Properties of Solutions
Chapter 13
Vocabulary: A Review
• Solution
• Solute
• Solvent
• A homogeneous mixture.
• The item dissolved.
• What the solute is
dissolved in.
Types of Solutions
State of solution State of solute
gas
gas
State of solvent
example
gas
air, natural gas
liquid
gas
liquid
carbonated water
solid
gas
solid
hydrogen in platinum
liquid
liquid
liquid
alcohol and water
liquid
solid
solid
solid
liquid sea water
solid metal alloys
Solution Composition
•
•
•
•
• Relatively little amount solute
• Relatively large amount solute
Dilute
Concentrated
Molarity
Mass percent or
weight percent
• Mole fraction
• Molality
Molarity versus Molality
• Molarity: Moles solute/Liters solution
• It is expressed as [solute] = M
• Liquids change density with change in
temperature.
• Therefore: Molarity is not constant
with temperature changes
Molarity versus Molality
• Molality: moles solute/kg solvent
• The weight of the liquid is constant
with changes in temperature.
Question:
• A solution is prepared
by mixing 1.00 gram of
ethanol (C2H5OH) with
100 gram water to
give a final volume of
101 mL. Calculate the
molarity, mass
percent, mole fraction
and molality of ethanol
in this solution.
• Molar mass of ethanol
is 46.07 g/mol.
• 0.0217 mol ethanol.
• Volume 0.101 L
• Molarity 0.215 M
• Mass percent:
0.990 % ethanol.
(1g/101g)*100
• Mole fraction: 0.00389
0.0217 mol
•
5.56 mol H2O + 0.0217 mol etOH
• Molality: 0.217 m
• 0.0217 mol/0.1 kg
Normality
• A concentration measure.
• Defined as the number of equivalents
per liter.
• For acids: The [H+] per liter
• 1 M HCL is 1 N HCL
• 1 M H2SO4 is 2 N H2SO4
• For redox: The [e-] per liter or
electron consumption per liter.
The Molar Mass, Equivalent Mass,
Molarity and Normality for some
acids and bases
Acid/base
• HCL
• H2SO4
• NaOH
• Ca(OH)2
MM
36.5
98
40
74
Equ M
36.5
98/2=49
40
74/2=37
M vs N
1M=1N
1M=2N
1M=1N
1M=2N
Heat of solution
formation
• Why are some things soluble and not
others?
• Why does “like dissolve in like”?
• Why do solution behave as they do?
• Demo?
step
what happens
DH
1
solute particles separate into
their individual components
+
2
Overcoming the IMF’s of the
solvent particles make "space" or
“expanding” for solute
+
3
solute and solvent particles
"interact“ to form solution
-
Enthalpy heat of solution
• The enthalpy of the heat of a
solution is the sum of the enthalpy of
the three steps.
• ΔH solu = ΔH 1 + ΔH 2 + ΔH 3
Which picture best
describes a solution of HCl?
Probability
• Why is NaCl so soluble in water if it
actually takes a little energy to form
a solution (4 kJ/mol)?
• The mixed state is more likely to
occur as there are many more ways
of placing the mixed state ions in
water than the one unmixed state.
• Think Entropy: ΔS.
•saturated: no more solute will
dissolve
•unsaturated: able to dissolve more
solute
•super-saturated: contains more solute
than will dissolve under ordinary
conditions