Solutions _ Solubility - SCH3U-BCALC-Q3 by hcj

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									Solutions & Solubility

                  Unit 4
Solutions
 Solutions = a homogenous mixture of
  substances composed of a least one solute and
  one solvent
 Solute = a substance that is dissolved in a
  solvent (e.g. salt, NaCl)
 Solvent = the medium in which a solute is
  dissolved; often the liquid component of a
  solution (e.g. water)
Solutions
Homogenous vs. Heterogeneous
 Homogenous mixture = a uniform mixture
  of only one phase
 Heterogeneous mixtures = a non-uniform
  mixture of two or more phases
Homogenous vs. Heterogeneous
Homogenous vs. Heterogeneous
Classifying Solutions
   Aqueous Solution = a solute dissolved in water

   Types of Solutions:
       Electrical Conductivity
           Electrolyte
           Nonelectrolyte

       pH (Acidity or Bacisity)
           Acidic
           Basic
           Neutral
Conductivity Test
   Electrolyte = a compound that in an aqueous
    solution conducts electricity
       Mosty ionic compounds
   Nonelectrolyte = a compound that, in an
    aqueous solution, does not conduct electricity
       Mostly molecular compounds
Litmus Test
 Acid = a substance that, in aqueous solution,
  turns litmus paper red
 Base = a substance that in an aqueous
  solution, turns litmus paper blue
 Neutral = a substance that, in aqueous
  solution, has no effect on either red or blue
  litmus paper; neither acidic nor basic
Explaining Solutions
 Intramolecular Forces = a specific
  attraction within a molecule
 Intermolecular Forces = an attraction
  between molecules

   Why do only some chemicals dissolved in
    water? Why are some chemicals mutually
    attracted to one anonther?
“like dissolves like”
 Polar substances dissolve in polar solutions
 Non-polar substances dissolve in non-polar
  solutions
 In other words:
       like-polarity substances dissolve in each other
The Effects of Polarity & Hydrogen Bonding
 Polar molecules have a high solubility in water
 Polar solute molecules are surrounded and
  suspended in solution by polar solvent
  molecules
Recall: Hydrogen Bonding
Recall: Hydrogen Bonding
 Hydrogen    Bonding = a relatively
 strong dipole-dipole force between a
 positive hydrogen atom of one molecule
 and a highly electronegative atom (F, O or
 N) in another molecule
Hydrogen bonds with Ammonia
Predicting Solubility
   Page 276
Ionic Compounds in Water
 More ionic compounds dissolve in water than
  in any other known solvent…
 Ionic compounds dissociate into individual
  aqueous ions

   Dissociation = the separation of ions that
    occurs when an ionic compound dissolves in
    water
Ionic Compounds in Water
Ionic Compounds in Water
Explaining Non-aqueous Mixtures
   London Dispersion forces are weak
    intermolecular forces responsible for non-
    polar substances dissolving in non-polar
    solvents
Solution Concentration
 Concentration = the quantity of a given
  solute in a solution
 Dilute = having a relatively small quantity of
  solute per unit volume of solution
 Concentrated = having a relatively large
  quantity of solute per unit volume of solution
Solution Concentration

Concentration =
Percentage Concentration
   Percentage Weight by Volume
       % W/V


   Percentage Volume by Volume
       % V/V
Very Low Concentrations
   Parts per million (ppm) = units used for
    very low concentrations

 Used for very dilute solutions
 Example:
       Toxic substances found in the environment
       Chlorine in a swimming pool
       Metals in drinking water
Molar Concentrations
   Molar Concentrations (C)= the amount of
    solute, in moles, dissolved in one liter of
    solution

 C = n/v
 Units = mol/L


   Molarity of a solution
Drinking Water
 Over 70% of the earth is covered with water
 Only 0.02% of the water on Earth is fresh
  water
 0.6% is ground water
Lucky Canadians
 Most abundant supply of fresh water in the
  world
 Surface water = Great Lakes
 Ground water = thousands of aquifers


