Permanent Magnet levitates above a superconducting

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Permanent Magnet levitates above a
superconducting disk in a pool of liquid
noitrogen.
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Redox Reactions

• Redox is a combination word from the two
  processes Reduction and Oxidation. Recall that
  Reduction is the gain of electrons while
  oxidation is the loss of electrons. These
  processes may be shown in half-cell reactions.

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Redox Reactions

• Half-cell reactions
• Oxidation half-cell
• Red Ox n e
• Reduction half-cell
• Ox n e Red
• A net reaction is the sum of the two half-cell
  reactions. The same number of electrons are lost
  in the oxidation reaction as gained in the
  reduction reaction

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Redox Reactions

• Half-cell reactions
• Oxidation half-cell
• Red Ox n e
• Reduction half-cell
• Ox n e Red
• Memory Devices
• LEO says GER, that is Oxidation is the loss of
  electrons, Reduction, the gain.
• OIL RIG, Oxidation loss, Reduction gain

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Redox Reactions

• The relative strength of oxidizing and reducing
  substances is given by the Table of Reduction
  Potentials (Appendix C, p 354ff).
• The potential (voltage) is a measurement of the
  electrical work needed to move electrons between
  the two electrodes.

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Redox Reactions

• In Appendix C all half-cells are written as
  reduction reactions as
• Al3 3 e - Al Eo -1.677 volts
• (-) values for the electrode potential means
  that this reduction is more difficult to do ()
  values indicate that that reduction is easier.
• F2 2 e - 2 F - Eo 2.890 volts

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Redox Reactions

• Note that the presence of complexing agents, the
  existence of the element in a different
  compounds, or the oxidation state of the element
  affects the E0 value. Examples
• Cu e - Cu Eo 0.518 volts
• Cu2 2 e - Cu Eo 0.339 volts
• Cu(edta)-2 2 e - Cu edta Eo -0.216
  volts

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Redox Reactions

• We will come back to additional considerations
  regarding the electrical potentials of net redox
  reactions, but sufficient now is to note that for
  a redox reaction to occur spontaneously, the E0
  value must be positive. Also, note that E0
  refers to standard conditions for the reaction.
  Standard conditions are conc 1.00 M, pgas 1
  atm (or 1 bar), T 298 K. Non-standard values
  may be calculated with the Nernst equation which
  we will also consider later.

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Redox Titrations

• Redox titrations use a standardized solution
  of an oxidant or reductant to carry out a
  titration to determine the quantity of reducing
  or oxidizing species present as the analyte.

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Redox Titrations

• In order for a redox reaction to be the basis
  of a successful titration
• The value of K must be large (alternately, E0net
  must be large and positive.)

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Redox Titrations

• In order for a redox reaction to be the basis
  of a successful titration
• The value of K must be large (alternately, E0net
  must be large and positive.)
• The net redox reaction must be known

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Redox Titrations

• In order for a redox reaction to be the basis
  of a successful titration
• The value of K must be large (alternately, E0net
  must be large and positive.)
• The net redox reaction must be known
• There must be some way of determining the
  equivalence point, that is when stoichiometric
  quantities of analyte and titrant have reacted.

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Redox Titrations

• The end point might be established
• By a visual indicator that change color at a
  given electrical potential.

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Redox reactions
Redox Reactions
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Redox Titrations

• The end point might be established
• By following the titration with a voltmeter the
  curve is similar to an acid/base titration curve.

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Titration curve for the redox reaction of Ce4
and Fe2 and Tl3 and Fe2
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Redox Titrations

• The end point might be established
• A few Redox reactions are colorful enough to
  self-indicate the end point because the colors of
  the oxidized and reduced forms are sufficiently
  different.
• MnO4- Mn2
• Purple Colorless

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Redox Titrations

• The end point might be established
• A few Redox reactions are colorful enough to
  self-indicate the end point because the colors of
  the oxidized and reduced forms are sufficiently
  different.
• I2 2I
• Yellow Colorles
• in presence of starch
• Blue Colorless

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