Mixtures

• Heterogeneous - A mixture in which its components are not evenly distributed throughout the mixture.

  e.g.  cereal, bag of different-colored marbles

• Homogeneous - A mixture in which its components are thoroughly dispersed throughout the mixture, so that it is uniform.  This is also called a SOLUTION.

Solutions

• Characteristics that determine if a substance is a solution or not:
  1. It was well-stirred when it was made.
  2. The dissolved particles precipitate regardless of how long the solution is allowed to stand.
  3. The solution is clear and transparent (though it may have color).  The particles are microscopic and not visible by the naked eye.
  4. The dissolved particles can pass through a filtration.
  5. The solution is in a single phase.
• Components of a solution
  1. Solute - The substance that is dissolved in the solution.
  2. Solvent - The substance that does the dissolving in a solution.

     e.g.  In a salt-water solution, salt is the solute and water is the solvent.

• Types of solutions
  1. Gas solutions - gases or vapors dissolved in one another.  A mixture of gases such as air.
  2. Liquid solutions - A liquid solvent in which a solid, liquid, or gas is dissolved.
     • Miscible - Two liquids are miscible if they dissolve in each other.
     • Immiscible - Two liquids are immiscible if they do not dissolve in each other.

       e.g.  oil and water are immiscible.

     • Examples of liquid solutions:
       • Salt water - solid in liquid
       • Wine - liquid in liquid
       • Club soda - gas in liquid
• Solubility - The ratio of the maximum amount of solute to the volume of solvent in which the solute can dissolve.
  • Factors that affect solubility
    1. The nature of the solute and solvent.
    2. The temperature of the solution.  In general, solids dissolve more easily in liquids at higher temperatures, and gases dissolve in liquids better at lower temperatures.
    3. Pressure (only affects solubility of gases).
  • Factors affecting the rate of solubility
    1. Size of solute particles
    2. Stirring
    3. Amount of solute
    4. Temperature

In general, remember:

LIKE DISSOLVES LIKE

In other words:

• Polar solutes are usually soluble in polar solutes.

  e.g.  H₂O is an example of a polar solvent.  Salts are examples of polar solutes (NaCl).

• Nonpolar solutes are usually soluble in nopolar solvents.

  e.g.  CCl₄ is an example of a nonpolar solvent.  Hydrocarbons are examples of nonpolar solutes (CH₄).

• Alcohols are a type of compound in which one of the H atoms in a hydrocarbon is replaced by a hydroxide (OH) group.
  • Smaller alcohols are infinitely soluble in water.

    e.g.  CH₃OH (methanol) and CH₃CH₂OH (ethanol)

  • As the length of the hydrocarbon chain increases, alcohols become less soluble in water to the point where the largest hydrocarbons are completely insoluble in water.

    e.g.  CH₃(CH₂)₉OH (decanol) is insoluble in water.

  • The polar OH end of larger alcohols are hydrophillic ("water loving") because they can form hydrogen bonds with the adjacent water molecules.  The positive H⁺ end of a water molecule is attracted to the negative OH^- end of an alcohol.
  • The nonpolar C-H chain, or tail, or larger alcohols are hydrophobic ("water hating") because it has no attraction to water.

Chemical Separations

• Distillation - A method of separating liquids based on differences in boiling points.
• Extraction - A method of separating the components of a mixture based on differences in the solubility of their components in polar versus nonpolar solvents.
• Chromatography - ("writing with color") A method of separating the components of a mixture based on differences in their affinity for a stationary and a mobile phase.  It was first used to separate the colored pigments in plants.
• Recrystallization - A method of separating components of a solid mixture based on differences in the solubilities of the various components in different solvents.

Next:  "Concentration"