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Chapter 13

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  • We will be focusing on solutions
  • A solution has 2 main components:
    • Solute
      • Minor component
    • Solvent
      • Major component
    • The solute is the small amount of substance going into water, and water is the solvent.
    • A solute is the thing that is always in the smaller amount
    • We need to be able to count the number of particles in solution
      • "How much stuff is in this solution"
      • Ionic vs Covalent
      • Nomenclature
      • Dissolution
      • Disassociation
      • Electrolytes
  • Types of solutions and solubility
    • A solution is a homogenous mixture containing small particles that will not separate. This leads to many transparent mixtures being made
    • An aqueous solution is a solution where water is the solvent
    • Solubility is the amount of substance that will dissolve
    • Types of solutions that you can have are in table 13.1, p 564
    • Why do solutions form?
      • Entropy ($\Delta S$)
        • The number of ways a system can be arranged
          • Randomness/disorder (not as correct)
        • Entropy always increases
        • Entropy is favorable
    • The effects of IMF's
      • Dissolves: a solid going into a liquid
      • A gas can also go into a liquid
      • Miscible: the liquids are soluble
    • Like dissolves like
      • The IMF's of the solute are similar or favorable to the solvent
      • Three main interactions when making solutions
        • Solute-solute interactions - break these
        • Solvent-solvent interactions - break these
        • Solute-solvent interactions - form these
      • Energy needs to be favorable to make a solution
      • Oil and water do not mix due to this same thing
  • Energetics of solution formation
    • Energy changes in solution formation
      • Separate solute particles ($+\Delta H_{solute}$)
      • Separate solvent particles ($+\Delta H_{solvent}$)
      • Form solute-solvent interactions ($-\Delta H_{mixing}$)
    • Add energy to pure components
    • The first step is at an energy cost to us
    • The second step is an energy cost to us
    • The third step releases energy, we just don't know how much
      • Endothermic or exothermic
    • $\Delta H_{solution} = \Delta H_{solute} + \Delta H_{solvent} + \Delta H_{mixing}$
    • Heat of hydration
      • The enthalpy change when one mole of the substance dissolves in water
      • $\Delta H_{solution} = \Delta H_{solute} + \Delta H_{hydration}$
      • $\Delta H_{solute}$ is actually equal to the $-\Delta H_{lattice}$
    • Will a solution form?
      • Up to Gibb's free energy
      • $\Delta G = \Delta H - T\Delta S$
      • If $\Delta G$ is negative, it is a spontaneous reaction
      • If $\Delta G$ is positive, it is a non-spontaneous reaction
  • Solution equilibrium and factors affecting solubility
    • Saturated: the solubility limit has been reached
    • Unsaturated: more solute will dissolve
    • Supersaturated: more solute is dissolved than should be able
    • Effect of temperature on the solubility of solids
      • As temperature is increases, solubility increases IN MOST CASES
    • Factors affecting the solubility of gases
      • As temperature increases, solubility decreases
      • As pressure increases, solubility increases
        • Henry's Law: $S_{gas} = k_{H} \times P_{gas}$
          • $M (\frac{mol}{L}) = \frac{M}{atm} \times atm$
  • Expressing solution concentrations
    • Molarity
      • $\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{moles of solution}}$
    • Molality
      • $\text{Molality (m)} = \frac{\text{moles of solute}}{\text{kg of solvent}}$
    • At low concentrations, these are very similar
    • $\text{Mole fraction (X)} = \frac{\text{moles of component}}{\text{total moles making up the solution}}$
    • $\text{Mass percent} = \frac{\text{mass of component}}{\text{total mass of solution}} \times 100$
    • $\text{Parts per million (ppm)} = \frac{\text{mass of component}}{\text{total mass of solution}} \times 10^6$
    • $\text{Parts per billion (ppb)} = \frac{\text{mass of component}}{\text{total mass of solution}} \times 10^9$
    • If you are not told how much you have, you have to assume
      • Make it easy for yourself. Assume 1L, 1kg, or 100g, depending on what you are calculating
        • Density will also be used
  • Colligative properties
    • These depend only on the amount of dissolved particles, not on their chemical identities
    • How many particles does that solute make.
    • 4 main properties
      • Vapor pressure lowering
      • Freezing point depression
      • Boiling point elevation
      • Osmotic pressure
    • Vapor pressure lowering
      • The solution that is made will have a lower vapor pressure than that of its pure solvent
      • Add solute, lower vapor pressure of solution
      • Raoult's law
        • $P_{\text{solution}} = X_{\text{solvent}} \times P_{\text{solvent}}$
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