1. Solutions and Their Properties
McMurray and Fay ch. 11

2. Vocabulary: Molar enthalpy of solution OR Heat of solution (DHsoln)
Total energy absorbed or released when a solute dissolves in a solvent

3. Breaking bonds takes energy Forming bonds releases energy
Solution thermodynamics: Why is energy released or absorbed when a solute dissolves?
Breaking bonds takes energy
Forming bonds releases energy

4. When something dissolves… What bonds are being broken
When something dissolves… What bonds are being broken? What bonds are being formed? O H O H
Cl-
Na+ O H O H
Cl-
Na+ O H O H
Cl- O H
Na+ O H O H O H

5. When something dissolves… What bonds are being broken
When something dissolves… What bonds are being broken? What bonds are being formed? O H O H O H
Cl-
Na+ O H
Cl-
Na+ O H O H
Cl- O H
Na+ O H O H O H

6. 1. IMFs between solvent molecules are brokenH
Cl- O H O H
Na+ O H
Cl-
Na+ O H
Cl- O H
Na+ O H O H O H O H

7. 2. IMFs or bonds between solute molecules are brokenH O H O H
Cl-
Na+ O H
Cl-
Na+ O H O H
Cl- O H
Na+ O H O H O H

8. 3. IMFs are formed between solute and solventH O H O H
Cl-
Na+
Na+ O H
Cl-
Na+ O H O H O H
Cl- O H O H O H

9. Heat of Solution: A Hess’s Law view
Energy
Add energy to
separate solvent
particles
Energy released as solute
and solvent form IMFs
Add energy to
separate solute
particles
Energy difference between
initial & final energies = heat of solution
Separate solute
+ solvent

10. Heat of Solution
Bonds broken: Bonds formed: Solvent-solvent Solvent-solute Solute-solute

11. Is formation of a solution exothermic or endothermic? Compare:
Bonds broken: Bonds formed:
Solvent-solvent Solvent-solute
Solute-solute

12. Is formation of a solution exothermic or endothermic? Compare:
Bonds broken: Bonds formed:
Solvent-solvent Solvent-solute
Solute-solute
If there are strong bonds between solvent molecules
or if there are strong bonds between solute molecules
a lot of energy is required to break these bonds
If there are strong bonds between
solvent & solute molecules
a lot of energy is released when forming these bonds
If there are weak bonds between solvent molecules
or if there are weak bonds between solute molecules
very little energy is required to break these bonds
If there are weak bonds between
solvent & solute molecules
very little energy is released when forming these bonds

13. Is formation of a solution exothermic or endothermic? Compare:
Bonds broken: Bonds formed:
Solvent-solvent Solvent-solute
Solute-solute
Breaking strong bonds + forming weak bonds = endothermic reaction
Breaking weak bonds + forming strong bonds = exothermic reaction

14. NaCl dissolving in hexane

15. Bonds broken? C H
Cl-
Na+
Cl-
Cl-
Na+ C H
Cl-
Na+
Na+

16. Bonds formed? C H
Cl-
Na+
Cl-
Na+
Cl- C H
Cl-
Na+
Na+

17. The bonds broken are so much stronger than the bonds formed that it is very hard to dissolve NaCl in hexane at room temperature C H
Cl-
Na+ C H
Cl-
Cl-
Na+
Cl-
Na+
Na+

18. When IMFs of very different strengths are present in a solute and a solvent, the solute is less likely to dissolve.

19. Solubility: ‘Like dissolves like’
Polar solvents dissolve polar solutes
Non-polar solvents dissolve non-polar solutes

20. POLAR SOLVENTS (substances that form dipole-dipole forces or hydrogen bonds) like to mix with other polar substances

21. NON-POLAR SOLVENTS (substances that only have London dispersion forces) like to mix with other non-polar substances

22. In which of the following will NaCl be the most soluble?
Benzene, C6H6 Carbon tetrachloride, CCl4 Hexane, C6H14 Methanol, CH3OH

23. In which of the following will Vitamin D will be the most soluble?
Hexane, C6H14 Chloromethane, CH3Cl Methanol, CH3OH Water, H2O

