1. Factors Affecting Solubility
As To , rate
1. temperature
As size , rate
2. particle size
More mixing, rate
3. mixing
4. nature of solvent/solute (“like dissolves like”, polar dissolves polar)

2. Measuring Concentration
Concentration…a measure of solute-to-solvent ratio
concentrated vs dilute
“lots of solute” “not much solute”
“watery”
Add water to dilute a solution; boil water off to concentrate it.

3. Measuring Concentration “The amount of solute in a solution”
A. Parts per million (ppm)  also, ppb and ppt = g solute/1,000,000 g solution
– commonly used for minerals or
contaminants in water supplies
B. Molarity (M) = moles of solute
L of solution
– used most often
mol L M
C. Molality (m) = moles of solute
kg of solvent

4. One mole, in solution.

5. Molarity
liter of solution

6. Molarity
Find the molarity of a solution containing 75 g of MgCl2 in 250 ml of water.
75 g MgCl2
1 mol MgCl2
95.21 g MgCl2
0.25 L water
= 3.2M MgCl2

7. Molality
mass of solvent only
1 kg water = 1 L water

8. Molality
Find the molality of a solution containing 75 g of MgCl2 in 250 ml of water.
75 g MgCl2
1 mol MgCl2
95.21 g MgCl2
0.25 kg water
= 3.2m MgCl2

9. Molality
How many grams of NaCl are req’d to make a 1.54m solution using kg of water?
0.500 kg water
1.54 mol NaCl
1 kg water
58.44 g NaCl
1 mol NaCl
= 45.0 g NaCl

10. Factors Affecting Solubility
As To , rate
1. temperature
As size , rate
2. particle size
More mixing, rate
3. mixing
4. nature of solvent/solute (“like dissolves like”, polar dissolves polar)

11. Solubility (“Dissolution”)
Temperature
-The solubility of most solids in water increases as the temperature of the sol’n increases.
-The solubility of gases in water decreases with increasing temperature

12. Solubility (“Dissolution”)
Experiment 1:
Add 1 drop of red food coloring
Before
AFTER
Miscible – “mixable”
two gases or two liquids
that mix evenly
Water
COLD
Water
HOT
Water
COLD
Water
HOT
You should observe that temperature effects the rate of solution. As the temperature of the liquid solvent increases, the molecules move faster, and the food coloring dissolves more quickly.
A B
A B 12

13. Solubility (“Dissolution”)
Experiment 2:
Add oil to water and shake
AFTER
Before
Immiscible – “does not mix”
two liquids or two gases
that DO NOT MIX
Oil
You should observe that for solutions to mix they must be chemically similar. Polar and polar molecules will mix, non-polar and non-polar molecules will mix, but polar and non-polar molecules will not mix. The reasons for this will be explained later.
Remember, ‘like dissolves like’. polar dissolves polar
non-polar dissolves non-polar
Water
Water
T0 sec
T30 sec 13

14. Gas Solubility Higher Temperature …Gas is LESS Soluble CH4 O2
2.0 O2
Higher Temperature
…Gas is LESS Soluble
Solubility CO
1.0
The general rule of thumb is that the solubility of gases decreases when temperature increases. He 10 20 30 40 50
Temperature (oC)

15. Solubility: forming a “saturated” solution in equilibrium
UNSATURATED SOLUTION
more solute dissolves
SATURATED SOLUTION
no more solute dissolves
SUPERSATURATED SOLUTION
becomes unstable, crystals form
increasing concentration

16. “Oil and Water Don’t Mix”
Oil is nonpolar
Water is polar
“Like dissolves like”, nonpolar dissolves nonpolar, nonpolar does not dissolve polar
Lycopodium Powder demonstration.
Lycopodium powder is a nonpolar hydrocarbon that doesn’t mix with water. It is dry to the touch and not oily feeling. Sprinkle lycopodium powder on top of a beaker of water. Slowly, push your finger through the surface of the lycopodium powder into the water. Slowly withdraw your finger, it remains dry the entire time. Why?
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 470

17. Water Molecule H2O d+ d+ d- d- Water is a POLAR molecule O2- H+ H+
Draw the Lewis dot structure of a water molecule.
Recall, oxygen has 6 valence electrons and hydrogen has one valence electron.
The ‘electron cloud’ is more dense around the oxygen than the hydrogen. Therefore, the oxygen side of the molecule is more negatively charged and has a partial negative charge. The hydrogen have a lower electron density around them and receive a partial positive charge. This molecule does not have a formal (+) and (-) charge – as in an ionic compound.

18. Dissolving of NaCl in Water
ions
Na+
Water molecules
When sodium chloride crystals are dissolved in water, the polar water molecules exert attracting forces which weaken the ionic bonds. The process of solution occurs the ions of sodium and chloride become hydrated.
NaCl(s) + H2O  Na+(aq) + Cl-(aq)

19. Ethanol is Polar d - O d + Polar bond C C H H H H H H
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 469

20. Ethanol and Water are SolubleC
‘Like dissolves like’
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 469

21. Lava Lamp
a philosophy
an art form
progressive
post-modern

22. Cleaning Action of Soap
Micelle
Timberlake, Chemistry 7th Edition, page 573

23. MODEL OF A SOAP MOLECULE
emulsifying agent (emulsifier):
-- molecules w/both a polar AND a nonpolar end
-- allows polar and nonpolar substances to mix
e.g., soap
detergent
lecithin
eggs
MODEL OF A SOAP MOLECULE
Na1+
NONPOLAR
HYDROCARBON
TAIL
POLAR
HEAD

