11/20/2013
14 Solutions
Brass, a solid solution of Zn and Cu, is used to make
musical instruments and many other objects.
Foundations of College Chemistry, 14th Ed.
Chapter Outline
14.1
General Properties of Solutions
14.2
Solubility
14.3
Rate of Dissolving Solids
14.4
Concentration of Solutions
14.5
Colligative Properties of Solutions
14.6
Osmosis and Osmotic Pressure
Morris Hein and Susan Arena
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
General Properties of Solutions
Solutions Practice
Solution: a homogeneous mixture of one or more
solutes and a solvent.
Soda is a mixture of sugar in water.
Which substance is the solute?
Solute: substance being dissolved.
Solvent: dissolving agent that is usually the
most abundant substance in the mixture.
Note: a solution does not always just refer to liquids.
Example: Air is a solution composed of N2, O2, Ar and CO2
N2 is the solvent as it composes 78% of air.
a. sugar
b. water
c. soda
A solution is prepared by adding 25 mL of ethyl alcohol
to 75 mL of water. Which substance is the solvent?
a. ethyl alcohol
b. water
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Common Types of Solutions
Properties of a True Solution
1. A homogeneous mixture of two or more components
whose ratio can be varied.
2. The dissolved solute is molecule or ionic in size
(< 1 nm).
3. Can be colored or colorless, though solutions are
usually transparent.
4. The solute remains dissolved and does not settle
(precipitate) out of solution over time.
5. The solute can be separated from solvent by physical
means (usually evaporation).
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© 2014 John Wiley & Sons, Inc. All rights reserved.
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Solubility
Solubility: the amount of a substance that will dissolve
in a specific amount of solvent at a given temperature.
Solubility Rules
Insoluble
Soluble
Na+, K+, NH4+
Miscible: when two liquids dissolve in each other.
Nitrates (NO3-)
Acetates, (C2H3O2-)
Immiscible: when two liquids do not dissolve one another.
Cl-, Br-, I-
Except
Ag+, Hg22+, Pb2+
Sulfates (SO42-),
Ag+, Ca2+ (slightly)
Except
Ba2+, Sr2+, Pb2+
Example
27 g KBr/100g H2O at 23 ºC
A mixture of oil
and water is
immiscible.
NH4+, Group I
b. insoluble
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Solutions Practice
Solutions Practice
Predict the solubility of silver nitrate.
a. soluble
b. insoluble
Most sulfates are soluble, except Ba2+.
Predict the solubility of NaCl.
b. insoluble
All NO3- salts are soluble.
Predict the solubility of silver hydroxide.
a. soluble
a. soluble
Carbonates (CO32-)
Phosphates (PO43-)
OH-, Sulfides (S2-)
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Predict the solubility of barium sulfate.
a. soluble
Except
b. insoluble
Most hydroxides are insoluble.
Predict the solubility of ammonium carbonate.
All Na+ salts are soluble.
a. soluble
b. insoluble
All NH4+ salts are soluble.
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Factors Affecting Solubility
Factors Affecting Solubility
Ionic Compound Solubility in Polar Solvents
“Like Dissolves Like”
Polar compounds dissolve in polar solvents.
Ethanol (CH3OH) dissolves in water (HOH).
Nonpolar compounds dissolve in nonpolar solvents.
Several ionic compounds dissolve in water,
due to strong ion-dipole forces.
The individual cations and anions are surrounded
by H2O molecules (i.e., hydrated).
The cation is attracted to the partially negative O atom.
The anion is attracted to the partially positive H atoms.
Carbon tetrachloride (CCl4) dissolves in
hexanes (CH3(CH2)4CH3).
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© 2014 John Wiley & Sons, Inc. All rights reserved.
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Temperature and Solubility
Pressure and Solubility
Pressure does not affect solubility of liquids or solids.
Gas solubility in a liquid is proportional to
the gas pressure over the liquid.
Example : A bottle of root beer is under high pressure.
