01:160:159 Lecture 11: chap11notes
Chapter 11 – Properties of Solutions
11.1 Solution Composition
A. Molarity
1.
Molarity(M ) =
moles
solute
liters
of
solution
B. Mass Percent
æ
mass
of
solute
ö
ç
÷
1.
Mass
percent
= ç
÷
´100
ç
of
÷
è mass
solution ø
C. Mole Fraction
1.
Mole
fraction
of
componentA = xA
=
n
A
nA + nB
D. Molality
1.
Molality =
moles
of
solute
ki log ram
of
solvent
E. Normality
1.
Normality
=
equivalents
liter
of
solution
2. Equivalents of acids and bases
a. Mass that donates or accepts a mole of protons
3. Equivalents of oxidizing and reducing agents
a. Mass that provides or accepts a mole of electrons
11.2 The Energies of Solution Formation
A. “Like Dissolves Like”
1. Polar molecules and ionic compounds tend to dissolve in polar solvents
2. Nonpolar molecules dissolve in nonpolar compounds
B. Steps of Solution Formation
1. Breaking up the solute into individual components (expanding the solute)
a. Endothermic
2. Overcoming intermolecular forces in the solvent to make room for the
solute (expanding the solvent)
a. Endothermic
3. Allowing the solute and solvent to interact to form the solution
a. Often exothermic
C. Enthalpy (Heat) of Solution
1. DH
sol'n
= DH
step1
+ DH
step2
+ DH
step3
1. D
sol’n may have a positive sign or a negative sign
3. Enthalpy (Heat) of Hydration, D
hyd
a. Include D
of step 2 and step 3
1
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D. Factors Favoring the Solution Process
1. Negative value for
sol’n
2. Increase in entropy
3. For positive values of
sol’n it is the increase in entropy that outweighs
the increase in energy and causes the solution process of occur
11.3 Factors Affecting Solubility
A. Structure Effects
1. Polar (hydrophilic) dissolves in polar
a. Water soluble vitamins
2. Nonpolar (hydrophobic) in nonpolar
a. Fat soluble vitamins
B. Pressure Effects
1. Henry’s Law
a. The amount of a gas dissolved in a solution is directly proportional
to the pressure of the gas above the solution
b. P = kC
(1) P = partial pressure of the gaseous solute above the solution
(2) C = concentration of the dissolved gas
(3) k = constant characteristic of a particular solution
c. Henry’s Law works best for dilute solutions of gases that do not
dissociate or react with the solvent
C. Temperature Effects
1. Solids
a. Increases in temperature always cause dissolving to occur
more rapidly
b. Increases in temperature usually increases solubility (the amount
that can be dissolved)
2. Gases
a. Solubility of gases always decreases with increasing temperature
11.4 The Vapor Pressure of Solutions
A. Nonvolatile Solutes
1. Nonvolatile electrolytes lower the vapor pressure of a solute
a. Nonvolatile molecules do not enter the vapor phase
b. Fewer molecules are available to enter the vapor phase
B. Raoult's Law
1.
P
= X
P0
where X
solvent
is the mole fraction of the solvent in
so ln
solvent solvent
the solution
a. a linear equation (y = mx)
2. Molar mass of a solute can be calculated from experimental results for
vapor pressure lowering
C. Ionic solutes
1. Dissociation of ionic compounds has nearly two, three or more times
the vapor pressure lowering of nonionic (nonelectrolyte) solutes.
2
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Document Summary
11. 1 solution composition: molarity, molarity(m ) = liters of solution moles solute, mass percent, mass percent, mole fraction mass of solute. Mole of componenta = xa = fraction na na + nb: normality, molality = moles of solute ki log ram of solvent, normality = equivalents liter of solution. Equivalents of acids and bases: mass that donates or accepts a mole of protons. Equivalents of oxidizing and reducing agents: mass that provides or accepts a mole of electrons. = dh: dh, d sol"n may have a positive sign or a negative sign, enthalpy (heat) of hydration, d hyd. + dh step1 step2 step3: include d of step 2 and step 3. 1: factors favoring the solution process, negative value for sol"n, increase in entropy, for positive values of sol"n it is the increase in entropy that outweighs the increase in energy and causes the solution process of occur.
