1. Physical Properties of Solutions
Chapter 12
Solution Stoichiometry
end of Chapter 4
Problems: 12.12, 12.15, 12.16, 12.17, 12.18, 12.21, 12.22, 12.28, 12.36, 12.38, 12.51, 12.54, 12.55, 12.57, 12.60, 12.65, 12.76, 12.77,
4.12, 4.60, 4.70, 4.72, 4.74, 4.77, 4.88

2. A solution is a homogenous mixture of 2 or more substances
The solute is(are) the substance(s) present in the smaller amount(s)
The solvent is the substance present in the larger amount
12.1

3. An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity.
A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity.
nonelectrolyte
weak electrolyte
strong electrolyte
4.1

4. A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.
An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.
A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.
Sodium acetate crystals rapidly form when a seed crystal is
added to a supersaturated solution of sodium acetate.
12.1

5. Three types of interactions in the solution process:
solvent-solvent interaction
solute-solute interaction
solvent-solute interaction
DHsoln = DH1 + DH2 + DH3
12.2

6. “like dissolves like”
Two substances with similar intermolecular forces are likely to be soluble in each other.
non-polar molecules are soluble in non-polar solvents
CCl4 in C6H6
polar molecules are soluble in polar solvents
C2H5OH in H2O
ionic compounds are more soluble in polar solvents
NaCl in H2O or NH3 (l)
12.2

7. Concentration Units
The concentration of a solution is the amount of solute present in a given quantity of solvent or solution.
Percent by Mass
x 100%
mass of solute
mass of solute + mass of solvent
% by mass = =
x 100%
mass of solute
mass of solution
Mole Fraction (X)
XA =
moles of A
sum of moles of all components
12.3

8. Concentration Units Continued
Molarity (M)
M =
moles of solute
liters of solution
Molality (m)
m =
moles of solute
mass of solvent (kg)
12.3

9. 5.86 moles ethanol = 270 g ethanol
What is the molality of a 5.86 M ethanol (C2H5OH) solution whose density is g/mL?
m =
moles of solute
mass of solvent (kg)
M =
moles of solute
liters of solution
Assume 1 L of solution:
5.86 moles ethanol = 270 g ethanol
927 g of solution (1000 mL x g/mL)
mass of solvent = mass of solution – mass of solute
= 927 g – 270 g = 657 g = kg
m =
moles of solute
mass of solvent (kg) =
5.86 moles C2H5OH
0.657 kg solvent
= 8.92 m
12.3

10. Convert % mass to Molarity
What is the Molarity of a 95% acetic acid solution? (density = g/mL)
If you assume 1 L, that amount of solution = 1049 g
95% of the solution is acetic acid
1049 g solution x 0.95 = 997 g solute
997 g X 1 mol/60.05 g = 16.6 mol solute
Since we assumed 1 L, that’s 16.6 mol / 1 L or
16.6 M

11. Temperature and Solubility
Solid solubility and temperature
solubility increases with increasing temperature
solubility decreases with increasing temperature
12.4

12. Fractional crystallization is the separation of a mixture of substances into pure components on the basis of their differing solubilities.
Suppose you have 90 g KNO3 contaminated with 10 g NaCl.
Fractional crystallization:
Dissolve sample in 100 mL of water at 600C
Cool solution to 00C
All NaCl will stay in solution (s = 34.2g/100g)
78 g of PURE KNO3 will precipitate (s = 12 g/100g). 90 g – 12 g = 78 g
12.4

13. Temperature and Solubility
Gas solubility and temperature
solubility usually decreases with increasing temperature
12.4

14. Pressure and Solubility of Gases
The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law).
c is the concentration (M) of the dissolved gas
c = kP
P is the pressure of the gas over the solution
k is a constant (mol/L•atm) that depends only
on temperature
low P
high P
low c
high c
12.5

15. Chemistry In Action: The Killer Lake
8/21/86
CO2 Cloud Released
1700 Casualties
Trigger?
earthquake
landslide
strong Winds
Lake Nyos, West Africa

16. Solution Stoichiometry (Chapter 4)
The concentration of a solution is the amount of solute present in a given quantity of solvent or solution.
M = molarity =
moles of solute
liters of solution
What mass of KI is required to make 500. mL of
a 2.80 M KI solution?
M KI
M KI
volume KI
moles KI
grams KI
1 L
1000 mL x
2.80 mol KI
1 L soln x
166 g KI
1 mol KI x
500. mL
= 232 g KI
4.5

17. 4.5

18. Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution.
Dilution
Add Solvent
Moles of solute
before dilution (i)
after dilution (f) =
MiVi
MfVf =
4.5

19. How would you prepare 60.0 mL of 0.2 M
HNO3 from a stock solution of 4.00 M HNO3?
MiVi = MfVf
Mi = 4.00
Mf = 0.200
Vf = 0.06 L
Vi = ? L
Vi =
MfVf Mi =
0.200 x 0.06
4.00
= L = 3 mL
3 mL of acid
+ 57 mL of water
= 60 mL of solution
4.5

20. Gravimetric Analysis Dissolve unknown substance in water
React unknown with known substance to form a precipitate
Filter and dry precipitate
Weigh precipitate
Use chemical formula and mass of precipitate to determine amount of unknown ion
4.6

