Solutions and Colloids

I.  Solutions
    Definitions to know:

    solution:  homogenous mixture; uniform throughout

    solvent:  substance that does the dissolving; ** substance which is in greater quantity.

    solute:  substance that is dissolved;  ** substance which is in smaller quantity.

              Water is the most common solvent!  Why?

               1.  Water is a polar molecule because of the lone pairs on oxygen.
                2.  Thes lone pairs of electrons are attracted to ions on crystal surfaces.
                     This attraction seperates the ions from each other and the crystalline
                     solid dissolves.

    dissociation:  seperation of ions from each other.

    solvation:  occurs when the solvent surrounds th particles of solute.

    electrolyte:  substances that break up (ionize or dissociate) in water to produce ions.
                         They are able to conduct electric current.  They usually consist of ionic compounds.
                         (Acids and bases are electrolytes)

    nonelectrolyte:  substances that do not break apart and do not conduct electricity.
                                   They are usually covalent compounds with the exception of acids.

II.  Solubility

      Main rule of solubility -- like dissolves like

                  1.  Polar solvents dissolve polar solutes.
                  2.  Nonpolar solvents dissolve nonpolar solutes.

      hydration:  occurs when water dissolves a polar solute.

III.  Solids, Liquids, and Gases in Solutions

       Possible Solution Combinations
Solvent
Solute
Common Example
gas
gas
helium-oxygen (deep-sea diver's gas)
gas
liquid
air-water (humidity)
gas
solid
air-naphthalene (mothballs)
liquid
gas
water-carbon dioxide (soft drink)
liquid
liquid
water-acetic acid (vinegar)
liquid
solid
water-salt (seawater)
solid
gas
palladium-hydrogen (gas stove lighter)
solid
liquid
silver-mercury (dental amalagam)
solid
solid
gold-silver (ring) 

        miscibility:  the ablity of two liquids to be mixed.

        example:   Water and acetic acid are miscible.  (vinegar)
                          Oil and water are immiscible.  (They don't mix)
 

IV.  Solution Equilibrium

       solution equilibrium:  occurs when the rates of particles leaving and returning to solution are equal.

       3 Types of Solutions

    1.  saturated:  when undissolved solute is in equilibrium with the dissolved solute.

     2.  unsaturated:  contains less than the saturated amount of solute for that temperature.

     3.  supersaturated:  contains more solute than a saturated solution can normally hold.
 

        solubility:  the quantity of solute that will dissolve in a specified amount of solvent at a specific temperature.

        SOLUBILITY CURVES
 
 
 
 
 
 

V.  Factors that Affect Rates of Solution

         1.  Agitation
              - increases solubility
              - brings solvent into contact with more of the surface area of the solute

        2.  Temperature
             - if temperature increases, solubility increases.
             - An increase in kinetic energy, increases the frequency and force of collisions of solvent and solute which breaks solute apart.

        3.  Particle Size
             - smaller particles dissolve faster because they have less suface area

VI.  Concentration of Solution

        concentrated solution:  large amount of solute in small amount of solvent

        dilute solution:  small amount of solute in large amount of solvent

                  Determining Concentration by Different Methods

                        1.  Molarity  (M)

                          Molartiy =  moles of solute
                                                liters of solvent

                           example:  What is the molarity of a solution in which 58 g of NaCl are dissolved in 1.0 L of solution?

                                           58 g NaCl  | 1 mol NaCl      =      1 mol NaCl
                                                               |  58 g NaCl

                                            Molarity =   1 mol NaCl
                                                                  1 liter

                                            Molarity = 1 M NaCl

                      2.  Molality (m)

                           Molality =   moles of solute
                                                   Kg of solvent

                            Example:  What is the molality of a solution in which 3.0 moles of NaCl is dissolved in 1.5 Kg of water?

                            Molality =  3.0 moles of NaCl
                                                 1.5  Kg of water

                            Molality =  2.0 m NaCl

                      3.  Normality (N)

                           Normality =  Molarity   x   total positive oxidation number of solute

                            Example:  What is the normality of 3.0 M of H2SO4 ?

                           Normality = 3.0 x total positive oxidation number

                          total positive oxidation number =  +1(2) = 2       This is because hydrogen's oxidation number is +1 and there are 2 hydrogens.

                           Normality = 3.0  x   2

                           Normality =  6.0 N

VII.  Types of Mixtures

        1.  Colloids:  mixtures composed of two phases of matter

                     Two phases are:

                      -- dispersed phase - particles are larger than particles in solution but smaller than suspensions
                      -- continous phase

              Classification of Colloids

               aerosols:  liquids and solids dispersed in gases.  Examples:  fog and smoke

               foams:  gases dispersed in liquids and solids.  Examples:  whipped cream and marshmallows

              emulsions:  liquids dispersed in other liquids or solids.  Examples:  mayonnaise - liquid emulsion
                                                                                                                                      cheese - solid emulsion

              sols:  solids dispersed in liquids or other solids.  Examples:  jelly and paint
 

        2.  Suspensions:  dispersed phase contains particles much larger than in colloids or solutions.

            *** Because the particles in a suspension are so large, the particles are suspended but eventally settle out upon standing.
 
 

VIII.  Properties of  Solutions, Colloids, and Suspensions
 
Solutions
Colloids 
Suspensions
Do not settle out Do not settle out Settle out upon standing
Pass unchanged through ordinary filter paper Pass unchanged through ordinary filter paper Separatated by filter ordinary filter paper
Pass unchanged through a membrane Pass unchanged through a membrane Separated by membrane
Do not scatter light Scatter light Scatter light

      Tyndall Effect:  the ability of colloids and suspensions to scatter light
                                   examples:  1.  If a window blind in opened in a dark room, suspended dust particles scatter light.
                                                      2.  If a search light is used in the night air, light is scattered by suspended water droplets.

        Brownian Motion:  chaotic movement of particles in a colloid or suspension
                                           example:  Hitting two chalkboard erasers together allows you to see the chaotic movement of suspended
                                                            dust particles.