1. Solutions Chapter 14 Hein and Arena
Eugene Passer Chemistry Department Bronx Community College
© John Wiley and Sons, Inc
Version 2.0
12th Edition

2. Chapter Outline 14.1 General Properties of Solutions
Solutions: A Reaction Medium
Concentration of Solutions
Solubility
Factors Related to Solubility
Colligative Properties of Solutions
Rate of Dissolving Solids
Osmosis and Osmotic Pressure

3. 14.1 General Properties of Solutions

4. A solution is a system in which one or more substances are homogeneously mixed or dissolved in another substance.
The solute is the component that is dissolved or is the least abundant component of the solution.
The solvent is the dissolving agent or the most abundant component in the solution.

6. Properties of True Solutions

7. The dissolved solute is molecular or ionic in size.
A mixture of two or more components–solute and solvent –is homogeneous and has a variable composition.
This means that the ratio of solvent to solute can be varied.
The dissolved solute is molecular or ionic in size.
It is either colored or colorless and is usually transparent.

8. The solute remains uniformly distributed throughout the solution and will not settle out with time.
The solute can generally be separated from the solvent by purely physical means such as evaporation.
The solute particles of a true solution are molecular or ionic in size.
The particle size range is 0.1 nm to 1 nm (10-8 cm to10-7cm).

9. Formation of a Solution
solute
solvent
solution

10. 14.2 Solubility

11. Solubility describes the amount of solute that will dissolve in a specified amount of solvent.

12. Solubilities of substances vary widely.

13. Terms that describe the extent of solubility of a solute in a solvent:
very soluble
soluble
moderately soluble
slightly soluble
insoluble

14. methyl alcohol and water
Terms that describe the solubility of liquids:
miscible: liquids that are capable of mixing and forming homogeneous solutions.
methyl alcohol and water
immiscible: liquids that are insoluble in each other.
oil and water

15. Solubility of Various Common Ions in Cold Water
14.2

16. 14.3 Factors Related to Solubility

17. Factors that affect solubility are:
ion size
interactions between solute and solvent
temperature

18. The Nature of the Solute and Solvent

19. The general rule for predicting solubility is “like dissolves like”.

20. Polar compounds tend to be more soluble in polar solvents than nonpolar solvents.
NaCl (sodium chloride) is
soluble in water
slightly soluble in ethyl alcohol
insoluble in ether and benzene
Solvent Polarity

21. Dissolution of sodium chloride in water.
The hydrated ions slowly diffuse away from the crystal to become dissolved in solution.
As the attraction between the ions weakens, the ions move apart and become surrounded by water dipoles.
Polar water molecules are attracted to Na+ and Cl- ions in the salt or crystal, weakening the attraction between the ions.
14.3

22. Nonpolar compounds tend to be more soluble in nonpolar solvents than in polar solvents.
benzene is
insoluble in water
soluble in ether
Solvent Polarity

23. The Effect of Temperature on Solubility

24. Most solutes have a limited solubility in a specific solvent at a fixed temperature.

25. Effect of Temperature on the Solubility of a Solid in a Liquid
For most solids dissolved in a liquid, an increase in temperature results in increased solubility.
Some solids increase in solubility only slightly with increasing temperature.
Some solids decrease in solubility with increasing in temperature.
Any point on any solubility curve represents a saturated solution of that solute

26. large increase in solubility with temperature
slight increase in solubility with temperature
decrease in solubility with increasing temperature

28. Effect of Temperature on the Solubility of a Gas in Water
The solubility of a gas in water usually decreases with temperature.
Kinetic molecular theory accounts for this decreased solubility.
For the gas to dissolve it must form bonds of some sort with the molecules of the liquid.
At higher temperatures the kinetic energy of the gas molecules is sufficient to break the gas water bond.

29. large decrease in solubility with increasing temperature

30. The Effect of Pressure on Solubility

31. Small pressure changes have little effect on the solubility of
solids in liquids
liquids in liquids
Small pressure changes have a great effect on the solubility of gases in liquids.
The solubility of a gas in a liquid is directly proportional to the pressure of that gas above the liquid.

32. Effect of Pressure on the Solubility of a Gas
number of gas particles doubles
solubility of gas doubles
liquid

33. Saturated, Unsaturated and Supersaturated Solutions

34. At a specific temperature there is a limit to the amount of solvent that will dissolve in a given amount of solute.
When this condition occurs the solution is said to be saturated.

