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An analyte is the substance that is being analyzed. For example, the concentration of glucose in blood is commonly analyzed by diabetics. Glucose is the analyte.

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CH 104: TITRATIONS WITH PERMANGANATE An analyte is the substance that is being analyzed. For example, the concentration of glucose in blood is commonly analyzed by ... – PowerPoint PPT presentation

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Title: An analyte is the substance that is being analyzed. For example, the concentration of glucose in blood is commonly analyzed by diabetics. Glucose is the analyte.


1
CH 104 TITRATIONS WITH PERMANGANATE
  • An analyte is the substance that is being
    analyzed. For example, the concentration of
    glucose in blood is commonly analyzed by
    diabetics. Glucose is the analyte.
  • A titrant is a solution of reagent that reacts
    with the analyte. The concentration of this
    reagent is accurately and precisely known.
  • In a titration, incremental volumes of titrant
    are added to the analyte until the reaction is
    complete.
  • A buret is often used to measure the volume of
    titrant added to the analyte.

2
REQUIREMENTS OF A TITRATION
  • The reaction must be stoichiometric. For example,
    the net ionic equation for the reaction of
    potassium permanganate (KMnO4) and sodium oxalate
    (Na2C2O4) is quantitative. Exactly 2 moles of
    KMnO4 react with exactly 5 moles of Na2C2O4.
  • 2MnO4(aq) 16H(aq) 5C2O42(aq) ? 2Mn2(aq)
    8H2O(l) 10CO2(g)
  • The reaction should be rapid.
  • The reaction should be specific that is, there
    should be no competing reactions. Systematic
    error caused by interferences must be eliminated
    or reduced.

3
REQUIREMENTS OF A TITRATION
  1. There should be a marked change when the reaction
    is complete. For example, this reaction is
    self-indicating. The titrant (KMnO4) is deep
    purple. The analyte (Na2C2O4) and products
    (Mn2, H2O, and CO2) are nearly colorless. The
    titration is done when the first fraction of a
    drop of excess MnO4 changes the solution from
    nearly colorless to a faint and stable pink.

4
EQUIVALENCE POINT, END POINT, AND INDICATORS
  • The equivalence point occurs when the volume of
    titrant added to the analyte is the exact
    stoichiometric amount that is needed to bring the
    reaction to completion.
  • The end point occurs when the indicator changes
    color.
  • We want to measure the equivalence point. We
    actually measure the end point.
  • Obviously, the faint pink MnO4 end point does
    not occur at the equivalence point. This end
    point occurs a fraction of a drop after the
    equivalence point. This error is small and can
    be corrected with a blank, or during
    standardization.
  • How would you use a blank to correct this error?
  • The volume of MnO4 used to reach the end point
    during the titration of distilled water (a blank)
    is subtracted from all standards and all samples.
  • How would you standardize to correct this error?
  • All standards and all samples are titrated to the
    same end point. We will do this today.

5
EQUIVALENCE POINT, END POINT, AND INDICATORS
  • Titration using Permanganate as a Self-Indicator
  • When do you stop adding titrant to the analyte?
  • At the end point.

6
STANDARDIZATION
  • Today we will standardize KMnO4 against Na2C2O4.
  • 2MnO4(aq) 16H(aq) 5C2O42(aq) ? 2Mn2(aq)
    8H2O(l) 10CO2(g)
  • This is an oxidation-reduction reaction. That
    is, electrons are transferred from 1 reactant to
    another reactant.
  • Oxidation is a loss of an electron or electrons
    by an atom or group of atoms.
  • Reduction is a gain of an electron or electrons
    by an atom or group of atoms.