As the bottle opens, the pressure decreases,
and the bubbles formed indicate gas loss from the liquid.
Solubility increases with temperature for most solids (red lines)
Solubility decreases with temperature for all gases (blue lines).
As a gas increases in temperature, the kinetic energy
increases, which means it interacts less with the liquid,
making it less easy to solvate.
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Saturated and Unsaturated Solutions
Supersaturated Solutions
There are limits to the solubility of a compound
at a given temperature.
Supersaturated solutions: contain more solute than
needed to saturate a solution at a given temperature.
Saturated solutions: contain the maximum amount
of dissolved solute in a solvent.
Saturated solutions are still dynamic; dissolved solute
is in equilibrium with undissolved solute.
undissolved solute
dissolved solute
Unsaturated solutions: contain less than the maximum
amount of possible dissolved solute in a solvent.
How is this possible?
Heating a solution can allow more to dissolve.
Upon cooling to ambient temperature,
the solution is supersaturated.
These solutions are unstable -- disturbing the solutions
can cause precipitation of solute.
Some hotpacks release heat by crystallization
of a supersaturated solution of sodium acetate.
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Solubility Practice
Rate of Dissolving Solids
Will a solution prepared by adding 9.0 g of KCl to
20.0 g of H2O be saturated or unsaturated at 20 ºC?
Effect of Particle Size
Using Table 14.3, 34.0 g of KCl will dissolve
in 100.0 g of H2O at 20 ºC.
A solid can only dissolve at a surface that
is in contact with the solvent.
6.8 g of KCl will then dissolve in
20.0 g of water at that temperature.
Since smaller crystals have a higher surface to volume
area, smaller crystals dissolve faster than larger ones.
The KCl solution should be saturated.
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
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Rate of Dissolving Solids
Rate of Dissolving Solids
Effect of Solute Concentration
Effect of Temperature
Increasing the temperature normally increases the rate
of dissolution of most compounds.
Rate is highest at higher concentration and
decreases at lower concentration.
As the solution approaches the saturation point,
the rate of solute dissolving decreases.
Solvent molecules strike the solid surface more often,
causing the solid to dissolve more rapidly.
The solute molecules are more easily separate from the
solid due to a higher kinetic energy.
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Rate of Dissolving Solids
Surface Area
Surface Area of Two Crystals
Effect of Agitation/Stirring
Surface area = 6(side)2 = 6(0.1)2 = 0.06 cm2
Stirring a solution briskly breaks up a solid
into smaller pieces, increasing surface area,
thereby increasing the rate of dissolution.
1000 cubes have a total surface area of
1000 x 0.06 cm2 = 60 cm2
What is the surface area of a 1 cm square crystal?
Surface area = 6(side)2 = 6(1)2 = 6 cm2
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Solutions: A Reaction Medium
Concentration of Solutions
The purpose of dissolving reactants in a solution is
often to allow them to come in close contact to react.
Example:
Solid-solid reactions are generally very slow
at ambient temperature
KCl (s) + AgNO3 (s)
KCl (aq) + AgNO3 (aq)
Dilute: a solution that contains a relatively small
amount of dissolved solute.
Example:
No Reaction
By dissolving both compounds in water,
the ions can collide with one another and react
to form an insoluble compound.
K+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)
Qualitative Expressions of Concentrations
AgCl (s) + KNO3 (aq)
AgCl(s) + K+(aq) + NO3-(aq)
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A 0.1 M HCl solution is dilute acid.
Concentrated: a solution that contains a relatively large
amount of dissolved solute.
Example:
A 12 M HCl solution is concentrated acid.
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Concentration of Solutions
Mass Percent
Quantitative Expressions of Concentrations:
Units
Symbol
Mass percent
% m/m
Part per million
ppm
Mass/Volume percent
% m/v
Volume percent
% v/v
Molarity
M
Molality
m
Definition
mass solute
x 100
mass solution
mass solute
x 1,000,000
mass solution
mass solute
x 100
mL solution
mL solute
x 100
mL solution
mol solute
L solution
mol solute
kg solvent
Calculate the mass % of NaCl in a solution prepared
by dissolving 50.0 g of NaCl in 150.0 g of H2O.
