1. Chapter 18 - Solutions 18.1 Properties of Solutions
18.2 Concentrations of Solutions
18.3 Colligative Properties of Solutions
18.4 Calculations Involving Colligative Properties

2. 18.1 Properties of Solutions
Solution Formation
How do solutions form? How do the properties of a solution change?
Solvent: the substance that does the dissolving.
Solute: the substance that is dissolved.
Factors influencing how fast a substance dissolves:
agitation (stirring), temperature, surface area or particle size.

3. 18.1 Properties of Solutions
Solubility
What is it?
Solvation and desolvation – saturation. (pp )

4. 18.1 Properties of Solutions
Factors Affecting Solubility
Our “old friends” temperature and pressure…

5. 18.1 Properties of Solutions
Henry’s Law and Supersaturated solutions
Henry’s Law: As the pressure of the gas above the liquid increases, the solubility of the gas also increases (and vice versa):
S1/P1 = S2/P2
When the temperature of the saturated solution in contact with a small excess of solid solute is raised, some or all of the excess solute generally dissolves. When the solution is allowed to cool slowly to its original temperature, the solute may not crystallize out of solution and it may now contain more solute than it typically should – it is supersaturated.

6. 18.2 Concentrations of Solutions
Molarity (M)
Concentration: a measure of the amount of solute that is dissolved in a given quantity of solvent.
Dilute vs. concentrated solutions…
Molarity: the number of moles of solute dissolved per liter of solution.
Ex: 16 M HCl = 16 moles HCl / L of solution
16 mol HCl = 584 g HCl

7. 18.2 Concentrations of Solutions
Percent Solutions
When the solute ad the solvent are both solutions, it is convenient to make concentrations by volume.
Percent by volume (% v/v)
Percent mass/volume (% m/v)
Example:

8. Ch 18 Assignments
CPQ’s 1 pg.528
#40,43,45,47,49,50,52,53,54

9. 18.3 Colligative Properties of Solutions
Physical properties of a solution differ from those of a pure solvent used to make the solution.
Colligative properties: properties which depend only on the number of particles dissolved in a given mass of solvent.
Examples: vapor pressure lowering, boiling-point elevation, freezing-point depression.

10. 18.3 Colligative Properties of Solutions
Boiling-Point Elevation
Recall boiling point…
The difference in temperature between the boiling point of a solution and that of a pure solvent.
Freezing-Point Depression
The difference in temperature between the freezing point of a solution and that of a pure solvent.

11. 18.4 Calculations Involving Colligative Properties
Molality and Mole Faction
Molality = moles solute / kg solvent
Example: .55 mol KI / 1 kg H20 = .55 molal (m)
Mole Faction: the ratio of moles of solute in solution to the total number of moles of solute and solvent:
XA = nA / nA + nB
XB = nB / nA + nB
Example pg

12. 18.4 Calculations Involving Colligative Properties
BP Elevation and FP Depression
How can we predict/determine how much elevation of depression for a solution?
Use of molality and a proportionality constant:
D Tb = Kb x m
D Tf = Kf x m
Examples:

13. Ch 18 Assignments CPQ’s 1 pg.528 CPQ’s 2 pg.528
#40,43,45,47,49,50,52,53,54
CPQ’s 2 pg.528
#55,57,58,59