Transcript CHAPTER 14: SOLUTIONS AND THEIR PROPERTIES

CHAPTER 14: SOLUTIONS AND THEIR
PROPERTIES
 SOLUTION homogeneous mixture of two
or more substances in a single phase.
 Solvent component present in the largest
amount, substance doing the dissolving
 Solute component present in the smallest
amount, the substance dissolved.
Quantitative ways to describe a solution,
solute, solvent (moles, mass, or volume)
 Molarity (M) = mole of solute/liter solution
 Molality (m) = moles of solute/kg of solvent
 Mole fraction (X) = nA / (nA + nB …)
moles of a given component divided by the
total # of moles of all components.
Quantitative ways to describe a solution,
solute, solvent (moles, mass, or volume)
 Weight % =
mass of solute/mass of solution * 100
 ppm = mg solute/l L solvent
 Normality (N) = # Equivalents / L
Practice
 A solution is prepared by mixing 1.00 g
ethanol (C2H5OH) with 100.0 g water to
give a final volume of 101 mL.
 Calculate the molarity,
molality,
mole fraction,
weight %,
and ppm of ethanol in this solution.
Solution Process
 Intermolecular forces (likes dissolve likes)
 When liquids mix and form a solution they
are miscible
 Immiscible liquids do not mix.
 Terms with solutions
Solution Terms
 SATURATED - A stable solution in which the
maximum amount of solute has been dissolved
 UNSATURATED -The concentration of solute is
less than the saturated amount.
 SUPERSATURATED- A solution that contains
more than the saturated amount of solute
Solution Diagrams
How Solutions Form
Thermodynamics
 The formation of solutions is favored because
it creates a more disordered system.
 If the process requires too much energy, the
process will not occur. The energy can be
calculated.
Thermodynamics
of Solutions
 For an ionic crystal, first the crystal must
break apart, negative the (negative) lattice
energy, therefore a positive enthalpy.
 Then the ions must hydrate (be
surrounded by water molecules) which has
a negative enthalpy.
Thermodynamics
of Solutions
 Dissolve CaCl2 in water and describe the
relationship between lattice energy and the
energy of hydration
 Dissolve NH4Cl in water and describe the
relationship between lattice energy and the
energy of hydration
Thermodynamics
of Solutions
Thermodynamics
of Solutions
Thermodynamics
of Solutions
Thermodynamics
of Solutions
Factors Affecting Solubility
Pressure and Temperature:
 Gases dissolved in water demonstration
 Bromothymol Blue solution and
Alka-Seltzer in 200 mL DI water
Factors Affecting Solubility
Pressure and Temperature:
 Pressure: Solubility of Gases in Liquids:
 Henry's Law: Sg = k H Pg
Factors Affecting Solubility
Pressure and Temperature:
 Solubility Diagrams
Factors Affecting Solubility
Pressure and Temperature:
Factors Affecting Solubility
Pressure and Temperature:
Factors Affecting Solubility
Pressure and Temperature:
Colligative Properties
 Changes in Vapor Pressure: Raoult’s Law
 The vapor pressure over the solution is lower than the
vapor pressure of pure solvent.
 The vaopr pressure of the solvent Psolv is propotional to
the relative number of solvent molecules in the solution,
the solvent vapor pressure is proportional to the solvent
mole fraction.
 Colligative Properties Definitions
Raoult’s Law
 Psolv = Xsolv Posolv
 Raoult’s Law applies to ideal solutions
Roult’s Law Diagram
Colligative Properties
Colligative Properties
 Raoult’s Law Adding a non volatile solute
to a solvent lowers the vapor pressure of
the solvent so the change in vapor
pressure of the solvent can be calculated
as a function of the mole fraction.
Colligative Properties
Colligative Properties
Colligative Properties
Colligative Properties
 The boiling point of a solution is related
to the solute concentration.
 The boiling point elevation D Tbp is
directly proportional to the molality of
the solute:

D T bp = Kbp msolute
 molal boiling point elevation constant
has the units of degrees/molal (oC / m).
Colligative Properties
 What quantity of elthylene glycol,
HOCH2CH2OH must be added to 125 g
of water to raise the boiling point of
1.0oC?
 Kbp of water is + 0.5121oC/m
Colligative Properties
 The freezing point of a solution is related to
the solute concentration.
 The freezing point depression D Tfp is directly
proportional to the molality of the solute:
D Tfp = Kfp msolute
 molal freezing point depression constant has
the units of degrees/molal (oC / m).
Colligative Properties
 In the northern United States, summer
cottages are usually closed up for the winter.
When doing so the owners “winterize” the
plumbing by putting antifreeze,
HOCH2CH2OH, in the toilet tanks. Will
adding 525 g of anitfreeze to 3 kg of water
ensure that the water will not freeze at -25oC.
 Kfp of water is -1.86 oC/m
Colligative Properties
 Colligative Properties and Molar Mass
Determination
Colligative Properties
 Van’t Hoff Factor i
 When an ionic compound dissolves in a
solvent, the number of ions determines the
behavior of the solvent.
 For example, 1 m NaCl will lower the f.p. of
water twice as much as 1 m sugar because
NaCl breaks into 2 ions
Colligative Properties
 Van’t Hoff Factor I
Diagrams & Photo
 Actually only dilute solutions behave in this
manner.
 Officially, i = D Tfp measured
D Tfp calculated
 So often the value of i approaches a whole
number.
Colligative Properties
Osmosis is the movement of solvent molecules
through a semipermeable membrane from a region of
lower to a region of higher solute concentration.
Colligative Properties
Osmotic Pressure the pressure created by the column
above the solution measured by the difference in
height between the solution in the tube and the level
of water in the beaker.
Osmotic Terms
Colligative Properties
Osmotic Pressure is related to concentration.
Recall the Ideal Gas Law PV = nRT
Rearrange the equation so the concentration is (n/V)
P = (n/V) R T
Change the symbols P to P for osmotic pressure
and (n/V) to c
The resulting equation for Osmotic Pressure is
P=cRT
R = .082 L x atm
mol x K
Colligative Properties
Osmosis
isotonic similar concentrations of solutes
hypotonic solution with lower solute concentrations
hypotonic solution with higher solute concentrations
reverse osmosis using pressure to purify water.
Colligative Properties
Colloids
Colligative Properties
Colloids are classified according to the state of
dispersed phase and the dispersing medium.
Hydrophobic ‘water fearing’ weak attractive forces
between water and surface of colloidal particles.
Hydrophilic ‘water loving’ are strongly attracted to
the water molecules
Emulsions are colloidal dispersions of one liquid in
another by using an emulsifying agent such as
protein or soap.
Colligative Properties
Surfactants are emulsifying agents
Hydrocarbon end soluble in oil
Polar end soluble in water