SOLUTIONS

• Solution


  Homogeneous mixture of two or more pure substances
• Solute


  Substance dispersed uniformly throughout the solvent
• Ability of substances to form solutions

  • Natural tendency toward mixing
  • Intermolecular forces
• Properties of a true solution

  • Homogeneous mixture of 2 or more components whose ratio can be varied
  • Dissolved solute is molecular or ionic in size (less than 1 nm)
  • Liquid or gaseous solutions can be colored or colorless and are usually transparent
  • The solute will not settle out of the solution
  • The solute can be separated from the solvent by physical means
• Natural tendency toward mixing

  Mixing of gases is a spontaneous process, each gas acts as if it is alone to fill the container, mixing causes more randomness in the position of the molecules, increasing entropy, the formation of solutions is favored by the increase in entropy that accompanies mixing
• Intermolecular forces of attraction

  Any intermolecular force of attraction can be the attraction between solute and solvent molecules, solute-solute interactions must be overcome, solvent-solvent interactions must be overcome, solvent-solute interactions occur as the particles mix
• Energetics of solution formation

  Cardinal rule of solubility is "like dissolves like", a polar solvent must be used to dissolve a polar or ionic solute, a nonpolar solvent must be used to dissolve a nonpolar solute

  
• Energetics of solution formation

  1. Solute particles separate from each other (endothermic)

  2. Solvent particles separate from each other (endothermic)

  3. Solute and solvent particles mix (exothermic)
• ΔHsoln = ΔHsolute + ΔHsolvent + ΔHmix
• Energy terms for various types of solutes and solvents

  • Polar solute, polar solvent
  • Nonpolar solute, polar solvent
  • Nonpolar solute, nonpolar solvent
  • Polar solute, nonpolar solvent
• Factors that affect solubility

  • Solute-solvent interactions (structure effect)
  • Pressure (for gaseous solutes)
  • Temperature

  
• Solute-solvent interaction


  Molecular structure determines polarity, if the solute and solvent have similar polarities, solubility is favored, nonpolar substances are described as hydrophobic, polar substances are described as hydrophilic, the stronger the solute-solvent interaction, the greater the solubility of a solute in that solvent
• Pressure effects


  The solubility of solids and liquids are not appreciably 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

  
• Temperature effects


  For most solids, as temperature increases, solubility increases, for all gases, as temperature increases, solubility decreases

  
• Solution concentrations


  • Mass percentage (%)
  • Parts per million (ppm)
  • Parts per billion (ppb)
• Solution concentrations

  • Mole fraction (X)
  • Molarity (M)
  • Molality (m)
• Colligative property

  A property of a solution that depends only on the quantity of solute, NOT on the identity of the solute particles
• Colligative properties


  • Vapor pressure lowering
  • Boiling-point elevation
  • Freezing-point depression
  • Osmotic pressure

  
• Vapor pressure lowering


  Because of solute-solvent intermolecular attraction, higher concentrations of nonvolatile solutes make it harder for solvent to escape to the vapor phase, therefore, the vapor pressure of a solution is lower than that of the pure solvent
• Raoult's Law


  The vapor pressure of a volatile solvent over the solution is the product of the mole fraction of the solvent times the vapor pressure of the pure solvent, in ideal solutions

  
• Boiling-point elevation


  The boiling point of the solution is higher than the pure solvent
• Freezing-point depression


  The freezing point of the solution is lower than the pure solvent
• Osmotic pressure


  The pressure applied to prevent osmosis
• Vapor pressure lowering


  Because of solute–solvent intermolecular attraction, higher concentrations of nonvolatile solutes make it harder for solvent to escape to the vapor phase. Therefore, the vapor pressure of a solution is lower than that of the pure solvent
• Raoult's law


  The vapor pressure of a volatile solvent over the solution is the product of the mole fraction of the solvent times the vapor pressure of the pure solvent

  
• In ideal solutions, it is assumed that each substance will follow Raoult's Law
• Raoult's law


  Psoln = χsolv * P°solv
• Non-ideal solutions


  For liquid–liquid solutions where both components are volatile, a modified Raoult's law applies: PTOTAL = χA * PA° + χB * PB°

  
• When a solute and solvent release large quantities of energy (exothermic) in the formation of a solution, we expect a negative deviation from Raoult's law
• If two liquids mix endothermically, it indicates that the solute–solvent interactions are weaker than the interactions among the molecules in the pure liquids, positive deviations from Raoult's law are observed
• For a solution of very similar liquids, the enthalpy of solution is very close to zero, and thus the solution closely obeys Raoult's law (ideal behavior)

  
• Boiling-point elevation


  Since vapor pressures are lowered for solutions, it requires a higher temperature to reach atmospheric pressure. Hence, boiling point is raised
• Freezing-point depression


  The construction of the phase diagram for a solution demonstrates that the freezing point is lowered while the boiling point is raised
• van't Hoff factor (i)

  It takes into account dissociation of solutes in solution. Theoretically, we get 2 particles when NaCl dissociates. So, i = 2. In fact, the amount that particles remain together is dependent on the concentration of the solution
• Osmosis


  The net movement of solvent molecules from solution of low to high concentration across a semipermeable membrane
• Osmotic pressure


  The applied pressure to stop osmosis. It is a colligative property: Π = MRT
• Do you have one of these? I got a little obsessed with mine. In fact I got a little obsessed with all my stuff. Have you ever wondered where all the stuff we buy, comes from and where it goes when we throw it out? I couldn't stop wondering about that.
• Stuff moves through a system

  1. Extraction

  2. Production

  3. Distribution

  4. Consumption

  5. Disposal
• This system is called the materials economy
• This system is a linear system and we live on a finite planet and you can not run a linear system on a finite planet indefinitely