1. Solutions
AP Chemistry

2. Heat of Solution Substance Heat of Solution (kJ/mol) NaOH -44.51
The Heat of Solution is the amount of heat energy absorbed (endothermic) or released (exothermic) when a specific amount of solute dissolves in a solvent.
Substance
Heat of Solution
(kJ/mol)
NaOH
-44.51
NH4NO3
+25.69
KNO3
+34.89
HCl
-74.84

3. Steps in Solution Formation
H1 Step 1 - Expanding the solute
Separating the solute into individual components

4. Steps in Solution Formation
H2 Step 2 - Expanding the solvent
Overcoming intermolecular forces of the solvent molecules

5. Steps in Solution Formation
H3 Step 3 - Interaction of solute and solvent to form the solution

6. Predicting Solution Formation
Solvent/
Solute
H1
H2
H3
Hsol’n
Outcome
Polar/
Polar
+ large
- large
+/-small
Solution
forms
Nonpolar
+ small
+/- small
No solution
Nonpolar/
+/-
small
polar

7. Solubility Chart

8. Vapor Pressure - Henry’s Law
The concentration of a dissolved gas in a solution is directly proportional to the pressure of the gas above the solution
Applies most accurately for dilute solutions of gases that do not dissociate or react with the solvent
Yes  CO2, N2, O2
No  HCl, HI

9. Raoult’s Law Psolution = Observed Vapor pressure of
The presence of a nonvolatile solute lowers the vapor pressure of the solvent.
Psolution = Observed Vapor pressure of
the solution
solvent = Mole fraction of the solvent
P0solvent = Vapor pressure of the pure solvent

10. Liquid-liquid solutions in which both components are volatile
Modified Raoult's Law:
P0 is the vapor pressure of the pure solvent
PA and PB are the partial pressures

11. Raoult’s Law – Ideal Solution
A solution that obeys Raoult’s Law is called an ideal solution

12. Negative Deviations from Raoult’s Law
Strong solute-solvent interaction results in a vapor pressure lower than predicted
Exothermic mixing = Negative deviation

13. Positive Deviations from Raoult’s Law
Weak solute-solvent interaction results in a vapor pressure higher than predicted
Endothermic mixing = Positive deviation

14. Colligative Properties
Colligative properties are those that depend on the concentration of particles in a solution, not upon the identity of those particles.
Boiling Point Elevation
Freezing Point Depression
Osmotic Pressure 14

15. Freezing Point Depression
Each mole of solute particles lowers the freezing point of 1 kilogram of water by 1.86 degrees Celsius.
Kf = 1.86 C  kilogram/mol
m = molality of the solution
i = van’t Hoff factor 15

16. Boiling Point Elevation
Each mole of solute particles raises the boiling point of 1 kilogram of water by 0.51 degrees Celsius.
Kb = 0.51 C  kilogram/mol
m = molality of the solution
i = van’t Hoff factor 16

17. Freezing Point Depression and Boiling Point Elevation Constants, C/m
Solvent Kf Kb
Acetic acid
3.90
3.07
Benzene
5.12
2.53
Nitrobenzene
8.1
5.24
Phenol
7.27
3.56
Water
1.86
0.512 17

18. The van’t Hoff Factor, i
Electrolytes may have two, three or more times the effect on boiling point, freezing point, and osmotic pressure, depending on its dissociation. 18

19. Dissociation Equations and the Determination of i
NaCl(s) 
Na+(aq) + Cl-(aq)
i = 2
AgNO3(s) 
Ag+(aq) + NO3-(aq)
i = 3
MgCl2(s) 
Mg2+(aq) + 2 Cl-(aq)
i = 3
Na2SO4(s) 
2 Na+(aq) + SO42-(aq)
AlCl3(s) 
Al3+(aq) + 3 Cl-(aq)
i = 4 19

20. Ideal vs. Real van’t Hoff Factor
The ideal van’t Hoff Factor is only achieved in VERY DILUTE solution. 20

21. Osmotic Pressure
The minimum pressure that stops the osmosis is equal to the osmotic pressure of the solution 21

22. Osmotic Pressure Calculations
i = van’t Hoff Factor
M = Molarity of the solution
R = Gas Constant = Latm/molK 22

23. Suspensions and Colloids
Suspensions and colloids are NOT solutions.
Suspensions: The particles are so large that they settle out of the solvent if not constantly stirred.
Colloids: The particles intermediate in size between those of a suspension and those of a solution.

24. Types of Colloids Examples Dispersing Medium Dispersed Substance
Colloid Type
Fog, aerosol sprays
Gas
Liquid
Aerosol
Smoke, airborn germs
Solid
Whipped cream, soap suds
Foam
Milk, mayonnaise
Emulsion
Paint, clays, gelatin
Sol
Marshmallow, Styrofoam
Solid Foam
Butter, cheese
Solid Emulsion
Ruby glass
Solid sol

25. The Tyndall Effect
Colloids scatter light, making a beam visible. Solutions do not scatter light.
Which glass contains a colloid?
colloid
solution