Can have an adverse reaction in ponds and lakes in the hot summer months.

23. Concentrations There are many methods for expressing concentration.
Percent
mass / mass
volume / volume
mass / volume

24. Concentrations ppm (106) or ppb (109)
Mole fraction = moles A / total moles
Molarity (M) – Chapter 4
Molality (m)

26. Colligative Properties
Why do we put “salt” on our roads in the winter?
Why do we add “antifreeze” to the radiator in our cars?
Can we reduce the vapor pressure of “volatile” liquids?
Yes!

27. Colligative Properties
Any property that depends only on the quantity of solute particles and not their identity.
Vapor Pressure lowering
Freezing-pt depression
Boiling-pt elevation
Osmotic Pressure

28. Vapor Pressure
A non-volatile solute (solid) can be added to a volatile solvent and LOWER its vapor pressure.
Pa = ca Pao
Mole fraction is for the solvent and Pao is the vapor pressure for the pure solvent (dependent on T).
Addition of a nonvolatile solute reduces the rate of vaporization, decreasing the amount of vapor

29. Vapor Pressure
Two volatile liquids, of similar intermolecular forces, will both contribute a partial pressure.
Raoult’s Law
Ptotal = caPao + cbPbo
Graphical interpretation
Fractional distillation

30. Ideal vs. Non-ideal Behavior

31. BP and FP When a solute is added to a solvent: Formulas are similar:
the freezing-pt is lowered.
the boiling-pt is raised.
Formulas are similar:
DT = Kf cm
DT = Kb cm

32. Osmosis
In biological systems, the cellular walls are made up of cellulose.
Cellulose allows water molecules to pass in and out of the cells.
Larger molecules or ions are generally “blocked” from entering.
Note: glucose is transported into the cells via a complex process.

33. Osmosis
When two solutions of different concentrations are separated by a semi-permeable membrane, solvent molecules will flow from lower solute concentration to higher solute concentration.

34. Osmosis
This is important in maintaining water in our cells.

35. Osmotic Pressure The osmotic pressure is measured in atmospheres.
p = MRT
M is the molarity of the solution
R = L atm/mol K
T = temperature, K

36. Molar Masses
Many experiments involving colligative properties can find a molar mass of a solute.
Generally, this requires us to work backwards through several formulas.

37. Ionic Solutes
Because ionic solutes break apart into ions, an adjustment to our formulas must be made.
i = van’t Hoff factor.
Equals the number of ions per formula unit.
True factor depends on the concentration. As the concentration increases, i becomes less than predicted.
Why?

38. Ionic Solutes

39. Ionic Solutes Assume “ideal” values for each electrolyte.
Becomes multiplier in all formulas.
What is i for:
CaCl2
Na2CO3
Al(NO3)3
NH3

40. Colloids
When larger solute particles remain suspended in a solution, they form a colloid.
Colloids will exhibit the Tyndall Effect due to the larger particles.

41. Colloids
Tyndall effect in nature.

42. Colloids There are several types of colloids.
Aerosol = a liquid or solid in a gas.
fog, smoke
Foam = a gas in a liquid or solid.
whipped cream, marshmallow
Emulsion = a liquid in a liquid or a solid in a solid.
milk, butter, mayo
Sol = a solid in a liquid or solid.
cement, paint, gems