35. In a saturated solution two processes are occurring simultaneously
The solute is crystallizing out of solution.
The solid is dissolving into the solution.
solute (undissolved)
solute (dissolved)

36. Dissolving a Solid in a Liquid
Solution is saturated.
A saturated solution may be either dilute or concentrated, depending on the solubility of the solute.
Solution is unsaturated. Solute dissolves
35 g KCl
34 g KCl
30 g KCl
5 g KCl
10 g KCl
15 g KCl
25 g KCl
20 g KCl
No more KCl can dissolve.
100 g H2O
20oC

37. Dissolving a Solid in a Liquid
A solution that is saturated at one temperature may not be saturated at another temperature.
Raise temperature
35 g KCl
Solute dissolves The solution is unsaturated
It may increase or decrease depending on the solute-solvent system.
A saturated solution may be either dilute or concentrated.
Solubility of a solute in a solvent changes with temperature.
100 g H2O
50oC
20oC

38. Dissolving a Solid in a Liquid
A stress to the system will cause the solute in excess of the saturation limit to come out of solution.
Whenever a solution contains solute in excess of its solubility limit the solution is supersaturated.
A supersaturated solution is unstable.
Cool Solution to 20oC
35 g KCl
At 20oC the solubility of KCl in water is 34 g/100 g H2O.
100 g H2O
The solution contains 1 gram of KCl in excess of the solubility limit.
No KCl precipitates.
20oC
50oC

39. 14.4 Rate of Dissolving Solids

40. Particle Size
A solid can dissolve only at the surface that is in contact with the solvent.
Smaller crystals have a larger surface to volume ratio than large crystals.
Smaller crystals dissolve faster than larger crystals.

41. 14.5

42. Temperature
In most cases, the rate of dissolving of a solid increases with temperature.
This occurs because solvent molecules strike the surface of the solid more frequently, causing the solid to dissolve more rapidly.

43. As solution concentration increases, the rate of dissolving decreases.
Concentration of the Solution Δt
As solution concentration increases, the rate of dissolving decreases. Δc Δt Δc
The rate of dissolving is at a maximum when solute and solvent are first mixed.

44. Agitation or stirring.
When a solid is first put into water, it comes in contact only with water. The rate of dissolving is a maximum.

45. Agitation or stirring.
When a solid is first put into water, it comes in contact only with water. The rate of dissolving is a maximum.
As the solid dissolves, the amount of dissolved solute around the solid increases and the rate of dissolving decreases.

46. Agitation or stirring.
When a solid is first put into water, it comes in contact only with water. The rate of dissolving is then a maximum.
Stirring distributes the dissolved solute throughout the water; more water is in contact with the solid causing it to dissolve more rapidly.
As the solid dissolves, the amount of dissolved solute around the solid increases and the rate of dissolving decreases.

47. 14.5 Solutions: A Reaction Medium

48. Many solids must be put into solution to undergo appreciable chemical reactions.

49. sodium chloride reacts with silver nitrate

50. NaCl(s) + AgNO3(s) → no reaction
If the reactants are in the solid phase, no reaction occurs.

51. NaCl(s) + AgNO3(s) → no reaction
NaCl(s) and AgNO3(s) do not react because their ions are securely locked in their crystal lattices.

52. If the reactants are dissolved in water, an immediate reaction occurs.
Na+
Cl-
Ag+
If the reactants are dissolved in water, an immediate reaction occurs.

53. NaCl(s) + AgNO3(s) → AgCl(s) +NaNO3(aq)
Mobile Ag+ and Cl- ions come into contact and form insoluble AgCl which precipitates.

54. NaCl(s) + AgNO3(s) → AgCl(s) +NaNO3(aq)
Na+ and remain in solution.

55. 14.6 Concentration of Solutions

56. The concentration of a solution expresses the amount of solute dissolved in a given quantity of solvent or solution.

57. Dilute and Concentrated Solutions

58. The terms dilute and concentrated are qualitative expressions of the amount of solute present in a solution.
A dilute solution contains a relatively small amount of dissolved solute.
A concentrated solution contains a relatively large amount of solute.

59. Concentrated HCl contains 12 mol of HCl per liter of solution.
In some laboratories a dilute solution might be 6 mol of HCl per liter of solution.
In another laboratory dilute HCl might be 4 mol of HCl per liter of solution.

