1. AQUEOUS SOLUTIONS
HOLT MODERN CHEMISTRY

2. DISSOCIATION
Dissociation is separation of ions that occurs when an ionic compound is solvated - Ionic compounds have 100% dissociation
Ionization is the process of forming ions from a substance that was not ionic already
Substances that already contain ions (i.e. ionic compounds) merely release their ions as the crystal dissociates.

3. DISSOCIATION Write the equation for the dissolution of the following:
Al2(SO4)3
Al2(SO4)3  2 Al SO42-
Na2S
Na2S 2 Na S2-
Ba(NO3)2
Ba(NO3)2  Ba NO3-

4. IONIZATION
Process in which ions are formed from solute molecules by the action of the solvent
Substances that are neutral molecules (i.e. molecular/covalent compounds) must react with water to produce ions
HYDRONIUM ION – H3O+ formed from the hydration of H+

5. Strong vs. Weak Electrolytes
STRONG ELECTROLYTE
Any compound of which all or almost all of the dissolved compound exist as ions in an aqueous solution
EX: NaCl, HCl

6. Strong vs. Weak Electrolytes
A compound of which a relatively small amount of the dissolved compound exists as ions in an aqueous solution
EX: HF, CH3COOH

7. COLLIGATIVE PROPERTIES
Properties that depend on the concentration of solute particles but not on their identities
Concentration is given in molality
Vapor-pressure lowering
Freezing-point depression
Boiling-point elevation
Osmotic pressure

8. Vapor Pressure Lowering
Nonvolatile Substance
Has little tendency to become gas under existing conditions
Vapor pressure can be thought of as a measure of the tendency of molecules to escape from a liquid

9. Vapor Pressure Lowering
Nonvolatile solute changes the boiling and freezing points of solvents
Addition of nonvolatile solute lowers the concentration of solvent molecules at the surface of the liquid
This lowers the tendency of the solvent molecules to leave the solution and enter the vapor phase
Thus the vapor pressure of the solution is lower than the vapor pressure of the pure solvent
Vapor Pressure Lowering animation

10. Vapor Pressure Lowering
When vapor pressure is lowered, the solution remains in liquid over a larger temperature range, causing LOWER FREEZING POINT and HIGHER BOILING POINT
Boiling Point elevation animation

11. Freezing-Point Depression (Nonelectrolytes)
MOLAL FREEZING-POINT CONSTANT (Kf)
The freezing-point depression of the solvent in a 1-molal solution of a nonvolatile, nonelectrolyte solute
Kf H2O: –1.86 °C/m
See Table 14.2, page 438
FREEZING-POINT DEPRESSION
Difference between the freezing points of the pure solvent and a solution of a nonelectrolyte in that solvent; directly proportional to the molal concentration of the solution
Δtf = Freezing-pt. Depression
Kf = Molal Freezing-pt constant (°C/m)
m = molality (mol/kg)

12. F-pt Depression PROBLEMS
A solution consists of 10.3 g of glucose, C6H12O6, dissolved in 250. g of water. What is the freezing point depression of the solution?
In a laboratory experiment, the freezing point of an aqueous solution of glucose is found to be °C. What is the molal concentration of the solution?
If m of a nonelectrolyte solute are dissolved in g of ether, what is the freezing point of the solution?

13. Boiling-Point Elevation (Nonelectrolytes)
MOLAL BOILING-POINT CONSTANT (Kb)
The boiling-point elevation of the solvent in a 1-molal solution of a nonvolatile, nonelectrolyte solute
Kb H2O: °C/m
See Table 14.2, page 438
BOILING-POINT ELEVATION
Difference between the boiling points of the pure solvent and a solution of a nonelectrolyte in that solvent; directly proportional to the molal concentration of the solution
Δtb = boiling-point elevation
Kb = molal boiling point constant (°C/m)
m = molality (mol/kg)

14. B-Pt Elevation PROBLEMS
A solution contains g sucrose, C12H22O11, dissolved in g of water. What is a) the boiling point elevation and b) boiling point of the solution?
If the boiling point elevation of an aqueous solution containing a nonvolatile electrolyte is 1.02°C, what is the molality of the solution?
The boiling point of an aqueous solution containing a nonvolatile electrolyte is °C. What is a) the boiling-point elevation and b) the molality of the solution?

15. Electrolytes & Colligative properties
Electrolytes have a greater effect on the freezing and boiling points of solvents than do nonelectrolytes
Electrolytes cause changes in in colligative properties proportional to the total molality of all dissolved particles (# of ions produced) instead of formula units

16. Electrolytes & Colligative properties
i = # of ions per formula unit (Electrolytes)
Δtb = boiling-point elevation
Δtf = boiling-point elevation
Kb = molal b-pt constant (°C/m)
Kf = molal f-pt constant (°C/m)
m = molality (mol/kg)
SOLUTION
Ba(NO3)2 (s)  Ba2+(aq) + 2NO3-(aq)
Produces 3 ions (1 barium and 2 nitrate ions); i = 3
Δtf = iKfm
Δtf = (3)(-1.86°C/m)(0.5 m)
Δtf = -2.79°C
tf = 0°C + (-2.79°C) = -2.79°C
What is the freezing point of a 0.5 m aqueous solution of Ba(NO3)2 ?

17. Electrolytes & Colligative properties
What is the expected freezing-point depression for a solution that contains 2.0 mol of magnesium sulfate dissolved in 1.0 kg of water?
What is the expected boiling-point elevation of water for a solution that contains 150 g of calcium chloride in 1.0 kg of water?
The freezing-point of an aqueous solution of sodium chloride is -20.0°C. What is the molality of the solution?

18. APPLICATIONS

19. Osmotic Pressure SEMIPERMEABLE MEMBRANE OSMOSIS OSMOTIC PRESSURE
Allow the movement of some particles while blocking the movement of others
Allows only solvent to pass through
OSMOSIS
The movement of solvent through a semipermeable membrane from the side of lower solute concentration to the side of higher solute concentration
Solvent has a net flow towards more concentrated solution
Solvent tends to dilute the solution and make it more disorganized
OSMOTIC PRESSURE
The external pressure that must be applied to stop osmosis

20. Osmotic Pressure

21. Osmotic Pressure HYPERTONIC SOLUTION Cells Shrink!
Regulation of osmosis is vital to life of a cell because cell membranes are semipermeable
Hypertonic solution – more concentrated solution
Cells lose water and shrink when placed in a solution of higher concentration (PICKLES)
HYPERTONIC SOLUTION
Cells Shrink!

22. Osmotic Pressure Hypotonic solution – less concentrated solution
Cells gain water and swell when placed in a solution of lower concentration (turgor pressure in plants)
HYPOTONIC SOLUTION
Cells Swell & Burst!

23. Osmotic Pressure
In vertebrates, blood and lymph protect the cells from swelling and shrinking because they have the same concentration as the inside of the cell
Isotonic solution – same concentration

24. Tonicity

25. REVERSE OSMOSIS/DIALYSIS
Pressure is applied to the concentrated solution to reverse the flow of water
DESALINATION OF SALTWATER
Membrane is permeable to water but not to ions
DIALYSIS
Occurs at the walls of most plant and animal cells
Membrane allows transfer of both solvent and small solute molecules and ions

26. Kidney Dialysis Animation of the kidney dialysis process
Used in artificial Kidney Machines to purify blood
The resulting dialysis moves waste molecules into dialyzing solution and cleanses the blood
Animation of the kidney dialysis process

27. KIDNEY DIALYSIS