21. Equivalence point – the point at which the reaction is complete
Titrations
In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete.
Equivalence point – the point at which the reaction is complete
Indicator – substance that changes color at (or near) the
equivalence point
Slowly add base
to unknown acid
UNTIL
the indicator
changes color
4.7

22. What volume of a 1.420 M NaOH solution is
Required to titrate mL of a 4.50 M H2SO4
solution?
WRITE THE CHEMICAL EQUATION!
H2SO4 + 2NaOH H2O + Na2SO4 M
acid rx
coef. M
base
volume acid
moles acid
moles base
volume base
4.50 mol H2SO4
1000 mL soln x
2 mol NaOH
1 mol H2SO4 x
1000 ml soln
1.420 mol NaOH x
25.00 mL
= 158 mL
4.7

23. Chemistry in Action: Metals from the Sea
CaCO3 (s) CaO (s) + CO2 (g)
CaO (s) + H2O (l) Ca2+ (aq) + 2OH (aq) -
Mg2+ (aq) + 2OH (aq) Mg(OH)2 (s) -
Mg(OH)2 (s) + 2HCl (aq) MgCl2 (aq) + 2H2O (l)
Mg2+ + 2e Mg
2Cl Cl2 + 2e-
MgCl2 (l) Mg (l) + Cl2 (g)
Now back to Chapter 12…

24. Colligative Properties of Nonelectrolyte Solutions
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
Vapor-Pressure Lowering
P1 = X1 P 1
P 1
= vapor pressure of pure solvent
X1 = mole fraction of the solvent
Raoult’s law
If the solution contains only one solute:
X1 = 1 – X2
P 1
- P1 = DP = X2
X2 = mole fraction of the solute
12.6

25. Fractional Distillation Apparatus
12.6

26. Boiling-Point Elevation
DTb = Tb – T b
T b is the boiling point of
the pure solvent
T b is the boiling point of
the solution
Tb > T b
DTb > 0
DTb = Kb m
m is the molality of the solution
Kb is the molal boiling-point
elevation constant (0C/m)
12.6

27. Freezing-Point Depression
DTf = T f – Tf
T f is the freezing point of
the pure solvent
T f is the freezing point of
the solution
T f > Tf
DTf > 0
DTf = Kf m
m is the molality of the solution
Kf is the molal freezing-point
depression constant (0C/m)
12.6

28. 12.6

29. DTf = Kf m Kf water = 1.86 0C/m DTf = Kf m
What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is g.
DTf = Kf m
Kf water = C/m =
3.202 kg solvent
478 g x
1 mol
62.01 g
m =
moles of solute
mass of solvent (kg)
= 2.41 m
DTf = Kf m
= C/m x 2.41 m = C
DTf = T f – Tf
Tf = T f – DTf
= C – C = C
12.6

30. Colligative Properties of Nonelectrolyte Solutions
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
Vapor-Pressure Lowering
P1 = X1 P 1
Boiling-Point Elevation
DTb = Kb m
Freezing-Point Depression
DTf = Kf m
Osmotic Pressure (p)
p = MRT
12.6

31. Colligative Properties of Electrolyte Solutions
0.1 m NaCl solution
0.1 m Na+ ions & 0.1 m Cl- ions
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
0.1 m NaCl solution
0.2 m ions in solution
van’t Hoff factor (i) =
actual number of particles in soln after dissociation
number of formula units initially dissolved in soln
i should be
nonelectrolytes 1
NaCl 2
CaCl2 3
12.7

32. Change in Freezing Point
Which would you use for the streets of Bloomington to lower the freezing point of ice and why? Would the temperature make any difference in your decision?
sand, SiO2
Rock salt, NaCl
Ice Melt, CaCl2

33. Colligative Properties of Electrolyte Solutions
Boiling-Point Elevation
DTb = i Kb m
Freezing-Point Depression
DTf = i Kf m
Osmotic Pressure (p)
p = iMRT
12.7

34. Change in Freezing Point
Common Applications of Freezing Point Depression
Ethylene glycol – deadly to small animals
Propylene glycol

35. Change in Boiling Point
Common Applications of Boiling Point Elevation

36. Freezing Point Depression
At what temperature will a 5.4 molal solution of NaCl freeze?
Solution
∆TFP = Kf • m • i
∆TFP = (1.86 oC/molal) • 5.4 m • 2
∆TFP = oC
FP = 0 – 20.1 = oC

37. The Cleansing Action of Soap
12.8

38. Osmotic Pressure (p)
Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one.
A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules.
Osmotic pressure (p) is the pressure required to stop osmosis.
more
concentrated
dilute
12.6

39. Osmotic Pressure (p) p = MRT High P Low P
M is the molarity of the solution
R is the gas constant
T is the temperature (in K)
12.6

40. A cell in an: isotonic hypotonic hypertonic
solution
hypotonic
solution
hypertonic
solution
12.6

41. Chemistry In Action:
Desalination

42. Colloid versus solution
A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance.
Colloid versus solution
collodial particles are much larger than solute molecules
collodial suspension is not as homogeneous as a solution
12.8

43. Colloids
Brownian motion
Tyndall Effect

44. Suspensions These are mixed, but not dissolved in each other
Will settle over time
Particles are bigger than 1 micrometer (larger than colloid)
Examples: dust in air, muddy water