Knowns
50.0 g NaCl (solute mass)
150.0 g H2O (solvent mass)
200.0 g solution (solute + solvent mass)
Formula
mass % = mass solute x 100
mass solution
Calculate
mass % =
50 g NaCl
200 g soln
x 100 = 25% NaCl
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Mass Percent Practice
Mass-Volume Percent
What is the mass of Na2CO3 needed to make
350.0 g of a 12.3% aqueous solution?
Saline is a 0.9 m/v % NaCl solution. What mass of
sodium chloride is needed to make 50 mL of saline?
Knowns
12.3% solution (mass %)
350.0 g solution (solute + solvent mass)
Knowns
50.0 mL solution (solution volume)
0.90 m/v% (mass/volume %)
Solve for mass of solute (NaCl)
Solve for mass of solute (Na2CO3)
Formula
Formula
mass % x mass soln
mass % = mass solute x 100 mass solute =
100
mass solution
m/v % =
Calculate
Calculate
mass solute =
g solute
x 100
mL solution
12.3 x 350.0 g
= 43.1 g Na2CO3
100
mass solute =
m/v % x mL soln
100
mass solute = 50.0 x 0.90 = 0.45 g NaCl
100
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Mass-Volume Percent Practice
Volume Percent
What volume of a 3.0% H2O2 solution
will contain 10.0 g of H2O2?
a. 33.0 mL soln
b. 330. mL soln Knowns 10.0 g H2O2 (desired solute mass)
c. 3.00 L soln
3.0 m/v%
d. 165 mL soln
Solve for volume of solution
What volume of soda that is 6.0 % by volume alcohol
contains 200.0 mL of ethanol (CH3CH2OH)?
Formula
m/v % =
20.0 mL ethanol (solute volume)
6.0 volume %
Solve for volume of solution
Knowns
Formula
volume % =
g solute
x 100
mL solution
Calculate
mass solute =
mL solution =
10.0 g
3.0
g solute
m/v %
x 100
volume solute
x 100
volume solution
volume soln =
volume solute x 100
volume %
Calculate
x 100 = 330. mL sln
© 2014 John Wiley & Sons, Inc. All rights reserved.
volume soln =
200.0
x 100 = 3300 mL soda
6.0
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Volume Percent Practice
Molarity
A solution is prepared by mixing 20.0 mL of propanol
with enough water to produce 400.0 mL of solution.
What is the volume percent of propanol?
A common unit for solution concentration
due to convenience.
a. 20.0 %
b. 2.00 %
c. 5.00 %
d. 10.0 %
molarity =
Knowns
20.0 mL propanol (solute volume)
400.0 mL solution (solution volume)
Solve for volume percent
Formula
volume % =
volume solute
x 100
volume solution
Calculate
volume % =
20.0 x 100
= 5.00% propanol
400.0
mol solute
L solution
Example:
To prepare a 1.0 M KCl
solution, 1.0 mol of KCl is
dissolved in enough water to
make 1.0 L of solution.
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Molarity Practice
Molarity Practice
Calculate the molarity of a solution prepared by
dissolving 9.35 g of KCl in enough water to
prepare a 250.0 mL solution.
How many grams of KOH are required to prepare
600.0 mL of a 0.450 M KOH solution?