60. Mass Percent Solution

61. Mass percent expresses the concentration of solution as the percent of solute in a given mass of solution.

62. What is the mass percent of sodium hydroxide in a solution that is made by dissolving 8.00 g NaOH in 50.0 g H2O?
grams of solute (NaOH) = 8.0 g
grams of solvent (H2O) = 50.0 g

63. What masses of potassium chloride and water are needed to form 250
What masses of potassium chloride and water are needed to form 250. g of 5.00% solution?
The percent expresses the mass of the solute.
Dissolving 12.5 g KCl in 238 g H2O gives a 5.00% KCl solution.
250.g = total mass of solution
250.g – 12.5 g = 238 g H2O

64. A 34. 0% sulfuric-acid solution has a density of 1. 25 g/mL
A 34.0% sulfuric-acid solution has a density of 1.25 g/mL. How many grams of H2SO4 are contained in 1.00 L of this solution?
Grams of solution are determined from the solution density.
Step 1. Determine grams of solution.
1.00 L = 1.00 x 103 mL

65. A 34. 0% sulfuric-acid solution has a density of 1. 25 g/mL
A 34.0% sulfuric-acid solution has a density of 1.25 g/mL. How many grams of H2SO4 are contained in 1.00 L of this solution?
Solve the mass percent equation for grams of solute.

66. Mass/Volume Percent (m/v)

67. Mass /volume percent expresses the concentration as grams of solute per 100 ml solution.

68. A 3.0% H2O2 solution is commonly used as a topical antiseptic to prevent infection. What volume of this solution will contain 10. g of H2O2?
Solve the mass/volume equation for grams of solute.

69. Volume Percent

70. The volume percent is the volume of a liquid in 100 ml of solution.
Solutions that are formulated from liquids are often expressed as volume percent with respect to the solute.

71. Volumes are not necessarily additive.
A bottle of rubbing alcohol reads 70% by volume.
The alcohol solution could be prepared by mixing 70 mL of alcohol with water to make a total volume of 100 mL of solution.
30 mL of water could not be added to 70 mL of alcohol because the volumes are not necessarily additive.

72. Molarity

73. Molarity of a solution is the number of moles of solute per liter of solution.

74. Molarity can be expressed in grams of solute rather than moles of solute.

75. Preparation of a 1 molar solution
14.7

76. What is the molarity of a solution containing 1
What is the molarity of a solution containing 1.4 mol of acetic acid (HC2H3O2) in 250. ml of solution?
It is necessary to convert 250. mL to L since molarity = mol/L.

77. How many grams of potassium hydroxide are required to prepare 600
How many grams of potassium hydroxide are required to prepare 600. mL of M KOH solution?
The data are:
The calculation is:

78. Calculate the number of moles of nitric acid in 325 mL of 16 M HNO3.
moles = liters x M
Use the equation:
Substitute the data given in the problem and solve:

79. What volume of 0. 250 M solution can be prepared from 16
What volume of M solution can be prepared from 16.0 g of potassium carbonate?
The data are:
The conversion is:

80. HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(aq)
How many mL of 2.00 M HCL will react with 28.0 g NaOH?
Step 1 Write and balance the equation for the reaction.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(aq)
Step 2 Find the number of moles of NaOH in 28.0 g NaOH.

81. How many mL of 2.00 M HCL will react with 28.0 g NaOH?
Step 3 Solve for moles and volume of HCl.

83. Dilution Problems

84. If a solution is diluted by adding pure solvent:
the volume of the solution increases.
the number of moles of solute remain the same.

85. Na+
NaNO3 solution

86. Moles of solute remain the same.
Na+
Solution volume is doubled.
Solution concentration is halved.
Moles of solute remain the same.

87. Calculate the molarity of a sodium hydroxide solution that is prepared by mixing 100. mL of 0.20 M NaOH with 150. mL of water. Assume volumes are additive.
Step 1 Calculate the moles of NaOH in the original solution.

88. solution volume = 100. mL + 150. mL = 250. mL
Calculate the molarity of a sodium hydroxide solution that is prepared by mixing 100. mL of 0.20 M NaOH with 150. mL of water. Assume volumes are additive.
Step 2 Solve for the new molarity.
solution volume = 100. mL mL = 250. mL

89. V1 and V2 must have the same volume units.
Alternative Solution
When the moles of a solute in a solution before and after dilution are the same, the moles before and after dilution may be set equal to each other.
mol1 = mol2
before dilution
after dilution
V1 and V2 must have the same volume units.

90. Calculate the molarity of a sodium hydroxide solution that is prepared by mixing 100. mL of 0.20 M NaOH with 150. mL of water. Assume volumes are additive.
V1 = 100. mL
M1 = 0.20 M
V2 = 250. mL
M2 = unknown
(100. mL)(0.20 M) = (250. mL)M2

91. 2AgNO3(aq) + BaCl2(aq) → 2AgCl(s) + Ba(NO3)2(aq)
How many grams of silver chloride will be precipitated by adding sufficient silver nitrate to react with mL of M barium chloride solution?
2AgNO3(aq) + BaCl2(aq) → 2AgCl(s) + Ba(NO3)2(aq)
Step 1 Determine the number of moles of BaCl2 in 1500 mL of M solution.

