1. Chapter 13 Properties of Solutions
Chemistry, The Central Science, 11th edition
Theodore L. Brown, H. Eugene LeMay, Jr., and Bruce E. Bursten
Chapter 13 Properties of Solutions
John D. Bookstaver
St. Charles Community College
Cottleville, MO
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2. Solutions
Solutions are homogeneous mixtures of two or more pure substances.
In a solution, the solute is dispersed uniformly throughout the solvent.
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3. 13-4 Ways of Expressing Concentrations of Solutions
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4. Mass Percentage mass of A in solution Mass % of A =
total mass of solution
Mass % of A =
 100
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5. Parts per Million and Parts per Billion
Parts per Million (ppm)
mass of A in solution
total mass of solution
ppm =
 106
Parts per Billion (ppb)
mass of A in solution
total mass of solution
ppb =
 109
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6. total moles in solution
Mole Fraction (X)
moles of A
total moles in solution
XA =
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7. You will recall this concentration measure from Chapter 4.
Molarity (M)
mol of solute
L of solution
M =
You will recall this concentration measure from Chapter 4.
Since volume is temperature-dependent, molarity can change with temperature.
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8. Molality (m) mol of solute m = kg of solvent
Since both moles and mass do not change with temperature, molality (unlike molarity) is not temperature-dependent.
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9. Choice of units depends on the purpose of the experiment
Mole fraction – used for gases and vapor pressures of solutions
Molarity – commonly used since volumes of solutions are easy to measure
Molality – temperature independent
Percent by Mass – temperature independent and need not know molar masses
Conversion between units requires the use of density if any mass to volume or volume to mass conversion in needed.

10. Determine the a) molality, b) percent by mass and c) the ppm concentrations of a solution prepared by dissolving g of glucose (C6H12O6) in 255 g of water.
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11. Molar mass of glucose = 180.2 g/mol
a) molality
Molar mass of glucose = g/mol
m =
mole
0.255 kg of H2O
= m

12. b) percent by mass
c) ppm
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13. Molarity 1.00 g C2H5OH is added to 100.0 g of water to make
101 mL of solution. Find the molarity, mass %, mole
fraction and molality of ethanol.
Molarity

14. Mass Percent Also called weight percent
Percent by mass of the solute in the solution

15. Mole Fraction ratio of number of moles of a part of
solution to total number of moles of solution

16. Molality
Number of moles of solute per kg of solvent

17. What is the molality of a 5
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

18. An aqueous antifreeze solution is 40% ethylene glycol (C2H6O2) by mass
An aqueous antifreeze solution is 40% ethylene glycol (C2H6O2) by mass. The density of the solution is 1.05 g/cm3. Calculate the molality, molarity and mole fraction of ethylene glycol

19. Mass of water (solvent) = 100-40 = 60.0 g
where EG = ethylene glycol (C2H6O2)
V =
mass d
d =
mass
Volume
100 g
1.05 g/ml =
= 95.2 ml

20. # mol EG = 0.644 mol EG # mol water = 60.0/18.0 = 3.33 mol
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21. Mass of solution = 5.0 g of toluene + 225 g of benzene = 230 g
A solution with a density of g/mL contains 5.0 g of toluene (C7H8) and 225 g of benzene. Calculate the molar concentration of the solution?
Mass of solution = 5.0 g of toluene g of benzene = 230 g
mass
230 g
Volume = =
= 263 ml
density
0.879 g/ml
0.054 mole
M =
= 0.21 M
0.263 L
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22. 13-5 Colligative Properties
Changes in colligative properties depend only on the number of solute particles present, not on the identity of the solute particles.
Among colligative properties are
Vapor pressure lowering
Boiling point elevation
Melting point depression
Osmotic pressure
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23. Vapor Pressure
Because of solute-solvent intermolecular attraction, higher concentrations of nonvolatile solutes make it harder for solvent to escape to the vapor phase.
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24. Vapor Pressure
Therefore, the vapor pressure of a solution is lower than that of the pure solvent.
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25. Raoult’s Law PA = XAPA where
XA is the mole fraction of compound A, and
PA is the normal vapor pressure of A at that temperature.
NOTE: This is one of those times when you want to make sure you have the vapor pressure of the solvent.
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26. Boiling Point Elevation and Freezing Point Depression
Nonvolatile solute-solvent interactions also cause solutions to have higher boiling points and lower freezing points than the pure solvent.
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27. Calculate the vapor pressure of a solution
made by dissolving 115 g of urea, a nonvolatile
solute, [(NH2)2CO; molar mass = g/mol]
in 485 g of water at 25°C.
(At 25°C, )

