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					Properties of

 Solutions
Changes In State
             A Review of Matter
• Types of matter
• Pure substances
  – Elements – cannot be broken down by chemical
              means
  – Compounds – two or more elements combined in
                 definite proportions
• Mixtures
  – Homogeneous – evenly mixed, uniform throughout
  – Heterogeneous – unevenly mixed, varied composition
Increasing Surface Area
 Increases Dissolution
              What is a Solution?
• Homogeneous mixture of substances in the
    same state.
•   A solution may be;
    –   A solid n solid. Ex. Zn + Cu  brass (alloy)
    –   Gas n gas. Ex. Air.
    –   Liquid n liquid. Ex. alcohol + water
    –   And, most familiar to you, a substance, usually a
        solid, dissolved in water.Ex. NaCl + water.(sea water)
    Components of a Solutions
• A solute is the substance being dissolved.
• The solvent is the substance that exists in
  the greater amount, into which the solute
  is mixed.
• Ex. In sea water, salt is the solute, while
  water is the solvent.
• Water’s properties make it a universal
  solvent.
The Secret To Waters Dissolving
 Power is it’s Polarized Nature




The polar water molecules surround the solute molecules, forming H-bonds
and dipole attractions
          Aqueous Solutions
• Solutions of a substance dissolved in
  water are termed aqueous and are written
  as follows;
• NaCl (s)  Na+ (aq) + Cl- (aq) (where
  s = solid, aq = aqueous, and g = gas)
• The particles of a homogeneous aqueous
  solution are very small, will not settle and
  will pass through a filter.
Mixtures Can Be Separated
       Properties of Mixtures

• Light will pass directly through a solution.
• The light beam will not be visible in the
  body of the solution.
• Light will be scattered by the larger
  particles of heterogeneous solutions.
• This is called the Tyndall Effect, after the
  scientist who discovered it.
   Colloids and Suspensions
Scatter Light. Solutions Do Not.
Summary of Solution Properties

• Aqueous solutions are homogeneous
  mixtures
• They are clear and do not disperse light.
• Can have color (ex. CuSO4 is blue).
• Particles will not settle when left standing.
• Particles pass readily through a filter.
                  Solubility

• Ability of a substance to dissolve in
  another substance.
• “Like dissolves like.”
  – Polar molecules dissolve in polar substances
  – Non-polar (lipids, oils) dissolve in non-polar.
• All materials do not dissolve in equal
  concentrations.
                    Solubility
• Highly soluble materials are said to be soluble
    or miscible.
•   Materials that dissolve very little are said to be
    insoluble or immiscible.
•   A material dissolves because the attraction of the
    solvent molecules is greater than the attractive
    force holding the solute molecules together.
•   Insoluble materials have a greater affinity for
    their own molecules.
•   These last 2 points is why oil pools together in
    water
      Temperature and Pressure
• Solubility is relative to changing temperature.
• Generally, solubility increases with increasing
    temperature.
•   Pressure has NO EFFECT on the solubility of
    solids and liquids (that compressibility thing
    again) ONLY GASES.
•   Gases behave oppositely, they are more soluble
    at higher pressure and lower temperature
    (open a warm seltzer bottle and a cold one at
    the same time).
 Gas Mixtures React Opposite to
Liquids in Terms of Pressure and
           Temperature
            Solubility Graphs

• We can look at a graph of solubility curves
  to determine how much solute can
  dissolve in a specific quantity of solvent.
• We need to know;
  – Which solute
  – What temperature
• See reference tables F and G.
                  Table F

• Guidelines for solubility (Table F)
  – Table F is broken down into Ionic compounds
    that are soluble. Try learning the exceptions,
    there are fewer and you’ll know the rules by
    default.
• There are many Ionic compounds that are
  insoluble and many exceptions (use the
  table).
                  Table G
• Graph of solubility curves
• Broken down into;
  – X axis = Temperature in Celsius
  – Y axis = amount of solute per 100g H2O.
• How to read graph
  – Trace given info, grams or °C, along curve of
    X and Y axis to find desired data point for
    given solute.
                  Saturation
• There is an upper limit to how much solute a
    given solvent can hold at a certain temperature.
•   When holding the maximum amount of solute the
    solution is said to be saturated.
•   When a solution is saturated the addition of any
    more solute will cause a precipitate to form.
•   Ex. Have you ever found un-dissolved substance
    on the bottom of your coffee or ice tea?
    Using Table G (solubility curves)
 To Predict Solubility of Substances
• Find KNO3 (potassium nitrate) in table G.
• At approximately 32°C, 100 grams H20 can hold
    a maximum of ~50grams of KNO3. It is
    saturated at this mass and temperature.
•   If the temperature was raised to 50°C, 100g of
    solvent could hold up to ~83 grams of KNO3.
•   One could add an additional 33 grams of solute
    to re-saturate the solution.
•   If you do not add more solute, the solution
    would be called unsaturated.
               Supersaturation
• This occurs when a solution is heated, saturated
    and then slowly cooled, creating a new
    saturation point.
•   The solution maintains it’s homogeneous
    appearance.
•   Supersaturated solutions are very unstable.
•   Addition of a single crystalline molecule will
    cause the solution to form a precipitate.
         Determining Saturation
• Visual inspection: Does the solution contain un-
    dissolved particles?
•   Addition of more solid solute:
    1. Does the solid fall to the bottom?
       • Yes  solution is saturated
       • No  solution is not saturated
    2. Does a precipitate form (material comes out of
       solution)?
       • Yes  solution is supersaturated
       • No  return to (1)
      Concentration of Solutions
• Compositions of homogeneous mixtures can
    vary.
•   Two terms are commonly used;
    – Dilute
    – Concentrated
• The above terms are relative, that is, they are
    not very precise and tell little about how much
    solute is present.
•   More precise terms are; molarity, % mass, %
    volume & ppm (parts per million).
                 Molarity

• Molarity is the number of moles of solute
  per liter of solution.
              M = # mol solute
                      L solution
• Molarity can be used as a conversion
  factor to find Volume and # of mols.
            M (mol/L) x V (L) = # of mol
           Percent by Mass

• Mass of a certain ingredient divided by the
 total mass.

     % Mass = Mass of part x 100
                 Mass of Whole
           Parts Per Million

• PPM is used when very small amounts are
  present.
• Generally used to report acceptable levels
  of toxins, pollutants, poisons or other
  trace amounts of substances.
       PPM = grams of solute x 106
               grams of solution
                 Dilution

• The process of preparing a less
  concentrated solution from a more
  concentrated one.
               M1 V1 = M2 V2
• Where M1 and M2 equal the old and new
  molarities and…
• V1 and V2 equal the old and new volumes.

				
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