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Aqueous Reactions and Solution Chemistry

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Title: Aqueous Reactions and Solution Chemistry


1
Aqueous Reactions and Solution Chemistry
  • Prof. G. Matthews

2
General Properties of Aqueous Solutions
  • A solution is a homogeneous mixture of two or
    more substances.
  • Solute The substance being dissolved.
  • Solvent The substance present in the greater
    amount which is known as the dissolving medium.
  • Aqueous solution The dissolving medium is water.

3
General Properties of Aqueous Solutions
  • Electrolytic Properties
  • A solution that contains ions conducts
    electricity.
  • Electrolyte A substance whose aqueous solutions
    contain ions. (Ionic compounds)
  • Nonelectrolyte A substance whose aqueous
    solutions do not form ions. (Molecular compounds)
  • The number and type of ions in solution can be
    predicted from the nomenclature of the substance.

4
General Properties of Aqueous Solutions
  • Ionic compounds dissolve in water through a
    process known as solvation which results in ions.
  • Molecular compounds do not dissociate in water
    rather they exist as intact molecules dispersed
    through the solution.

5
General Properties of Aqueous Solutions
  • Strong Electrolyte Those solutes that exist in
    solution mainly as ions-equilibrium lies to the
    right.
  • Weak Electrolyte Those solutes that exist in
    solution mainly as molecules equilibrium lies to
    the left.
  • The solubility of the electrolyte does not mean
    that it is a strong or weak electrolyte (Acetic
    acid vs.Ba(OH)2)

6
Precipitation Reactions
  • The driving forces that allow a chemical reaction
    to take place
  • An insoluble solid is produced.
  • A gas is released.
  • An acid neutralizes a base.
  • One of the ions can oxidize another.

7
Precipitation Reactions
  • In a exchange or metathesis reaction two ionic
    compounds in aqueous solution switch anions and
    produce two new compounds.
  • There is not a reaction if no precipitate is
    formed since there is no driving force.

8
Precipitation Reactions
  • Molecular Equations - reactants and products are
    written using their full formulas as if they were
    molecules.
  • Ionic Equations - any reactants or products which
    completely dissociate in water are shown in terms
    of their free ions.
  • Net Ionic Equation - the equation for the net
    change that takes place during the reaction the
    spectator ions are not included.

9
Precipitation Reactions
  • Write molecular, ionic and net ionic equations
    for the reaction betweenPb(NO3)2 and (NH4)2SO4
    SnCl2 and NaOH NaNO3 and BaCl2.
  • Write the molecular, ionic, and net ionic
    equations for the reaction between nitric acid
    and calcium hydroxide.
  • Net ionic equations point out the similarities
    between large numbers of reactions involving
    electrolytes.

10
Acid-Base Reactions
  • Acids
  • Ionize in aqueous solutions to form hydrogen
    ions.
  • Different types of acids
  • Monoprotic HCl
  • Diprotic H2SO4
  • Triprotic H3PO4
  • Bases
  • Produce OH- ions in water.

11
Acid-Base Reactions
  • Strong Acids and Bases
  • Strong electrolytes since they dissociate
    completely in water.
  • Weak Acids and Bases
  • Weak electrolytes since they only partly ionize
    in water.

12
Oxidation-Reduction Reactions
  • Oxidation and Reduction
  • Oxidation Losing Electrons
  • Reduction Gaining Electrons
  • Oxidizing agent Accepts electrons.
  • Reducing agent Donates electrons.
  • Oxidation-reduction occur at the same time.

13
Oxidation-Reduction Reactions
  • Oxidation Numbers
  • For an atom in its elemental form the oxidation
    number is always zero.
  • For any monoatomic ion the oxidation number
    equals the charge on the ion.
  • Nonmetals usually have negative oxidation numbers
    although they can sometimes be positive.
  • The sum of the oxidation numbers in a compound
    equals the charge on the compound.

14
Oxidation-Reduction Reactions
  • In a single replacement reaction a metal
    displaces another metal or hydrogen, from a
    compound or aqueous solution that is below it in
    the Activity Series.

15
Oxidation-Reduction Reactions
  • Active metals
  • Include most of the metals in Group I, II.
  • Ligt Kgt Bagt Srgt Cagt Na
  • Active metals react directly with water
  • 2Na 2H2O(l) 2NaOH(aq) H2(g)
  • Activity Series for Nonmetals
  • Fgt Clgt Brgt I

16
Oxidation-Reduction Reactions
  • Oxidation and reduction can also be described as
  • Oxidation Gain of oxygen or loss of hydrogen.
  • Reduction Loss of oxygen or the gain of
    hydrogen.
  • Methane is combusted in sufficient oxygen to
    produce carbon dioxide and water. Which element,
    C or H is reduced, which is oxidized?

17
Concentrations of Solutions
  • Molarity
  • expresses the concentration of a solution as the
    number of moles of solute in a liter of solution.
  • Expressing the Concentration of an Electrolyte
  • The relative concentrations of the ions
    introduced into the solution depend on the
    chemical formula of the compound.

18
Concentrations of Solutions
  • Dilution
  • Process of making a more dilute solution by
    adding water to a more concentrated solution.
  • What volume of 2.50 M lead nitrate solution
    contains 0.075 mol of Pb2?
  • How many mL of 5.0M K2Cr2O7 solution must be
    diluted to prepare 250 mL of 0.20 M solution?

19
Solution Stoichiometry and Chemical Analysis
  • Titrations
  • Determines the concentration of a particular
    solute in a solution.
  • Equivalence Point
  • Stoichiometrically equivalent quantities of acid
    and base are brought together.
  • Indicators
  • show the equivalence point.

20
Solution Stoichiometry and Chemical Analysis
  • How many mL of 0.120 M HCl are needed to
    completely neutralize 50 mL of 0.101 M Ba(OH)2
    solution?
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