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1. Dipole-Dipole Interactions – e.g., Hydrogen Bonding– Between H2O to H2O or – R-OH to H2O or – R-OH to R-OH – (R is an organic unit)
04/19/23 OFB Chapter 6 12
Kinetic Theory of Liquids and Solids
04/19/23 OFB Chapter 6 13
6-3 Phase Equilibrium
• Coexisting phase equilibrium– Vapor pressure
Phase: A sample of matter that is uniform throughout, both in its chemical constitution and in its physical state.
04/19/23 OFB Chapter 6 14
Correcting for the Vapor Pressure of Water in “Wet Gases”
• Many chemical reactions conducted in aqueous solution often generate gaseous products
• The gas collected will be “humid” or “wet” due to the coexistence of the gas and water vapor.
• A correction is made to account for the water vapor present
04/19/23 OFB Chapter 6 15
Exercise page 6-2:
Passage of an electric current through a dilute aqueous solution of sodium sulfate produces a mixture of gaseous hydrogen and oxygen according to the following equation:
2 H2O(l) 2 H2(g) + O2(g)
One liter of the mixed gases is collected over water at 25oC and under a total pressure of 755.3 torr. Calculate the mass of oxygen that is present. The vapor pressure of water is 23.8 torr at 25oC.
04/19/23 OFB Chapter 6 16
For ideal gas mixtures
P of a gas is proportional to the number of moles of gas
2 H2O(l) 2 H2(g) + O2(g)
Exercise page 6-2:
atm9625.0P
atm 0.0313atm 0.9938P
PPP
gases
gases
O2
Htotalgases
atm 0.32083 /atm 0.962
P 1/3H moles 2O 1mole
O 1moleP gases
22
2
2O
04/19/23 OFB Chapter 6 17
atm9625.0P
atm 0.0313atm 0.9938P
PPP
gases
gases
O2
Htotalgases
atm 0.32083 /atm 0.962
P 1/3H moles 2O 1mole
O 1moleP gases
22
2
2O
gramsm
m
Mm
n
moles
KLatm
RT
VPn
RTnVP
O
O
O
O
OO
421.032
01316.0
01316.0
)298)(082.0()0.1)(32.0(
2
2
2
2
22
2
04/19/23 OFB Chapter 6 18
6-6 Colligative Properties of Solutions
• For some properties, the amount of difference between a pure solvent and dilute solution depend only on the number of solute particles present and not on their chemical identify.
• Called Colligative Properties• Examples
1. Vapor Pressure
2. Melting Point
3. Boiling Point
4. Osmotic Pressure
04/19/23 OFB Chapter 6 19
Colligative Properties of Solutions
Mass percentage (weight percentage):
mass percentage of the component =
100%mass of component total mass of mixture
Mole fraction: The chemical amount (in moles) divided by the total amount (in moles)
X1 = n1/(n1 + n2)
X2 = n2/(n1 + n2) = 1 - X1
04/19/23 OFB Chapter 6 20
Molality
msolute =
moles solute per kilograms solvent
= mol kg-1
Molarity
csolute =
moles solute per volume solution
= mol L-1
04/19/23 OFB Chapter 6 21
Exercise 6-7:
Suppose that 32.6 g of acetic acid, CH3COOH, is dissolved in 83.8 g of water, giving a total solution volume of 112.1 mL. Calculate the molality and molarity of acetic acid (molar mass 60.05 g mol-1) in this solution.
1solute
1solute
kg mol 6.48kg 0.0838
mol 0.543
kgg
1000
g 83.8
molg
60.05
g 32.6
m
kg molsolvent kg
solute molesmMolality
04/19/23 OFB Chapter 6 22
Exercise 6-7:
Suppose that 32.6 g of acetic acid, CH3COOH, is dissolved in 83.8 g of water, giving a total solution volume of 112.1 mL. Calculate the molality and molarity of acetic acid (molar mass 60.05 g mol-1) in this solution.
1. Lowering of Vapor Pressure– Vapor Pressure of a solvent above a
dilute solution is always less than the vapor pressure above the pure solvent.
2. Elevation of Boiling Point– The boiling point of a solution of a
non-volatile solute in a volatile solvent always exceeds the boiling point of a pure solvent
Ideal Solutions and Raoult’s Law
04/19/23 OFB Chapter 6 25
Elevation of Boiling Point
Where m = molality
(moles of solute per kilogram of solvent)
The Effect of Dissociation
i = the number of particles released into the
solution per formula unit of solute
e.g., NaCl dissociates into i =
e.g., Na2SO4 dissociates into i =
(2 Na+ + 1 SO4-2)
04/19/23 OFB Chapter 6 26
3. Depression of Freezing Point
ΔTf = − m Kf
ΔTf = − i m Kf
04/19/23 OFB Chapter 6 27
Osmotic Pressure• Fourth Colligative Property• Important for transport of molecules
across cell membranes
Osmotic Pressure = Π = g d h
Π = c RT
ΠV = n RT
ΠV = i c RT
04/19/23 OFB Chapter 6 28
Exercise 6-17
A dilute aqueous solution of a non-dissociating compound contains 1.19 g of the compound per liter of solution and has an osmotic pressure of 0.0288 atm at a temperature of 37°C. Compute the molar mass of the compound
cGiven
Strategy
lmole
lg
moleg
M Rearrange .)3
massMolar g
molethat Recall 2.)
mol/L in c the find to cRT Π use 1.)
04/19/23 OFB Chapter 6 29
Exercise 6-17
A dilute aqueous solution of a non-dissociating compound contains 1.19 g of the compound per liter of solution and has an osmotic pressure of 0.0288 atm at a temperature of 37°C. Compute the molar mass of the compound
g/mol1.05x10mol/l 1.132x10
lg1.19
lmole
lg
moleg
M Rearrange 3.)
mol/l 1.132x10c
273.15K))(37Kmol atm L (0.0820
atm 0.0288RTΠ
c
RTΠ
cor cRT Π use 1.)
olution
33
3
11
M
S
04/19/23 OFB Chapter 6 30
6-8 Colloidal Dispersions• Colloids are large particles dispersed
in solution– 1nm to 1000 nm in size– E.g., Globular proteins 500nm
• Examples– Opal (water in solid SiO2)– Aerosols (liquids in Gas)– Smoke (solids in Air)– Milk (fat droplets & solids in water)– Mayonnaise (water droplets in oil)– Paint (solid pigments in liquid)– Biological fluids (proteins & fats in
water)• Characteristics
– Large particle size colloids: translucent, cloudy, milky)
– Small particle size colloids: can be clear
04/19/23 OFB Chapter 6 31
6-8 Colloidal Dispersions– Tyndall Effect
• Light Scattering
04/19/23 OFB Chapter 6 32
Chapter 6Condensed Phases and Phase
Transitions
Examples / Exercises– All (6-1 thru 6-17, skip 6-18)