Transcript No Slide Title

Calculations Involving
Colligative Properties
Review
Molarity (M) = moles of solute
liter of solution
Dilutions:
M1 x V1 = M2 x V2
Percent by volume (%(v/v)) = volume of
solute x 100%
volume of solution
Percent by mass (%(m/m)) = mass of
solute x 100%
Review
• Colligative Property: A property that depends only upon the
solute concentration and not on the solute’s identity.
• Four Important Colligative Properties of Solutions.
– Vapor-pressure lowering
– Boiling-point elevation
– Freezing-point depression
– Vapor Pressure
Molarity (M) = moles of solute
liter of solution
Molality (m) = moles of solute_
kilogram of solvent
• Molality is the number of moles of solute dissolved in 1 kilogram
(1000 g) of solvent.
Mole Fraction (another way to express
concentration)
Mole Fraction: the ratio of the moles of the solute to the total
number of moles of solvent and solute.
XA=
nA___
nA + n B
XB=
nB___
nA + n B
Freezing-Point Depression & BoilingPoint Elevation
Freezing-Point Depression
•
∆Tf = Kf m i
∆Tf = Freezing Point Depression
– Difference between the freezing point of the solution and the
freezing point of pure solvent
•
Kf = Molal Freezing Point Depression Constant
– Equals to the change in freezing point for a 1-molal solution
of a nonvolatile molecule solid
– Values are listed in a table
– Depends upon the solvent
– Units (°C/m)
•
•
m = Molal Concentration
i = Number of Ions from each formula unit
Freezing Point Depression
• Applications
–salting icy roads
–making ice cream
–antifreeze
• cars (-64°C to 136°C)
• fish & insects
Boiling-Point Elevation
•
•
•
•
∆Tb = Kbm i
∆Tb = Boiling-Point Elevation
– Difference between the boiling point of the solution and the
boiling point of pure solvent
Kb = Molal Boiling Point Elevation Constant
– Equals to the change in boiling point for a 1-molal solution of
a nonvolatile molecule solid
– Values are listed in a table
– Depends upon the solvent
– Units (°C/m)
m = Molal Concentration
i = Number of Ions from each formula unit
Solution Calculations
• What is the molarity of a 1.11
ppm solution of Zn2+ ions?
•
1.11m g Zn 2
1g
1 m oleZn
*
*
 1.70X 105 M
1 liter
1000m g 65.39g
How Vapor Pressure Depression
Occurs
• Solute particles take up space in a
solution.
• Solute particles on surface decrease
# of solvent particles on the surface.
• Less solvent particles can evaporate
which lowers the vapor pressure of
a liquid.
Vapor Pressures of Pure Water and a Water Solution
The vapor pressure of water over pure water is greater than the
vapor pressure of water over an aqueous solution containing a
nonvolatile solute.
Solute particles take up
surface area and lower
the vapor pressure
Raoult’s Law
• Vapor pressure of a solution varies
directly as the mole fraction of
solvent
Vapor Pressure Solution =
(mole fractionsolvent)(Vapor Pressuresolvent)
Solid Calculations
• Chemical analysis showed 1.23 mg Fe in a
15.67 g sample of soil.
• What is the Fe concentration in ppm?
1.23m g Fe
1g
6
*
*10  78.5 ppm
15.67g sam ple 1000m g
Unusual concentration units
• How many nano moles of Cu are
present in 12.3 µL of 25 ppm
CuSO4?
6
1L
25 mg 1 m mole 10 n mole
12.3L * 6 *
*
*
 1.93 n mole
10 L
L
159.65mg 1 m mole