1. Chapter 12.2 The Solution Process

2. POINT > Describe the dissolving process
POINT > Identify factors that affect dissolving
POINT > Define solubility and saturation
POINT > Describe effects of temperature and pressure on solubility
POINT > Examine the energetics of the solution process

3. POINT > Describe the dissolving process
As a solution forms, the solvent particles pull solute particles apart and surround, or solvate, them.

4. POINT > Describe the dissolving process
The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles

5. POINT > Describe the dissolving process
For example, if an ionic salt is soluble in water, it is because the ion-dipole interactions are strong enough to overcome the lattice energy of the salt crystal

6. AgCl is insoluble in water. Why is this?
WB CHECK:
AgCl is insoluble in water. Why is this?
a) Ionic bonding is stronger than covalent bonding
b) Water is not attracted to the AgCl crystal surface
c) The intermolecular forces between water molecules and AgCl particles are balanced
d) The AgCl lattice energy is stronger than the attractions between water and AgCl

7. POINT > Identify 3 factors that affect dissolving rate?
1. Increasing the surface area for interactions to occur (i.e. crushing up the solute crystal)
2. Mixing/stirring the solution: increases solvent/solute contact
3. Heating the solution: increases solvent/solute contact

8. POINT > Define solubility and saturation
Solubility is a description of how well a solute dissolves in a solvent. For example:
“NaCl is highly soluble in water”
“sucrose is highly soluble in water”
“lead sulfate is insoluble in water”
“water is poorly soluble in gasoline”
What governs this?
Intermolecular forces (of course!)

9. WB CHECK:
What are three factors that affect the rate of dissolving a solute in a solvent?

10. POINT > Define solubility and saturation
Chemists use the axiom “like dissolves like”:
Polar substances tend to dissolve in polar solvents
Nonpolar substances tend to dissolve in nonpolar solvents
So, fats, oils, waxes, hydrocarbons, etc. (all nonpolar), are poorly soluble in polar compounds like water

11. POINT > Define solubility and saturation
The more similar the intermolecular attractions, the more likely one substance is to be soluble in another (ex. ethanol in water)

12. POINT > Define solubility and saturation
Solubility is quantified as the mass of solute that will dissolve in a specified amount of solvent at a given temperature
For example, solubility of potassium nitrate in water:
31.6g per 100.0g H2O at 20.0C
At this point the solution is “saturated”

13. POINT > Define solubility and saturation
Saturated:
The solvent holds as much solute as is possible at that temperature
Dissolved solute is in dynamic equilibrium with solid solute particles

14. POINT > Define solubility and saturation
Unsaturated:
Less than the maximum amount of solute is dissolved in the solvent

15. POINT > Define solubility and saturation
Supersaturated:
Solvent holds more solute than is normally possible at that temperature
These solutions are unstable; crystallization can occurs by adding a “seed crystal” or even scratching the side of the flask

16. POINT > Describe effects of temperature and pressure on solubility
The solubility of liquids and solids does not change appreciably with pressure
The solubility of a gas in a liquid is directly proportional to its pressure (Read Henry’s Law)

17. POINT > Describe effects of temperature and pressure on solubility
Generally, the solubility of solid solutes in liquid solvents increases with increased temperature
The effect varies widely depending on the solute

18. POINT > Describe effects of temperature and pressure on solubility
The opposite is true of gases:
Carbonated soft drinks are more “bubbly” if stored in the refrigerator
Warm lakes have less O2 dissolved in them than cool lakes

19. WB CHECK:
Which is true?
a) Solubility of gases is unaffected by temperature
b) Solubility of a solid in a liquid increases with increasing pressure
c) Solubility of a gas in a liquid decreases with higher pressure
d) Solubility of a gas in a liquid decreases with higher temperature

20. POINT > Examine the energetics of the solution process
Three processes affect the energetics of the solution process:
1. Separation of solute particles (requires energy)

21. POINT > Examine the energetics of the solution process
Three processes affect the energetics of the solution process:
1. Separation of solute particles (requires energy)
2. Separation of solvent particles (requires energy)

22. POINT > Examine the energetics of the solution process
Three processes affect the energetics of the solution process:
1. Separation of solute particles (requires energy)
2. Separation of solvent particles (requires energy)
3. New interactions between solute and solvent (releases energy)

23. POINT > Examine the energetics of the solution process
The enthalpy change, H, of the overall process depends on H for each of these 3 steps

24. POINT > Examine the energetics of the solution process
The enthalpy change of the overall process depends on H for each of these steps

25. Homework:
READ THE BOOK!
Complete Section 12.2 F.A. #1-7