Chapter 11 - Aqueous Solutions

I. Definitions

• Solution - a homogenous mixture of a solute in a solvent
• Solute - the substance that dissolve (present in the least)
• Solvent - medium that disperses the solute (present in the most)
• Miscible - when two liquids form a solution (mix)
• Immiscible - when two liquids do not mix
• Solid dissolving in a liquid - forms a solution

Ionic Solids
Ex: NaCl
breaks down in Na+ and Cl- ions
Water surrounds ions - ION-DIPOLE FORCES

NaCl(s) Na+(aq) + Cl-(aq)

Molecular solids
ex: Methyl Alcohol, sugar

II. Solubility of Compounds in Water

• Soluble - when a compound dissolves in the solvent to an appreciable amount
• Insoluble - very little or none of the substance dissolves
• Solubility - the maximum amount of a solute that dissolves in a specific amount of solvent at a certain temperature.
• Different amounts of solute dissolved in Solvent

  • Saturated - when a specific amount of solvent contains the maximum amount of dissolved solute.
  • Unsaturated - if less than the maximum amount of solute is present in solution
  • Supersaturated - an unstable condition may exist in which there is actually more solute present in solution than its solubility would indicate. Solid may precipitate out spontaneously.

• Use Solubility rules to predict if a compound will dissolve in water.
• Solubility Vs. Temperature: In General, Solubility increases when temperature increases Not always true (see Fig.11-4)

III. Concentration

• Concentration- the amount of solute present in a given amount of solvent.
• Percent by Mass =

• Molarity =
  
  
• Molality =

IV. Dilution

• In dilution, we do not change the number of moles present
  #moles = # moles
• M₁V₁ = M₂V₂

V. Stoichiometry

• We can now use concentration to determine # of moles
  

VI. Physical Properties of Solutions (and Colligative Properties)

• Conductivity
  • Aqueous solutions conduct electricity - electrolytes
    Compound that do not conduct electricity - nonelectrolytes
  • Ions conduct electricity
    • Strong electrolytes
    • Weak electrolytes
    • Nonelectrolytes
      
      
• Vapor Pressure
  • Presence of a solute in a solvent lowers the equ. Vapor Pressure of the solvent
    
• Boiling point
  • Presence of a solute in a solvent raises the Boiling point of the solvent
  • DT_b = K_bm
    m = molality
    
    
    
• Freezing point
  • Presence of a solute in a solvent lowers the freezing point of the solvent
  • DT_f= K_fm
    
• Osmotic Pressure
  • P = MRT