Goals:
1. Calculate solution concentration.
2.Describe the solution process.
3.Apply colligative properties of solutions.
4.Describe colloids and their applications.

A solution is a
______________ mixture of 2 or more substances in a single phase.
One constituent is usually regarded as the
SOLUTES .
SOLVENT and the others as

Solute Solvent
Gas Gas
____ _____
Liquid Liquid
____ _____
____ _____
Solution
Gas
_____
Example
Air (O
2 in N
2
)
_____ Club soda (CO
Liquid
2 in H
Wine (alcohol in H
2
2
_____ Saline sol. (NaCl in H
O)
O)
2
O)
14-karat gold (Ag in Au)
Aqueous solutions – those in which __________is the solvent.

Is __________ – reactants are changing to products, products to reactants; but at the same rate, there is no change in concentration of reactants or products.

• Dynamic equilibrium – when the number of particles (ions or molecules) leaving the surface of the crystals is equal to the number that is returning.
– The net quantity of particles in solution and that in undissolved crystals remain constant.
• Saturated solution – a solution that contains all the solute that it can at
equilibrium and at a given temperature.
– 36 g NaCl per 100 g of H
2
O
• Unsaturated solution – contains less than this quantity.
– Any other with less: ex. 20 g NaCl per 100 g of H
2
O

• Solutions can be classified as
or
.
• A saturated solution contains the ________
______________ that dissolves at that temperature.

• Precipitate – an insoluble or nearly insoluble solid that separates from a solution.
– When a saturated solution is cooled, solute precipitates until the equilibrium is once again established at the lower temperature.
60 o C100 g water
5 o C100 g water dissolve 95 g of lead (II) nitrate: Pb(NO dissolve 40 g of lead (II) nitrate
3
)
2
The excess 55 g will separate as precipitate upon cooling, increasing the quantity of undissolved solute.
• Supersaturated solution – a solution containing solute in excess of what it could contain if it were at __________.
– It is not a stable system because it is not _______________.
– Solute may precipitate when the solution is stirred or the inside of the container is scratched with a glass rod.
– Addition of a “seed” crystal will nearly always result in __________
___________________________________________________

• Solutions can be classified as unsaturated or saturated.
• A saturated solution contains the maximum quantity of solute that dissolves at that temperature.
• ________________
SOLUTIONS contain more than is possible and are unstable.

• The solubility of a given solute depends on the relative __________________particles in the pure substances and in the solution.
• Three things must happen:
– The attractive forces holding the ions of the solute together must be overcome.
– The attractive forces holding at least some of the solvent molecules must be overcome.
– The solute and solvent molecules must interact; they must attract one another.
• _____________ – process in which water molecules surround the solute ions.

• The polarity of water molecules enables them to attract (and be attracted by) ions. Several ion-
dipole interactions surround each ion and overcome the stronger ion-ion interactions.

• Almost all compounds of the Group 1A elements are soluble in water: NaCl, Na
2
SO
4
, K
3
PO
4
, LiBr
• Many solids in which both ions are doubly or triply charged are essentially insoluble in water (forces holding the ions together are so strong that they cannot be overcome by the hydration of the ions): CaCO
3
, AlPO
4
, BaSO
4.

• Na +
• Mg 2+
• Cs +
Energy of hydration depends on the
________ of the ion and the _______ between the ion and the dipole.

• ___________– substances that can be mixed in all proportions
(water and alcohol).
• __________– the quantity that will dissolve is near zero (iron in water).
• ___________– an appreciable quantity dissolves (sugar in water).

• Like dissolves like. Nonpolar (or slightly polar) solutes dissolve best in nonpolar solvents; polar solutes dissolve best in polar solvents.
• Water solubility of covalent compounds depends mainly on the ability of water to form _____________ to the solute molecules. Molecules containing a high
proportion of nitrogen or oxygen atoms will dissolve in water.

Which of the following will dissolve in water?
CH
3
CH
3
CH
3
CH
3
C
12
H
22
OH
(CH
(CH
2
2
CHO
O
11
)
2
CH
2
)
10
CH
2
OH
OH
Methyl alcohol
Butyl alcohol
Lauryl alcohol
Acetaldehyde
Sucrose

Carbonated beverages (CO
Ammonia (NH
3 in water)
2 in water)
Formalin (HCHO (formaldehyde gas))
• Unlike most solids, gases become less soluble in water as the
temperature _____________. The gas molecules acquire more kinetic energy and escape the solution.
• At constant T, the solubility of a gas in water is directly
proportional to the __________ of the gas in equilibrium with the aqueous solution. The higher the _______, the more gas will dissolve in a given volume of water.
– The pressure inside soda bottles is high enough to dissolve the wanted CO
2
, once the bottle is opened, the pressure is released and the gas escapes.