24. Liquids dissolving in Liquids

25. Hexane and water: will they mix?C H O H O H O H C H O H O H O H O H

26. What bonds would be broken?C H O H O H O H C H O H O H O H O H

27. What bonds would be formed?C H O H O H C H O H O H O H O H

28. Keeping the water and hexane separate is a more stable (lower energy) stateC H O H O H O H C H O H O H O H O H

29. Gases dissolving in liquid

30. CO2 in water C O C O C O O H O H O H O H O H O H O H O H O H O H

31. CO2 in water Bonds broken? Bonds formed? O H C O C O O H O H O H O H O

32. Henry’s Law: Effect of Pressure on Gas Solubility

33. Cgas = kHPgas Henry’s Law Henry’s Law constant Concentration of
gas in solution
Pressure of gas above solution

34. The Henry’s Law constant for N2 at 25 oC is 6. 8 x 10-4 mol/L atm
The Henry’s Law constant for N2 at 25 oC is 6.8 x 10-4 mol/L atm. What is the concentration of N2 in water when the pressure of nitrogen is 0.8 atm?
Cgas = kHPgas

35. Calculate the concentration change for CO2 when a sealed soft drink can (PCO2= 4.0 atm) is opened (PCO2 = atm). kH for CO2 at 25oC is 3.1 x 10-2 mol/L atm.
Cgas = kHPgas

36. If you don’t know kH:
Cgas = kHPgas so
kH = Cgas/Pgas
C C2
P P2 =

37. The solubility of methane, the chief component of natural gas, in water at 20o C and 1.0 atm pressure is g L-1. What is its solubility in water at 1.5 atm and 20.0oC?
C C2
P P2 =

38. Concentration Units for Solutions

39. Units of concentration
Molarity (M): moles per liter
Mole fraction (XA)
Mass percent(also called w/w)
ppm
ppb
Molality (m): moles per kilogram of solvent

40. Mole Fraction nA XA = nA + nB + nC + ….
Tells what fraction of the total number of moles a given component constitutes
# of moles
of component A nA
nA + nB + nC + ….
XA =
Mole fraction
of component A
Total # of moles
(add up # of moles of each component)

41. Mole Fraction (XA) nA XA = nA + nB + nC + ….
Example: A solution is made of 10 moles of ethanol and 20 moles of water. Ethanol comprises what mole fraction? nA
nA + nB + nC + ….
XA =

42. Mole Fraction (XA) nA XA = nA + nB + nC + ….
Example: A solution is made of 10 moles of water, 15 moles of acetone, and 25 moles of toluene. Acetone comprises what mole fraction? nA
nA + nB + nC + ….
XA =

43. Mass Percent (w/w) mass of solute Percentage by mass = x 100%
(or any component of a thing)
Percentage by mass = x 100%
mass of solute
mass of solution
(the total mass)

44. 39.55 g salt is dissolved in 1000. g of water.
What is the percentage by mass of salt in the solution?
Mass percent = x 100%
mass of solute
mass of solution

45. Problem solving strategies for harder concentration problems
Identify which measure of concentration you need to calculate
2. Use the definition for that measure of concentration to determine what you need to know
3. Based on information given, create and carry out a plan to find what you need to know. If necessary, start plan by assuming 100.
4. Do calculations for measure of concentration

46. What is the molarity of a 3% (w/w) H2O2 solution?
The density of this solution is 1.00 g/mL.
Mass percent = x 100%
mass of solute
mass of solution

47. Identify which measure of concentration you need to calculate
What is the molarity of a 3% (w/w) H2O2 solution?
The density of this solution is 1.00 g/mL.

48. What is the molarity of a 3% (w/w) H2O2 solution?
2. Use the definition for that measure of concentration to determine what you need to know
What is the molarity of a 3% (w/w) H2O2 solution?
The density of this solution is 1.00 g/mL.
molarity =
moles of solute
L of solution
Need to find:
moles of solute
L of solution

49. 3. Based on information given, create and carry out a plan to find what you need to know. If necessary, start plan by assuming 100.
Calculate: moles of H2O2; L of solution
100.0 g of solution mL of solution
a. Calculate g of solution
a. Calculate g of H2O2
b. Calculate g of H2O2
b. Calculate moles of H2O2
c. Calculate moles of H2O2
c. Calculate L of solution
d. Do molarity calculation
d. Do molarity calculation

50. What is the molarity of a 3% (w/w) H2O2 solution?
The density of this solution is 1.00 g/mL.
Mass percent = x 100%
mass of solute
mass of solution
100.0 g of solution mL of solution
a. Calculate g of H2O2
a. Calculate g of solution
b. Calculate moles of H2O2
b. Calculate g of H2O2
c. Calculate L of solution
c. Calculate moles of H2O2
d. Do molarity calculation
d. Do molarity calculation

51. Very small percentages by mass
ppm (parts per million)
1 ppm =1/1,000,000 of the mass of a solution
For example: 1 mg in 1000 g of solution
in aqueous solution: 1 ppm =1 mg/L
ppb (parts per billion):
1 ppb =1/1,000,000,000 of the mass of a solution

52. Molality moles of solute Molality (m)= kg solvent
Densities of liquids can change with temperature
Molality used when temperature is a consideration

53. moles of solute Molality (m)= kg solvent
What is the molality of a solution created by adding 20.7 g of KBr to g of water?