   Aquifer = an underground formation of
    permeable rock or loose material that can
    produce useful quantities of water when
    tapped by a well
    Hydrologic Cycle
   Evaporation  condensation  precipitation 
Water Contamination
 3 Categories:
 Biological
       Viruses, bacteria, and algae
   Physical
       Suspended particles that make the water appear
        “dirty”
   Chemical
       All dissolved substances, including metals,
        manufactured chemicals, and even artificially high
        levels of natural minerals
              Common Sources of Water
                  Contamination
                Source                    Typical Contamination
Inadequate septic system or leaky sewer   Untreated sewage contaminating bacteria,
line                                      nitrates and phosphates
Landfill leachate                         Heavy metals, e.g. mercury, lead, cadmium;
                                          bacteria; acids, organic compounds
Road salt                                 Sodium, potassium and calcium chloride

Livestock waste                           Nitrates, heavy metals, bacteria

fertilizers                               Nitrates and phosphates

Crop and forest spraying                  Pesticides

Leaky tanks or pipelines containing       Gasoline; other organic compounds
petroleum
Mining and mine tailing                   Sulfides; cyanides, sulfuric acid; toxic heavy
                                          metals e.g. lead, mercury, cadmium, arsenic
           Environmental Effects of Some
                Water Contaminants
   Contaminant                   Environmental or Health Effect
Acid                    Kills soil bacteria; reduces plant growth

Bacteria                Causes infection, possibly resulting in illness or death

Heavy Metals            Interfere with brain and nerve development in vertebrates

Mineral Solids          Make water cloudy, inhibiting aquatic plant growth

Nitrates & Phosphates   Encourage plant growth, sometimes results in algal blooms
                        causing deoxygenation of water
Organic Compounds       Poisonous or carcinogenic; sometime interfere with oxygen
                        diffusion into surface water
Pesticides              Toxic to many invertebrates; may bioaccumulate to levels toxic in
                        vertebrates

Salt                    Kills freshwater organisms; makes water unsuitable for drinking
Water Treatment
1.   Collection
2.   Coagulation, Flocculation & Sedimentation
3.   Filtration
4.   Disinfection
5.   Aeration
6.   Softening
7.   Fluoridation
8.   Post-Chlorination
9.   Ammoniation
Solution Preparation
   Standard Solution = a solution for which
    the precise concentration is known

 Used in research laboratories and industrial
  processes
 Used in chemical analysis and precise control
  of chemical reactions
Solution Preparation
   Equipment needed to prepare a standard
    solution:
       Electronic balance
       Volumetric flask
Volumetric Flask
Graduated & Volumetric Pipets and Bulb to
transfer small quantities of liquid
Preparing a Solution by Dilution
   Dilution = the process of decreasing the
    concentration of a solution, usually by adding
    more solvent

   Stock Solution = a solution that is in stock
    or on the shelf (i.e., available); usually a
    concentrated solution
Calculating the New Concentration
of the Diluted Solution
            v i x C i = vf x C f

 Vi = initial volume
 Ci = initial concentration
 Vf = final volume
 Cf = final concentration
Solubility
   Saturated solution = a solution containing
    the maximum quantity of a solute at specific
    temperature and pressure conditions
       Look for the presence of undisclosed solids in the
        solution

   Solubility = a property of a solute; the
    concentration of a saturated solution of a
    solute in a solvent at a specific temperature
    and pressure
Solubility
   Unsaturated solution = a solution
    containing less than maximum quantity of a
    solute at specific temperature and pressure
    conditions

   Supersaturated solution = a solution that
    contains more of the dissolved material than
    could be dissolved by the solvent under
    normal circumstances
Solubility of Solids
 Solubility of a substance changes with
  temperature
 Higher solubility at higher temperatures


   Solubility Curve = a graph of solubility and
    temperature of a solution
Solubility Curve of Solids
Solubility of Gases
   Higher solubility at lower temperatures