24. Interstitial Spaces Oil Non-polar "immiscible" Polar dissolved solid
Layer
Water
Water
Polar
This is an overly simplified model of spaces between water molecules. However, it is in these interstitial spaces that gases (e.g. oxygen and carbon dioxide) dissolve and solids also dissolve.
red food
coloring

25. Clogged Pipes – Hard Water
Step 1: Acid rain is formed
H2O CO H2CO3
carbonic acid
Step 2: Acid rain dissolves limestone
H2CO CaCO Ca(HCO3)2
Water softner
H2CO MgCO Mg(HCO3)2
‘hard’ water

26. Pipes develop Scales Ca(HCO3)2 CaCO3(s) + H2O + CO2
Step 3: Hard water is heated and deposits scales
Ca(HCO3) CaCO3(s) H2O CO2
Mg(HCO3) MgCO3(s) H2O CO2 D
scales on pipes D

27. Water Purification Cation Exchanger Anion Exchanger Hard Water
Deionized
Water H+
OH- H+
OH- H+
Mg2+
OH-
Na+ H+
(a)
(b)
OH-
(c)
OH-
Fe3+
Ca2+ H+ H+
OH- H+
In some areas of the country, the minerals dissolved in water give it a high concentration of various ions that make the water suitable neither for drinking nor for agriculture. Such water is called hard water. Sometimes the mineral content in hard water is so great that it causes plumbing and corrosion problems. Hard water typically contains a high concentration of the following ions: Ca2+, Mg2+, Fe3+, Cl1-, CO32-, SO42-, and PO43-. Water is deionized (softened) by removing the minerals using an ion exchange system. Water is passed through a resin that has both cation and anion exchange components. First, cations such as Na+ in the water are exchanged for hydrogen ions on the resin. Second, anions such as Cl- in the water are exchanged for hydroxide ions. The net result is that the resin removes all ions from water passing through the deionizing system.
OH- H+
OH-
Hard water is softened by exchanging Na+ for Ca2+, Mg2+, and Fe3+.
The cations in hard water are exchanged for H+.
The anions in hard water are exchanged for OH-.
The H+ and OH- combine to give H2O.
Corwin, Introductory Chemistry 2005, page 361

28. Pure water does not conduct an electric current
Source of
electric power
Pure
water
Pure water doesn’t conduct electricity because it contains no ions. Ions (cations have (+) charges) carry electrons in solution. The flow of electrons is called electricity.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 215

29. Ionic Solutions conduct a Current
Source of
electric power
Free ions
present
in water
To make a solution that conducts electricity (an electrolyte) – an ionic salt is added. An alternative method is to add acid. In truth, most acids are oxysalts dissolved in water.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 215

30. electrolytes: solutes that dissociate in solution
-- conduct electric current because of free-moving ions
e.g., acids, bases, most ionic compounds
-- are crucial for many cellular processes
-- obtained in a healthy diet
-- For sustained exercise or a bout of the flu, sports drinks
ensure adequate electrolytes.
nonelectrolytes: solutes that DO NOT dissociate
-- DO NOT conduct electric current (not enough ions)
e.g., any type of sugar

31. Strong electrolytes exhibit nearly 100% dissociation.
NaCl Na Cl1–
NOT in water:
in aq. solution:
Weak electrolytes exhibit little dissociation.
CH3COOH CH3COO1– H1+
NOT in water:
in aq. solution:
“Strong” or “weak” is a property of the substance.
We can’t change one into the other.

32. Electrolytes Electrolytes - solutions that carry an electric current
strong electrolyte
weak electrolyte
nonelectrolyte
NaCl(aq) Na+ + Cl-
HF(aq) H+ + F-
Timberlake, Chemistry 7th Edition, page 290

33. Colligative Properties  depend on concentration of a solution
Compared to solvent’s… a solution w/that solvent has a…
…normal freezing point (NFP) …lower FP
FREEZING PT.
DEPRESSION
…normal boiling point (NBP) …higher BP
BOILING PT.
ELEVATION 33

34. Applications (NOTE: Data are fictitious.)
1. salting roads in winter FP BP
water
0oC (NFP)
100oC (NBP)
water + a little salt
–11oC
103oC
water + more salt
–18oC
105oC
2. antifreeze (AF) /coolant FP BP
water
0oC (NFP)
100oC (NBP)
water + a little AF
–10oC
110oC
50% water + 50% AF
–35oC
130oC
Why do you think some towns use calcium chloride on roads in the winter versus sodium chloride?
CaCl2 yields three ions while NaCl yields only two ions. Calcium chloride will work in colder weather. Calcium chloride will work better than sodium chloride. Secondly, calcium chloride doesn’t kill grass like sodium chloride.

35. Effect of Pressure on Boiling Point
Boiling Point of Water at Various Locations
Location
Feet above sea level
Patm (kPa)
Boiling Point (C)
Top of Mt. Everest, Tibet
29,028 32 70
Top of Mt. Denali, Alaska
20,320
45.3 79
Top of Mt. Whitney, California
14,494
57.3 85
Leadville, Colorado
10,150 68 89
Top of Mt. Washington, N.H.
6,293
78.6 93
Boulder, Colorado
5,430
81.3 94
Madison, Wisconsin
900
97.3 99
New York City, New York 10
101.3
100
Death Valley, California
-282
102.6
100.3