Types of Chemical Reactions and Solution Stoichiometry

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Chapter 4

• Types of Chemical Reactions and Solution
  Stoichiometry

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Water, the Common Solvent

• Oxygen has a greater attraction for electrons
  than does hydrogen
• The oxygen atom gains a slight excess of negative
  charge (partial negative charge ), and the
  hydrogen atoms become slightly positive (partial
  positive charge ).
• Water is said to be a polar molecule.

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An Ionic Solid Dissolving in Water

• The positive ends of water molecules are
  attracted to the negatively charge anions.
• The negative ends are attracted to the positively
  charge cations.
• This process is called hydration.

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Polar water molecules
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Ethanol molecule in Water
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Strong Electrolytes

• Soluble salts NaCl, KCl, NH4Cl
• Strong acids HCl, HNO3, H2SO4
• Strong bases NaOH, KOH

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HCI container
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NaOH container
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Weak Electrolytes

• Weak acid acetic acid
• HC2H3O2(aq) ? H(aq)C2H3O2-(aq)
• Weak base ammonia dissolving in water
• NH3(aq)H2O(l) ?NH4(aq) OH-(aq)

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Acetic acid
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NH3 in water
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Standard Solution

• A standard solution is a solution whose
  concentration is accurately known.
• Primary Standard A primary standard is a highly
  purified compound that serves as a reference
  material in all volumetric and mass titrimetric
  methods.
• Secondary Standard A second standard is a
  solution of known concentration by titration with
  a solution of primary standard.

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Preparing Standard Acid Solutions

• Hydrochloric acid is widely used for titration of
  bases.
• Dilute solutions of HCl are stable indefinitely
  and do not cause troublesome precipitation
  reactions with most cations.
• 0.1 M solutions of HCl can be boiled for as long
  as one hour without loss acid.
• 0.5 M solutions of HCl can be boiled for at least
  10 min without significant loss.

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• Solutions of perchloric acid and sulfuric acid
  are also stable and are useful for titration
  where chloride ion interferes by forming
  precipitates.
• Solutions of nitric acid are seldom encountered
  because of their oxidizing properies.

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Requirements for a Primary Standard

• High purity
• Atmospheric stability
• Absence of hydrate water- composition of the
  solid does not change with relative humidity
• Ready availability at modest cost
• Reasonable solubility in the titration medium
• Reasonably large molar mass-the relative error
  associated with weighing

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Several Excellent Primary Standards

• 1. Potassium Hydrogen Phthalate KHC8H4O4 (KHP)
• 2. Benzoic Acid its solubility in water is
  limited, this reagent is ordinarily dissolved in
  ethanol prior to dilution water.
• 3. Potassium Hydrogen Iodate KH(IO3)2 is an
  excellent primary standard with a high molecular
  mass per mole of protons.

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Preparation of standard solutionor stock solution
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Types of Chemical Reactions

• Precipitation reactions
• Acid-base reactions
• Oxidation-reduction reactions

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Precipitation Reactions
K2CrO4 /Ba(NO3)2
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Reaction of KCI/AgNO3
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Ag/Ba/Fe precipitation