Post on 05-May-2023
The Nature of Solutions
Chapter 18 – Solutions
Chapter 17.3 Aqueous Solutions
Definitions
•• Solution Solution -- homogeneous mixture
Solvent Solvent - present in
greater amount, doing the dissolving
Solute Solute - substance being dissolved
Types of Solutions-17.4
Phase Solute Solvent Example
Gas
Liquid
Liquid
Solid alloys
marshmallow
Kool-aid
antifreeze
soda
airgas
liquid
liquid
liquid
solid
solidsolid
gas
solid
liquid
gas
gas
Liquid
Solid
B. Solvation
•• Solvation Solvation –– the process of dissolving
solute particles are separated and pulled into solution, forming new
IMF’s between solute and solvent
solute particles are surrounded by
solvent particles, where the IMF’s
between solute molecules are broken
B. Solvation
•• DissociationDissociation
– separation
of an ionic
solid into
aqueous
ions
NaCl(s) →→→→ Na+(aq) + Cl–(aq)
B. Solvation
•• Molecular Molecular SolvationSolvation– molecules stay
intact, but are pulled apart thanks to partial charges
C6H12O6(s) →→→→ C6H12O6(aq)
B. Solvation
NONPOLAR
NONPOLAR
POLAR
POLAR
“Like Dissolves Like”““Like Dissolves LikeLike Dissolves Like””
B. Solvation
•• Soap/DetergentSoap/Detergent– Long nonpolar “tail” with polar “head”
– dissolves nonpolar grease in polar water
C. Solubility
SATURATED SOLUTION
no more solute dissolves
UNSATURATED SOLUTIONmore solute dissolves
SUPERSATURATED SOLUTION
Too much dissolved*unstable*
increasing concentration
Solubility Table
LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 517
shows the dependence
of solubility on temperature
Solubility of Sodium Acetate
Temperature (oC)
025 50 75 100
So
lub
ility
(g/1
00
g H
2O
)
50
100
150Supersaturated
solution
Unsaturated solution
Saturated
Charles H.Corwin, Introductory Chemistry 2005, page 378
Solubility and Solvation Factors
Factors that affect Solvation
• Solvation-the process of dissolving
• We are looking for factors that affect
rate…not amount
• Solvation only occurs when and where the
solute and solvent particles come into contact
with one another
• So how do we increase the contact?
Would it dissolve faster if
• the mixture was shaken?
– Agitation increases solvation because
– ________________________
– ________________________
Would it dissolve faster if I
• Tried to dissolve a sugar cube or powdered
sugar?
– Surface area increases solvation because
– ________________________
Would it dissolve faster if I…
• Heated the mixture, or cooled the mixture?
– Heat increases solvation because
– ________________________
– ________________________
– ________________________
Solubility Factors
• Factors that affect the amount of solute
dissolved
Pressure
• When we open a soda bottle, what happens?
• What really happens….
– _________________________
– _________________________
• Henry’s Law
– ________________ proportional
Temperature
0 10 20 30 40 50 60 70 80 90 100
Solubility vs. Temperature
So
lub
ility
(g
ram
s o
f so
lute
/10
0 g
H2O
)
KI
KCl
20
10
30
40
50
60
70
80
90
110
120
130
140
100
NaNO3
KNO3
HCl NH4Cl
NH3
NaCl KClO3
SO2
•Generally, higher temperature
leads to higher solubility for
liquids and solids
•However, higher temperature
leads to lower solubility for gases
Why?-As liquids/solids warm,
they are easier to break-apart
and dissolve. When gases warm
up, it is easier to escape and not
dissolve.
gases
solids
18.2 + 18.4- Math
• Percent Mass/volume (m/v %)
• Percent by Volume (v/v %)
• Molarity (M)
• Molality (m)
• Dilution
• Stoichiometry
Mass Percent
• Percent (Mass/volume)=
Mass of solute (g) x100%
Solution volume (mL)
Percent by Volume
• Percent (volume/volume)=
volume of solute x100%
Solution volume
Be sure that both volume units are the same.
Molarity (M)
• Molarity=
moles of solute
Liters of Solution
• No need to multiply by 100 to get a %
• Convert grams to moles if needed
• 1 L = 1000mL, so divide mL by 1000 to get to Liters
• You know when moles are mentioned, stoichiometry is not far behind
Molality (m)
• Molality=
moles of solute
kg of solvent
• No need to multiply by 100 to get a %
• Multiply kilograms by 1000 to get grams
• Divide grams by 1000 to get kilograms
• We’ll need this when we work with colligative properties.
Colligative Properties
18.3 + 18.4
Definition
• Physical properties of liquids affected by the
number of solute particles dissolved, not the
identity of the solute
• “depending on the collection”
Vapor Pressure
• _____________________________________
• The more solute particles, the less the vapor
pressure from the solvent
Vapor Pressure
Boiling Point Elevation
and
Freezing Point Depression
Boiling Point Elevation
• When is this used?
– _________
– _________
• Why do solute particles raise the boiling
point?
Freezing Point Depression
• When is this used?
– _________
– _________
• Why do solute particles lower the freezing
point?
The math
• Freezing Point Depression=ΔTf
ΔTf=iKfm
i= number of aqueous solute particles
Kf=freezing point constant for solvents, water = 1.86
m= molality of solution
The math
• Boiling Point Elevation=ΔTb
ΔTb=iKbm
i= number of aqueous solute particles
Kb=boiling point constant for solvents, water = 0.512
m= molality of solution
What is the freezing point depression of a solution containing 478 g of sodium chloride
in 3202 g of water?
Why is CaCl2 used as rock salt?