1. Solubility, Concentrations, & Molarity
April 26-May 7, 2010

2. Solutions Definitions
Solution - homogeneous mixture consisting of two parts
Solute - substance being dissolved
Solvent - the substance that is dissolving the solute (present in greater amount)

3. Measuring Concentration
Concentration…a measure of solute-to-solvent ratio
Common Units:
Molarity  moles solute / L of solution
ppm  g solute / 1,000,000 g of solution
% → g solute/ 100 g of solution
concentrated vs dilute
“lots of solute” “not much solute”
“watery”
Add water to dilute a solution; boil water off to concentrate it.

4. Measuring Concentration “The amount of solute in a solution”
A. mass % = mass of solute
mass of solution
B. parts per million (ppm)  also, ppb and ppt
– commonly used for minerals or
contaminants in water supplies
C. molarity (M) = moles of solute
L of solution
– used most often in this class
% by mass – medicated creams
% by volume – rubbing alcohol
mol L M
M =
mol L

5. Tro's Introductory Chemistry, Chapter 13
Mass Percent
Parts of solute in every 100 parts solution.
If a solution is 0.9% by mass, then there are 0.9 grams of solute in every 100 grams of solution.
Or 10 kg solute in every 100 kg solution.
Since masses are additive, the mass of the solution is the sum of the masses of solute and solvent.
Tro's Introductory Chemistry, Chapter 13

6. Molarity
liter of solution

7. QUICK REVIEW OF MOLES!!
The concentration can then be used to convert the moles of solute into the liters of solution, or visa versa.
Since we normally measure the amount of solute in grams, we will need to convert between grams and moles.
How many moles are in 258 g of K2S?

8. Solution Concentration Molarity
moles of solute
liters of solution
If a sugar solution concentration is 2.0 M , 1 liter of solution contains 2.0 moles of sugar, 2 liters = 4.0 moles sugar, 0.5 liters = 1.0 mole sugar:

9. Tro's Introductory Chemistry, Chapter 13
Example 13.4—How Many Liters of a M NaOH Solution Contains 1.24 mol of NaOH?
Given:
Find:
1.24 mol NaOH
volume, L
Solution Map:
Relationships:
mol NaOH
L solution
1.00 L solution = mol NaOH
Solve:
Check:
The unit is correct, the magnitude seems reasonable as the moles of NaOH > 10x the amount in 1 L.
Tro's Introductory Chemistry, Chapter 13

10. 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

11. Calculating Molarity
What is the molarity of a potassium chloride solution that has a volume of 400 ml and contains 85.0 grams of KCl?

12. Example 2
Vinegar contains 5.0 grams of acetic acid,CH3COOH, in ml of solution. Calculate the molarity of acetic acid in vinegar.

13. Tro's Introductory Chemistry, Chapter 13
Practice—Determine the Mass of CaCl2 (MM = ) in 1.75 L of 1.50 M Solution, Continued.
Given: 1.75 L solution Find: g CaCl2 Equivalence: 1.50 mol CaCl2  1 L solution; g = 1 mol CaCl2 Solution Map:
L solution
mol CaCl2
g CaCl2
Apply Solution Map:
Check Answer:
Units are correct.
Tro's Introductory Chemistry, Chapter 13

14. g solute / g of solution x 1,000,000=
Parts Per Million (ppm)
g solute / g of solution x 1,000,000=
EXAMPLE
There are 2.2 mg of lead in exactly 500g of water. Convert this to ppm.

15. Assignment
Page 45
#1, #2, #3, #4, #5, #6, #8

16. Answers to Page 45
2. 3.

17. Answers to assignment Page 45

18. Solubility Salt is soluble in water. Oil is insoluble in water.
When one substance (solute) dissolves in another (solvent) it is said to be soluble.
Salt is soluble in water.
When one substance does not dissolve in another it is said to be insoluble.
Oil is insoluble in water.
There is usually a limit to the solubility of one substance in another.
Gases are always soluble in each other.
Two liquids that are mutually soluble are said to be miscible.
Alcohol and water are miscible.
Oil and water are immiscible.
The maximum amount of solute that can be dissolved in a given amount of solvent is called solubility.