29. Boiling Point Elevation
The change in boiling point is proportional to the molality of the solution:
Tb = Kb  m
where Kb is the molal boiling point elevation constant, a property of the solvent.
Tb is added to the normal boiling point of the solvent.
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30. Freezing Point Depression
The change in freezing point can be found similarly:
Tf = Kf  m
Here Kf is the molal freezing point depression constant of the solvent.
Tf is subtracted from the normal boiling point of the solvent.
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31. Boiling Point Elevation and Freezing Point Depression
Note that in both equations, T does not depend on what the solute is, but only on how many particles are dissolved.
Tb = Kb  m
Tf = Kf  m
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32. Calculate a) the freezing point and b) the
boiling point of a solution containing 268 g of
ethylene glycol and 1015 g of water. (The
molar mass of ethylene glycol (C2H6O2) is
62.07 g/mol. Kb and Kf for water are
0.512°C/m and 1.86°C/m, respectively.)

33. a) freezing point

34. b) boiling point

35. Colligative Properties of Electrolytes
Since these properties depend on the number of particles dissolved, solutions of electrolytes (which dissociate in solution) should show greater changes than those of nonelectrolytes.
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36. Collegative properties of electrolytes solutions
Ionic compounds (salts) should have a bigger effect.
When they dissolve they dissociate.
NaCl dissociate into Na+ and Cl- ions
1 mole of NaCl makes 2 moles of ions.
1mole Al(NO3)3 makes 4 moles ions.

37. Solutions of Electrolytes
Dissociation of strong and weak electrolytes affects the number of particles in a solution
van’t Hoft factor (i) – accounts for the effect of dissociation

38. NaCl(s)  Na+(aq) + Cl-(aq) Ag+(aq) + NO3-(aq) AgNO3(s)  MgCl2(s) 
i = 2
NaCl(s) 
Na+(aq) + Cl-(aq)
i = 2
AgNO3(s) 
Ag+(aq) + NO3-(aq)
i = 3
MgCl2(s) 
Mg2+(aq) + 2 Cl-(aq)
i = 3
Na2SO4(s) 
2 Na+(aq) + SO42-(aq)
AlCl3(s) 
Al3+(aq) + 3 Cl-(aq)
i = 4

39. Modified Equations for Colligative Properties

40. van’t Hoff Factor
One mole of NaCl in water does not really give rise to two moles of ions.
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41. van’t Hoff Factor
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42. The freezing-point depression of a 0.100 m
MgSO4 solution is 0.225°C. Determine the
experimental van’t Hoff factor of MgSO4 at
this concentration.
Copyright McGraw-Hill 2009

43. One approach:
Note, at this concentration the dissociation of MgSO4 is not complete.

44. Osmosis
Some substances form semipermeable membranes, allowing some smaller particles to pass through, but blocking other larger particles.
In biological systems, most semipermeable membranes allow water to pass through, but solutes are not free to do so.
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45. Osmosis
Final
Initial
In osmosis, there is net movement of solvent from the area of higher solvent concentration (lower solute concentration) to the are of lower solvent concentration (higher solute concentration).
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46. Osmotic Pressure n V  = ( )RT = MRT
The pressure required to stop osmosis, known as osmotic pressure, , is n V
 = ( )RT = MRT
where M is the molarity of the solution.
where R is L.atm/mol . K
T is in kelvins
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47. Osmosis in Blood Cells
If the solute concentration outside the cell is greater than that inside the cell, the solution is hypertonic.
Water will flow out of the cell, and crenation results.
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48. Osmosis in Cells
If the solute concentration outside the cell is less than that inside the cell, the solution is hypotonic.
Water will flow into the cell, and hemolysis results.
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49. Modified Equations for Colligative Properties