HC

Chapter 13 - Properties of Solutions

  • Solutions - Homogeneous mixtures of two or more pure substances.
  • Solute - Part being dissolved. Usually smaller in quantity.
  • Solvent - Thing that dissolves.
  • Solvation - Dissolving process.
  • Hydration - The dissolving process with water as the solvent.
  • Substances depend on these to form solutions.
    • Intermolecular forces
    • Natural tendency to mix.

Natural Tendency to Mix

  • Mixing of gases is spontaneous.
  • Mixing causes more randomness in the position of molecules increasing the entropy.

Attractions involved when forming a solution

  • Solute-solute interactions - Must be overcome to disperse these particles when making a solution.
  • Solvent-solvent interactions - Must be overcome to make room for the solute.
  • Solvent-solute interactions - Occur as the particles mix.

Energetics of Solution Formation

  • ΔH solvent - Energy required to vaporize.
  • Solubility - How much solute can be dissolved in a given amount of solvent at a given temperature.
  • Saturated solutions - Can’t add more solute. More than enough.
  • Unsaturated solutions - Can add more. Not enough.
  • Supersaturated solutions - Temporary situation where the solution is cooled slowly and for it to react, a crystal from the solute is added.

Factors that affect solubility

  • Solute-solvent interactions
  • Temperature
    • As it goes up, more solute is dissolved
  • Pressure (for gas solutes)
    • As it goes up, more solute can be added.

Pressure Effects

  • Solubility of solids and liquids isn’t affected by pressure.

  • Gas solubility is affected by pressure

  • Henry’s Law - The solubility of a gas is proportional to the partial pressure of the gas above the solution. It’s only true at a constant temperature.

  • Henry's Law when given two points

Temperature Effects on Solubility

  • For most solids, as temperature increases, solubility increases.
  • For all gases, as temperature increases, solubility decreases.

Solution Concentration Conversion Between Units

  • Mass percentage (% m/m)
  • Parts per million (ppm)
  • Parts per billion (ppb)
  • Mole fraction (X)
  • Molarity (M)
  • Molality (m)

Colligative Properties

  • They depend only on the quantity, not on the identity of the solute.
    • Vapor pressure reduction
    • Boiling point elevation
    • Freezing point depression
    • Osmotic pressure

Vapor pressure reduction

  • Raoult’s Law

Boiling point elevation

  • i - Van-Hoff factor, the number of ions you get when dissolving the compound.
  • Kb is a constant different for all compounds.

Freezing point depression

  • Kf is a constant different for all compounds.

Osmotic Pressure

  • Osmosis - The net movement of solvent molecules from a solution of low to a high concentration of solute across a semipermeable membrane.
    • Semipermeable membrane - Smaller particles pass through it, but it blocks larger particles.
  • Osmotic pressure - The applied pressure to stop bigger particles.
  • If two solutions separated by a semipermeable membrane have the same osmotic pressure, no osmosis occurs.

Colloids

  • Colloids - Suspension of particles larger than individual ions or molecules, but too small to be settled out by gravity.
    • Ex. → Blood
  • They have a hydrophobic end (tail) and a hydrophilic end (head).