CHEM 3.1

• Solution


  A homogeneous mixture of two or more pure substances
• Solute


  The pure substance present in lesser amounts
• Solvent


  The more abundant substance
• How solutions can be classified

  • Based on the phase of the solvent
  • Based on saturation
  • Based on concentration
• Liquid solutions


  • Solutions where the solvent is a liquid
• Solid solutions


  • Solutions where the solvent is solid
• Gaseous solutions


  • Solutions where the solvent is a gas
• Unsaturated solution


  The amount of solute is less than the solute's solubility at a given volume and temperature
• Saturated solution


  The amount of solute is equal to the solute's solubility at a given volume and temperature
• Supersaturated solution


  The amount of solute is greater than the solute's solubility at a given volume and temperature
• Concentrated solution


  A solution that contains an excessively large amount of solute
• Diluted solution


  A solution of low concentration, prepared through the process of dilution
• Upon dilution, the concentration of the new solution is lower than the stock solution, but the number of moles remains the same
• Liquid-liquid solutions


  • Carbonated drinks
• Liquid-solid solutions


  • Amalgam (mercury in gold)
• An aliquot does not have the same concentration as the stock solution
• Based on the phase of the solvent: air

  • Gaseous solution
• Based on concentration: 0.5 M potassium permanganate, KMnO4


  • Diluted solution
• Based on the phase of the solvent: rubbing alcohol

  • Liquid-liquid solution
• Nitric acid fuming: 'by W. Oelen'
• Almost all substances dissolve in water under observable temperature and pressure. But some substances do not.
• Oil


  • Forms immiscible bubbles that do not mix with water
• Substances that mix easily

  Possess "compatible" intermolecular forces of attraction
• Explain the effect of temperature on the solubility of a solid and of a gas

  STEM_GC11PP-IIId-f-113
• Explain the effect of pressure on the solubility of a gas

  STEM_GC11PP-IIId-f-114
• Intermolecular Forces of Attraction (IMFAs)


  Particles of substance exhibit intermolecular forces of attraction and repulsion to one another
• London dispersion forces (LDFs)


  Exist in all molecules, polar or nonpolar. Strength depends on size, surface area, and polarizability
• Ion-ion interactions


  Between charged substances. Strength follows Coulomb's law
• Dipole-dipole interactions


  Between polar, uncharged substances. Strength depends on electronegativity of atoms in a bond
• Induced Dipole Interactions


  Ions and dipoles induce formation of temporary dipoles on nonpolar molecules
• Hydrogen Bonding


  Polar molecules that have H atoms bonded to O, N, or F (e.g., H2O, NH3, and HF)
• Solution Process


  Solute particles must be dissolved in solvent particles. A change in IMFAs between the particles: solvent-solvent interaction, solute-solute interaction, solute-solvent interaction
• Molar enthalpies


  Energy changes that accompany each of the interactions
• Heat of Solution, ΔHmixing


  Also referred to as ΔHsoln. Sum of all the enthalpy changes associated with each step
• ΔHmixing = ΔH1 + ΔH2

  Is always positive
• Sign of ΔHmixing


  Depends on the magnitudes of the three enthalpy changes
• ΔHmixing > 0


  Is endothermic. ΔH1 + ΔH2 is greater than ΔH3. Solvent-solvent and solute-solute interactions are stronger than solute-solvent interactions
• ΔHmixing < 0


  Is exothermic. ΔH1 + ΔH2 is less than ΔH3. Solvent-solvent and solute-solute interactions are weaker than solute-solvent interactions
• Entropy (ΔS)


  The inherent tendency toward disorder in highly favorable processes. The chaos when solute and solvent particles mix in comparison to their initial ordered states
• Solubility


  The extent to which a solute dissolves in solvent at a particular temperature, governed by both ΔHmixing and ΔSmixing