Chapter 14
Solutions
I. Characteristics of Mixtures
Type of
solution
Solution
Homogeneous
Colloid
Heterogeneous
Suspension
Heterogeneous
Particle
size
Atoms, ions,
molecules…
less than 1 nm
larger molecules…
1- 1000 nm
larger particles…
over 1000 nm
Separation
ability
does not
separate
does not
separate
DOES separate
Filterable
No
No
Light
effects
Does not
scatter light
Tyndall effect
(scatters light)
Yes
Not
transparent
Solutions
• Made up of a…
SOLUTE - the substance being dissolved
SOLVENT - what the solute is dissolved in
• Can be any combination of gas, liquid or solid
ex: air, 14-karat gold, seltzer, black coffee
• SOLUTES can be…
-ions (conduct electricity) ex: NaCl
-molecules (do not conduct electricity) ex: C6H12O6
Colloids
• Any combination of solid, liquid or gas
• Sol - when a solid is dispersed in a liquid
ex: paint; mud
• Gel - when a solid network extends throughout the liquid
ex: Jello
• Foam - gas dispersed in a liquid
ex: shaving cream; whipped cream
• aerosols - solid or liquids dispersed in a gas
ex: fog; smoke ; clouds
• emulsion - liquid dispersed in a solid
ex: butter
II. The Solution Process
A. Improve the rate of dissolving a solid solute by:
1) increase the surface area of the solute particles
ex: crushed sugar vs. sugar cubes
2) agitating the solvent to increase solvent/solute
interaction
ex: stirring the solution
3) heating the solution - increased energy speeds
motion of solute/solvent
B. Solubility terms:
1) saturated - the solvent contains the maximum solute at
this oC.
[note: “saturated” does NOT mean “concentrated”]
2) unsaturated - the solvent can still dissolve more solute
3) supersaturated - the solvent contains more than its
maximum
4) solubility value - the amount of solute that can be
dissolved in a given amount of solvent at a given temperature
5) miscible - when liquids dissolve freely in one another
6) immiscible - when liquids are not soluble in one another
C. “like dissolves like” - solvents that are polar will
dissolve solutes that are polar…… solvents that are
nonpolar will dissolve solutes that are nonpolar
ex:
• salt (polar) dissolves in water (polar)
• sugar (water) dissolves in water (polar)
• oil (nonpolar) does not dissolve in vinegar (polar)
• crayons (nonpolar) do not dissolve with water (polar)
• grease (nonpolar) does not dissolve in water (polar)
General Rules :
1) Substances are polar if they are
a) ionic compounds ex: NaCl, MgBr2, LiNO3
b) covalent compounds that contain an OH bond
ex: C2H5OH
c) covalent compounds with some halogens
ex: CHCl3
2) Substances are nonpolar if
a) they are covalent compounds without OH
ex: C6H12
b) covalent compounds with only C and halogens
ex: CCl4
D. Effects of temperature and pressure on solubility
solids
increased temp.
increased pressure
increased
solubility
(no effect)
gases
decreased
solubility
increased
solubility
Q: What will be the effect of warming soda before opening it?
Q: What is the effect on blood gases when diving at great depths?
E. Calculations of solubility values
1) How many grams of KCl can be dissolved in 50 g of
water at 75 oC to make a saturated solution?
2) How much water is needed to dissolve 80 g of NH4Cl at
25 oC and prepare a saturated solution ?
3) How much KCl will precipitate out 100 g of a saturated
75 oC solution is cooled to 40 oC?
F. Heats of Solution
1) heat of solution - the change in heat because of a
solute becoming dissovled in a solvent
2) exothermic - release of heat due to a chemical reaction
or from dissolving a solute (I.e. feels HOT)
3) endothermic - absorption of heat due to chemical
reaction or dissolving a solute (I.e. feels COLD)
4) solvated - when solute particles become surrounded
by solvent molecules
III. Calculating Concentrations of Solutions
A. Molarity - ratio of moles of solute per liter of
solution
M = moles solute
liters of sol’n
notes:
1) called a “molar” solution when following a number
2) REMEMBER: moles = grams/molecular weight
3) grams of solute = Molarity X Liters X MW
B. molality = ratio of moles of solute per kg of solvent
m = moles of solute
kg solvent
Examples:
1) What is the molarity of a solution prepared by
dissolving 90.0 g of NaCl in 3.50 L of water?
2) How many moles of HCl are present in 800. mL of a
0.500 M solution of HCl?
3) What volume of 6.0 M K2CrO4 will contain 23.4 g of
K2CrO4 ?
4) How many grams of NaCl are needed to prepare 250
mL of a 0.250 M solution?
Examples:
1) Find the molal concentration of a solution prepared
by dissolving 17.1 g of C12H22O11 in 125 g of water.
2) How much iodine, in grams, is needed to prepare a
0.480 m solution in CCl4 if 100.0 g of solvent is used?
C. Percent Composition by mass:
percent = mass of solute
x 100
TOTAL mass of solution
D. Mole Fraction:
X=
moles of solute
moles solute + moles solvent
Examples: Calculate the percent composition and mole
fraction when 25 g of NaCl are dissolved in 100. grams of
H2O
IV. Colligative Properties
A. Properties of solutions that depend only on the
number of particles, not their identity
B. Solutions experience a change in these properties
compared with pure water:
1) vapor pressure is lower
2) freezing points are lower [“depression”]
3) boiling point is raised [“elevated”]
4) osmotic pressure is lower
C. Vapor Pressure Lowering
P = Xsolvent Po
Notes:
P = new vapor pressure
X = mole fraction of solvent
Po = normal vapor pressure
Ex: Calculate the vapor pressure of a solution at 20 oC that
has 25 g NaCl dissolved in 100. grams water.
[Powater at 20 oC = 23.7 torr]
D. Boiling Point Elevation/Freezing Point Depression
∆t = K x m x i
Notes: ∆t = CHANGE in temperature…not the new temp
K = constant …specific for each solvent
…different for boiling and freezing
m = molality
i = Van Hof’t Constant = # particles
Ex: Calculate the new boiling point/freezing point of a
solution that has 25 g NaCl dissolved in 100. grams water.
[Kf = 1.86 oC/m …. Kb = 0.52 oC/m]
E. Osmotic Pressure Calculation
  MRT
Notes: pressure in atmospheres
M = molarity
R = 0.0821
T = Kelvin

Ex: Calculate the new osmotic pressure of a solution that
has 25 g NaCl dissolved in 100. grams water.
Osmotic Pressure Comments:
a) Red blood cells have the same osmotic pressure as:
5% glucose solution OR
0.9% NaCl solution
b) Isotonic = same osmotic pressure
c) Hypotonic = the solution has a lower osmotic pressure
than the rbc’s
d) Hypertonic = the solution has a higher osmotic pressure
than the rbc’s
e) Osmosis = flow of water through semipermeable
membrane from a region where water content is higher to
a region where water content is lower.
Osmotic Pressure Comments:
What will happen when rbc’s are placed in 10% NaCl
solution?
What will happen when rbc’s are placed in pure water?