Solutions and their Behavior. Goals: Calculate solution concentration . Describe the solution process . Apply colligative properties of solutions. Describe colloids and their applications. Solutions. A solution is a ______________ mixture of 2 or more substances in a single phase. .
Calculate solution concentration.
Describe the solution process.
Apply colligative properties of solutions.
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 SOLVENT and the others as SOLUTES.
Solute Solvent Solution Example
Gas Gas Gas Air (O2 in N2)
____ _____ _____ Club soda (CO2 in H2O)
Liquid Liquid Liquid Wine (alcohol in H2O)
____ _____ _____ Saline sol. (NaCl in H2O)
____ _____ _____ 14-karat gold (Ag in Au)
Aqueous solutions – those in which __________is the solvent.
Equilibrium – the ______ of the forward and reverse reactions are _______.
Is __________ – reactants are changing to products, products to reactants; but at the same rate, there is no change in concentration of reactants or products.
60oC 100 g water dissolve 95 g of lead (II) nitrate: Pb(NO3)2
5oC 100 g water dissolve 40 g of lead (II) nitrate
The excess 55 g will separate as precipitate upon cooling, increasing the quantity of undissolved solute.
Energy of hydration depends on the ________ of the ion and the _______ between the ion and the dipole.
CH3OH Methyl alcohol
CH3(CH2)2CH2OH Butyl alcohol
CH3(CH2)10CH2OH Lauryl alcohol
Carbonated beverages (CO2 in water)
Formalin (HCHO (formaldehyde gas))
Ammonia (NH3 in water)
Sg = kHPg
Gas solubility (mol/L) = kH • Pgas
When Pgas drops, solubility drops.
Think about: When would Henry’s Law not apply?
– change in T, P, concentration of reactants or products.
Simple correlations of solubility with structure or thermodynamic parameters are generally not successful.
Sodium acetate has an ENDOthermic heat of solution.
NaCH3CO2 (s) ----> Na+(aq) + CH3CO2-(aq)
Therefore, formation of solid sodium acetate from its ions is EXOTHERMIC.
Na+(aq) + CH3CO2-(aq) ---> NaCH3CO2 (s)
DHosoln = DHof products – DHof reactants
On adding a solute to a solvent, the props. of the solvent are modified.
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.
M = moles/L
m = moles/Kg
Molality is Temperature _______________!
Student should be familiar with concentration calculations.
VP of H2O over a solution depends on the number of H2O molecules per solute molecule.
Psolventproportional to Xsolvent
Psolvent = Xsolvent • Posolvent
Vapor Pressure of solvent over solution = (Mol frac solvent)•(VP pure solvent)
An _______ solution is one that obeys Raoult’s law.
PA = XA • PoA
Because mole fraction of solvent, XA, is always less than 1, then PA is always less than PoA.
The vapor pressure of solvent over a solution is always LOWERED!
See Figure 14.14
Elevation in BP = ∆TBP = KBP•m
(where KBP is characteristic of solvent)
The freezing point of a solution is ________ than that of the pure solvent.
FP depression = ∆TFP = KFP•m
Water with and without antifreeze
When a solution freezes, the solid phase is pure water. The solution becomes more concentrated.
∆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
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
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.
Water flows out of the cell and cell wrinkles (crenation).
Water flows into the cell and cell is swollen and may burst (plasmolysis).
Water desalination plant in Tampa
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.
Phospholipid and vesicle
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.
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.
Surfactant (soap molecule) and micelles