 Think: Pop
 Can of pop from the fridge versus a can of pop
  at room temperature
 Can of pop is also stored under pressure
 Increased pressure = increased solubility
Solubility of Liquids
   Difficult to generalize about, but:
       For polar liquids solubility usually increases with
        increase in temperature

 Immiscible = two liquids that form separate
  layers instead of dissolving
 Miscible = liquids that mix in all proportions
  and have no maximum concentration
Solubility Categories
 High solubility = with a maximum
  concentration at SATP (standard ambient
  temperature and pressure) of greater than or
  equal to 0.1mol/L
 Low solubility = with a maximum
  concentration at SATP of less then 0.1mol/L
 Insoluble = a substance that has a negligible
  solubility at SATP
 SATP = standard ambient temperature and
  pressure, = exactly 25°C and 100kPa
Using a Solubility Table
 Solubility of ionic compounds
 Anions paired with particular cations have
  either:
     High solubility (equal or greater than 0.1mol/L)
    OR
     Low solubility (less than 0.1mol/L)
Reactions in Solution
   If a chemical reaction results in the formation
    of a compound which has low solubility the
    compound will not be dissolved in the solution
    and is said to precipitate out of solution

   Precipitate = the solid formed in a chemical
    reaction or by decreased solubility
Acids and Bases: Arrhenius Definition
   Base = an ionic hydroxide that dissociates in
    water to produce hydroxide ions (OH-)

   Acid = a compound that ionizes in water to
    form hydrogen ions (H+)
Strong vs Weak Acids
   Strong Acid = an acid that ionizes completely
    (~100%) in water to form aqueous H+ ions


   Weak Acid = an acid that ionizes only partially
    (less than 50%) in water to form aqueous H+ ions


   Percentage ionization = the percentage of
    molecules that form ions in solution
pH of a Solution
   pH is a way of indicating the concentration of
    H+ ions present in a solution

   pH = Power of Hydrogen
Calculating Ion Concentration


         [H+] =   10-pH




        pH = -log [H+]
pH and Ion Concentration
Type of     pH          [H+]         Color of
Solution                              litmus
Acidic     < 7.00   > 1x10-7 mol/L     red

Neutral    = 7.00   = 1x10-7 mol/L No change

 Basic     > 7.00   < 1x10-7 mol/L     blue
pH Scale
Acid-Base Titration
   Titration = a laboratory procedure involving
    the carefully measured and controlled adding
    of a solution from a buret into a measured
    volume of a sample solution

 Titrant = the solution in the buret during a
  titration (KNOWN concentration)
 Standard solution = a solution of precisely
  and accurately known concentration
Titration Apparatus
Titration of a Strong Acid
(with a Strong Base)
   In the buret  standard solution of base
    (KNOWN concentration)

 In the flask  precise volume of acid
  (UNKNOWN concentration)
 In the flask  indicator to detect the end
  point
Titration of a Strong Base
(with a Strong Acid)
   In the buret  standard solution of acid
    (KNOWN concentration)

 In the flask  precise volume of base
  (UNKNOWN concentration)
 In the flask  indicator to detect the end
  point
Endpoint vs Equivalence Point
   Endpoint = the point in a titration at which a
    sharp change in a property occurs (e.g. a colour
    change)
       More than neutral

   Equivalence Point (Stochiometric Point) =
    the point at which the exact amount of the titrant
    has added which is stoichiometrically equal to the
    amount of moles of substance (known as analyte)
    present in the sample
       Exactly neutral
The Endpoint
     Steps of a Titration
1.   Place standard solution in buret
2.   Place a precise volume of a solution of unknown
     concentration in a flask
3.   Add an indicator to the flask
4.   Record the volume in the buret as your initial reading
5.   Open the stopcock of the buret and allow the standard
     solution to enter the flask, while swirling the flask
6.   Slow down the flow of standard solution being added to
     ensure you don’t surpass the equivalence point by too much
7.   Once the end point is reached, record the final volume in
     the buret
8.   Subtract the initial volume from the final volume in the buret
     to obtain the total volume of standard solution used to
     neutralize the unknown solution.
Sample Titration Data

								
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