GEN CHEM

• Solutions


  Homogeneous mixtures of two or more pure substances that can be varied in composition
• Solvent


  The substance in which a solute dissolves, present in greatest amount
• Solute


  The substance being dissolved, other components present in the solution
• Solubility


  The maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature
• Solubility examples


  • Sodium chloride (39.12 g/100 ml water at 100OC)
  • Silver chloride (0.0021 g/100 ml water at 100OC)
• Solvation


  The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles
• Hydration


  Solvation when the solvent used is water
• How a solution forms

  Solvent pulls solute particles apart and surrounds, or solvates, them

  
• Types of solutions

  • Dilute (low solute concentration)
  • Concentrated (high solute concentration)
  • Saturated (maximum solute dissolved)
  • Unsaturated (less than solubility)
  • Supersaturated (more than solubility)
• Saturated solution


  Contains the maximum amount of solute that the solvent can dissolve at a given temperature, additional solute will no longer dissolve if added
• Saturated solution


  Dissolved solute is in dynamic equilibrium with solid solute particles
• Unsaturated solution


  Contains an amount of solute less than its solubility, has the capacity to dissolve more solute
• Supersaturated solution


  Contains an amount of solute greater than the solubility, an unstable solution
• Classification of solutions

  • Organic (compounds containing carbon except CO2, CO, carbonates, and cyanides)
  • Inorganic (compounds of other elements including acids, bases, and salts)
• Classification by ionization

  • Strong electrolytes (completely dissociate into ions)
  • Weak electrolytes (produce small amounts of ions)
  • Nonelectrolytes (do not dissociate into ions)
• Liquid solution process


  1. Separation of solute particles

  2. Separation of solvent particles

  3. New interactions between solute and solvent

  
• Enthalpy of solution (ΔHsol'n)


  Enthalpy change associated with formation of solution
• If ΔHsol'n is positive the process is endothermic, if ΔHsol'n is negative the process is exothermic
• Like dissolves like


  Polar substances tend to dissolve in polar solvents, nonpolar substances tend to dissolve in nonpolar solvents
• The more similar the intermolecular attractions, the more likely one substance is to be soluble in another
• For liquid-liquid solutions, polar molecules mix with other polar molecules, nonpolar molecules mix with other nonpolar molecules, polar and nonpolar molecules do not mix
• For solid-liquid solutions, the "like dissolves like" rule also applies
• For gases: As temperature increases


  Solubility decreases
• Gases have lower solubility at higher temperatures because the gas molecules move more quickly and escape the liquid more easily
• For solids: As temperature increases

  Solubility increases
• Henry's Law


  The solubility of a gas is proportional to its partial pressure above the liquid
• The solubility of liquids and solids does not change appreciably with pressure, but the solubility of gases increases with increasing pressure
• Larger gas molecules have stronger dispersion forces and are more soluble in water