• The solubility of a gas in a liquid is directly proportional to the gas pressure.
S g
= k
H
P g

Gas solubility (mol/L) = k
H
• P gas
When P gas drops, solubility drops.
Think about: When would Henry’s Law not apply?

• A change in any of the factors determining an equilibrium causes the system to adjust so as to reduce or counteract the effect of the change.
Henri Louis Le Chatelier (1884).
– change in T, P, concentration of reactants or products.
• Temperature affects solubility.
• For all gases in water, solubility decreases with temperature.

Simple correlations of solubility with structure or thermodynamic parameters are generally not successful.

• If the enthalpy of formation of the solution is more negative that that of the solvent and solute, the enthalpy of solution is negative.
• The solution process is
!

• One application of a supersaturated solution is the sodium acetate “heat pack.”
• Sodium acetate has an
ENDOthermic heat of solution.
Sodium acetate has an ENDOthermic heat of solution.
NaCH
3
CO
2
(s) + heat ----> Na + (aq) + CH
3
CO
2
(aq)
Therefore, formation of solid sodium acetate from its ions is EXOTHERMIC.
Na + (aq) + CH
3
CO
2
(aq) ---> NaCH
3
CO
2
(s) + heat

D
o soln
D H o soln
=  D H o f products –  D H o f reactants

On adding a solute to a solvent, the props. of the solvent are modified.
• Vapor pressure decreases
• Melting point
• Boiling point decreases increases
• Osmosis is possible (osmotic pressure)
These changes are called COLLIGATIVE
PROPERTIES.
They depend only on the NUMBER of solute particles relative to solvent particles, not on the KIND of solute particles.

• An
concentration of solute.
is one where the properties depend only on the
• Need concentration units to tell us the number of solute particles per solvent particle.
• The unit “molarity” does not do this!

• Molarity: Moles of solute per liter of solution.
M = moles/L
• Molality: Moles of solute per kilogram of solvent.
m = moles/Kg
Molality is Temperature
_______________!

MOLALITY, m mol solute m of solute = kilograms solvent
X
A
MOLE FRACTION, X
For a mixture of A, B, and C

mol fraction A = mol A mol A + mol B + mol C
WEIGHT % = grams solute per 100 g solution ppm = grams solute per 1 million g solution

What is the m of a 29.5% by mass ethanol solution (mw ethanol = 46g/mol)?
Student should be familiar with concentration calculations.

• Depend only on the _______________
______________ relative to solvent particles, not on the KIND of solute particles
• When a solute is present, the vapor pressure of the solvent is __________.

• To understand colligative properties, study the
LIQUID-
VAPOR
EQUILIBRIU
M for a solution.

VP of H
2
O over a solution depends on the number of H molecule.
2
O molecules per solute
P solvent
proportional to X solvent
P solvent
= X solvent
• P o solvent
Vapor Pressure of solvent over solution
= (Mol frac solvent)•(VP pure solvent)
RAOULT’S LAW

P
A
= X
A
• P o
A
Because mole fraction of solvent, X
A
, is always less than 1, then P
A is always less than P o
A
.
The vapor pressure of solvent over a solution is always LOWERED !

VP Pure solvent VP solvent after adding solute
1 atm
P
BP pure solvent
BP solution
T
See Figure 14.14

A nonvolatile solute particle (purple) can block the escape of the solvent particles (blue) but has no effect on the return of the solvent particles from the vapor to the solution.
gas liquid

Elevation in BP = ∆TBP = KBP•m
(where KBP is characteristic of solvent)

The rate at which solvent molecules (blue) leave the pure solid solvent is unaffected by the presence of solute particles (purple) nearby in the solution, but their rate of return to the solid is reduced.
liquid solid

Pure water Ethylene glycol/water solution
The freezing point of a solution is
than that of the pure solvent.
FP depression = ∆T
FP
= K
FP
•m

Water with and without antifreeze
When a solution freezes, the solid phase is pure water. The solution becomes more concentrated.

D
• Antifreeze
• Ice cream makers
• CaCl
2 winter on icy roads in
• Measure molar masses
• Distinguish between electrolytes and nonelectrolytes.

∆T = K•m•i
A generally useful equation i = van’t Hoff factor = number of particles produced per formula unit.
Compound Theoretical Value of i glycol
NaCl
CaCl
2
1

How much NaCl must be dissolved in 4.00 kg of water to lower the Freezing Point to -10.00 o C?