92. 2AgNO3(aq) + BaCl2(aq) → 2AgCl(s) + Ba(NO3)2(aq)
How many grams of silver chloride will be precipitated by adding sufficient silver nitrate to react with mL of M barium chloride solution?
2AgNO3(aq) + BaCl2(aq) → 2AgCl(s) + Ba(NO3)2(aq)
Step 2 Use the mole-ratio method to calculate the moles and grams of AgCl.

93. 14.7 Colligative Properties of Solutions

94. Colligative Properties
When a nonvolatile solute is added to a solvent, three physical properties of the solvent will change:
Boiling point elevation.
Freezing point depression.
Vapor pressure.
Colligative Properties

95. Colligative Properties
Colligative properties of a solution depend only on the number of solute particles in a solution and not on the nature of those particles.
Boiling point elevation.
Freezing point depression.
Vapor pressure.
Colligative Properties

96. Each solvent shows a characteristic:
freezing point depression constant
boiling point elevation constant

97. The vapor pressure of a liquid depends on the ease with which its molecules can escape from the liquid’s surface.
H2O(l) → H2O(g)

98. If 10% of the molecules in a solution are nonvolatile solute molecules, the vapor pressure of the solution is 10% lower than that of the pure solvent.
H2O(l) → H2O(g)

99. A liquid boils when its vapor pressure equals atmospheric pressure.
A solution will have a lower vapor pressure, and consequently a higher boiling point.
Vapor Pressure Curve of Pure Water and Water Solution: Boiling Point Elevation

100. A solution will have a lower vapor pressure, and consequently a lower freezing point.
A liquid freezes when its vapor pressure equals the vapor pressure of its solid.
Vapor Pressure Curve of Pure Water and Water Solution: Freezing Point Depression
water vapor pressure curve
solution vapor pressure curve
ice vapor pressure curve

101. Molality

102. The freezing point depression and the boiling point elevation are directly proportional to the number of moles of solute per kilogram of solvent.

103. Symbols used in the calculation of colligative properties
m = molality
Δtf = freezing point depression: oC
Δtb = boiling point elevation: oC
Kf = freezing point depression constant
Kb = boiling point elevation constant

104. The molar mass of CH3OH 32.04 g/mol
What is the molality (m) of a solution prepared by dissolving 2.70 g CH3OH in 25.0 g H2O?
The molar mass of CH3OH g/mol

105. Calculate moles of C2H6O2:
A solution is made by dissolving 100. g of ethylene glycol (C2H6O2) in 200. g H2O. What is the freezing point of the solution?
Calculate moles of C2H6O2:
Calculate kilograms of H2O

106. Calculate the freezing point depression.
A solution is made by dissolving 100. g of ethylene glycol (C2H6O2) in 200. g H2O. What is the freezing point of the solution?
Calculate the freezing point depression.
freezing point solution = freezing point solvent – Δtf.
= 0oC – 15oC = – 15oC

107. A solution made by dissolving 4
A solution made by dissolving 4.71 g of a compound of unknown molar mass in g of H2O has a freezing point of –1.46oC. What is the molar mass of the compound?
Δtf = oC

108. Convert 4.71 g solute/100 g H2O to g/mol.
molar mass of the compound

109. 14.8 Osmosis and Osmotic Pressure

110. Osmosis is the diffusion of water, either from a dilute solution or from pure water, through a semipermeable membrane into a solution of higher concentration.

111. 14.9

112. A 0.90% solution of sodium chloride in water is known as physiological saline solution. It is isotonic with blood plasma.
Red blood cells do not shrink or swell in an isotonic solution.

113. Red blood cells swell in a hypotonic solution.
Red blood cells shrink in a hypertonic solution.

114. Osmotic pressure is a colligative property.
Osmtoic Pressure
Osmotic pressure is dependent only on the concentration of the solute particles in a solution and is independent of their nature.
The osmotic pressure of a solution can be measured by applying enough pressure to stop the flow of water due to osmosis.
The difference between the applied pressure and the atmospheric pressure is the osmotic pressure.
Osmotic pressure is a colligative property.

115. water passes through the cellophane
In osmosis,the net transfer of solvent is always from the more concentrated to the less concentrated solution.
water passes through the cellophane
14.9

116. The End