1. COLLIGATIVE PROPERTIES

2. STATE PERFORMANCE OBJECTIVES
Calculate concentration in terms of molality
Calculate the freezing point depression and boiling point elevation of a solution. (This requires determining mole fraction.)

3. COLLIGATIVE PROPERTIES
Solute particles may physically alter certain physical properties of a solution.
These properties of the solutions will be different form those of the pure solvent
these properties are determined by the number of particles in the solution as opposed to the type of particles in solutions

4. Examples Vapor pressure freezing point boiling point
rate of diffusion of the particles through a membrane ( osmotic pressure)

5. VAPOR PRESSURE EVAPORATION
vapor - refers to the gaseous state of a substance that is a liquid or s
solid at room temperature.
vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid
Volative
Nonvolative solute

6. VAPOR PRESSURE
A solution that contains a nonvolative solute always has a lower VP than does the pure solvent
Dec in VP is directly related to the # of particles of solute
If substance dissociates – it has greater impact on VP than 1 that does not dissociates

7. BOILING POINT
Addition of nonvolative soute to liquid solvent lowers the VP of the solvent.
For the liquid to escape as a vapor, it needs
More kinetic energy
You see an increase in temperature

8. FREEZING POINT
When a substance freezes, the particles take on an orderly patter
Solutes disrupts this formation.
More kinetic energy must be removed from the solution in order for the solvent to solidify. The freezing point is lowered.

9. MOLALITY
The property of the solution is dependent upon the number of solute particles present within a given mass of solvent.
This makes it more convenient to express the concentration of the solution in terms of moles of solution per mass of solvent
formula

10. SAMPLE PROBLEM
If 52 grams of potassium carbonate are dissolved in 518 grams of water, what is the molality of the resulting solution?
homework

11. RAOULTS’ LAW
Any nonvolative solute at a specific concentration lowers the vapor pressure of a solvent by an amount that is characteristic of that solvent.

12. RAOULT’S LAW CONTINUED
STATES: vapor pressure of a solution varies directly as the mole fraction of a solvent.
To determine the vapor pressure of a solution, must 1st adjust the vapor pressure of the pure solvent for the presence of the solute.
formula

13. SAMPLE PROBLEM
Sugar is extremely soluble in water and is not a volatile substance. What would the vapor pressure of water be at 700C if 1.0 x 102 grams of water have dissolved 2 x 102 grams of sucrose?

14. MOLAL BP Constant
Kbp
1 mole of nonvolatile solute particles will raise the boiling Temperature of 1 kg of water by 0.515oC
Process that is occuring

15. MOLAL FREEZING POINT CONSTANT
Kfp
1 mole of nonvolatile solute particles will lower the freezing point of 1 Kg of water by 1.853oC
Process

16. SAMPLE PROBLEM
If 85 grams of sugar are dissolved in 392 grams of water, what will be the boiling point and freezing point of the resulting solution?

17. IONIC SOLUTIONS Will affect the BP and FP of the solutions
Must adjust for the moles of the ionic compound because of dissociation

18. SAMPLE PROBLEM
If 26.4 grams of nickel(II)bromide are dissolved in 224 grams of water, what will be the boiling and freezing point of the resulting solution. Assume 100% ionization of the compound.

19. Determination of the molecular mass
Formula
sample problem
If 99.0 grams of a nonionizing solute are dissolved in 669 grams of water and the freezing point of the resulting solution is
-0.960oC,what is the molecular mass of the solute?