54. What is the molality of a solution created by adding 122 g of sucrose (C12H22O11) to 587 g of water?

55. A 6. 79 M solution of HCl has a density of 1. 15 g/cm3
A 6.79 M solution of HCl has a density of 1.15 g/cm3. What is the molality of the solution?
Identify measure of concentration to calculate
2. Use definition for that measure of concentration to determine what you need to know
3. Based on information given, create & carry out a plan to find what you need to know. Start plan by assuming 100.
4. Do calculations for measure of concentration

56. Definition: Colligative Properties
Properties of solutions that change depending on concentrations of solute in the mixture.
Vapor pressure of a solution (Raoult’s Law)
Boiling point elevation
Freezing point depression
Osmotic pressure

57. Raoult’s Law (part 1) Psoln = Xsolvent P0solvent
Explains the relationship between vapor pressure and concentration
Psoln = Xsolvent P0solvent
Vapor pressure of the solution
Vapor pressure of the pure solvent (without any solute)
Mole fraction of the solvent

58. The vapor pressure of pure water is 23. 8 mm Hg
The vapor pressure of pure water is 23.8 mm Hg. If 103 g of seawater contains 3.5 g NaCl and 99.5 g water, what is the vapor pressure of seawater?
Psoln = Xsolvent Posolvent

59. Raoult’s Law for solutions with two or more volatile components
Psoln = XA P0A + XB P0B+ …

60. What is the vapor pressure of a solution containing 18
What is the vapor pressure of a solution containing 18.6 moles water (P0= 23.8 torr) and 25.8 moles hydrogen peroxide (P0 = 1.97 torr)?
Psoln = XA PoA + XB PoB

61. van’t Hoff factor
Changes in colligative properties may be determined by the number of particles in solution Ionic compounds dissociate in water 1 M NaCl = 2 M ions (1 M Na+, 1 M Cl-) so i = 2* 1 M CaCl2 = 3 M ions (1 M Ca2+, 2 M Cl-) so i = 3* 1 M glucose = 1 M particles so i = 1
* In an ideal world…

62. Boiling point elevation by solutes
Addition of a solute changes the vapor pressure of a liquid and therefore also changes the boiling point
DTb = i Kbm
Molality of the solution
Change in boiling point
van’t Hoff factor
Molal boiling-point-depression constant

63. A chef, wanting to cook pasta, increases the boiling temperature of water by adding 1 T of salt (~15 g of NaCl) to 2.00 kg of water. How much does he change the boiling temperature? (Kb for water = oC/m)
DTb = iKbm

64. Acetic acid has a normal boiling point of 118. 5 oC. If 56
Acetic acid has a normal boiling point of oC. If 56.0 g sucrose (C12H22O11) is added to g of acetic acid, what will the boiling point of the mixture be? (Kb = 3.07 oC/m)
DTb = iKbm

65. Freezing point depression by solutes
Solutes interfere with the formation of intermolecular forces that turn liquids into solids
DTf = i Kfm
Molality of the solution
Change in freezing point
van’t Hoff factor
Molal freezing-point-depression constant

66. Artificial seawater can be created by adding 35. 5 g of NaCl to 1000
Artificial seawater can be created by adding g of NaCl to g water. At what temperature will artificial seawater freeze? (Kf for water is 1.86 oC/m)
DTf = iKfm

67. Definition: Osmosis
Net shift of solvent (usually water) through a membrane that only allows passage of solvent molecules

68. Membranes and Permeability
Membrane: separator that keeps mixtures separated Permeability: ability of a membrane to allow substances to pass through permeable inpermeable semi-permeable

69. Cell membranes are semi-permeable
e.g. aquaporins only let water through

70. Why does osmosis happen?
Unequal concentrations on either side of the membrane
System tries to reach equilibrium by making concentrations similar
Only solvent can pass through membrane

71. Osmotic Pressure
A. Solution B separated from pure water, A, by osmotic membrane. (No osmosis yet)
B. Osmosis has occurred; volume of fluid in tube higher.
C. Pressure needed to prevent osmosis = osmotic pressure.

72. Calculating Osmotic Pressure
PV = i nRT P = i MRT

73. An aqueous solution of a sugar was prepared at a concentration of 0
An aqueous solution of a sugar was prepared at a concentration of 0.42 g/L at 25 oC. Its osmotic pressure was 2.5 torr. Calculate the molecular mass of the compound.
P = i MRT