Aqueous Reactions and Solution Chemistry

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Aqueous Reactions and Solution Chemistry

• Prof. G. Matthews

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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.

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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.

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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.

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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)

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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?

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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.

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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?

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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.

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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?