2. An Aqueous Solution and Pure Water in a Closed Environment
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3. Liquid/Vapor Equilibrium
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4. Vapor Pressure Lowering: Addition of a Solute
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5. Vapor Pressures of Solutions
Nonvolatile solute lowers the vapor pressure of a solvent.
Raoult’s Law:
Psoln = observed vapor pressure of solution
solv = mole fraction of solvent
= vapor pressure of pure solvent
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6. A Solution Obeying Raoult’s Law
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7. Nonideal Solutions
Liquid-liquid solutions where both components are volatile.
Modified Raoult’s Law:
Nonideal solutions behave ideally as the mole fractions approach 0 and 1.
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8. Vapor Pressure for a Solution of Two Volatile Liquids
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9. Summary of the Behavior of Various Types of Solutions
Interactive Forces Between Solute (A) and Solvent (B) Particles
ΔHsoln
ΔT for Solution Formation
Deviation from Raoult’s Law
Example
A  A, B  B  A  B
Zero
None (ideal solution)
Benzene-toluene
A  A, B  B < A  B
Negative (exothermic)
Positive
Negative
Acetone-water
A  A, B  B > A  B
Positive (endothermic)
Ethanol-hexane
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10. Hexane (C6H14) and chloroform (CHCl3) Ethyl alcohol (C2H5OH) and water
CONCEPT CHECK!
For each of the following solutions, would you expect it to be relatively ideal (with respect to Raoult’s Law), show a positive deviation, or show a negative deviation?
Hexane (C6H14) and chloroform (CHCl3)
Ethyl alcohol (C2H5OH) and water
Hexane (C6H14) and octane (C8H18)
a) Positive deviation; Hexane is non-polar, chloroform is polar.
b) Negative deviation; Both are polar, and the ethyl alcohol molecules can form stronger hydrogen bonding with the water molecules than it can with other alcohol molecules.
c) Ideal; Both are non-polar with similar molar masses.
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