19. Descriptions of Solubility
Saturated solutions have the maximum amount of solute that will dissolve in that solvent at that temperature.
Unsaturated solutions can dissolve more solute.
Supersaturated solutions are holding more solute than they should be able to at that temperature.
Unstable.
Tro's Introductory Chemistry, Chapter 13

20. 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

21. Changing Temperature = Changing Solubility
When a solution is saturated, it is holding the maximum amount of solute it can at that temperature.
The solubility of the solute in the solvent depends on the temperature.
If the temperature is changed, the solubility of the solute changes.
Higher temperature = Higher solubility of solid in liquid.
Lower temperature = Higher solubility of gas in liquid.
Tro's Introductory Chemistry, Chapter 13

22. Saturation Problems!! Page 44 (#1)
NaCl has a solubility of 35.9 g/100ml of water. Determine whether the following soln are sat., unsat., supersat.
85 g of NaCl dissolved in 150 mL of water
25 g of NaCl dissolved in 750 g of water
135 g of NaCl dissolved in 750 g of water

23. Saturated, Unsaturated & Super Saturated Problems
Problems on Page 47
Do one for example
Assign other two

24. Assignment Page 45-46 (concentration problems) #9, #10, #11
Page 47 (saturation problems)
#2, #3
**DUE on Friday**

25. Concentration Lab
April 22, 2009

26. Tasks: Thursday 4-23
Complete Lab write-up from the Concentration Lab and 7th Chromatography Lab also
Page 46
#14, #15, #16, #18
grams grams
grams mol/ liter

27. Page 44
Page 43
2. a. Unsaturated (0.789) b. Unsaturated (0.975) c. Unsaturated (0.66) 3. a. Supersaturated (5.1 x10-4) b. Supersaturated (0.029) c. Supersaturated (7.08 x 10 -5)
189 grams
0.18 L
0.082L

28. Physical Properties & Characteristics of Solutions
April 24
Physical Properties & Characteristics of Solutions

29. Physical Properties of Solutions
Conductivity:
Ability to conduct an electric current
Depends on whether it contains charged particles
Do all compounds conduct electricity?

30. 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

31. Electrolytes
Electrolytes are substances whose aqueous solution (dissolved ions) is a conductor of electricity. Not all electrolytes conduct same amount of electricity.
In strong electrolytes, all the electrolyte molecules are dissociated into ions.
In nonelectrolytes, none of the molecules are dissociated into ions. No electric current.
In weak electrolytes, a small percentage of the molecules are dissociated into ions.

32. Healthy Info 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.
e.g., any type of sugar
nonelectrolytes: solutes that DO NOT dissociate
-- DO NOT conduct electric current (not enough ions)

33. Colligative Properties
The properties of the solution are different from the properties of the solvent.
Any property of a solution whose value depends only on the number of dissolved solute particles is called a colligative property.
It does not depend on what the solute particle is.
The freezing point, boiling point, and osmotic pressure of a solution are colligative properties.
Tro's Introductory Chemistry, Chapter 13

34. Ice Cream Lab Data Average measurements over the entire day:
6 Tbs. salt= -8*C
12 Tbs. salt = -10*C
18 Tbs. salt = -15*C
The more salt that was added the lower the freezing point became!

35. Surfactants Types: Definition:
Detergent- synthetic, works in hard water
Emulsion- solution of two immiscible substances (a colloid in which both phases are liquids; "an oil-in-water)
Soap- used to surround a molecule making it miscible (ex: surrounds oil-allows it to dissolve in water)
A chemical agent capable of reducing the surface tension of a liquid in which it is dissolved
Occurs at the boundary of immiscible solutions

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

37. Tro's Introductory Chemistry, Chapter 13
Why Do We Do That?
We spread salt on icy roads and walkways to melt the ice.
We add antifreeze to car radiators to prevent the water from boiling or freezing.
Antifreeze is mainly ethylene glycol.
When we add solutes to water, it changes the freezing point and boiling point of the water.
Tro's Introductory Chemistry, Chapter 13

38. 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.

39. Polar water molecules hydrates Na+ and Cl- ions
hydrated ions - + -
Cl-
Timberlake, Chemistry 7th Edition, page 287

40. 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)

41. Tro's Introductory Chemistry, Chapter 13
Will It Dissolve?
Chemist’s rule of thumb:
Like dissolves like
A chemical will dissolve in a solvent if it has a similar structure to the solvent.
When the solvent and solute structures are similar, the solvent molecules will attract the solute particles at least as well as the solute particles to each other.
Tro's Introductory Chemistry, Chapter 13

42. “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

43. Will It Dissolve in Water?
Ions are attracted to polar solvents.
Many ionic compounds dissolve in water.
Generally, if the ions total charges < 4.
Polar molecules are attracted to polar solvents.
Table sugar, ethyl alcohol, and glucose all dissolve well in water.
Have either multiple OH groups or little CH.
Nonpolar molecules are attracted to nonpolar solvents.
b-carotene (C40H56) is not water soluble; it dissolves in fatty (nonpolar) tissues.
Many molecules have both polar and nonpolar structures—whether they will dissolve in water depends on the kind, number, and location of polar and nonpolar structural features in the molecule.

44. Allowable Limits