1. Ask a chemist, they always have
Ask a chemist, they always have
Solutions

3. Definitions
Mixture: several pure substances mixed together in an indefinite ratio
Homogeneous
Heterogeneous
Solution: a homogenous mixture that form when one or more substances dissolve into another.
Suspensions: cloudy mixtures that form when two or more substances mix but do not dissolve.
Emulsions: suspension of 2 liquids

4. Solutes and Solvents Solution: a homogenous mixture
Solution: a homogenous mixture
Solute: thing that dissolves
Solvent: thing that does the dissolving (found in the largest amounts)
If the solvent is water, then it is called an aqueous solution

5. Solubility
Example: iced tea
Solute
sugar
tea
Solvent
water

6. Solubility: Ionic Compounds
Ions form, separate (dissociate) and move throughout the solution
The forces that hold the ions together are overcome by the ions’ attractions to polar water.
Ion- dipole interaction
Because ions are present, ionic solutions can conduct a current
Current is just movement of electrons

7. Figure 15.1: Dissolving of solid sodium chloride.
Solvation animation
Animation with Audio

8. Figure 15.2: Polar water molecules interacting with positive and negative ions of a salt.

9. Solubility: Polar Compounds
“Like dissolves like”
Typically, hydrogen bonding occurs between the substance being dissolved and the polar water molecules
Example:
Sugar in water
Ethanol in water

10. Figure 15.3: The polar water molecule interacts strongly with the polar O—H bond in ethanol.

11. Figure 15.4: Structure of common table sugar.
Get interactions between water molecules the polar regions on the sugar (the Os) , and some hydrogen bonding at the -OH groups

12. “They go together like oil and water
“They go together like oil and water.” (things that don’t dissolve or mix)
Anything nonpolar will not mix well with anything polar
Examples:
Oil spill
Salad dressing
Can mix when shaken (LDF) and then may separate out (other forces)

13. How much is too much?
There is a limit to the amount of a substance dissolved
Saturated: the solution holds as much solute as possible at that temperature.
Unsaturated: solution has not reached the limit

14. Can you have too much? YES!
Can you have too much? YES!
Supersaturated: have as much solute dissolved as possible, then cooled and all the solute stays dissolved.
In other words…the solution contains more dissolved solid than a saturated solution created at the same temperature.
These can begin crystallization of the solute at the slightest change

15. Energy changes and Solvation
Any chemical change (including solvation) requires a change in energy
Energy removed from or added to the reactants from the surroundings
NaOH(s) Na+ (aq)+ OH- (aq) ΔH= kJ/mol
(that’s 44.5kJ released, so exothermic, per mole of NaOH)
Because you are breaking the ionic bond, energy must be either released when breaking the bond, or consumed when making the new ions
ALL changes in formula indicate a change in energy.
However, sometimes the energy change is so small, you can’t tell that a change has occurred

16. Why some coffees “Put hair on your chest.”
“Strong” coffee has more coffee dissolved in a given amount (say 1 pot) than “weak” coffee.
Strong coffee = concentrated
Weak coffee = dilute
Concentration: the amount of solute in a given amount of solvent (or solution).

17. Molarity (M) M = moles of solute
Most common way to express concentration
Molarity is the number of moles of solute dissolved in each liter of solution
Formula
M = moles of solute
liters of solution
Dependent on temperature
The higher the molarity the stronger the concentration

18. Molality (M ) M = moles solute .
Another way to calculate concentration
Formula
M = moles solute
kilograms of solvent
Not dependent on temperature
The higher the molality the stronger the concentration

19. Colligative properties
Colligative properties
In the winter, why do we throw salt when it snows?
Why does Emeril add salt to boiling water when cooking pasta?

20. Freezing point depression
By adding salt (or other solutes) to water, the temperature of freezing drops it freezes at a lower temperature
Because H bonding is disturbed
Dependent on how much solute is added

21. Freezing Point Depression Calcs
Antifreeze protects cars from freezing and overheating. Calculate the freezing point depression of a solution of 100. g of ethylene glycol (C2H6O2) antifreeze in kg of water. Kf water = 1.86 oC/m
Formula:
Tf = Kfm i
Kf : Molal Freezing Point depression constant (oC/m)
i= Pieces that the material dissociates into (for ionic compounds only)
(Keep I at 1 (one) for covalent compounds)

22. Freezing Point Depression and Boiling Point Elevation
Freezing Point Depression and Boiling Point Elevation
Solvent
Formula
Melting Point (°C)
Boiling Point (°C) Kf
(°C/m) Kb
Water
H2O
0.000
1.858
0.521
Acetic acid
HC2H3O2
16.60
118.5
3.59
3.08
Benzene
C6H6
5.455
80.2
5.065
2.61
Camphor
C10H16O
179.5
... 40
Carbon disulfide
CS2
46.3
2.40
Cyclohexane
C6H12
6.55
80.74
20.0
2.79
Ethanol
C2H5OH
78.3
1.07

23. Boiling point elevation
By adding salt (or other compounds) to water, the temperature of boiling goes up it boils at a higher temperature
Interrupts H bonding
Need more vapor molecules and greater pressure to get bubbles to form
Takes more time to get vapors to add to bubbles
The molecules that do get into the bubbles need more energy
Dependent on how much solute is added

24. Boiling Point Elevation Calculations
Water with salt added boils at a higher temperature than pure water. By how much will the boiling point change if 100.g of salt is added to 500. g of water? Kbwater = 0.52 oC/m
Formula:
Tb = Kbm i
Kb : Molal Boiling Point elevation constant (oC/m)
i= = Pieces that the material dissociates into (for ionic compounds only)
(Keep I at 1 (one) for covalent compounds)

25. Freezing Point Depression and Boiling Point Elevation
Solvent
Formula
Melting Point (°C)
Boiling Point (°C)
Kf(°C/m) (
Kb(°C/m)
Water
H2O
0.000
1.858
0.521
Acetic acid
HC2H3O2
16.60
118.5
3.59
3.08
Benzene
C6H6
5.455
80.2
5.065
2.61
Camphor
C10H16O
179.5
... 40
Carbon disulfide
CS2
46.3
2.40
Cyclohexane
C6H12
6.55
80.74
20.0
2.79
Ethanol
C2H5OH
78.3
1.07

26. Figure 15.10: Pure water.

27. Figure 15.9: A bubble in the interior of liquid water surrounded by solute particles and water molecules.

28. Figure 15.10: Solution (contains solute).
Figure 15.10: Solution (contains solute).

29. Vapor Pressure Reduction
Vapor pressure changes as IMFs change
For the same reasons boiling point is disturbed
What would evaporate faster:
Salt water
Distilled water
WHY?

30. Colligative properties interactive