1. Solutions
Chapter 13

2. Solution Process Solution – homogeneous mixture of solute and solvent
Can be gases, liquids, or solids
Solvent is component present in the largest amount (rest are solutes)
Intermolecular forces are rearranged with solutions of condensed phases.
Ex. NaCl in Water – Water molecules orient themselves on NaCl; H-bonds between waters have to be broken; NaCl dissociates; ion-dipole forces form; interaction is called solvation or hydration

4. The Solution Process

5. Solubility Dissolution – formation of a solution
Crystallization – “destruction” of a solution
If these processes are in equilibrium, the solution is saturated.
Solubility is the amount of solute required to form a saturated solution.
Unsaturated
Supersaturated

6. Factors affecting Solubility
Nature of the solute and solvent
Intermolecular forces – favorable?
Miscible vs. immiscible / soluble vs. insoluble
Temperature
Generally, as temperature increases, solubility increases.
Sometimes not the case – gases are less soluble at higher temperatures
Pressure
Solubility of a Gas is a function of the pressure of the gas over the solution.
Increase pressure, increase solubility

7. Solubility: Pressure

8. Solubility Graph

9. Solubility Graph (gases)

10. Concentration Amount of solute per amount of solvent
Qualitative – dilute vs. concentrated
Quantitative – Molarity (M)

11. Colligative Properties
Colligative properties depend on quantity of solute molecules.
(E.g. freezing point depression and melting point elevation.)
Lowering Vapor Pressure
Non-volatile solutes reduce the ability of the surface solvent molecules to escape the liquid.
Therefore, vapor pressure is lowered.
The amount of vapor pressure lowering depends on the amount of solute.

12. Vapor Pressure

13. Colligative Properties
Boiling-Point Elevation
Non-volatile solute lowers the vapor pressure.
Therefore the triple point - critical point curve is lowered
At 1 atm (normal boiling point of pure liquid) there is a lower vapor pressure of the solution. Therefore, a higher temperature is required to reach a vapor pressure of 1 atm for the solution (Tb).

15. Colligative Properties: Freezing Point Depression
At 1 atm (normal boiling point of pure liquid) there is no depression by definition
When a solution freezes, almost pure solvent is formed first.
Therefore, the sublimation curve for the pure solvent is the same as for the solution.
Therefore, the triple point occurs at a lower temperature because of the lower vapor pressure for the solution.

16. Colligative Properties: Freezing Point Depression
The melting-point (freezing-point) curve is a vertical line from the triple point.
The solution freezes at a lower temperature (Tf) than the pure solvent.
Decrease in freezing point (Tf) is directly proportional to molality (Kf is the molal freezing-point-depression constant):