Knowns
9.35 g KCl (solute mass)
250.0 mL solution (solution volume)
Formula
Solve for molarity
Calculate
9.35 g KCl x
molarity =
mol solute
L solution
1 mol KCl
= 0.125 mol KCl
74.551 g KCl
a. 0.270 g KOH
Knowns 600 mL (solution volume)
b. 4.81 g KOH
0.450 M (solution molarity)
c. 1.52 x 104 g KOH
d. 15.1 g KOH
Plan Solve for moles, then grams using molarity and
molar mass as conversion factors
mol solute
Formula molarity =
mol solute = molarity x L soln
L solution
0.125 mol KCl
= 0.502 M KCl
molarity =
0.250 L solution
Calculate moles solute = 0.450 M KOH x 0.600 L = 0.270 mol KOH
0.270 mol KOH x 56.11 g KOH = 15.1 g KOH
1 mol KOH
© 2014 John Wiley & Sons, Inc. All rights reserved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Solution Stoichiometry
Solution Stoichiometry Practice
Similar to previous stoichiometry problems, but we can
now use molarity as an additional conversion factor.
How many grams of AgCl will form by adding enough
AgNO3 to react fully with 1500. mL of
0.400 M BaCl2 solution?
How many mL of 0.175 M Hg(NO3)2 are needed
to precipitate 2.50 g of KI?
Hg(NO3)2 (aq) + 2 KI (aq)
Plan
g KI
mol KI
2 KNO3 (aq) + HgI2 (s)
mol Hg(NO3)2
mL soln
Calculate
2.50 g KI ×
1 mol Hg(NO3)2
1 mol KI
1000 mL soln
×
×
166.00 g KI
0.175 mol Hg(NO3)2
2 mol KI
= 43.0 mL Hg(NO3)2
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2 AgNO3 (aq) + BaCl2(aq)
2 AgCl (s) + Ba(NO3)2 (aq)
a. 172 g AgCl
b. 86.0 g AgCl
c. 8.37 x 10-3 g AgCl
d. 36.0 g AgCl
Plan
Volume BaCl2
mol BaCl2
mol AgCl
g AgCl
Calculate
0.400 mol BaCl2
2 mol AgCl × 143.4 g AgCl
1500. mL ×
×
1000 mL
1 mol BaCl2
1 mol AgCl
= 172 g AgCl
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11/20/2013
Dilution
Dilution Practice
Dilution: Adding a solvent to a concentrated solution to
make the solution less concentrated (i.e. dilute).
What volume of 12 M HCl is needed to make
500.0 mL of a 0.10 M HCl?
When a solution is diluted, only the volume changes.
The number of moles of solute remains constant.
12 M HCl M1
0.10 M HCl M2
500.0 mL V2
Knowns
moles before dilution = moles after dilution
Molarity1 x Volume1 = Molarity2 x Volume2
M 1 × V1 = M 2 × V 2
V1 =
V2M2
M1
=
500 mL x 0.10 M
12 M
= 4.2 mL
Dilution Practice
Learning Objectives
Knowns 0.20 M NaOH M1
100 mL sln V1
100 + 150 = 250 mL V2
Solving for:
molarity NaOH M2
b. 0.050 M NaOH
c. 0.080 M NaOH
d. 12.5 M NaOH
M 1 × V1 = M 2 × V2
Calculate
V2
Calculate
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a. 2.0 M NaOH
M1V1
M 1 × V1 = M 2 × V2
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Calculate the molarity of a NaOH solution prepared by
mixing 100. mL of 0.20 M NaOH with 150 mL of H2O.
M2 =
Solving for:
volume of 12 M HCl V1
=
0.20 M x 100 mL
250 mL
= 0.080 M NaOH
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14.1 General Properties of Solutions
List the properties of a true solution
14.2 Solubility
Define solubility and the factors that affect it.
14.3 Rate of Dissolving Solids
Describe the factors that affect the rate
at which a solid dissolves.
14.4 Concentrations of Solutions
Solve problems involving mass percent, volume percent,
molarity, and dilution.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Learning Objectives
14.5 Colligative Properties of Solutions
Use the concept of colligative properties to calculate
molality, freezing point, boiling point, freezing point
depression, boiling point elevation of various solutions.
14.6 Osmosis and Osmotic Pressure
Discuss osmosis and osmotic pressure and
their importance in biological systems.
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