7
STANDARDIZATION
  • Today we will standardize KMnO4 against Na2C2O4.
  • 2MnO4(aq) 16H(aq) 5C2O42(aq) ? 2Mn2(aq)
    8H2O(l) 10CO2(g)
  • In this reaction, C2O42 is oxidized to CO2, and
    MnO4 to reduced to Mn2.
  • What is the Lewis structure for C2O42?
  • What is the Lewis structure for CO2?
  • Why is the C of CO2 more oxidized than the C of
    C2O42?
  • The C in CO2 is in the 4 oxidation state
  • (1 x 4) (2 x 2) 0. Each C in C2O42 is
    in the 3 oxidation state (2 x 3) (4 x 2)
    2. Therefore, each C lost 1 electron and was
    oxidized during this reaction.

8
STANDARDIZATION
  • Today we will standardize KMnO4 against Na2C2O4.
  • 2MnO4(aq) 16H(aq) 5C2O42(aq) ? 2Mn2(aq)
    8H2O(l) 10CO2(g)
  • What is the oxidation state of Mn in MnO4?
  • The 7 oxidation state (1 x 7) (4 x 2)
    1.
  • What is the oxidation state of Mn2?
  • The 2 oxidation state (1 x 2) 2.
  • Why is the Mn of Mn2 more reduced than the Mn of
    MnO4?
  • Mn2 is in the 2 oxidation state. The Mn of
    MnO4 is in the 7 oxidation state. Therefore,
    Mn gained 5 electrons and was reduced during this
    reaction.

9
STANDARDIZATION
  • Na2C2O4 is a primary standard.
  • For example, a solution was made by dissolving
    1.095 g of Na2C2O4 in 100.0 mL of distilled
    water. The molar mass of Na2C2O4 is 134.0 g/mol.
    A 25.00 mL sample of this Na2C2O4 solution was
    titrated with 39.58 mL of a KMnO4 solution to a
    self-indicating end point. What is the molarity
    (M) of this KMnO4 solution?

10
REQUIREMENTS OF A PRIMARY STANDARD
  • A primary standard should be 100.00 pure
    although a 0.01 to 0.02 impurity is tolerable
    if it is accurately known.
  • A primary standard should be stable at drying
    temperatures, and it should be stable
    indefinitely at room temperature. (A primary
    standard is always dried before weighing, unless
    it is a hydrate.)
  • It should be readily available.
  • It should have a relatively large formula weight.
    Therefore, a relatively large mass of it will be
    weighed for titration. This will reduce error.
  • Explain this last point.

11
OXIDATIONREDUCTION TITRATION WITH PERMANGANATE
  • After the KMnO4 is standardized, we will measure
    the Fe(II) content of an unknown salt.
  • MnO4(aq) 8H(aq) 5Fe2(aq) ? Mn2(aq)
    4H2O(l) 5Fe3(aq)
  • What is oxidized?
  • The Fe is oxidized from 2 to 3.
  • What is reduced?
  • The Mn is reduced from 7 to 2.

12
SAFETY
  • Give at least 1 safety concern for the following
    procedure.
  • Using oxidizing agents (KMnO4), reducing agents
    (Na2C2O4 and unknown Fe(II) salt), and acids
    (H2SO4 and H3PO4).
  • These are irritants. Wear your goggles at all
    times. Immediately clean all spills. If you do
    get either of these in your eye, immediately
    flush with water.
  • Your laboratory manual has an extensive list of
    safety procedures. Read and understand this
    section.
  • Ask your instructor if you ever have any
    questions about safety.

13
SOURCES
  • Christian, G.D. 1986. Analytical Chemistry, 3rd
    ed. New York, NY John Wiley Sons, Inc.
  • Harris, D.C. 1999. Quantitative Chemical
    Analysis, 5th ed. New York, NY W.H. Freeman
    Company.
  • McMurry, J., R.C. Fay. 2004. Chemistry, 4th ed.
    Upper Saddle River, NJ Prentice Hall.
  • Petrucci, R.H. 1985. General Chemistry Principles
    and Modern Applications, 4th ed. New York, NY
    Macmillan Publishing Company.
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