• 0.1 m glucose
• 0.06 m NaCl
• 0.06 m Na
2
SO
4
Student should be familiar with predicting freezing and boiling point of solutions.

Semipermeable membrane: solvent molecules can pass, but flow of solute is restricted.
_________– net diffusion of water through a semipermeable membrane. Net flow of solvent from the more dilute solution
(or pure solvent) into the more concentrated solution.

Equilibrium is reached when pressure — the
OSMOTIC PRESSURE,
∏ — produced by extra solution counterbalances pressure of solvent molecules moving thru the membrane.
Solvent molecules move from pure solvent to solution in an attempt to make both have the same concentration of solute.
Driving force is entropy

• Osmotic Pressure
( p
) like the ideal gas law: follows an equation much p
V = nRT or, p
= MRT
R = 0.0806 L atm/molK
M = concentration of particles (moles or ions) in mol/L
Useful for determining molar masses of large molecules like proteins and polymers.

– Examples of osmosis are found in living organisms: Cells are semipermeable; their function and survival depend on maintenance of the same osmotic pressure inside the cell and outside in the extracellular fluid.
– Isotonic solution – Iso-osmotic – a solution having the same osmotic pressure as body fluids (0.89% NaCl
(mass/vol)).

– ___________ solution – a solution having higher osmotic pressure than body fluids (larger than 0.89% NaCl).
– ___________ solution – a solution having lower osmotic pressure than body fluids (less than 0.89% NaCl).
Normal cell
Water flows out of the cell and cell
wrinkles (crenation).
Water flows into the cell and cell is swollen and may
burst (plasmolysis).

• Reverse Osmosis
Water desalination plant in Tampa

• Dialyzing membranes – membranes that pass small molecules and ions while holding back large molecules and colloidal particles.
• Ions and small molecules always diffuse from higher concentration to lower concentration.
• Dialysis – process in which small molecules and ions pass through a dialyzing membrane. In osmosis, osmotic membranes pass only solvent molecules.
– Bags of cellophane or collodion.
– Kidneys are a complex dialyzing system responsible for the removal of waste products from the blood.
• Creatinine concentration > 900 mmol/L indication to start dialysis (kidney failure).

• Suspension – two substances momentarily mixed, but solute will settle to the bottom of the container. It can be separated by ___________ . It is a
_______________ mixture (sand and water).
• Colloids – halfway point (particles of 1 nm-1000 nm) between true solutions (particles less than 1 nm) and suspensions (particles of 1000 nm or more).

• Left: Fine sand (silica) added to water will quickly settle, producing a heterogeneous mixture with water on top and silica on the bottom.
• Right: The same proportion of silica, specially prepared (Ludox), produces a colloidal dispersion. The particles of hydrated silica, SiO
2
*xH
2
O, are much larger than atoms and ordinary molecules. However, the sodium hydroxide used in preparing the dispersion causes the silica particles to acquire a negative charge from adsorbed hydroxide ions. The similarly charged silica particles repel one another and stay suspended indefinitely.

– Appear milky or cloudy; some may appear clear.
– Tyndall effect – John Tyndall, 1968 – scattering of a beam of light.
The light beam is not visible as it passes through a true solution
(left), but it is readily visible as it passes through colloidal iron
(III) oxide in water.

– Particles in a colloid are often charged, due to the adsorption of ions on the surface of the particle.
Because like charges repel, particles tend to stay away from one another (they do not form particles large enough to settle out).
– May separate by adding highly charged ions (it will coalesce).
– Are stabilized by addition of a protective coating material – soap added to emulsify oil in water. Milk is an emulsion of fat droplets stabilized by casein, a protein molecule.
• Emulsifying agents – stabilize emulsions.

• Cationic emulsion technology – for the absorption of substances that are not soluble in water and large molecules. The technology can be used for injectables, eye drops (ophthalmology), creams/lotions (dermatology) and capsules (oral administration).
• Cationic agent is used because the cell wall has negative charges.

The ionic portion of the surfactant is more stable when solubilized by water, whereas the nonpolar portion of the surfactant is more stable when surrounded by other nonpolar chains. They might form micelles.
Phospholipid and vesicle
Surfactant (soap molecule) and micelles
Phospholipids spontaneously form vesicles in water, encapsulating a small water droplet in a spherical shell of phospholipid molecules. Both the inner and outer wall of the shell are composed of hydrophilic heads, whereas the inside of the vesicle shell is the alkane tails. The image below is a slice through a spherical vesicle.

• Go over all the contents of your textbook.
• Practice with examples and with problems at the end of the chapter.
• Practice with OWL tutor.
• Work on your assignment for Chapter 14.